Shelf Life Determination of Idaho and Red Potatoes

Stored in Three Types of Bags

By

Heather Krieger

A Research Paper Submitted in Partial Fulfillment of the

Requirements for the Master of Science Degree

In

Food and Nutritional Sciences

Approved: 2 Semester Credits

~~-L~ Carol Seaborn, Ph.D, RD, CD, CFCS

The Graduate School

University of Wisconsin-Stout

August, 2010

Author:

Title:

The Graduate School University of Wisconsin-Stout

Menomonie, WI

Krieger, Heather

Shelf Life Determillatioll of Idaho ami Red Potatoes Stored ill Tltree

Types of Bags

Graduate Degree/ Major: Food and Nutritional Sciences

Research Adviser: Carol Seaborn, Ph.D., RD, CD, CFCS

MonthNear: August, 2010

Number of Pages: 52

Style Manual Used: American Psychological Association, 6th edition

Abstract

On average, common losses throughout harvest and storage of potatoes range from

2

40%. Factors that impact loss include storage conditions such as temperature, absence of light,

and humidity. When changes occur in the carbohydrate composition, enzymatic activity, and

moisture loss the quality of the potato deteriorates. The purpose of this research study was to

investigate whether the type of storage bag impacted the carbohydrate composition, enzymatic

activity andlor moisture loss in potatoes. Two types of potatoes, Idaho (Russet) and Norland red,

were used in the study. Three types of mesh polymer bags were used; knitted L sewn bag,

wicked claf mesh bag, and a claf half-n"halfbag. The type of storage bag did not affect

carbohydrate composition, enzymatic activity, or moisture loss of either the Idaho (Russet) or

Norland red potato. Thus, when stored under conditions of98% relative humidity and 42° F, the

3

type of polymer bag does not appear to significantly affect carbohydrate composition, enzymatic

activity, or moisture content of the Idaho (Russet) or Norland red potatoes.

The Graduate School University of Wisconsin Stout

Menomonie, WI

Acknowledgments

4

I would like to give many thanks to Dr. Carol Seaborn for her dedication in helping with

the completion of this thesis paper. She has been a great inspiration and mentor all throughout

my college career and is one of the people who have helped me get where I am today. Thanks to

Volm Bag Corporation for the donation of bags to complete this research project. I would also

like to thank Dr. Janice Coker for her dedication in assisting and mentoring me in the beginning

of my thesis. A big thanks to the chemistry and packaging departments; Dr. Schultz and Laura

Giede as well as Ken Neuburg for helping me use their labs and equipment to complete my

testing processes. I would like to thank both Susan Greene and Dr. Lee for helping with the

statistical methods and analysis. Lastly, I would like to thank my parents and my husband for

their love, persistence and dedication in helping me finish my thesis paper.

5

Table of Contents

.................................................................................................................................................... Page

Abstract ............................................................................................................................................ 2

List of Tables ................................................................................................................................... 7

List of Figures .................................................................................................................................. 8

Chapter I: Introduction ......................................................... , .. , .. " ........ " .. , ... , .................. " .............. 9

Statement of the Problen1 ........... , .............. "", ... , ... ", ............................................................ 9

Purpose of the Study .......................................................................................................... 10

Assumptions of the Study .................................................................................................. 10

Definition of Terms ............................................................................................................ 10

Limitations of Study ........................................ , ................................................................. 12

Methodology ...................................................................................................................... 13

Chapter II: Literature Review ........................................................................................................ 15

History of Potato ................................................................................................................ 15

Potato Production ............................................................................................................... 17

Storage ............................................................................................................................... 21

Potato Composition ............................................................................................................ 23

Storage Temperatures ........................................................................................................ 26

Ventilation in Storage ........................................................................................................ 27

Packaging and Moisture Loss ........................................................................................... 28

Analyses .................................... ,', .......... " ....................... , .................................................. 29

6

Chapter III: Methodology .............................................................................................................. 32

Subject Selection and Description ..................................................................................... 35

Instlumentation .................................................................................................................. 37

Data Collection Procedures ................................................................................................ 38

Data Analysis ..................................................................................................................... 38

Limitations ......................................................................................................................... 39

Summary ............................................................................................................................ 39

Chapter IV: Results ........................................................................................................................ 40

Item Analysis .................................................................................................................... 40

Chapter V: Discussion ................................................................................................................... 46

Limitations ......................................................................................................................... 46

Conci us ions ........................................................................................................................ 4 7

Recommendations .............................................................................................................. 4 7

References ...................................................................................................................................... 49

7

List of Tables

Table 1: Stages of Growth in Tubers ................................................................................................ 20

Table 2: Total Sugar Content of Tubers Under Investigation: Idaho and Red (Norland) ................ 25

Table 3: Potato Storage Diagram of Potato Types under Investigation ............................................ 33

Table 4: Comparison of Carbohydrate Composition in Idaho Potatoes Stored in Three Different Bags ........................................................................................................... 41

Table 5: Comparison of Enzymatic Activity in Idaho Potatoes Stored in Three Different Bags .................................................................................................................... 41

Table 6: Comparison of Moisture Loss in Initial Weight ofIdaho Potatoes Stored in Three Different Bags ........................................................................................................... 41

Table 7: Comparison of Moisture Loss in the Sample Weight of Idaho Potatoes Stored in Three Different Bags .......................................................................................... 42

Table 8: Comparison of Carbohydrate Composition in Red Potatoes Stored in Three Different Bags ........................................................................................................... 43

Table 9: Comparison of Enzymatic Activity in Red Potatoes Stored in Three Different Bags .......................................................................................................... 44

Table 10: Comparison of Moisture Loss in Initial Weight of Red Potatoes Stored in Three Different Bags .......................................................................................... 44

Table 11: Comparison of Moisture Loss in Sample Weight of Red Potatoes Stored in Three Different Bags .......................................................................................... 45

8

List of Figures

Figure 1: Idaho or Russet potato ...................................... , ................................. 17

Figure 2: Norland red potato ............................................................................ 17

Figure 3: Amylose molecule ............................................................................ 24

Figure 4: Amylopectin molecule ....................................................................... 25

Figure 5: Rachel knitted L sewn bags ................................................................. .35

Figure 6: Wicketed daf mesh bags ..................................................................... 36

Figure 7: Claf half-n-half bags .......................................................................... 36

9

Chapter I: Introduction

The shelflife study was conducted at University of Wisconsin-Stout, Menomonie. A

Midwestern plastics company provided three types of polymer bags for experimentation. The

research conducted sought to determine if the shelf life of two varieties of potatoes would be

impacted by the types of polymer bags used for storage.

Statement of the Problem

After tubers are harvested and put through the curing process, storage is the critical step

in shelf life of tubers and maintaining slow natural decomposition. When stored, it is very

crucial that the storage area be dark, well ventilated, and temperatures maintained near 4° C (39°

F). For short term storage the temperatures may increase to 7° C (45° F) to 10° C (50° F). If

temperatures are lower than 4°C (39° F) the starch converts to sugar, which may account for

higher levels of acrylamide and alter flavor and cooking qualities of the potatoes (Kohli, 2009).

Moreover, the enzymatic activity and moisture loss within tubers deteriorates the quality

of the product under temperature variations and storage conditions. On average, common losses

throughout harvest range from 5-40% depending on the types of tubers (Sira, 2000). When

conditions such as temperature and storage are compromised, this can influence and be very

crucial to the quality as well as overall flavor and physical appearance of the tuber. By

monitoring these conditions during tuber processing as well as the enzyme activity and moisture

loss, tubers can be stored for about 10 months under favorable conditions of 4° C (39° F) and 98

% relative humidity (Kohli, 2009). When consumers buy tuber products, they have much less

time to consume the product as the shelf life is not adequately and conditionally maintained in

the home for the highest quality and palatability.

