Food Science and Food Safety: Processing Losses, Hazards and Additive Arithmetic
Food Science and Food Safety asks you to connect food composition and processing to what actually reaches the patient's plate, and to identify where biological, chemical and physical hazards enter the chain. Exam items favour thermal effects on vitamins, foodborne pathogens and their toxins, and additive/contaminant calculations.
How processing changes nutrients
Losses depend on heat, water, light, oxygen and pH. Thiamin is destroyed by heat, especially in alkaline media; vitamin C is lost to heat, oxidation, light and leaching; folate is heat- and oxidation-labile; riboflavin degrades in light. Water-soluble vitamins leach into cooking water, so steaming and quick stir-frying preserve more than long boiling. Maillard browning between reducing sugars and lysine lowers protein quality and generates acrylamide in starchy foods fried or baked above about 120 C. Milling removes bran and germ, losing B vitamins, iron and fibre - the rationale for enrichment and fortification.
Hazards and control
- Biological: Salmonella (poultry, eggs), Staphylococcus aureus preformed toxin (cooked food held warm), Bacillus cereus (cooked rice held at room temperature), Clostridium botulinum (anaerobic, low-acid canned foods), Vibrio parahaemolyticus (raw seafood), Listeria monocytogenes (refrigerated ready-to-eat foods, still grows at 4 C), E. coli O157:H7 (undercooked beef, unpasteurised juice).
- Chemical: aflatoxin from Aspergillus flavus in mouldy peanuts and maize (hepatocellular carcinoma), pesticide residues, lead/cadmium/methylmercury, 3-MCPD in refined oils.
- Temperature control: danger zone 5-60 C; hold hot food above 60 C, cold below 5 C; cool cooked food from 60 to 21 C within 2 hours and to 5 C within 6 hours in total.
- HACCP has seven principles: hazard analysis, CCP determination, critical limits, monitoring, corrective actions, verification, record-keeping. It is preventive and cannot be replaced by end-product testing.
Additives
An ADI in mg/kg body weight per day is normally the NOAEL divided by 100, reflecting two 10-fold safety factors.
Worked example
An additive has an ADI of 0.5 mg/kg bw/day, so a 60 kg adult has a ceiling of 30 mg/day. A beverage contains 10 mg/L and a snack 5 mg/kg: 2 L of beverage (20 mg) plus 100 g of snack (0.5 mg) gives 20.5 mg, still under the ceiling. If the same person also takes a supplement containing 15 mg, the total of 35.5 mg exceeds the ADI and the supplement, not the beverage, is the item to cut.
Traps that cost marks
Equating sterilisation (about 121 C, commercially sterile) with pasteurisation (63 C for 30 min or 72 C for 15 s). Attributing staphylococcal illness to live bacteria rather than preformed toxin. Believing refrigeration stops Listeria. Confusing aflatoxin (Aspergillus, peanuts and maize) with other mycotoxins or bacterial toxins.