Introduction to Food Science and Food Spoilage
What this domain tests
This domain checks whether you can link food composition to keeping quality and name the agent responsible for a spoilage symptom. Questions often ask you to classify a food by perishability or to pick the factor that allowed a spoilage organism to grow.
Core concepts
- Food science studies composition, chemistry, microbiology and engineering of foods; food technology applies that knowledge to processing and preservation.
- Perishability classes: highly perishable (milk, fish, meat, ripe mango, leafy vegetables); semi-perishable (potato, onion, apple, nuts); stable (cereals, pulses, sugar, honey).
- Spoilage agents: microorganisms (bacteria, yeasts, moulds), enzymes (polyphenol oxidase browning), chemical reactions (oxidation, rancidity), physical factors (moisture migration, light, heat) and biological pests (insects, rodents).
- Intrinsic factors include pH, water activity (aw), nutrient content, redox potential and natural antimicrobials such as lysozyme in egg white and allicin in garlic. Extrinsic factors are temperature, relative humidity and gas atmosphere.
- Typical aw values: fresh fruit 0.98-0.99, jam 0.75-0.80, dried fruit 0.60-0.65. Most bacteria need aw above 0.90; xerophilic moulds can grow near 0.65.
- Most bacteria grow best above pH 4.6; yeasts and moulds tolerate lower pH.
Worked example
A bottle of tomato juice (pH about 4.3) left open in a warm room turns sour and gassy. The low pH has suppressed many putrefactive bacteria, but lactic acid bacteria and yeasts tolerate it; the open neck admits oxygen and contaminants, and 30-35°C speeds growth. The result is fermentation-type spoilage. In a low-acid food such as milk, the same conditions would give proteolysis and putrefaction.
Traps that cost marks
Do not equate spoilage with food poisoning: spoiled food may not be poisonous, and dangerous food may look normal. Not every microorganism spoils food. Water activity is not the same as moisture content, and 4.6 is the acidity boundary used in canning.