Effects Of Freezing On Nutritional Properties And Microbiological Quality Of Meat

NUVINI SAMARATHUNGADepartment Of Food Science & Technology

University Of PreadeniyaSri 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

0.9530.9070.8640.8230.68

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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