10

Tubers need to be stored at a relative humidity of 95-99% and in a dark, dry area to help

minimize shrinkage and pressure bruising during their storage. Additionally, a temperature of 7

to 10° C (45-50° F) helps minimize conversion of non-reducing sugars, such as starch, to

reducing sugars, such as glucose, which darken during cooking (Voss, 2000).

Purpose of the Study

The purpose of this research study was to investigate whether the type of storage bag

impacted carbohydrate composition, enzymatic activity, and/or moisture loss in two types of

tubers.

Assumptions of the Study

The study assumed the reliability of equipment used for testing and the seasonal

availability of tuber crops. The reflection of typical moisture and carbohydrate content in the

tuber as well as absence of human enor in the specific testing methods and perfection of the

methodology was also assumed in this study.

Definition of Terms

Alpha amylase. Alpha amylase is an enzyme that breaks down polysaccharides. Alpha

amylase is synthesized in plants and fruit during the ripening phase, which causes a sweet taste.

The enzyme cleaves at the (1, 4) glycosidic linkages of amylose (starch/polysaccharide) breaking

down to glucose thus decreasing the total complex carbohydrate remaining.

Carbohydrate. An essential structural component of plants that is used for an energy

source within the human diet. Carbohydrates occur in foods as polysaccharides, such as starch,

or simple sugars, such as glucose. The total storage carbohydrate contained in a tuber over a

period of time determines product deterioration.

1 1

Enzyme activity. A catalytic effect exerted by an enzyme, expressed in milligrams of

enzyme. In this study the enzyme activity was quantified by the measurement of absorbance in

11m.

Idaho (Russet) potato. An oblong, white potato high in starch and mainly used for

baking.

Moisture content. M = (mwlmsample) x 100. The percent moisture equation can be

expressed as M being the total moisture content using mw (the mass of the water) and dividing it

by the msample (the sample mass). The mass of the water is determined by the number of water

molecules (nw) by using the equation of mw = nwMwlN A to define mw where as Mw is the

molecular weight of water (18.0 g per mole) and NA is Avadagro's number (6.02 x 1023

molecules per mole). In theory, the sample mass can be determined accurately by using the mass

of the water molecules present in a known mass of a sample.

Moisture loss. The constant depletion or lost of moisture within a product over time due

to drying.

Polymer bag. A bag made from a thin flexible plastic material. Bags can be mesh, solid

or vented for produce storing purposes. Bags are also available in different sizes and shapes.

Relative humidity. The measurement of the water in the air divided by the air it could

hold. If the air is capable of holding 100, then a relative humidity of 80% would indicate the air

can hold 8011 00 of what it is capable of holding at a specific temperature.

Red Norland potato. A brown skinned, oblong tuber (potato) which has a mealy flesh

and high starch content.

12

Solanum tuberosum tubers. Temperate tuber plant belonging to the Solanum tuberosum

family. The tuber is the edible portion of the Solanum tuberosum plant. The seasonal crop is

grown in temperate regions all over the world, but primarily in the northern hemisphere.

Spectrophotometry. Spectrophotometry is a quantitative study of a spectrum that

determines a sample's absorption range of color absorbed. A sample with an absorbance value

close to zero is colorless. The sample appears transparent because all of the light penetrates the

sample and is completely transmitted through the sample.

Suberization. Conversion of the cell walls into a cork tissue by development of suberin

(a waxy waterproof substance present in the cell walls of cork tissue of plants). In exposed tissue

these commonly take their place as does a callus forms over a wound.

Tubers. Tubers are starchy plants that yield stems, roots, rhizomes, and tubers. Tubers

are mainly grown for food and are generally defined as the small bulky flesh located at the end of

the stem underground.

Limitations of the Study

This research study controlled humidity and temperature throughout the duration of the

testing. The variations in humidity and temperature of the controlled environment were limited

in this research study and did not examine other humidity conditions and temperatures that might

also affect shelf life.

Tuber products were pre-selected to red Norland and Idaho (Russet) potatoes, seasonal

crops common to the Midwest. Thus, only two types of tubers were tested. Due to space, the

weight of the tubers consisted of predetermined amounts (weights) and the shape of each type of

bag was similar for consistency in the controlled environment. Thus, other produce bag shapes

and other product weights were not examined.

13

All storage bags were made of polymer plastics and varied only in mesh type. Thus,

other polymer plastics and other mesh types that may have been available were not tested.

Limited space in the controlled environment allowed for onlylO bags to be shelved at any given

research time. Therefore, all test bags could not be stored at one time but were tested over time.

Methodology

The independent variables in the study included the type of potato, Red or Idaho, and

three types of mesh polymer bags: knitted sewn bag, wicked cIafmesh bag, and a cIafhalf-n-half

polypropylene bag.

The dependent variables were total carbohydrate, enzyme activity, and overall moisture

loss over time. Data from these three testing methods should indicate which polymer plastic bag

would be the best for consumer use and whether it could extend the shelf life of the tuber

products.

The purpose of the investigation was to compare the moisture loss, enzyme activity, and

total carbohydrate of two varieties of potatoes stored in three different types of polymer plastic

bags. The first test used was a phenol-sulfuric acid test which used a weighed amount of freeze

dried sample of potato which was fmther tested by extracting the carbohydrate using a

condensation of phenol. The sulfuric acid was then used to agitate and create a yellow orange

color. This method determined the amount of total carbohydrate that was present in potatoes.

This test is simple, rapid, sensitive and widely applied.

14

'The second test used an extracted pulp sample which was combined with a Tris Buffer

solution. After 15 minutes, the sample was strained and mixed with a 1 % starch solution and

analyzed using a spectrophotometer recording the absorbance (620 11m blue). This method

determined the amount of amylase enzyme activity present within the potatoes. The final

method used the overall weight of randomly selected samples. A standard sample from each bag

type and potato was collected and weighed each week to detennine the overall moisture loss over

the duration of the 10 week study. This determined the amount of moisture the product was

retaining or losing during the study.

15

Chapter II: Literature Review

The name potato was derived from the Spanish word palata, which is known as a

compound of the Taino batala (sweet potato) and the Quechua (potato). Many times in the

United States terms commonly referred to as "Irish potatoes or "white potatoes" help distinguish

other potatoes vs. sweet potatoes (Purdue University Department Horticulture, n.d.).

History of Potato

The potato (tuber) originated in the region of southern Peru and became first

domesticated between 3000 BC and 2000 BC. Historical records from local agriculturalists

along with DNA analyses show evidence that the most widely cultivated potato variety

worldwide was the Solanum tuberosum ssp. tuberosum. Moreover, tubers provided the principal

energy source for the Inca Empire, its predecessors and its Spanish successor nearly 10,000 years

previous (National Research Council, 1989).

In Spain, Solanum tuberosums (tubers) were considered a food for the disadvantaged

people (Theisen, 2007). In the late 1530's the western man stumbled upon the tuber when

traveling through Peru. In the 1570's, the tubers made their way back to Europe where they

were examined and cultivated by amateur botanists. Upon studying the potato the botanists

described the plant as poisonous which put it in limited use. The tuber was only fed to the

impoverished Spanish colonies and utilized for food for hospital inmates in the Old World. For

the next three decades the tuber spread through Europe (Theisen, 2007).

