Understanding Food Spoilage

• The presentation is about food spoilage.
• The objectives are to define key terms and concepts in Food Technology.
• The objectives are to discuss theories and apply principles in food spoilage.

Food Spoilage Defined

• Food spoilage is a metabolic process making food undesirable or unacceptable for consumption due to changes in sensory characteristics.
• Spoilage is a natural process where food undergoes deterioration, affecting organoleptic desirability, nutritional value, safety, and aesthetic appeal.

Undesirable Changes in Food Due to Spoilage

• Change in color, such as long-stored bananas.
• Change in smell, such as the rancid odor of spoiled oils.
• Change in consistency, such as the splitting of milk.
• Change in texture, such as rotting carrots.
• Damage due to mechanical factors like broken eggshells.

Causes of Food Spoilage

• Biological factors involving microorganisms like bacteria, yeasts, and molds.
• Activities of food enzymes such as Enzymatic Browning.
• Infestation by insects, parasites, and rodents.
• Physical damage such as freezing and drying.
• Presence of foreign bodies or contamination with chemical agents.
• Chemical changes in a food are not catalyzed by enzymes of the tissues or of microorganisms, such as chemical oxidation of fats producing rancidity.
• Maillard Browning is a non-enzymatic browning reaction in foods.

Classification of Food by Spoilage

• Non-perishable foods are items that do not spoil easily without careless handling such as sugar, flour, and dry beans.
• Semi-perishable foods remain unspoiled for a long time if properly handled and stored.
• Potatoes and apples are examples of semi-perishable foods.
• Perishable foods are daily foods that spoil quickly, such as meats, fish, poultry, milk, eggs, and fruits and vegetables.

Role of Microorganisms

• Microbial spoilage of foods starts the complex natural process of decay.
• This decay recycles elements in animal or plant tissues back into the natural environment.

Sources of Potential Spoilage Organisms in Food

• The natural microflora of living plants and animals are one source of microorganisms that cause spoilage.
• The natural microflora can be added in various ways, including aerosols, spoiled foods, processing equipment, raw materials, and diseased plant and animals.
• Other sources include packing materials, pests, faeces, humans, sewage, soil, and dust.

Types of Food Spoilage

Bread

• Moldy caused by Rhizopus nigerians, Penicillium
• Ropy caused by Aspergillus niger, Bacillus subtilis

Maple Sap and Syrup

• Ropy caused by Enterobacter aerogenes
• Yeasty caused by Saccharomyces, Zygosaccharomyces

Fresh Fruits and Vegetables

• Soft rot caused by Rhizopus, Erwina
• Gray mould rot caused by Botrytis
• Black mould rot caused by Aspergillus niger

Fresh Meat

• Putrefaction caused by Alcaligenes, Clostridium, Proteus vulgaris, Pseudomonas fluorencens

Cured Meat

• Moldy caused by Aspergillus, Rhizopus, Penicillium
• Souring caused by Pseudomonas, Micrococcus
• Greening or slime caused by Lactobacillus, Leuconostoc

Fish

• Discoloration caused by Pseudomonas
• Putrefaction caused by Alcaligenes, Flavobacterium

Eggs

• Green rot caused by Pseudomonas fluorescens
• Colourless rot caused by Pseudomonas
• Black rot caused by Alcaligenes

Poultry

• Slime or odor caused by Pseudomonas, Alcaligenes

Methods to Control Food Deterioration

• Pickling uses vinegar to prevent microorganism growth because placing food in a low pH solution inhibits microorganism.
• Fermentation uses biological processes to make products, converting glucose (sugar) to alcohol or lactic acid by enzymes.
• Adding large quantities of sugar inhibits microorganism growth by making water unavailable.
• Jams, marmalades, and jellies are manufactured using the principle of adding sugar.
• Salting or brining reduces the moisture content of food.
• Dehydration reduces the water activity level, weight, and bulk of food for preservation.
• Pasteurization extends shelf life by killing most food spoilage and pathogenic organisms with heat.
• Sterilization uses a combination of high temperature and time to destroy nearly all microorganisms in food.
• Canning destroys microorganisms and their spores through heat, sterilizing food within airtight containers to prevent re-contamination.
• Irradiation is used to inhibit sprouting of vegetables, delay ripening of fruits, and reduce microorganisms causing spoilage or poisoning.
• Freezing uses very low temperatures to inhibit microorganism growth, retard enzymatic, and chemical activity.
• The formation of ice crystals draws available water away from food, preventing microorganism growth.
• Modified Atmosphere Packaging encloses food in a package with altered proportions of carbon dioxide, oxygen, nitrogen, water vapor, and trace gases.

Basic Principles of Food Preservation

• Prevention or delay of microbial decomposition is achieved by keeping out microorganisms, removing microorganisms, hindering microorganism growth, and killing microorganisms.
• Prevention or delay of self-decomposition of food is achieved by destruction or inactivation of food enzymes and by prevention or delay of purely chemical reactions.
• Preventing damage from insects, animals, and mechanical causes, etc., is done by chilling or freezing food to inhibit microorganism growth and enzyme activity.
• Heating food destroys microorganisms and prevents enzyme activity.
• Storing food in airtight containers deprives microorganisms of oxygen and prevents further contamination.