Food Processing Methods

Food Processing Methods

1. 1. Size Reduction: Cutting, grinding, milling, slicing, shredding, chopping, homogenisation (liquid/emulsion)

   • Functions
     • To increase surface area for subsequent processing
     • To provide correct functional properties, e.g. flour, spices, icing sugar
     • To impart physical stability (shelf life extension) - e.g. milk and milk beverages
     • To increase yield - e.g. Fruit juice extraction
   • Effects on sensory properties of food
     • Small changes in colour and aroma due to oxidation (as a result of increased sufarce ara) - especially grinding and milling
     • Large changes in texture - e.g. homogenisation improves mouthfeel (smoothness) of milk and milk beverages
   • Effects on nutritional value
     • Loss of nutrients (e.g polyunsaturated fatty acids and antioxidants) through increased oxidation due to increased surface area
     • Increased loss of water soluble vitamins (C and B), e.g. 78% loss of vitamin C in sliced cucumber
     • Loss of nutrients due to enzymatic reactions; e.g. vitamins C and E oxidases, lipoxygenase
     • Loss of nutrients due to separation of certain components; e.g. bran from rice and wheat

2. 2. Blanching: A type of mild heat treatment using hot water or steam (70-100 Degrees - 2 to 7 mins)

   • Functions
     • A pre-treatment of food materials before freezing and dehydratino (drying)
     • To activate enzymes in vegetables and some fruits
     • some reduction in microbial count
   • Effects on sensory properties
     • Small changes in colour and aroma; some loss of volatile flavour compunds esp. with steam blanching
     • Some softening of vegetable tissues (textual changes), due to heat effect
   • Effects on nutritional value
     • Some loss of water soluble nutrient (minerals and water-soluble vitamins)
       • Mainly due to leaching (using hot water) and thermal destruction; to a lesser extent due to oxidation
     • Use loss of vitamin C as an indicator of nutrient loss

3. 3. Pasteurisation: A relatively mild heat treatment (<100degrees)

   • Functions
     • For low-acid foods (pH > 4.6); e.g. Milk, liquid Egg
       • To improve food safety by killing most common pathogens
       • To extend shelf-life of foods for days by inactivating spoilage microbes
     • For high-acid foods (pH < 4.6); e.g fruit juice, beer
       • To extend food shelf-life for months by inactivating spoilage microbes
   • Effects on sensory properties
     • Small changes in colour of fruit juices (browning)
     • Small loss of aroma compounds (volatiles)
     • May result in slight 'cooked' flavour (milk and milk beverages)
   • Effects on nutritional value
     • Minor loss of nutrients; major loss of nutrients in vitamin C
     • Milk pasteurized by HTST; <5% of whey proteins/amino acids, 5% loss of vitaminc E, 4% loss of thiamine, 10% loss of biotin, and vitamin B12, >50% loss of vitamin C

4. 4. Sterilization: A very severe heat treatment to destroy all microbes and enzymes in foods

   • Functions
     • Sterilized foods have an ambient shelf-ife of at lest six months (not immortal; quality deterioration
   • Effects on sensory properties
     • Colour changes - can be very substantial e.g. darkened meat
     • Aroma and taste changes - can be very significant, e.g. cooked flavour of UHT milk
     • Texture - can be drastic, e.g. softening tissues of fruits; cotton-like canned lychee vs fresh lychee
   • Effects on nutritional value
     • Breakdown of carbohydraets and lipids - no change in their nutritive value
     • Coagulation of proteins, loss of amino acids; e.g. lysine by <35%, trytophan and methionine by 6-9%
     • significant of loss vitamins: e.g. 50-75% thiamin, 20-35% pantothenic acid, 50% pyridoxine