Ireland adopted the tuber in 1780's as an abundant and cultivated crop. As this crop was

considered a nutritious food, containing vitamins for sustenance; tubers became popular and

could provide food for 10 people on each acre. Throughout the 1800' s the tuber cultivation

created an upsurge of the human population, primary known as the fundamental part of their diet

16

(O'Grada,2000). Soon the crop growth became vulnerable to disease due to its lack of genetic

diversity. The plant disease known as Phytophthora infestans, caused the potatoes to turn green

and taste bitter, leading to human illnesses when consumed. Soon the disease spread rapidly

through poor communities of western Ireland resulting in crop failure and the Great Irish Famine

(O'Grada,2007). The Potato Famine in Ireland cut population by half through starvation and

immigration. It wasn't until 1883 that an effective fungicide was found by a French botanist,

Alexandre Millardet, which could kill the devastating fungus.

In France, Antoine Augustine Parmentier was an intellectual, a pharmacist and a chemist.

While in prison he ascertained the nutritional significance of tubers for the French diet. After his

release from prison following the Seven Year War, he worked to increase the cultivation of the

tuber crop throughout Europe and influenced its travel back to North America (Block, 2008). As

the potato gained acceptance across Europe it eventually made its way back over the Atlantic

Ocean to North America by the mid 1800's. By 1900 the potato would become one of the

world's main crops exceeding one million bushels.

In the first decade of the twenty-first century, an annual average of potato consumption

reached a global level of 33 kg (73 Ibs) per person. The United States, Asia, and Europe view

the tuber crops valuable and use this crop as an essential part of their diets. Today, China and

India are the leaders in potato production throughout the world producing nearly one-third of the

world's potatoes supply (Hijmans, 2001). Europe, Asia and North America represent the leading

producers for the potato production and consumption in the world. Formerly, the United States

was the leader in the crop production. Asia and Europe have enlarged their consumption which

together account for 80% of the use of the world's production (International Society for Tropical

Root Crops and F AO, 2008).

17

Potato Production

CUlTently, the Solanum Tuberosums is the fourth in production as a familiar crop in the

Western diet. Although most of the consumption is in the form of fried or processed products,

third world countries also use the crop for nutritional value (Fernie & Willmitzer, 2001).

Belonging to the Solanum tuberosum family, the potato, as a root or modified stem, contains

mostly starch, fiber, and other minerals and vitamins (Sira, 2000). The most common mid

western potatoes are known as the Idaho or Russet (Figure 1) and Norland red potatoes

(Figure 2).

Figure 1: Idaho or Russet potato (Photo taken by Heather Krieger)

Figure 2: Norland red potato (Photo Taken by Heather Krieger)

Potato plants are herbaceous perennials growing to approximately 60 cm high depending

on their variety and produce flowers that have colors ranging from pink, blue, red, white and

18

purple with yellow stamens. Tuber development and growth occurs in five stages; sprout

development, plant establishment, tuber initiation, tuber bulking, and tuber maturation as seen in

Table 1 (Dwelle & Love, 2001). Throughout these stages, various variables are necessary for

proper growth. Time for the growth stages may vary upon conditions such as environment,

elevation, temperature, soil type, cultivar selection, location (geographical) and moisture

availability. Typically in northern latitudes, growth stage one allows for new plant emergence

that can vary from the months of March to as late as June, while harvest can occur in August or

as late as October for growth stage five (Dwelle & Love, 2001).

During stage two or vegetative growth stage, favorable conditions help the development

of the tuber crops. Warmer storage temperatures generally 3 to 4 0 C (380 to 400 F) with steady

cooler temperatures maintained during the rest period create favorable conditions for growth to

occur. The plant establishment stage refers to the development of the roots and shoots of the

potato. This stalis from early sprouting until initiation of new tubers occurs. Also referred to as

"vegetative growth," the plant establishment is important to establish a good root system, which

is important for subsequent growth and can allow for re-growth after the eady season. The

mother tuber or seed piece is also important during this stage for this reason but becomes less

important as more plants are established (Dwelle & Love, 2001).

In stage three, known as tuber initiation, the tips of the stolen hook and begin to swell,

resulting in the initiation of a new tuber. This process for the tuber types occurs during the early

flowering. For this stage, proper amounts of nitrogen and cool nights are needed for optimal

tuber growth. If an inadequate water supply is present, this will lead to earlier tuber initiation

(Dwelle & Love, 2001).

19

Next, in stage four, tubers bulk up. It is critical for optimal growing conditions during

this time as growth rates remain relatively constant and are referred to as linear. Typical Russet

Burbanks and Southern Idaho grow six to ten hundredweight (cwt) per acre a day. This is typical

unless an interruption of ideal conditions reduces tuber growth rates causing losses in yield and

quality. Three main factors that have been found to influence tuber yield include photosynthetic

activity, duration ofthe leaf canopy, and the length of the linear growth phase of the tubers

(Dwelle & Love, 2001).

Other major influences on production in stage four are environment and fertilizer. Some

environmental limitations do not allow for healthy foliage, disrupting tuber growth, or shifting

dry matter decreasing potential yield. These environmental factors include temperature,

fertilization, seed physiological age, plant spacing, planting date, irrigation, and pest

management. The key factor which helps vine growth is temperature which allows for optimal

soil temperature to be about 16° C (61 ° F) and air temperature to be approximately 25° C (77°

F). Due to the canopy from the leaves, it is possible to obtain these two temperatures. This helps

also when the potato vines and tubers complete for nutrient resources (Dwelle & Love, 2001).

The other key factor, fertilization, allows for the proper delivery of nutrients to the tuber

plants. Deficiencies in nutrients limit canopy growth and shorten canopy duration resulting in a

reduced carbohydrate production and tuber growth rates. Fertilization in excess will cause

imbalances in nutrients and slow tuber growth rate (Dwelle & Love, 2001).

In the last stage of tuber growth, stage five, tuber maturation occurs. This is when the

vines die back and the skin or periderm hardens and thickens providing greater protection for the

tuber during the harvest, handling and storage. In this stage the conversion of free sugars to

starch occurs. Tubers also obtain lower respiration rates in storage during this stage. Low

20

respiration rates result in less dry matter loss, the tubers remain dormant longer and sprout later

thus improving the quality for fresh market consumption. Properly mature potatoes have a

greater ability to resist pathogens in storage. Over mature potatoes can cause starch to convert

back to sugar, decreasing specific gravity. With experience and knowledge of the harvesting and

conditions, growers can manage their crops to yield the highest quality tubers (Dwelle & Love,

2010).

Table 1

Stages o/Growth in Tubers

I

Growth Stage i Characteristics Sprout develops from eyes on seed tubers and grows upward to emerge

Stage 1 from the soil. Sprout Development Roots begin to develop at the base of emerging sprouts.

Leaves and branch stems develop from above ground nodes along Stage 2 emerged sprouts. Vegetative Growth Roots and stolons develop at ground nodes. Photo synthesis begins.

Stage 3 Tubers form at stolon tips but are not yet appreciably enlarging.

Tuber Initiation In most cultivars the end of this stage coincides with early flow~ring. Tuber cells expand with accumulation of water, nutrients, and

Stage 4 carbohydrates. Tubers become the dominant site for deposition of carbohydrates and

Tuber Bulking mobile inorganic nutrients. .. --... --.

Vines turn yellow and lose leaves, photosynthesis decreases, tuber growth Stage 5 slows, and vines eventually die.

