ITD – MST : Physical preservation of meat

1. ITD – MST : Physical preservation of meat

3. PHYSICAL PRESEVATION OF MEAT • Thermal preservation, • Dehydration, • Irradiation

4. Chilling and Freezing Low temperature for preservation • slows down the speed of chemical reaction in the preserved food. • slows down the activities that spoil the preserved food. • only inhibits microbial growth that spoils the preserved food, not kills it. • Freezing reduces the amount of water in the form of fluid needed by microbes to spoil the preserved food.

5. Chilling and Freezing • Chilling and freezing are food preservation technology by heat transfer from the food. • Heat transfer from a product results in the temperature decrease of the product  slowing down biochemical reaction and microbial growth  extended shelf life • The benefit of chilling and freezing is the presence of minimum changes in product characteristics. • Sensory changes due to enzymatic reactions or microbial activities occur very minimally. • The nutrients of product can be maintained. • Chilling: the process of heat transfer from food products so that the temperature reaches -1 until 8oC • Freezing: the product temperature is reduced until below 0oC such as -7oC even until -40oC. • Chilling is often combined with other food preservation process, such as fermentation, irradiation or pasteurization.

6. Thermophilic, the range of growth is 35 – 55oC • Mesophilic, the range of growth is 10 – 40oC • Psycrophilic, the range of growth is -5 – 15oC

7. Chilling • Chilling is meat storage at low temperature in certain period of time to reduce microbial spoilage, • The temperature of carcass is reduced to 5℃ (-4 – -9℃), • Factors that affect the chilling rate: specific heat of carcass, carcass weight, amount of external fats, temperature of environment, distance between carcasses, chilling rate, and relative humidity. • Quick chilling below 12-19℃ pre-rigor will lead to cold shortening. It can be prevented by chilling the carcass at 12-19℃ until rigor mortis, then chilling and refrigeration (0-3℃) until further processing.

8. Freezing • The meat is from healthy animal, • Bleeding is completed after slaughter, • Chilling has been carried out, • Aging duration is limited, • Good protection of carcass, • Freezing temperature below -18℃. • Quality of frozen meat • Duration of chilling storage, • Freezing rate, • Freezing condition (temperature, humidity, and packing), • Animal age, • Meat pH, • Contamination by heavy metal, • The initial amount of microbes.

9. Freezing methods • Still air freezing: the medium is cold air, the freezing temperature is -10 until -30℃, the heat transfer is by convection, • Plate freezing: the medium is metal plate, the freezing temperature is -20 until -30℃, the heat transfer is by conduction, • Rapid freezing: the medium is cold air, the freezing temperature is -20 until -40℃, the heat transfer is by convection. • Liquid immersion freezing; used for poultry meat or fish; materials required are sodium chloride, glycerol or glycol; the heat transfer is by conduction, • Cryogenic freezing; direct immersion, sprinkle of cryogenic liquid, cryogenic materials are liquid nitrogen (-195℃), CO2 (-98℃), liquid nitrous oxide (-78℃).

10. Factors affecting the rate of carcass temperature decrease • Specific heat of carcass • Carcass weight • The amount of external fats • The air temperature of chilling environment • The number of carcass in the chilling room • The distance between carcasses in chilling room • The air speed in chilling room • The humidity in chilling room

11. Temperature and Duration of Frozen Storage • Freezing temperature at -18℃: minimal changes occur, meat juice is frozen efficiently, it inhibits microbes that spoil food, • The duration of food storage at -18℃ can reach 4-6 months, depending on the origin of the meat, • Rapid freezing on meat without any protective materials can cause freezer burn.

12. Change in frozen meat quality • Spoilage of several nutrients, • Decreased water holding capacity, • Improved tenderness, • Decreased meat juice, • Change in meat color, • Decline in meat flavor.

13. Thawing method • Cold air, • Warm water, • Water at room temperature, • Direct heating/cooking without thawing, • Open air, • Microwave. • Thawing duration • Temperature of meat, • Thermal capacity of meat, • Size of meat cut, • Medium being used, • Temperature of medium, • Circulation of medium.

14. Thermal process • Thermal process is a method used to kill spoilage and toxigenic microbes in meat and processed meat, • It is done by pasteurization (LTLT and HTST) and sterilization, • Bacterial classification based on temperature resistance; psycrophilic, mesophilic, thermophilic.

15. Effects of thermal process on meat quality • Decreased palatability, • Denaturation of protein, • Sulfhydryl flavor, • Coagulation and precipitation of proteins, • Connective tissue breakdown, • Damaged thiamin and ascorbat acids.

16. Pasteurization • Heating at the temperature below 100oC. • Destroying all pathogenic microbes (mycobacteria, salmonella, streptococcus and staphylococcus) • Destroying almost ≥99% spoilage microbes • Inactivating endogenous enzymes. • LTLT (low temperature long time), the temperature is at 62-65oC, 30 min. • HTST (high temperature short time), the temperature is at 72-75oC, 15-40 sec. • Flash pasteurization, the temperature is at 85oC, 1-2 sec. • UHT (ultra high temperature), the temperature is at 135-140oC, 1-2 sec.

17. Sterilization • Inactivating all types of microbes and spores until sterile, • Requiring a temperature reaching 150oC for 1-2 sec with pressure.

18. Dehydration • Decrease water content and water activity until a low level in order to inhibit the growth of microbes. • Has a relatively longer shelf life even though without refrigeration storage, • Meat dehydration usually makes use of hot air, • Factors affecting the quality of dried meat ; temperature, particle size, and circulation of hot air. • Dried meat still contain approximately 5-6% water • Dried meat can undergo rancidity, due to its composition which has relatively high fats (around 24%); it can be solved by vacuum packing, • The most obvious changes in the quality of dried meat are browning reaction, flavor change, and oxidative rancidity. • Drying above 60℃ causes gelatinization.

19. Drying Drying • Dehydrating food also dehydrates the microorganisms. • Microorganisms contain aprrox. 80% of moisture. • Freeze-drying (lyophilization) is the most efficient method. Freeze drying • Freeze drying is a drying process of meat in which the meat remains frozen. • The process of water evaporation from meat is called sublimation. • Freeze drying will result in meat with less than 2% water content. • Freezer-dried meat is more stable compared to raw meat, and has 2-4 times longer shelf life.

20. Irradiation • A method of meat preservation can use the method of ionizing radiation. • Ionizing radiation is radiation using high energy to release electrons and produce ions. • Ionizing radiation can kill meat microbes that this is called as cold sterilization. • Sterilizing meat requires radiation dose around 4,5 Mrad. • Ionizing radiation causes chemical changes (myoglobin turning to be metmyoglobin, oxidative rancidity, formation of aldehydes from carbohydrate), physical changes (tenderness, discolorization), and meat sensory (flavor and texture) • The use of ionizing radiation is now avoided due to the presence of toxic and carsinogenic chemical compounds. • Non ionizing radiation also kills microbes. • Non ionizing radiation uses microwave, infrared rays, and ultra violet rays. • Non ionizing radiation can produce heat on the object being radiated that it can be used in the hot processing or cooking of meat.