fst 101 exercise 1 experiment 3&4 results and discussion

8/9/2019 FST 101 Exercise 1 Experiment 3&4 Results and Discussion

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Experiment 3: Water Activity and Food Quality

Water Activity is defined as the unbound water in food that allows the growth of

microorganisms. elative !umidity" defined as the amount of water vapor in the air" affects the

amount of water in food. Food exposed in high relative humidity has high Aw since there is a

direct relationship between relative humidity and water activity. #ac$aging is employed order tomaintain stability in food. %he food becomes isolated from the environment through pac$aging

and the barrier prevents the entry of microorganisms. Also" pac$aging maintains the desired

water activity of the product by sustaining the humidity inside of the pac$aging e&ual to the

humidity of the product which is also called e&uilibrium relative humidity. %his experiment

demonstrates the effect of different relative humidity on food samples as shown in %able 3.'.

%able'.3. (ata and observations on cabbage before and after exposure to different relative

humidities.

)elative

!umidity

*!+

Appearance %exture ,ass ofcrucible -

cabbage" g

ain *-+/

0oss *1+" g

2efore After 2efore After 2efore After

' 0ight green"

fresh loo$ing

brown

pigmentation

but still

succulent

smooth soft 3'.' 3'. 1.'

4 0ight green"

5risp" fresh

loo$ing

brown

pigmentation"

dry

smooth slightly

rough

67.8 67.9 1.'

7 0ight green"

5risp" fresh

loo$ing

brown

pigmentation"

dry

smooth lightly

rough

68.9 69.; 1.7

9 0ight green"

5risp" fresh

loo$ing

brown

pigmentation"

very dry

smooth rough 64.4 6;.; 1'.'

3 0ight green"

5risp" fresh

loo$ing

brown

pigmentation"

very dry

smooth rough 6;.' 68.< 1'.7

5abbage was used as the food sample sub=ected to different relative humidities *!+ of

')" 4)" 7)" 9) and 3). 2efore the experiment" the cabbage leaves were light green in

color" smooth" crisp and fresh loo$ing. %he cabbage sub=ected to ') ! lost weight and there

was slight brown pigmentation observed yet the cabbage leaves are still succulent. %hose

exposed in 4) ! and 7) !" lost weight and the leaves were dried. 5abbage leaves

exposed in 9) ! were much drier that those exposed in 4) and 7) and a significant



decrease in weight could be observed. Among the samples exposed to different !" the cabbage

leaves exposed to 3) lost the greatest amount of weight.

%heoretically" it is expected for that the cabbage exposed to 3)" 9) and 7) !"

respectively" will lose weight because there is more moisture in the cabbage than in the air inside

the =ar. >n order to achieve e&uilibrium relative humidity" the cabbage will release water from itssystem. ?n the other hand" the cabbage exposed to 4) and ')" respectively" should have

gained weight. ince there is more moisture in the air in than the sample" the cabbage will absorb

water present in the air inside the =ar. #ossible errors may be from the balance *instrumental

error+ and the time allotted for the system or the =ar with sulfuric acid to achieve e&uilibrium

relative humidity. %he time allotted might not be sufficient to reach the correct ! for each

system.

esults gathered showed that low relative humidity causes loss in moisture thus" loss in

weight in food. %he food will ta$e up moisture if the relative humidity is greater that the water

activity of the food. ?n the other hand" the food will lose moisture on its surface if the relativehumidity is lower than the water activity of the food. 0astly" the food neither gains nor loses

weight if the relative humidity is e&ual to the water activity" which is also called e&uilibrium

relative humidity.

>n relation to food stability" foods that have low water activities are more stable since

their water activities are restricted. %here is an inverse relationship between water activity and

the stability of food. For instance" microorganisms have less chances of surviving if water is

made unavailable since they re&uire water to live and reproduce. %hus" spoilage of food will be

less and food &uality is increased.

Food pac$aging is very helpful in maintaining anaerobic conditions for food to prevent

microbial growth however it has different effects on fruits and vegetables. ince they mostly

contain water" their cells transpire causing moisture inside the pac$aging. For instance" a pechay

is to be wrapped in plastic for four days. ince the humidity inside the plastic is not controlled" it

is expected that the pechay will no longer be crispy due to transpiration of water from the pechay

to environment inside the plastic to achieve e&uilibrium. @ow that moisture is present in the

pac$aging" microorganisms can grow now grow and cause spoilage. ?n the contrary" putting the

pechay in the vegetable crisper of the refrigerator maintains the crispiness of the pechay.

efrigeration increase shelf1life of the food since low temperature delay microbial activities.



Experiment 4: Freezing of Water

Freezing is one of the most common food preservation techniques used. Low

temperature delay microial activity as well as reaction rates in foods. Freezing

causes expansion of water molecules present in foods causing damage to cellular

properties of foods resulting to unacceptale changes in frozen foods such as loss of texture integrity! destailization of emulsions! "occulation of proteins and increase

in toughness of #sh "esh. Freezing transforms water to ice in high degree of purity

and causes changes in p$! ionic strength! viscosity! osmotic pressure! vapor

pressure! and other properties. Large ice crystals resulted from slow drying while

tiny ice crystal found extra% and intracellularly resulted from rapid freezing. &rystal

growth of water has a direct relationship with temperature and it can e a'ected y

adding di'erent food additives as shown in tale 4.(.

)ale 4.( E'ect of di'erent food additives on the freezing of water.

*ample +ppearance and textureefore freezing after freezing,istilled water &lear colorless liquid &lear colorless liquid! unfrozen

)ap water &lear colorless liquid &lear colorless liquid! frozen-ango uice &loudy yellow! liquid mixture )urid! yellow liquid! slightly

viscous! liquid part on top/01 sucrose &lear colorless solution with small

ules

&olorless liquid! almost

completely unfrozen-il2 &ream colored thic2 mixture $eterogeneous mixture!

viscous! unfrozen-il2 and

gelatin

*emi%gelatinous mixture! cream

colored

$eterogeneous mixture!

viscous! unfrozen with

sediments at the ottom-il2 and egg

yol2

Leche "an%li2e mixture $omogenous! light yellow

liquid! viscous! unfrozen

)he distilled water and tap water still are oth clear and colorless yet tap

water froze. )he mango uice and sugar solution did not freeze. -il2 containing

sugar! vanilla and salt remains liquid upon freezing. )he sugar! which decreases the

size of ice crystals! and salt! which lowers the cooling e'ect of freezing! added

decreases the freezing point of mil2. 3n the other hand! vanilla doesnt have an

e'ect on the freezing point ut ust adds "avor and aroma. 3n the other hand! mil2added with gelatin and egg yol2! the solutions ecame liquid to semi%solid upon

freezing. )his is due to the egg or rennins present in the additive used facilitate the

formation of large crystals and thic2ening of the mil2.

Freezing and the addition of additives is important in food. Examples are ice

cream and sheret. 5ce cream contains sugar! cream or utter! egg products! fruit

ingredients and other "avorings are added to mil2. )he eggs serve as thic2ener and

fst 101 exercise 1 experiment 3&4 results and discussion

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