Maturation Tuber dry matter c0'l1tent reaches a maximum and tuber skins set.

The significance of the Solamun tuberosum L. species is exemplified by its status as the

third most widely consumed crop. In the United States, potatoes have been the most widely

starchy vegetable grown. In 2005, the United States per capita consumption of potatoes was

132.2 lbs (International Society for Tropical Root Crops and FaA, 2008).

21

Storage

Historically, potatoes have been stored in a variety of conditions and temperatures. An

effect oftemperature during the vegetative growth period is significant for tuber growth and

development during the length of a growing season (Sira, 2000). During the development of the

tubers temperature affects how carbohydrates are processed during the stages of; transpiration of

water, translocation of carbohydrate, photosynthesis of carbohydrate production and respiration

or carbohydrate breakdown. Kumar, Singh, & Kumar (2004) studied the effects of sugar content

in potatoes, and with some limited exceptions, showed the optimum temperature for tuber

formation and growth to be in the 15-20° C (59-68° F) range. Furthermore, the studies

concluded that temperatures affected sugar content as it increased with temperatures between 8-

12° C (46-53° F) and from 25-30° C (77-86° F)(Kumar et al., 2004).

The mode and manner of deterioration varies within the range and mixture of the

Solanum tuberosum L. By and large, tubers yield abundantly with little effort and adapt readily

to diverse climates providing the climate is cool and moist enough for the plants to gather

sufficient water from the soil to form the starchy tubers. On the other hand under unfavorable

conditions (uncontrolled temperatures, improper ventilation and humidity) make the tubers

vulnerable to molds that feed on the stored tubers, quickly tuming the tubers rotten. Even

though in comparison grain can be stored for several years without much risk of rotting, the

Solunum tuberosum L. has become an economically significant root crop globally. However,

storage conditions must be closely monitored to produce a marketable crop (Shetty, 2010).

22

As food suppliers cultivate, harvest and sell potato crops, companies who market the

crops look for better ways to ventilate, store and monitor moisture within tubers. Thus, storage

may help increase shelf life for consumer use. With regards to tuber storage, polymer plastics

have the potential to extend shelf life, maintain the carbohydrate composition, enzyme activity

and decrease overall moisture loss. Many varieties of tubers experience different growth and

development stages depending on the region of cultivation. With this in mind, storage at

different temperatures and types of tubers is an area for investigation. In the present study

examination of retaining the highest shelflife obtainable was considered in telIDS of maximizing

the moisture content and carbohydrate composition of a potato.

Ventilation is considered a key factor in determining respiration rates and metabolic

activity during the harvesting and storage of potatoes. By controlling metabolic breakdown of

stored carbon compounds or starch, temperature can also playa dual role in slowing the

breakdown as well as to help save the degradation of starch. Temperatures need to be kept

constant due to the heat production during the respiration process. When metabolic breakdown

occurs, heat is generated and can decrease the storage length and quality in potatoes. Moisture is

another way to control the quality of the potato crop. Tubers are made up of -80% moisture and

20% starch making it crucial to monitor how much moisture is lost during harvest and storage.

To control shrinkage due to moisture loss, vapor pressure or relative humidity is usually

monitored to help decrease the moister loss, decrease sprouting, and maintain the quality of the

potatoes. Ideally, potatoes should only lose -4-10% moisture during the harvest and storage

process (depending on length of time and storage conditions). Ventilation and respiration,

temperatures, and relative humidity are all crucial factors that play an important role in a storing

potato crops (Shetty, 2010).

23

Potato Composition

Vi11ually 4000 different varieties of tubers that have been agriculturally bred have

distinctive culinary attributes (Roach, 2002). Definite culinary attributes include the consistency

or quality of waxiness. Mealy (baking) or floury tubers have more starch (20-22%) then waxy

(boiling) potatoes (16-18%). Tubers also may vary in comparison due to starch compounds

known as amylose and amylopectin. Amylose, a long-chain molecule, diffuses out of the starch

granule when cooked in water, which may be seen in mashed potato dishes. Conversely, the

higher amylopectin content of a potato as well as a highly branched molecule helps retain the

shape of the tuber during the boiling process (Theisen, 2007).

Starch composition influences the storage life of the potato which is evident in the

laboratory analysis. Compromised ofa mixture of21-25% amylose and 75-79% amylopectin,

starch is a major polysaccharide of most plant crops. Amylose is a straight chain of glucose

units, whereas amylopectin includes many branches existing in approximately every 20 glucose

units. As a mixture, amylose and amylopectin are deposited in granular forms in the amyloplast

of storage cells of tubers, which store and synthesize starch (Lewis, Lancaster, Meredith, &

Walker, 1994). The major sugars in starch/polysaccharides are glucose, fructose, and sucrose.

Glucose and fructose have a free reducing group, known as reducing sugars (Rastoviski, 1987).

Sucrose is a disaccharide that has no free group due to the bonding of glucose and fructose.

Thus, sucrose is non-reducing. Considering the evidence of composition, both starch and sugars

play an important role in tuber formation (biosynthesis) and storage (starch breakdown) of

potatoes. Although metabolic interconversion cannot be fully explained, it contributes to

understanding some challenges in the post harvest of potatoes (Rastoviski, 1987).

24

Additional research shows starch synthesis and starch breakdown are generally associated

with starch and sugars in tubers. The synthesis group consists of ADP-glucose and

pyrophosphate from A TP and glucose-I-phosphate. Starch synthase catalyzes the linking ADP -

glucose to non-reducing end ofthe growing starch chain by a-(1,4) linkages acting on amylose

and amylopectin. For production of the branched points in amylopectin the starch synthase

activity was found to associate with the starch grain bound to starch enzymes and the stroma of

the plastid (Lewis et aI., 1994). The major degradation starch enzymes are starch phosphorylase

and amylases. Amylases catalyze the hydrolysis of a-(l, 4) linked glucans, directly yielding

sugars and oliosaccharides. Alpha amylases in most plant tissues playa major role in the

breakdown of starch. The initial attack on starch granules is by a - amylase; however, complete

degradation results from the combination action of other enzymes starch phosphorylase ~­

amylase, and debranching enzymes (Lewis et aI., 1994). The amlyose and amylopectin

molecules are shown in Figures 3 and 4 which were obtained from the Wikimedia Commons

(n.d.) web site and were modified to show linkage.

Alpha-I, 4 linkage

H OH H OH H OH H OH

Figure 3: Amylose molecule. Wikimedia Commons. (n.d.). Retrieved from

http://commons.wikimedia.org/wiki/File:Amylose.png, ineligible for copyright

0- enz.

25

I Alpha-I, 6 linkage /L-----__

OH OH OH

Figure 4: Amylopectin molecule. Wikimedia Commons. (n.d.). Retrieved from

http://commons.wikimedia.org/wiki/File:Amylopektin_Haworth.svg, ineligible for copyright

According to the United States Department of Agriculture, all of the sugars in a potato

are composed of sucrose, glucose, and fructose. Table 2 shows sugar content of Idaho and red

potatoes (USDA, 2005). Two potatoes, Idaho (Russet) and red (Norland), contain total sugar

amounts of 0.61 g and 1.44 g, respectively, in 100 g of product (USDA, 2005).

Table 2

Total Sugar Content of Tubers under Investigation: Idaho and Red (Norland)

Type of Tuber Sucrose (g) Glucose (g) I Fructose (g) Total Carbohydrate (g)

c-:::-:-... ...

