Food preservation

BY

ASSOC.PROF.DR.NARUMOL MATAN

Food preservation by irradiation

Electromagnetic spectrum

1. Low-quantum energy: There are wide range of wave and low quantum energy such as radio and infrared. The effect of this radiation is related to the vibration of thermal energy in food, molecules of food are stimulated, (excited state).

2. High-quantum energy: There are short wave and with high quantum energy. High-quantum energy can destroy organic compounds and microorganisms without causing heat in the product (Cold sterilization). Moreover, can separate particles of the substance into electrical charge (Inonizing radiation).

Ultraviolet Radiation

Ultraviolet light is used in the food industry. Certain wavelengths of ultraviolet light are highly damaging to microbial cells. The purine and pyrimidine bases in RNA and DND absorb ultraviolet light with a peak at 260 nm.

200 nm of ultraviolet light is absorbed violently by oxygen, ozone is produced but not affected by microorganisms.

Low-quantum energy

Reaction Mechanism by Radiation

1. Direct

M M + e

M*

Food preservation using ionizing radiation

2. Indirect H2O .H2O+ + e-

H2O*

H20* H20 + .H +.OH

.H20+ + H20 H30+ + .OH

.H + .OH H2O

e- aq + .OH OH-

e-aq+H3O+ H2O + .H

.OH + .OH H2O2

.H + .H H2

H2O2 + e-aq OH + OH-

H2 + .OH H2O + .H

Important Terminology

A rad is a unit equivalent to the absorption of 100 ergs/g of matter.

A kilorad (krad) is equal to 1,000 reds

A megarad (Mrad) is equal to 1 million rads.

1 Gray (Gy) = 100 reds

1. High-dose irradiation or rad apertization (> 10 kGy) such as bacon, shrimp

2. Medium-dose irradization (1-10 kGy)

Radurization

Radicidation

Applications of gramma in foods

3. Low-dose irradiation

Slow down the ripening of the fruit

Inhibits growth of sprouts on potatoes, onions, and garlic.

Kills insects found in wheat, flour, fruits, and vegetables.

Eliminates parasites such as trichinosis -causing parasites in pork such as Campylobacter jejuni

Radiation resistance of microorganisms

1. Capsule formation or swarming of bacteria could enhances the ability to resist radiation.

2. Yeast can resistant ultraviolet light batter than natural

bacteria 2-5 times. Moreover, resistant for inhibiting batter than bacteria 2-5 times. However, mold is the most resistant for inhibiting than bacteria 10-50 time, especially spore.

3. Gram-positive bacteria, are more sensitive to radiation than are most gram- negative bacteria.

4. If the food is alkaline, the bacteria will tolerate better destruction.

5. If the amount of oxygen in food is less, the radiation will destroy the microorganisms better.

than the radiation is better.

6. Foods with low water activity are more resistant to spoilage by bacteria

7. The lag phase is more easily destroyed.

Low-Temperature Food Preservation

The use of low temperature to preserve foods is based on the fact that the activities of foodborne microorganisms can be slowed at temperature.

Low temperatures are often used to slow down the chemical reaction and the activity of enzymes in food, including the growth of microorganisms. However, microbial metabolism continues to be lower than normal condition.

1 ระดบัของความเยน็ในการถนอมอาหาร 1.1 Cool Storage Common, Cellar Chilling Factors Influencing cold storage:

temperature, relative humidity, air circulation, volume and proportion of atmospheric gas and radiation

1.2 Frozen Storage Ice crystal formation

1.2.1 Slow Freezer

1.2.2 Quick Freezer

2. Reaction to microorganisms

2.1 Enzyme inhibition

2.2 Accumulation of toxins in microorganisms

2.3 Protein denaturation

Preservatives can be divided as follows

- Food preservative that have been used without specified by law such as organic acid, vinegar

- Food preservative that have been proven safe to use in food such as Propionic acid, Sodium chloride

- Food additive, this additive will be used when proven safe for human.

Food preservatives

Cells of microorganisms

Bacteria

Fungi

1. Damage the cell wall and cell membranes of microorganisms

Mechanisms to destroy microorganisms

2. Destroys substances during cell growth

3. Destroys genetic material of microorganisms

4. Destroy the enzymes of microorganisms

Propionates

Used to prevent mold in bakery products and prevent slime on bakery products. Moreover, prevent the growth of mold in many butter.

Short-chain fatty acids that affect the permeability of the cell membrane

Performance depends on pH

Benzoates

Used in jam, jelly, margarine, soft drinks and fruits salad etc. The inhibitory concentration of benzoates at pH less than 5.0

against most bacteria. The efficiency of benzoic acid will increase when the length of

the ester group increases.

Mechanisms to inhibit microorganisms

- Metabolism and oxidative phosphorylation of bacteria are inhibited by benzoic acid.

- Permeate to the cell walls in the form of acid

- Allowed from 0.15 to 0.25%

Sorbates

Sorbic acid and calcium salts or potassium sorbates are commonly used as antimicrobial agents by spraying. Dipping or coating the container of cheese, bakery, syrup, juice and jelly.

At pH 6.5 is the best for working.

Acetates

Acetates, that primary component of vinegar is some of the oldest food antimicrobials. Vinegar is commonly used in food seasoning such as mayonnaise, cucumber, sausage, etc.

Acetates has shown variable success as antimicrobial.

