FST 11 FOOD PRESERVATION AND PROCESSING

FOOD PRESERVATION

Any method of treating and handling food to maintain its desired properties, prevent decay or spoilage (safety), prevent loss of quality or nutritional value (quality), and prevent damage caused by insects or animals

METHODS OF FOOD PRESERVATION

1. Thermal Processing

2. Low-Temperature Preservation

3. Food Irradiation

High-Temperature Preservation

Based on the destructive effects of high temperature (above ambient) to inactivate enzymes and destroy microorganisms.

Levels of Thermal Processing:

• Blanching

• Pasteurization

• Sterilization

Blanching

A mild heat treatment applied to fruits and vegetables to inactivate natural enzymes that cause browning, rancidity, and other deteriorative reactions.

Reasons for Blanching:

1. To soften vegetables for packaging

2. To remove odors, flavors, and waxy surfaces

3. To reduce microbial load

4. To remove gases in vegetables

5. To inactivate enzymes (important in drying and freezing)

Pasteurization

A moderate heat treatment (below boiling point) used to inactivate enzymes and kill heat-sensitive microorganisms that cause spoilage, with minimal change in taste or nutrition.

Pasteurization OBJECTIVES

1. Destroy all disease-producing organisms (e.g., in milk, liquid eggs)

2. Reduce spoilage organisms (e.g., in vinegar)

Goal: Shelf-life extension.

LTLT (Low Temp, Long Time)

63°C (145°F) for 30 min

HTST (High Temp, Short Time)

72°C (161°F) for 15 sec

Sterilization

Complete destruction of all viable microorganisms (yeasts, molds, vegetative bacteria, and spores) in a food product.

Verification

Measured using plating or microbial enumeration techniques

Commercial Sterility

Condition achieved when Clostridium botulinum and other spore-forming pathogens are destroyed, preventing spoilage under normal storage.

Essential Operations:

1. Hermetic sealing (airtight)

2. Heating to ≥ 100°C

Acid Food

Food with a pH below 4.6 (naturally acidic), such as tomatoes, pears, and grapefruit.
Required Heat Treatment: Pasteurization

Acidified Food

Food that becomes acidic (pH below 4.6) after the addition of acids like vinegar; examples include sauerkraut and pickles.
Required Heat Treatment: Pasteurization

Low-Acid Food

Food with a pH above 4.6, such as meat, seafoods, milk, and vegetables.
Required Heat Treatment: Sterilization

LOW-TEMPERATURE PRESERVATION

Storage of food at or near freezing point (0–5°C) to slow down microbial activity and enzyme reactions.

Key Principle:
Low temperature decreases enzyme activity, slowing spoilage.

Refrigerated temperature

above 4°C

Chilling temperature

0–4°C

Freezer temperature

≤ –2°C

Changes During Freezing

Main Changes:

• Freezer burn

• Freeze concentration

• Water displacement

Changes During Freezing

Effects on Food:

1. Texture disruption

2. Emulsion breakage

3. Protein denaturation

4. Physical and chemical changes

FOOD IRRADIATION

Exposure of food to ionizing radiation to control spoilage, destroy pathogens, and extend shelf life by reducing microorganisms and insects.
Also known as: Cold sterilization (non-thermal process).

Purposes of Food Irradiation

• Control insects (replacement for fumigation)

• Inhibit sprouting or ripening

• Destroy vegetative microorganisms and enzymes

• Prevent foodborne illnesses

1. Gamma Rays – from Cobalt-60 or Cesium-137

2. X-rays

3. Electron Beams (E-beams)

Sources of Ionizing Radiation (Approved for Food Use)

Radurization

A low-dose (< 1 kGray) food irradiation process that inhibits sprouting, delays ripening, and kills insects.

Radicidation

A medium-dose (1–10 kGray) irradiation treatment that destroys food-poisoning bacteria and parasites, helping extend product shelf life.

Rappertization

A high-dose (> 10 kGray) irradiation process that sterilizes food, reduces bacterial and viral contamination, and inactivates enzymes.

Drying

Removal of moisture from food under natural conditions such as sunlight and wind (e.g., open sun drying, shade drying).

Dehydration

Removal of moisture by artificial heat under controlled conditions (temperature, humidity, airflow).

Objectives of Drying and Dehydration

• Reduce water activity to prevent spoilage

• Reduce weight and volume for easier shipment

• Achieve desirable texture and structure

• Encapsulate desirable components

Principle of Drying and Dehydration

Transfer sufficient heat to food to cause evaporation, sorption, or sublimation of water, lowering its water content to the desired level.

Factors Affecting Drying Rate

Surface area, temperature, air velocity, humidity, atmospheric pressure, and time.

Sun-Drying

Traditional and inexpensive method using solar radiation to heat the product and air, increasing water removal rate.

Solar Drying

A modified form of sun drying using a glass cover to trap heat and prevent contamination.