Idaho, raw fresh (100 g) 0.13 • 0.25 0.23 18.07 I

Red, raw fresh (100 g) 0.45 • 0.55 0.44 19.59

I [

Since chemical composition of potatoes defines storage parameters, processing

flexibility, and end use, the potato processing industry has had to take into account factors such

as dry matter content, sugars, proteins, and other nitrogen compounds. The dry matter content

was determined mainly by genetics and individual cultivars. As 60-80% of the dry matter

consisted of starch, major correlations exist between the dry matter and the starch content of the

26

potato. Other factors that have influenced the dry matter content of the potato are; 1) maturity,

2) growth patterns as influenced by nitrogen fertilizer application; and 3) climate, soil and

potassium fertilizer applications (Rastoviski, 1987).

The timing of the potato harvest has influenced the storage life of potatoes. Long-term

storage of potatoes requires specialized care in cold warehouses. Consideration of the storage

life of the potato has become increasingly important as temperature influences the nutrient values

and palatability. Southern states harvest potatoes at the size required for market and immediately

make them into chips regardless of their physical maturity (Peet, 2005). However, in the primary

crop production areas of the United States, storage life has been improved by leaving the tubers

in the fields until they had reached physiological maturity. The skin or periderm thickens and

"sets" from 90-100 days subsequent to the initial planting, thus improving shelf life (Peet, 2005).

As the quality of the storage life improves, the dry matter content peaks during this period.

Thus, the physiologically mature tubers have higher starch and protein levels and lower

respiration, water content, and sugar levels.

Storage Temperatures

The storage temperatures are dependent upon the intended final use. In the storage and

curing process, the tuber was often cured at 60° F and 95% relative humidity for two weeks in

order to suberize the outer layer of the potato skin and thicken the periderm. This process

reduces the chance for infection and water loss. Additionally, adequate ventilation aids in

preventing C02 buildup and the increase of sugar content. Reduction of the temperature

eliminates the breakdown of tubers, sprouting, and water loss, and leads to reducing glucose and

fructose accumulation (Peet, 2005). A natural internal donnancy occurred when tubers were kept

from sprouting for the first two or three months of storage. Beyond the initial two to three month

27

period, a CIPC (chlorpro-phom) could be introduced to the ventilating system to inhibit

sprouting. Before tubers were removed from storage, tubers stored below 50° F were warmed to

50-60° F to prevent further bruising during the shipping and handling process (Peet, 2005).

In a two year study of potato storage research at the Kimberly Research and Extension

Center five varieties of potatoes were influenced in dormancy length by three storage

temperatures of 42° F, 45°F and 48°F, respectively. Three separate repetitions per variety per

storage temperature and sprout inhibition treatments were tested. The results showed a

fluctuation of glucose concentration between the highest and the lower temperatures. Sugar

concentrations were the highest at 42°F, while at the other temperatures the tubers exhibited

nearly the same levels of concentration. The sprout inhibitor did not show significant differences

in glucose concentrations (Kleinkorpf & Brandt, 1999).

Although potatoes stored below 7° F generally produce dark colored potato chips due to

the reducing sugars that build up, this low storage temperature also reduced the fresh weight and

sprouting (Harvey, Genet, Lammerink, & Mann, 1998). The New Zealand Institute for Crop &

Food Research screened more than 600 potato cultivars, over the course of three seasons. The

primary goal of the experiment was to identify how low temperature storage affected potato

chips. The outcome of the New Zealand study shows resistance to cold-induced sweetening

(Harvey et aI., 1998).

Ventilation in Storage

In all facets of the modern potato industry, efficient and effective storage are a high

priority. In order to maximize economic returns from fresh, processed, and seed segments,

specific reducing sugar concentration quality standards must be met. Although storage interacts

28

with a large number of pre-harvest, as well as post-harvest factors, ventilation was one of the

most important factors in successful post harvest storage.

Directly affecting potato quality and shrinkage is the ventilation which is influenced by

several environmental parameters. Airflow volume, at a desired temperature and relative

humidity, was expected to provide uniformity among a potato crop. From storage structures,

ventilation removed field and respiratory heat from potatoes, and eliminated respiratory CO2

accumulation. Since airflow requirements changed through the storage seasons, proper

ventilation was found to be a much needed investment. The University ofIdaho conducted a

study on variations of ventilation units within commercial ventilation systems. A significant

reduction in product shrinkage resulted from using the VFD fan control, which provided the

stored potatoes with the correct volume of airflow in order to remove respiratory heat and C02

while avoiding excessive ventilation (Oberg & Kleenkorpt, 2003).

With the support of a grant, three researchers (Verma, Sharma, & Verma, 1974)

investigated the effects of low temperatures on the respiration changes in carbohydrate of potato

tubers. They studied samples over a three day period at specific times and determined that

sugars increased significantly after the potatoes were wounded. Chemical analyses showed an

increase in sugar content, thought to be caused by callus formation activity. In addition,

respiration caused by wounding was explained to be the basis ofthe sugar content in the cell

walls of the potato tuber (Verma, Sharma, & Verma, 1974).

Packaging and Moisture Loss

Storage facilities and storage containers always aim to minimize moisture loss by

monitoring their storage procedures, temperature and other environmental factors. During the

post harvest and storage periods, moisture loss was determined to be an important parameter in

29

product quality deterioration. Moisture transfer depended upon the characteristic of the potato

tuber or the storage moisture. The amount of the free water inside the tuber for transport to the

outside and the permeability of the skin detennined the quantitative water loss per unit of time.

The magnitude of these factors depends upon the water potential within the soil as well as the

degree of the suberization and periderm formation. In storage, the relative humidity of the

storage atmosphere and the maturity were also critical to govern and control moisture loss

(Rastovaki, 1987).

Packaging requirements depend on a number of factors. There are consumer needs,

storage, packaging and destination, method of transport, season, and possible plant disease. To

maintain quality, general requirements have been established in order to ensure packaging

integrity. In order to maintain potato product quality, allowances must be made to eliminate

CO2, water vapor, and heat. Packaging has influenced the amount of product respiration through

adequate ventilation and degrees of permeability. Companies carefully engineer packaging in

order to ensure quality and marketability (Rastovaki, 1987).

Analyses

Food products are complex, heterogeneous and biological materials which contain

substances that may interfere with measurements of the mono- and oligosaccharides. During

analysis of such products, it is important to choose the best method to ensure efficient and

accurate sample analysis. In some studies, interference arose from various compounds or

absorption of light of same wavelengths using spectrophotometric methods in the analysis of

carbohydrates (Nielson, Wischmann, Enevoldsen, & Lindberg, 1994), In addition, insoluble

colloidal material may scatter light wavelengths that are measured for absorbance. Furthermore,

aldehyde or ketone groups within sugar can react with other components. Amino groups of

30

proteins, especially in a non-enzymatic browning or Mallard reactions, produce color that

destroy the measurable sugars. For determination of mono- and disaccharides, extraction with

hot 80% ethanol can be used; carbohydrates are soluble in polar solvents. Most food is mostly

composed of polysaccharides and proteins, which are insoluble in hot 80% ethanol, making

extraction rather specific for mono- and disaccharides. The extract will contain other

components than that of carbohydrates such as particular ash, pigments, organic acids, and

perhaps free amino acids and low molecular weight peptides (Nielson et aI., 1994).

Testing methods in potato studies vary as a functional aspect of the growth and storage in

tubers being researched. The methods selected often depend on the various chemical

composition characteristics of foods. One characteristic noted was the composition of

carbohydrates. Carbohydrates are sensitive to high temperatures and strong acids. The phenol­

sulfuric acid method continues to be the most widely used condensation method. This method is

considered to be rapid, simple, sensitive, accurate, and specific for carbohydrate analysis. The

total carbohydrate, including sugar derivatives, oligo-, and polysaccarides can be determined.