- Effect to bacteria and Yeast >Mould

- The performance will increase when using with low pH

1. Definition of drying

Preservation of foods by drying

The process of removing water or moisture from a food product

Separation water from food

Reducing the moisture content of food prevents the growth of microorganisms and slows down enzymatic reactions that take place within food.

2. Drying method

Raw Material

Solid Liquid

Sun Drying

Tray Drying

Tennel Drying

Rotary Dryer

Fluidised Bed Dryer

Drum Dryer

Spry Dryer

Foam-mat Dryer

Freeze Dryer

Microwave&Infrared Dryer

3. Aw on the growth of microorganism

Water in food

Free water and Bound water

Intracellular water and Extracellular water

Table of relationship between aw values and microorganisms.

Organism aw Normal bacterial 0.81 Normal yeast 0.88 Normal mold 0.80 Halophillic bacterial 0.75 Xerophillic fungi 0.65 Osmophillic yeast 0.60

4.1 Microbiology before processing

Contamination during harvest

Microorganisms that grow on the surface of food.

Microorganisms from the environment

Microorganisms from humans

4.2 Microbiology during the drying process

Separation of raw materials.

Peeling vegetables or fruits.

Rinsing, dipping or sun drying

Blanching

4.3 Microbiology during the drying process

All yeast and bacteria are destroyed by heat but spore of bacteria, mold and thermophiles bacteria can found after drying.

Unsuitable condition during drying process. It may support the growth of microorganisms.

Can not detect microorganisms in good storage.

Thermophiles bacteria are the most surviving group and this group can detect in dried food.

4.4 Microbiology after drying

5. Important microorganisms in drying

Osmophile or Osmophilic M.O. eg. Zygosaccharomyces sp. and Saccharomyces rouxii

Osmoduric M.O.

Halophile or Harophilic M.O. eg. Micrococcus halodenitrificans, Vibrio costicolus, V.parahaemolyticus, Pediococcus halophilus, Halobacterium salinarum and Sarcina morrhuae.

Haloduric M.O. eg. Sarcina morrhuae. Xerophilic mold. eg. Aspergillus gluacus,

Fusarium, Penicillium and Toxin eg. Aflatoxin, Penicillic acid.

6. Dried food

Foods %Water

Dehydrated whole eggs 10-11

Wheat flour 13-15

Rice 13-15

Milk powder 15

Fat-free dehydrated

meat 15

Pulses 15

Dehydrated vegetables 14-20

Starch 18

Dehydrated fruit 18-25

Alarm Water Content Dried foods is a food after reduce the moisture and keep well because the moisture content is so low that spoilage organisms cannot grow.

aw < 0.70

Each dried food has a different percentage of water in the food. For example, dried egg should have a percentage of water in rage 10-11 %, the food will be safe from mold growth.

6.1 Dried fruits

- Dried fruits is fruit from which the majority of the original water content has been removed either naturally, through sun drying, or through the use of specialized dryers or dehydrators. In addition, the dried fruit will be flavored with other ingredients such as sugar salt and pepper.

- Moisture ≤ 18 % and aw ≤ 0.75 -The number of microorganisms in fresh fruits ranges from 200-300 cells / g,

mostly in the skin of fruits.

- Bacteria and spore of mold could found on the surface of dried fruits

6.2 Dried vegetables

Dried vegetables is a method of food preservation in which food is dried. Drying inhibits the growth of bacteria, yeasts, and mold through the removal of water. Vegetable have to blanched first and then dried by sun or drying using other energy.

aw ≤ 0.65 Microbial in dried vegetables; 0-1,000,000 cells per gram. Dried vegetable can damage by microorganism. Bacteria found in dried vegetables such as Escherichia, Enterobacter, Bacillus,

Clostridium, Micrococcus, Pseudomonas, Streptococcus, Lactobacillus, Leuconostoc

6.3 Dried eggs

Dried eggs are the complete hen’s eggs, both the white and the yolk, dried to a powder. Nothing is added.

The microorganisms are low 1-2 cells per gram in eggs. However, the microorganism can contaminate under critical conditions such as washing or the microbial are contaminated inside the egg before it is dried because eggs have been cracked.

Drying can reduce microbial growth from 10-100 times, but it is also found that dried eggs contain microorganisms 200-300 cells or more than 100 million cells/gram.

Bacteria found in dried eggs such as Micrococci, Streptococci, Coliforms, Fungi

6.4 Dried milk

Powdered milk or dried milk is a manufactured dairy product made by evaporating milk to dryness.

Microorganisms range from 200-300 cells to 1 million cells / g, depending on the drying condition.

Bacteria found in such as Streptococci, Micrococci and spore-forming bacteria.

7. Effect on food after drying

Changes the texture of solid foods Color peroxidese, catalase Metabisulfite or

Potassium sulfide + carbonyl group ruducing sungar no caramelization

Caroteniod, Anthocyanin

On rehydration the product absorbs water more slowly and dose not regain the firm texture associated with the fresh material.

To losses of nutrients and volatile.

Heat changes during drying cause food to deteriorate.

To losses of vitamin : Vit C, Thiamin, Riboflavin

Protein, lipid and carbohydrate degradation

8. Dry food storage

Dry food storage

Prevents flavour loss

Prevents air / moisture permeability

Sweating : Adjust the moisture content of the air in the crate to an appropriate level for storage.