1. refrigerator
1.1. considered as the safest way; food is kept at low temperature and this can effectively slow down the bacterial growth
1.2. a longer time of thawing is needed due to low temperature in the refrigerator
1.3. maintain the physicochemical characteristics closest to fresh samples and the least quality losses compared with other thawing methods
2. Food environment
2.1. Environmental pH
2.2. Osmotic Pressure
2.3. Temperature
3. DIRECT CONTACT – Food placed in direct contact with refrigerant (liquid nitrogen, “green” Freon, carbon dioxide snow)
3.1. - Faster - Expensive - freeze individual food particles
4. INDIRECT CONTACT – Food placed in direct contact with cooled metal surface.
4.1. - Relatively faster - More expensive
5. Deterioratve chemical and physical changes will occur during and after thawing
6. few methods of thawing that can be done at home
6.1. microwave
6.1.1. new thawing technique which is the fastest way for defrosting
6.1.2. frozen food is thawed in the microwave, it must be cooked or eaten instantly
6.1.2.1. because the temperature of some parts of the food may become higher than 30°C
6.1.2.1.1. may speed up the bacterial growth in food
6.2. electric oven with air circulation
6.2.1. still considered safe
6.2.1.1. Commonly, people just cook the frozen food in the oven without defrosting it first, thus making the cooking time may be about 50% longer than usual defrost.
6.3. in cold water
6.3.1. immersing in the water, specifically cold water is completely safe
6.3.1.1. To accelerate defrosting, water should be kept running.
6.3.2. Thawing in warm water needs to be avoided as it can lead to an uneven thawing process which risks bacteria being present
6.3.3. faster than refrigerator thawing but requires more attention because the bacteria from the surrounding environment could be introduced into the food if the food is not wrapped properly
6.4. room temperature
6.4.1. not recommended at all and should avoid
6.4.1.1. frozen food is placed at ambient temperature for a long time
6.4.1.2. unsafe as a lot of bacteria grows in the range of 40-100°F (4-38°C)
7. Storage death: Killing rate of microorganisms is rapid at the beginning of freezing followed by reducing of microorganisms gradually
8. Oxygen Concerntration
8.1. the higher the oxygen concentration, the higher microbial growth rate
8.2. lower concentration
9. Slow freezing may cause loss of texture, nutrients and colour and flavour during thawing.
10. cytoplasmic contents leak out through hydrophilic pores
11. Microorganisms can be classified into three groups depending on the sensitivity to freezing
11.1. Susceptible
11.1.1. vegetative cells of yeast and molds, and many Gram-negative bacteria
11.2. Moderately resistant
12. Textural changes can occur.
13. Fruits
13.1. • Blanching process for fruit can inactivate the enzymes of the fruits, but it will produce a soft texture and give the fruits cooked flavor. • In order to prevent oxidation, sugar syrup or sugar can be used by placed a small piece of crumpled waxed paper or water resistant wrapping material on the top and press the fruits down into the syrup before closing, sealing and freezing. • The sugar also can help in retaining volatile aroma
14. single strand DNA breaking increase
14.1. ribosomal RNA degradation
14.2. Inactivation of enzyme
15. 1. Use of cold air blasts or low temperature gases in contact with the food such as blasts, tunnel, fluidized bed, spiral, belt freezers
16. 2. Indirect contact freezing such as plate freezers which packaged foods or liquids in contact with metal surfaces (plate, cylinder) and cooled by cirulating refrigerant (multi-plate freezers)
16.1. Advantages of plate freezer
16.1.1. Better storage density in container.
16.1.2. High quality of the products.
16.1.3. High speed of freezing.
16.2. Disadvantages of plate freezer
16.2.1. Have limitation on the type of product can be handled.
16.2.2. High capital cost.
17. Cool/Chill Storage
17.1. storage at temperatures above the freezing point, from about 15 °C down to -2 °C