Monosaccharides were released when oligo- and polysacchrides reacted due to hydrolysis.

Under proper conditions, the phenol-sulfuric acid method was accurate to ±2% (Nielson et ai.,

1994). As a function of the structure of the sugar, this method was never stoichiometric;

therefore, standard curves must be used for sugar analysis. With concentrations greater than the

upper limits, dilutions were necessary in order to test within the limits of the standard curve

(Nielson et aI., 1994).

Iodine testing is another method used for quantitative analysis to measure the amount of

enzyme activity present in potato samples. Since starch molecules are glucose polymers linked

together by alpha-I, 4 and alpha-I, 6 glucosidic bonds, the color present in testing samples was

31

proportional to the amount of the starch present in solution. Quantification of a tested sample

can be measured by the amount of light produced at the given wavelength. As it passed through

the sample after a reaction had occurred with iodine, the recorded absorption value could be

determined as the rate of enzymatic breakdown of the starch.

32

Chapter III: Methodology

After potatoes are harvested and put through the curing process, storage is the critical

step in the shelf life of tubers to maintain a slow natural decomposition. Humidity, ventilation,

temperature, and moisture all play an important role in how the tubers decompose. Moreover,

the enzymatic activity and moisture loss within tubers deteriorates the quality of the product

under temperature variations and storage conditions. On average, common losses throughout

harvest range from 5-40% depending on the types of tubers (Sira, 2000). When conditions such

as temperatures and storage are compromised this can influence and be very crucial to the overall

flavor and physical appearance of the tuber. Poor storage produces off flavoring and

discoloration in potato products when they are processed for food products. By monitoring

conditions during tuber processing, the enzyme activity and moisture loss, tubers can be stored

for about 10 months under favorable conditions. When consumers buy tuber products they have

much less time to consume the product as there is a shorter shelf life because home storage

conditions are not adequately maintained for the highest quality and palatability.

During this study, testing was completed to determine the rate of tuber decomposition in

terms of carbohydrate composition, enzyme activity, and moisture loss. Three different bag

types were used in these tests; knitted L sewn, wicked claf mesh and claf half-n-half

polypropylene which were donated from a Midwestern plastics company. All bags were labeled

with a number 1 thru 10 and placed in shelf positions as shown in table 3. Bags 8, 9 and 10 were

located on the bottom of the shelf with bags 1,2,3,4,5,6, and 7 placed beside or slightly on top

of the other bags. Potato samples in each bag were consistent for each potato type and bag

shown in table 3. The bags were then stored in a controlled atmosphere at a relative humidity of

98% and a controlled temperature of 6° C (42° F).

33

Table 3

Potato Storage Diagram of Potato Types under Investigation

Idaho Potato- claf half-n-half bag (A), 11 potatoes per bag

1 2 10 3 4 8 9

7 6 5 Red Potato- claf half-n-half bag (A), 51 potatoes per bag

1 2 10 3 4 8 9

7 6 5 Idaho Potato- wicked claf mesh bag (B)- 11 potatoes per bag

1 2 10 3 4 8 9

7 6 5 Red Potato- wicked claf mesh bag (B)- 51 potatoes per bag

1 2 10 3 4 8 9

7 6 5 Idaho Potato-knitted sewn bag (C)- 10 potatoes per bag

1 2 10 3 4 8 9

7 6 5 Red Potato- knitted sewn bag (C)- 32 potatoes per bag

1 2 10 3 4 8 9

7 6 5

The first testing method was to study the total carbohydrate composition of the potatoes.

To test the carbohydrate content, the phenol-sulfuric acid method was utilized to determine the

total carbohydrate composition over the duration of the 10 week study (AOAC, 1990). The

underlying principle of this method is that carbohydrates are destroyed with heat and acids;

carbohydrates are patiicularly sensitive to strong acids and high temperatures. When these are

34

applied to a sample, a series of complex reactions occur. The first reaction occurs with

dehydration. With continual heat application various furan derivatives are produced. After the

products condense with themselves and other products, brown and black substances are

produced. In this method phenol condenses and produces compounds that are useful for

carbohydrate analysis. Phenol is the method most widely used due to its simplicity, rapid,

sensitive, accurate and specificity for carbohydrates. All types of carbohydrates can be analyzed

including oligo- and polysaccharides using this method. The phenol-sulfuric method is an

inexpensive, readily available and stable method to determine the amount of total carbohydrate

in the potato varieties and produces an accuracy of ±2% under proper conditions (AOAC, 1990).

The second testing method determined the amylase activity within the potatoes. When

cells of potatoes decompose, metabolic activities allow the breakdown of starch. To start potato

samples were collected, weighed and recorded. The sample was then pulverized into a paste

consistency using a mortar and pestle. To test enzyme activity the extracted pulp samplewas

combined with 20 mL ofTris Buffer solution. After briefly stirring and sitting for 10-15

minutes, the enzyme was brought into solution. The extracted sample was then strained,

weighed and stored on ice. For testing preparation test tubes were filled with 1 mL of prepared

1 % starch solution. To test enzyme activity 4 drops of extract were added to the starch solution

and processed for 30-45 minutes. In order to visibly see the starch present in samples, 1 drop of

potassium iodine solution was added to view colors varying from blue to purple. Blue indicated

present of starch while purple to avocado to brown indicated starch breakdown due to enzymatic

activity. To determine absorbance of each sample a single cell spectophotometer was used to

obtain an absorbance reading for each sample. Results were collected and recorded for

35

absorbance (620f.tm - blue color) for 10 weeks. This method determined the amount of amylase

enzyme activity present within the potatoes.

The last testing method used was overall moisture loss of the product. This method was

used to determine the moisture loss over time to determine if the potato products were

decomposing in terms of moisture depletion.

Subject Selection and Description

The samples were selected from a local grocery store as to be a popular seasonal crop

available in the Midwest. A total of 320 Idaho potatoes and 1340 red potatoes were used to

achieve similar weights for the storage bags during this 10 week research study. The

independent variables included the type of potato, red or Idaho, and three types of mesh polymer

bags: knitted sewn bag, wicked clafmesh bag, and c1af half-n-half bag. Pictures of the three bags

are shown in Figure 5, 6 and 7.

Figure 5. Raschel knitted L sewn bag. Picture used by permission of Volm Bag Corporation,

the company that provided the bags (http://www.volmbag.comlmeshbags.html)

36

Figure 6. Wicketed claf mesh bag, Picture used by permission of Volm Bag Corporation, the

company that provided the bags (http://www.volmbag.com/meshbags.html)

Figure 7. Claf half-n-half bag. Picture used by permission ofVolm Bag Corporation, the

company that provided the bags (http://www.volmbag.comlmeshbags.html)

37

Instrumentation

To prepare for the data collection a standard curve of glucose was produced by mixing

various concentrations of glucose with glucose dehydrogenase (GluDH) reagent and incubating

the flasks at room temperature for 30 minutes. Next, the various concentrations of glucose were

tested with the use of spectrophotometry to determine the absorbency which read from 0 to 0.78

11m. The standard curve helps increase accuracy and the sensitivity of the testing method

(Krause et aI., 1990).