Convection Air Drying

Drying with heated air using equipment like kiln, tray, truck tray, rotary flow, and tunnel dryers with horizontal or vertical air circulation.

Kiln Drier

Two-story dryer with a furnace below that heats air, which rises through a slotted floor to dry food above.

Tunnel Drier

Uses moving trays on carts; drying air may flow co-currently (same direction) or countercurrent (opposite direction) to the food.

Spray Drier

Uses atomization to convert food into minute droplets dried by heated air.
Fastest air-convection drier; ideal for heat-sensitive materials (milk, eggs, coffee).

Drum or Roller Drier

Spreads liquid food in a thin layer on a heated rotating drum (120–150°C).
The drum is steam-heated and speed-controlled for proper drying.

Vacuum Drying

Removes water at reduced air pressure, allowing boiling at lower temperatures.
Prevents oxidative deterioration; ideal for heat-sensitive, high-fat, or high-sugar foods.

Freeze Drying (Lyophilization)

Removes ice through sublimation and bound water through desorption.
Used for heat-sensitive foods containing vitamins, antibiotics, or microbial cultures.

Gas Control / Modified Atmospheric Packaging (MAP)

Use of a controlled gas blend (O₂, CO₂, N₂) in a sealed package to maintain food freshness and extend shelf life.

Advantages of MAP

• Maintains visual, textural, and nutritional quality

• Extends shelf life without preservatives

• Preserves freshness, flavor, and brand quality

Gas Blend

Optimized gas ratio adjusted to match each product’s respiration needs, slowing aging, spoilage, color loss, and odor formation.

pH Control

Regulation of a food’s hydrogen ion concentration to control chemical, biochemical, and microbial reactions affecting stability.

Factors Affecting pH

Variety, maturity, seasonal variation, and processing variables affect a product’s pH value.

Effects of pH on Microorganisms

• Low pH denatures microbial enzymes

• Organic acids lower cytoplasmic pH to inhibit growth

• Compounds like carbonate, sulfate, nitrate are microbial inhibitors at low pH

Effects of pH on Enzymes

• Low pH (≈3) inactivates lipoxygenase (prevents off-flavors)

• Pectin esterase is irreversibly inactivated at pH 2 or 12

Acidification

Addition of acids (e.g., vinegar, citric acid) to preserve foods like cucumbers and pickles.

Alkalinization

Addition of lye or bases that saponify fats, causing flavor and texture changes.

Aw Control (Water Activity Control)

Prevents growth of microbes, spore germination, and toxin production, extending shelf life by lowering available water.

Effects of Aw Control

• Inhibits microbial growth

• Increases lag phase of microorganisms

• Decreases growth rate of microbes

Methods of Aw Control

• Dehydration

• Crystallization

• Solute Addition

Food Fermentation

Oldest form of food preservation (aside from salting and drying). It’s a process using useful microorganisms or enzymes to alter the physical and chemical properties of raw materials, improving flavor, texture, and sometimes nutritive value.

Main Benefits of Fermentation

• Produces new and desired flavors

• Improves nutritional value

• Aids in food preservation

Roles of Fermentation

• Diet enrichment

• Preservation

• Biological enrichment of food substrates

• Food detoxification

• Effective use of live, useful microorganisms

How Fermentation Preserves Food

• Minimizes microbial contamination

• Inhibits growth of contaminating microflora

• Kills contaminating microorganisms

Molds in Fermentation

• Flavor compound production (e.g., soy sauce, cheese)

• Antibiotic and enzyme production

• Pigment production

• Spoilage inhibition

Yeasts in Fermentation

Used for:

• Alcoholic beverages and bread making

• Enzyme and protein source

• Cacao fermentation

• Inhibiting spoilage microorganisms

Bacteria in Fermentation

Used for:

• Enzyme and amino acid production

• Lactic and acetic acid production

• Killing spoilage and pathogenic microbes

Types of Fermentation

• Alcohol fermentation – Beer (5%), Wine (12%), Spirits (40%)

• Lactic acid fermentation – Yogurt, cheese, sauerkraut, buro, sausages, fish

• Acetic acid fermentation – Vinegar

• Mold fermentation – Soy sauce, tempeh

• Mixed culture fermentation – Kefir, sourdough

Meat

Edible flesh of animals (skeletal muscles, glands, organs such as liver, heart, kidneys, etc.).

Principal Sources of Meat

Cattle, hog, sheep, goat, and chicken (including organs and glands).

Postmortem Changes in Meat

• Pre-rigor: soft and pliable

• Rigor mortis: stiff

• Post-rigor: tenderized

Composition of Meat

Moisture > Protein > Fats (major)
Minor: carbohydrates, minerals, vitamins, bioactive compounds

Purpose of Chilling Meat

• Prevent microbial growth

• Reduce weight loss

• Minimize discoloration from hemoglobin oxidation

Artificial Tenderization Methods

1. Aging

2. Mechanical means

3. Addition of salts

4. Addition of proteolytic enzymes

5. Electrical stimulation

Meat Curing

Addition of curing agents (salt, nitrites, sugar, spices) to preserve, flavor, and tenderize meat (e.g., bacon, ham, corned beef, sausages).