17.2. Effect towards microorganisms activity
17.2.1. Reduction of chemical reactions
17.2.2. Enzyme activities retarded
17.2.3. Inhibition of microorganisms to grow and increase in number
17.3. produce cold shock
17.3.1. death and injury to cells due to damage of membrane
17.4. Food store by chilling affected by:
17.4.1. chilling temperature
17.4.2. relative humidity
17.4.3. air velocity
17.4.4. composition of the atmosphere
18. Mechanism of Low Temperature Treatment
18.1. Slower than freezing when conducted under same temperature differentials.
18.2. At rapid rate of freezing
18.2.1. water in food and inside cell froze equally when temperaruture is reduced below -20 degree celcius
19. Factors affect the Effectiveness of Low Temperature Treatment
19.1. 1. Level of low temperature
19.2. 2. Characteristics of microorganisms
19.3. 3. Food environment
20. Factors affecting of low temperature storage in controlling the microbial growth in food
20.1. Time of frozen storage
20.1.1. spores of Clostridium and Bacillus
20.1.2. Affects by number of viable microorganisms in the food
20.2. Characteristics of microoroganism
20.2.1. Some psychrophilic microorganisms grow temperature as low as 10 degree celcius
20.2.2. Many mesophilic and thermophilic cells can be sublethally injured and may die
20.2.3. Gram-negative rod-shaped bacteria are more susceptible to the damage effect of freezing than the Gram-positive spherical-shaped bacteria.
20.3. Room temperature storage
20.3.1. Storage temperature around 15-20°C
20.3.2. The deterioration of foods, such as fruits and vegetables, by their own enzymes and microorganisms is not prevented at room temperature, but it becomes slower at room temperature.
20.4. Level of low temperature
20.4.1. Refrigeration
20.4.1.1. Storage temperature around 0-7°C
20.4.1.2. Temperatures below 5 °C will prevent the growth of most food poisoning bacteria.
20.4.1.3. Suitable for storage of perishable and semi-perishable food
20.4.2. Freezing
20.4.2.1. Storage temperature below -8°C
20.4.2.2. Freezing temperatures prevent the growth of most microorganisms, but some can grow within the freezing range at an extremely slow rate
20.4.2.2.1. Chilling
20.5. Types of food
20.5.1. plant-based food
20.5.2. animal-based food
21. Characteristic of psychrophile
21.1. 1. enzyme able to work under cold condition.
21.2. can move and obtain energy and carbon from ions in solution
21.3. 4. Time of storage
22. Method of Freezing
22.1. Quick Freezing
22.1.1. Favors the formation of small, intracellular and extracellular ice crystals
22.1.2. Less mechanical destruction of cells of the food
22.1.3. Solidification can occur n a short time
22.2. Slow freezing
22.2.1. Favors formation of large extracellular ice crytals
22.2.2. External concentrations of solutes will increase and it cause plasmolysis and cell shrinkage due to water loss from the cell.
22.2.3. Reduce internal pH and damage cell proteins.
22.2.4. Crystal formation also cause cell damage by disrupting membranes, cell wall and intestinal structures. This cause mechanical destruction of food cells and removes juices from the cells
22.2.5. When temperature decreased to -2C, free water in the foods started forming ice crystals and increases in solute concentration ; Increases in freezing points and results in migration of water molecules from microbes to the environment ; and results in the degradation of microbial cells
22.2.5.1. The effects of water molecules migration from microbes to the environment is the exposed of microbes towards
22.2.5.1.1. Change of pH in microbial cells( due to concentration of ions
22.2.5.1.2. high viscocity
22.2.5.1.3. Low water activity (due to increase in the concentration of solutes)
22.2.6. Most lethal to microorganisms than quick freezing.
23. Example of Psychrophilic bacteria
23.1. Psychrophilic bacteria are defined as cold-loving bacteria. Specifically, their cardinal temperatures are 20 °C for maximal growth, 15 °C or lower for optimal growth, and 0 °C or lower for minimum growth (Morita, 1975), and this definition is accepted by most microbiologists.
23.2. Example: - Listeria monocytogenes - Aeromonas hydrophila - Clostridium botulinum - Yersinia enterocolitica.
24. Effect of Thawing
24.1. Temperature rises rapidly to near the melting point and remains throughout thawing process - aids chemical changes and microbial growth.
24.1.1. Cells are not exposed to solution effects
24.2. Release of lysosomal enzymes consisting of cathepsins, nucleases, phosphatases and glycosidases.
24.3. Injured bacteria, which may be difficult to detect in a frozen product, can recover the ability to grow after thawing and cause food spoilage or food poisoning.
24.4. Safe Thawing Methods
24.4.1. Refrigerator Thawing
24.4.1.1. Require longer period as food will defrost slowly in chilling temperature
24.4.2. Microwave Thawing
24.4.2.1. Have heat balance control and can improve response time
24.4.3. Cold Water Thawing
24.4.3.1. Faster thawing method compared to refrigerator thawing but it could take several hours depend on the weight.
24.5. Textural changes associated with freezing and facilitate the spoilage process
25. Characteristic of Acidophiles
25.1. can grow and reproduce at temperatures ≤0°C in high-altitude cloud droplets
25.1.1. 1. pH 0-1 of water at Iron Mountain.