Next, this method called for a 1 inch sample which was obtained from randomly selected

potato samples (samples were used and destroyed with each sample collection). Each sample

was freeze dried for 1~2 days. Upon completion of freeze drying, the samples were crushed into

a powder consistency with the use of a mortar and pestle. Next the extraction process took place

by using 10 mL hot ethanol (80%), followed by centrifuging, and then pouring off the liquid.

The sample was then placed under the ventilation hood, placed on a combination hot and stirring

plate using a stir rod. To evaporate any remaining liquid a heat plate and stirring rod were used.

Phenol solution at 5% dilution was mixed under the hood, followed by rapid drops of

concentrated sulfuric acid. The sample was agitated producing heat while a yellow orange color

was observed (Krause et aI., 1990). The sample was then tested for absorbency using an Agilent

8453 UV~Vis spectrophotometer.

For the enzyme determination, the potato was weighed whole, and then a sample was

acquired by cutting a 1 inch sample. With the use of a mortar and pestle the sample was ground

into a paste. Next, 20 mL of cold TRIS buffer solution was added and the reaction was allowed

to progress for 10-15 minutes. This step helped bring the enzyme into solution. Once stirred, the

pulp was removed and the extract stored on ice until a 1 % starch solution was prepared and

38

added to the extract sample. After 40-45 minutes, iodine was added to test for the starch present.

A blue color meant that all the starch was present, purple to avocado to brown meant that the

starch had broken down due to greater enzyme activity. The results were recorded using a single

cell spectrophotometer at an absorbency standard of 620 TJm (blue color). This test for enzyme

activity has been used for its simplistic method and time for rapid results. Tris buffer is an

inexpensive solution to obtain and use.

The final method used was the overall water loss of randomly selected samples. This

method was used over time to observe the moisture content which affects the loss of quality of

potato tubers. To obtain a testing sample, both types of potatoes from the three bags were

weighed whole and standard 1 inch samples from each potato and bag type were collected and

weighed each week to determine the overall moisture loss. This helped determine the amount of

moisture the product was retaining or losing during the 10 week study.

Data Collection Procedures

Data collection was obtained over a 10 week period using two to three samples of each

potato variety from each storage bag weekly to gather data to verify the total carbohydrate

composition, enzyme activity, and moisture loss during the storage process.

Data Analysis.

The statistical program SPSS was utilized to analyze the data. Oneway ANOVA tests

were used to analyze each of the three tests of the potatoes, carbohydrate composition, enzyme

activity, and moisture loss of potatoes.

39

Limitations

Limitations of this study include the testing equipment, space, time, and measurement

error. Within the first week samples were compromised due to equipment failure of the

controlled environment and week two started with a new selection of all variables.

Summary

The methods used in this study helped to determine the moisture and crude weight loss

over a period oftime as well as how the enzymatic breakdown affected the overall quality of the

starch composition. These methods were designed to help create limited variance and quality

results that could be used for further recommendations of the study.

40

Chapter IV: Results

Common losses throughout harvest and storage of potatoes range from 5-40%. Factors

that impact loss include storage conditions such as temperature, absence of light, and humidity.

When changes occur in the carbohydrate composition, enzymatic activity and moisture loss the

quality of the potato deteriorates. The purpose of this research study was to investigate whether

the type of storage bag impacted the carbohydrate composition, enzymatic activity and/or

moisture loss in potatoes. Two types of potatoes, Idaho and red were used in the study. Three

types of mesh polymer bags were used; knitted sewn bag, wicked claf mesh bag, and a claf half­

n-half polypropylene bag.

Item Analysis

A phenol-sulfuric acid method was used to determine the amount of total carbohydrate

that was present in the potatoes. Table 4 provides the means and the standard deviations on the

carbohydrate composition of tested Idaho potatoes using the three types of bags. The mean of

131 samples was 482.42 ± 20.75 11m The means + standard deviations were 478.94 ± 24.77,

484.05 ± 19.49, and 484.87 ± 16.12 11m, for the knitted L sewn, wicketed clafmesh and clafhalf­

n-half polypropylene bags, respectively. There was no significant difference on the carbohydrate

composition of the Idaho potato by storage in any of the three bags F (2, 128 1.084, p = 0.311).

4]

Table 4

Comparison of Carbohydrate Composition in Idaho Potatoes Stored in Three Different Bags

Mean± SD N

Knitted L Sewn 48 478.94 ± 24.77 _ ....... _ .... _- -----------------------.... ----

Wicketed ClafMesh 44 484.05 ± 19.49 -------------------------------.... ---

ClafHalf-n-Half 39 484.87 ± 16.12 Total 131 482.42 ± 20.75

The amount of blue color determined the amylase enzyme activity in the Idaho potatoes

which had been stored in the three different bags. Those with higher blue color had lower

enzyme activity. Twenty seven total samples were analyzed which represented values taken over

the nine weeks of storage beginning with week two (See Table 5). Although not significantly

significant, the Idaho potatoes stored in knitted L sewn bag had the lowest enzyme activity as

indicated by greater blue color and those stored in the claf half-n-half polypropylene bag had the

highest enzyme activity as indicated by less blue color F(2, 24 = 0.356, p 0.704).

Table 5

Comparison of Enzymatic Activity in Idaho Potatoes Stored in Three Different Bags

Knitted L Sewn Wicketed Claf Mesh Claf Half-n-Half Polypropylene Total

9 9 9

27

Mean± SD

.303 .090

.280 ± .095

.270 ± .076

.284 ± .085

42

The overall water loss of randomly selected whole Idaho potato samples was examined.

Whole Idaho potatoes were weighed over the nine weeks to record the moisture content. To

obtain testing samples, whole Idaho potatoes from the three bags were weighed each week to

determine the overall moisture loss. Table 6 indicates that the 144 potatoes that were weighed

had a mean weight of276.289± 40.057 g. Although not significantly different, the Idaho

potatoes stored in the wicketed clafmesh bags retained more moisture (mean 280.961 g) and the

claf half-n-half polypropylene bags L sewn bags retained the least moisture (mean 271.632 g) F

(2,141 = 0.648, P = 0.525).

Table 6

Comparison of Moisture Loss in Initial Weight of Idaho Potatoes Stored in Three Different Bags

Knitted L Sewn Wicketed Claf Mesh ClafHalf-n-HalfPolypropylene Total

n 48 48 48 144

Mean± SD

276.279 ± 63.094 280.961 ± 15.802 271.632 ± 24.638 276.289 ± 40.057

Standard 1 inch samples from each Idaho potato taken from each type of storage bag

were prepared and weighed each week to also determine moisture loss. When these samples

were analyzed (Table 7), no significant differences were found. In 144 samples (48 per bag), the

mean weight ± standard deviation was 10.022 ± 0.574 g.

Table 7

Comparison of Moisture Loss in the Sample Weight of Idaho Potatoes Stored in Three Difforent Bags

Mean± SD n

Knitted L Sewn 48 10.026 ± 0.608 Wicketed Claf Mesh 48 10.007 ± 0.518 Claf Half-n-Half Polypropylene 48 10.034 ± 0.604 Total 144 10.022 ± 0.574

43

The phenol-sulfuric acid test for carbohydrate used a weighed amount of freeze dried

sample of red potato which was further tested by extracting the carbohydrate using a

condensation of phenol. Sulfuric acid was then used to agitate and create a yellow orange color.

The method detelmined the amount of total carbohydrate that was present in the red potatoes.