Fruit Beverage Categories

Juices, Nectars, Soft drinks with fruit, Purees

Juice

Unfermented liquid from mature fruit obtained by mechanical extraction; retains original flavor, color, and aroma; preserved by heat.

Nectar

Unfermented product made by adding water and sweeteners to ≥25% fruit puree or sieved juice.

Soft Drinks with Fruit Content

Non-alcoholic drinks (carbonated or not) made from essences, fruit juices, or their combination.

Puree

Unfermented product from grinding, sieving, or milling fruit pulp (with juice retained).

Basic Juice Processing Steps

Raw material reception → Washing → Stem elimination → Sorting → Extraction → Clarification → Filling/Bottling

Milk

Lacteal secretion from female mammals, providing nutrition and containing casein and whey proteins.

Milk Composition

Water (86–88%), Sugar (5%), Fat (3–6%), Protein (3–4%), Minerals (0.7%)

Milk Standards

• Total solids ≈ 13%

• MSNF (non-fat solids) ≈ 9%

• Fluid milk: ≥3.25% fat, ≥8.25% MSNF

Approx. Milk Needed per Product

Butter – 22.8 kg
Cheese – 10.0 kg
Evaporated milk – 2.4 kg
Powdered milk – 7.6 kg
Ice cream (3.8 L) – 6.8 kg

Skim Milk

Whole milk with fat removed (0.05–0.1%), still contains nutrients except vitamins A & D (can be fortified).

Toned Milk

Reconstituted skim milk mixed with buffalo milk (7% fat); final fat < 3%.

Standardized Milk

Fat: 4.5%; SNF: 8.5%. Mixture of buffalo and skim milk.

Homogenized Milk

Fat globules reduced for creamier texture and whiter appearance.

Evaporated Milk

Half the water removed under vacuum (74–77°C), fortified, sterilized (118°C, 15 min), caramelized flavor.

Condensed Milk

Whole milk concentrated to ⅓ volume with 15% sugar; pasteurized, preheated, evaporated, and homogenized.

Flavored Milk

Pasteurized whole milk with added flavorings (e.g., rose, cardamom).

Milk Powder

Whole milk dehydrated (≈97% solids) using drum or spray dryers.

Ice Cream

Frozen dessert made from dairy, sugar, and flavorings; contains milk fat, sugar, stabilizer, emulsifier, and air.
Overrun: Increase in volume from air incorporation.

Cereals and Legumes

Grasses grown for edible grains (e.g., corn, rice, wheat, barley, sorghum) that serve as a major source of calories and protein for the world’s population. Also rich in vitamins and minerals when eaten as whole grains.

Uses of Cereals and Legumes

• Consumed as food or processed into flour, starch, syrup, oil, and bran

• Used as ingredients in food manufacturing

• Serve as livestock feed

General Composition of Cereals and Legumes

• Moisture: 10–14%

• Carbohydrates: 58–72%

• Protein: 8–13%

• Fat: 2–5%

• Fiber: ~11%

• Energy: 300–350 kcal per 100 g

Corn

Consumed in many forms:

1. Wet form – as a vegetable

2. Dried kernels – popcorn

3. Corn oil

4. Corn starch → corn syrup

5. Corn ethanol

6. Livestock feed

Corn Processing

• Dry milling: for flour production

• Wet milling: for separating proteins and starc

Rice (Oryza sativa)

Staple food for billions. Usually consumed as intact grains (minus hull, bran, and germ).

Rice Products

1. Convenience foods: puffed rice, rice crackers, quick-cook rice

2. Rice flour products: noodles, wrappers, cakes, dumplings

3. Other rice-based: bran oil, alcoholic beverages, vinegar, syrup, rice milk

4. Others: starch, wild rice stems

Wheat (Triticum aestivum)

Converted into flour for human consumption; the type (hard or soft) determines flour quality and uses.

Hard vs. Soft Wheat

• Hard wheat: used for pasta and bread (high gluten)

• Soft wheat: for products not requiring high gluten

• White flour: from endosperm only

• Germ flour: includes germ

• Whole wheat: entire kernel

Legumes and Oilseeds

• Legumes: plants with pods containing beans/peas

• Oilseeds: seeds with high oil content

• Composition: 20–40% protein; 20–50% fat

Primary Use of Wheat Flour

Used in the baking industry for:

• Breads, cakes, biscuits, doughnuts, crackers, cereals

• Pasta (macaroni, spaghetti, noodles, etc.)

Fruit Juice

Drink prepared by extracting or pressing the natural liquid from fruits. The word “juice” comes from Old French jus/juis/jouis meaning “liquid obtained by boiling herbs.”