Published on July 26, 2013
Effects Of Freezing On Nutritional Properties And Microbiological Quality Of Meat NUVINI SAMARATHUNGA Department Of Food Science & Technology University Of Preadeniya Sri Lanka.
WHAT IS FREEZING • Freezing is the unit operation in which the temperature of a food is reduced below its freezing point and a proportion of the water undergoes a change in state to form ice crystals.
FREEZING • It is a food preservation method • Potentially deliver a high degree of safety, nutritional value and sensory quality • Preventing, or at least minimizing, microbial and chemical changes
AT THE FREEZING TEMPERATURE • Form ice crystals • Death and injury occur • Mechanically damage cells • Some water will remain unfrozen • At these temperatures no microbial growth is possible
MAIN EFFECT OF FREEZING • Nutritional Effects • Microbiological Effect
NUTRITIONAL EFFECTS • Carbohydrates and protein may undergo limited oxidation • Fats are susceptible to rancidity • Vitamins are particularly susceptible to oxidative damage
EFFECTS OF FAT • Polyunsaturated fatty acids are particularly prone to oxidation • Formation of volatile products • Give rise to the aroma and taste characterized as ‘rancid’
EFFECTS OF VITAMINS • The vitamin E is damaged losses during freezing and storage • A survey of frozen meals analyzed after freezing, storage reported losses of up to 85% of thiamin, 55% of vitamin A, 33% vitamin E, 25% niacin and pyridoxine.
EFFECT OF FREEZING ON THE MICROBES IN MEAT • It is generally the case that total numbers of micro-organisms decrease slightly during freezing • The micro-organisms associated with raw meat, poultry and fish are varied. They include bacteria, protozoa, viruses and for meats
During freezing • The freezing point being lower than that of pure water • unfrozen water increases • microbial growth is possible • Further more freezing reduced water activity. • No microbial growth is possible Temperature (°C) aw 0 1 -5 -10 -15 -20 -40 0.953 0.907 0.864 0.823 0.68
MICROBIOLOGICAL EFFECT • Bacterial spores are virtually unaffected by freezing • Most vegetative gram-positive bacteria are relatively resistant • Gram-negatives bacteria show the greatest sensitivity
CONCLUSION • There is little loss of nutrients during the freezing • Proteins and carbohydrate are unchanged • Fats are susceptible to rancidity • The vitamin E is damaged • There are little loss of other vitamins • It is generally the case that total numbers of micro-organisms decrease • Cannot be completely destroy all micro-organisms in foods
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