Food Processing Methods II

Food Processing Methods II

1. 5. Dehydration: Application of heat to remove the majority of water normally present in foods; common methods include Evaporation & Spray-drying

   • Functions
     • Extension of shelf-life by reducing water activity of resultant foods
     • Inhibition of microbial growth and enzyme activity as a result of reduced water activity.
     • Temperature insufficient to kill microbes and enzymes, spoilage may occur if moisture rises during storage (if package tempered with)
       • Storage/packaging conditions critical - moisture, oxygen (relatively immortal if properly packaged)
   • Effects on sensory properties
     • Significant changes to textures
     • Less flavour in dried foods due to loss of volatile flavour compounds and lipid oxidation
     • Significant colour loss or change due to more exposure to oxygen and residual enzymes
   • Effects of nutritional value
     • Vitamin loss - vitamin C loss in apple flake: 8% during slicing, 62% from blanching, 5% from drying
     • No significant change in protein nutritional value

2. 6. Chilling: Reduced food temperature to between 0 to 7 degrees, mostly 4-7 degrees. (perceived as healthy/natural/fresh)

   • Functions:
     • As a form of preservation in conjunction with other processing methods (e.g pasteurisation, fresh-cut)
     • Extend shelf-life by slowing enzymatic and microbial processes.
     • Minimise changes to sensory properties and nutritional value of foods
     • Used to extend shelf-life of mildly processed foods (e.g. pasteurised milk, fresh-cut fruits and veges)
   • Effects on sensory properties
     • Little or no reduction in eating quality
     • hardening of fats due to solidification
     • Chemical, biochemical and microbial changes during storage - major factors for sensory quality deterioration and shelf-life determination
   • Effects on nutritional value
     • Insignificant changes to nutritional value
     • Major changes to nutritional value due to preparation (cutting, slicing, dicing), oxidation, enzymatic reactions
     • Loss of Vitamin C during storage: 18% per day for pineapple, 36% per day for orange
     • No significant loss of vitamin B group

3. 7. Freezing: Reduced food temperature to below freezing point, typically -20 degrees (household), 40 degrees (commercial)

   • Functions:
     • Majority of wateer turned into ice crystals, decreasing water activity
     • Combined effects of subzero temp and low water activity nearly stop enzymatic and microbial activities
   • Effects on sensroy properties
     • Negligible changes to colour and flavour
     • Major changes to texture due to cell and tissues damages caused by ice crystals
       • Quick freezing generates small ice crystals, causing less cell damage; slow freezing generates large ice crystals, causeing more cell dmage
     • Off-flavour can occur due to oxidation during storage
   • Effects on nutritional value
     • Negligible effect; loss of nutrients during thawing - drip loss, esp meat products
     • Loss of nutrients during storage
       • Meat: over 6 months at -18 degrees: 20% loss of vit B6 and panothenic acid, 10% loss of vit B1 and B2
       • Fruits and Vegetables over 6 months at -18 degrees: up to 50% loss vit C, 30% los of vit B1, 17% loss of vit B2, 16% loss of niacin

4. 8. Baking & Roasting: Use heated (dry) air to alter/enhance eating quality of foods, largely flavour

   • Functions:
     • Preserve foods by destroying microbes and reducing water activity particularly at the surface
     • Most baked food have short shelf-life, unless aided by packaging and chilling
   • Effects on sensory properties
     • Major changes to texture: vary with food composition and temperature/time
     • Significant changs to aroma: numerous volatile/aromatic compounds produced
     • Often browning occur: non-enzymatic
   • Effects on nutritional value
     • Major nutritional changes at the surface (high temp)
     • Physical changes to proteins and fats, no loss of nutritive value
     • Loss of amino acids in browning
       • Biscuits: 8-44% loss of tryptophan, 15-48% loss of methionine, 27-61% loss of lysine.
       • 88% loss of lysine in breakfast cereals from maize/corn
     • Loss of vitamins, esp Thiamine