Food preservation and postharvest losses — A/L Biology

What must I remember about Food preservation and postharvest losses?

• Postharvest losses refer to the measurable quantitative and qualitative degradation of agricultural foodstuffs occurring along the supply chain from harvest to human consumption, often exceeding 30-40% in developing tropical nations.
• Causes of postharvest loss: Physical/mechanical trauma during transit, physiological deterioration (accelerated respiration and ethylene-induced ripening), and microbiological decay by molds and bacteria.
• Principles of food preservation: Inhibiting or arresting microbial growth, inactivating autolytic endogenous enzymes, and preventing chemical oxidation/rancidity.
• Preservation by temperature manipulation: Low temperature (Refrigeration at 1-4°C retards microbial kinetics; Freezing at -18°C immobilizes liquid water as ice crystals, halting metabolic activities) versus High temperature (Pasteurization, commercial canning/thermal sterilization).
• Preservation by water activity reduction & chemical additives: Dehydration / sun drying and Osmotic dehydration (salting fish/meat and sugaring jams/jellies lowering water activity aw below microbial growth thresholds); Chemical preservatives (sodium benzoate in acidic beverages, potassium metabisulfite KMS, nitrates/nitrites preventing Clostridium growth in cured meats).

Test yourself (1 minute)

1. Water Activity (aw) concept

   Water activity represents the ratio of water vapor pressure of food to pure water; bacteria generally cannot grow below aw = 0.91, yeasts below aw = 0.88, and common molds below aw = 0.80.

2. Controlled Atmosphere Storage (CAS)

   Regulating warehouse atmospheric composition (lowering O2 to 1-3%, elevating CO2 to 2-5% at low temperature) drastically suppresses cellular respiration and ethylene synthesis, extending fruit/vegetable shelf life for months.

3. Proper harvest maturity & packaging

   Harvesting at physiological maturity rather than overripe stage, and using rigid plastic crates instead of compressing gunny sacks, slashes transport transit mechanical losses by over 70%.

Practise Food preservation and postharvest losses questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 10

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Where does Food preservation and postharvest losses fit in the syllabus?

Year 2 · Term 3