ITD – MST : Physical preservation of meat

Physical preservation of meat Topic Sub Topic 1 Introduction Scope of meat science and technology; 2 Meat microbiology Principles of microbiology of meat 3 Physical preservation of meat Thermal preservation, dehydration, irradiation 4 Chemical preservation of meat Curing, organic and inorganic acids, carbon dioxide, ozone, antibiotics, and smoking 5 Methods of meat cooking Boiling, frying, roasting, microwave,

PHYSICAL PRESEVATION OF MEAT Thermal preservation, Dehydration, Irradiation

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.

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.

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

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.

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.

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℃).

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

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.

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.

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.

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.

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.

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.

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

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.

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.

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.