Table 8 provides means and standard deviation on the carbohydrate composition of tested red

potatoes using the three types of bags. The mean of 131 samples was 490,87 ± 13.92 g. The

means in grams ± standard deviations were 492.52 ± 2.74, 487.53 ± 23.24, and 492.70 ± 2.85 for

the knitted L sewn, wicketed clafmesh and claf half-n-half polypropylene L sewn bags,

respectively. There was no significant difference on carbohydrate composition ofthe red

potatoes by storage in any ofthe three bags F (2, 128 = 2.002, 0.139).

Table 8

Comparison of Carbohydrate Composition of Red Potatoes Stored in Three Different Bags

Mean± SD n

Knitted L Sewn 42 492.52 ± 2.74 Wicketed Claf Mesh 45 487.53 ± 23.24 Claf Half-n-Half 44 492.70 ± 2.85 Total 131 490.87 ± 13.92

The method to determine the amount of amylase enzyme activity present within the red

potatoes used an extracted pulp sample which was combined with a Tris Buffer solution for 15

minutes. The sample was strained and was mixed with a 1 % starch solution and analyzed using

a spectrophotometer recording the absorbance (620 11m blue). The amount of blue color

determined the amylase enzyme activity in the potatoes which had been stored in the three

different bags; more blue color indicated less enzyme activity available to break down the starch

solution. Although not significant, the red potatoes stored in the claf half-n-half polypropylene

44

bags exhibited less enzymatic activity (indicated by more blue color) than the knitted L sewn

bags F (2, 24 = 0.270, P = 0.765).

Table 9

Comparison of Enzymatic Activity in Red Potatoes Stored in Three Different Bags

Mean± SD Bag Type n 11m Knitted L Sewn 9 .271 ± .091 Wicketed Claf Mesh 9 .279 ± .078 Claf Half-n-Half Polypropylene 9 .300 ± .091 Total 27 .284 ± .085

The overall water loss of randomly selected whole red potato samples was examined.

Whole red potatoes were weighed over the nine weeks to record the moisture content. To

obtain testing samples, whole red potatoes from the three bags were weighed each week to

determine the overall moisture loss. Table 10 indicates that the 144 potatoes that were

weighed had a mean weight of69.646 ± 16.532 g. Although not significantly different, the

red potatoes stored in the knitted L sewn bags retained more moisture (mean 73.179 g) and

the wicketed clafmesh bags retained the least moisture (mean 66.241 g) F (2, 141= 2.149, P

= 0.120).

Table 10

Comparison of Moisture Loss in Initial Weight of Red Potatoes Stored in Three Different Bags

Mean± SD Bag Type n g Knitted L Sewn 48 73.179 ± 14.710 Wicketed Claf Mesh 48 66.241 ± 14.776 Claf Half-n-Half Polypropylene 48 69.517 ± 19.295 Total 144 69.646 ± 16.532

45

Standard 1 inch samples from each red potato taken from each type of storage bag were

prepared and weighed each week to also determine moisture loss. When these samples were

analyzed (Table 11), no significant differences were found. In 144 samples (48 per bag), the

mean ± standard deviation was 9.707 ± 0.418 g.

Table 11

Comparison of Moisture Loss in the Sample Weight of Red Potatoes Stored in Three Different Bags

Mean± SD Bag Type n g Knitted L Sewn 48 9.984 ± 0.429 Wicketed Claf Mesh 48 9.641 ± 0.413 Claf Half-n-Half Polypropylene 48 9.796 ± 0.402 Total 144 9.707 ± 0.418

Chapter 4 has summarized the results obtained from the testing procedures for the two

types of potatoes stored in the three kinds of bags. Chapter 5 will discuss the significance of

these findings and recommendations for future research.

46

Chapter V: Discussion

This study investigated whether the type of storage bag impacted the carbohydrate

composition, enzymatic activity and/or moisture loss in two types of Idaho and red Norland

potatoes. Three types of mesh polymer bags were used; knitted sewn bag, wicked claf mesh bag,

and a claf half-n-half polypropylene bag.

Limitations

This research study controlled humidity and temperature throughout the duration of the

testing. The variations in humidity and temperature of the controlled environment were limited

to the humidity and temperature selected for the research study and did not examine other

humidity conditions and temperatures that might also affect shelf life of potatoes stored in the

different bags.

Tuber products were pre-selected to red and Idaho potatoes, seasonal crops common to

the Midwest. Thus, only two types of tubers were tested. Due to space, the weight ofthe tubers

consisted of predetermined amounts and the shapes of each type of bag were similar for

consistency in the controlled environment. Thus other product bag shapes and changes that

might occur if other product weights had been used were not examined.

All storage bags were made of polymer plastics and varied only in mesh type, therefore,

these research findings are limited to this particular type of polymer plastic and may not extend

to other plastic bags and mesh types which are available.

Time was the last item that could be manipulated to allow for gathering more data upon

potato types versus type of bag to determine storage capabilities, ventilation processes, and

temperature control variables. This could be extended for any given of period to help define the

bag and potato storage parameters.

47

Conclusions

This research study has shown no statistical difference for in the two tubers in regards to

their carbohydrate composition, enzyme activity or moisture loss in regardless of the bags tested.

The results lead to the conclusion that companies would find any of the bags tested suitable for

storage to help keep the potatoes properly ventilated and moisture controlled before

consumption.

Recommendations

It is suggested for future research with polymer bags that the structure and design of the

bags be modified for more options to test. It would also be beneficial to select a longer period of

time to test potatoes to understand the chemical and physical changes which occur during

prolonged storage.

Ventilation would also be a consideration for future research. This will help to define

different air flow, relative humidity and temperatures that may affect the overall palatability of

the potato products. By utilizing more bag types and variations of humidity and temperature

over varying time periods, more information would be available to companies in their selection

of polymer bags for potato storage.

Sensory evaluation is yet another area that would help create valuable information that

companies would need in making a sound decision about quality polymer bags for storage. By

testing more potato varieties with an assortment of storage bags following by pairing the stored

tubers with different cooking methods could result in additional information that could enhance

product marketing.

48

Permeability rates would be an additional research area to add to the future studies. The

results would help create viable information of how the polymer handles permeation over time

with regards to proper ventilation, temperature fluctuations, and relative humidity.

Lastly, by increasing the variety of potato types researched, the polymer plastic that

would be best suited for each potato type could be determined. By using four to five varieties of

tubers under the same conditions; ventilation, temperature, relative humidity, and also including

permeability rates and sensory evaluation, more data could be gathered that companies might use

in their research/development and marketing departments.

49

References

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characteristics of foods (pp.171-73). Washington D. C.: Association of Official Analytical

Chemists.

Block, B. 2008. Antoine-Augustin parmentier: Phalmacist extraordinare. Pharmaceutical

Historian, 38(1): 6-14.

Dwelle, R. B., & Love, S. L. (2001). Potato growth and development. Retrieved

from http://www.cals.uidaho.eduipotatolPotatoProductionSystems

IT opics/Growth&Devel opment. pdf

Fernie, A., & Willmitzer, L. (2001). Molecular and biochemical triggers of potato tuber

Development. Plant Physiology, 127, 1459-1465.

Harvey, W. J., Genet, R. A., Lammerink, J. P., & Mann, 1. D. (1998). Screening the New

Zealand potato germplasm collection for resistance to sugar accumulation during low

temperature storage. New Zealand Journal of Crop and Horticultural Science, 26,89-93.

Hijmans, R. 2001. Global distribution of the potato crop. American Journal of Potato

Research, 78 (6),403-12.

International Society for Tropical Root Crops and F AO. (2008). Potato World, International:

Year of the potato. Retrieved from http://www.potato2008.org/enlworld/imp/index.html

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