Food Preservation and Processing Techniques
What the exam tests
Preservation methods and the principle of hurdles: combining several mild stresses to inhibit or destroy microorganisms and enzymes while retaining quality.
Core methods
- Thermal: blanching (enzyme inactivation, about 70–95°C, followed by cooling), pasteurisation (for example 63°C for 30 min or 72°C for 15 s), sterilisation in retorts, UHT (135–150°C for a few seconds) with aseptic filling.
- Low temperature: chilling slows growth; freezing stops growth, with IQF giving free-flowing pieces.
- Dehydration and concentration lower water activity; spray drying and freeze drying produce powders with different heat exposure.
- Irradiation, high-pressure processing and pulsed electric fields are non-thermal methods.
- Chemical preservatives: salt, sugar, acidulants, sulphites, benzoates and sorbates, permitted only within FSSAI limits.
- Fermentation produces organic acids and competes with spoilage flora.
Worked example
Design a hurdle system for mango pickle. Reduce moisture by salting and sun drying; add salt to lower aw; add acid from lime juice or acetic acid to lower pH; add oil as an oxygen barrier; pack hygienically; store cool and dry. The reasoning is that no single hurdle is enough, but the combined stresses prevent growth of spoilage yeasts and moulds. The product is not sterile; it relies on a stable formulation and good hygiene.
Traps
Pasteurisation is not sterilisation and requires refrigeration for many products. Blanching without prompt cooling causes over-processing and texture loss. Commercial sterility means no viable pathogens of public health concern under normal storage, not the absence of all microorganisms. Do not use preservatives above permitted limits.