25.2. 2. Enzymes used to increase efficiency of animal feed.
25.3. 3. Enzymes help animals extract from feed more efficient and less expensive.
25.4. 4. Can live and grow well in acidic environment
25.4.1. 4. Can live and grow well in acidic environment
26. THAWING
26.1. Spoilage of food by microorganism, particularly psychropiles, can occur during and after thawing if proper precautions are not observed.
26.2. Most vegetables can generally be thawed and cooked by placing the frozen material directly in boiling water.
27. EFFECTS OF THAWING
27.1. Issues with frozen foods
27.1.1. There may be changes in meat texture, fat can crumble and meat colour may also change because freezing slows down but does not totally stop the actions of certain enzymes naturally present in animals and vegetables which would cause food components to degrade or oxidise.
27.1.1.1. Some foods blanched or sulfited before freezing. Vacuum packaging to keep out oxygen. Undesirable physical changes Fruits and vegetables lose crispness Drip loss in meats and colloidal type foods (starch, emulsions)
27.1.1.2. Freezing decrease the water activity
27.2. Slower rate than freezing
27.3. Foods thawed from frozen state spoil faster than similar fresh products. If drip occurs during defrost or condensed water has accumulated, bacteria spreads faster than unfrozen food.
27.4. Repeated freezing and thawing can destroy bacteria by disrupting cell membrane.
27.5. Faster thawing can increase the number of bacteria inactivated.
27.6. High thawing temperature can induce growth of mesophiles on the surface while the interior is still frozen.
27.7. During thawing, growth of microorganism is due to a solution rich in nutrients is released from food cells. Microorganisms penetrate damage tissue due to the denaturation of antimicrobial barriers and a liquid film condenses on the surface of the product.
27.8. Partial thawing can cause changes in tissue, enzyme systems, and microbial flora and therefore loss of quality in foods.
27.9. Refreezing of thawed products cause cause loss of textural and other qualities instead of any microbiological risk.
28. Disadvantages of freezing
28.1. Changes color, texture and flavor of food
28.2. Texture of some foods is undesirable because of freezing process.
28.3. Cause damage to cell by crystallization
28.4. Initial investment and cost of maintaining freezer is high.
28.5. Storage space limited by capacity of freezer
28.6. Temperature abuse
29. Preparation of Foods for freezing
29.1. Selecting
29.1.1. Cool freshly cooked dishes quickly before freezing. Putting foods that are still warm in the freezer can raise the temperature, and causing the surrounding frozen items to partially thaw and refreeze, which can alter the taste and texture of some foods.
29.1.2. Freeze items you wont use in the future. It is important to store all the foods at lower temperature in order to retain the vitamin content, colour, flavour and texture.
29.2. Sorting
29.3. Washing
29.4. Blanching
29.4.1. Achieved by:
29.4.1.1. immerse into hot water briefly
29.4.1.2. steam
29.4.2. Functions:
29.4.2.1. (e) Remove air in the plant tissues
29.4.2.2. (a) Inactivation of endogenous enzymes
29.4.2.3. (b) Enhancing or fixing the green color of certain vegetables
29.4.2.4. (c) Inactivation of microorganisms
29.4.2.5. (d) Facilitating the packing of leafy vegetables
29.5. Packaging
29.5.1. Use heavy foil, freezer bags or containers designed for freezing food.
29.5.1.1. Make sure to squeeze all the air out of freezer bags before sealing.
30. PREFERENCE TREATMENT:Things to be Considered Before Freezing Food
30.1. Vegetables
30.1.1. • Blanched the vegetables by dipped the product in boiling water within two minutes before freezing. This process was important to reduce the number of microorganism. • Other than that, slow or stops the action of enzymes. These enzymes are essential for growth and ripening. • The vegetables will continue maturing, develop off-flavors, discolor or toughen if the enzymes not stopped before freezing.
30.2. Meats
30.2.1. • After the meat and poultry being slaughtered, it need to b wrapped and store in chilling temperature to avoid the meat and poultry spoilage.
30.3. Fish
30.3.1. • Fish was susceptible to spoilage by psychrophilic bacteria and by its own enzymes system. • It is important to have good sanitary practices and to retain the fresh quality to a maximum extent, the fish need to prompt freezing. • Immersed the fish in a 6 % sodium chloride solution for a few second can help in reducing drip during thawing.
31. Important of thrawing - parts of food for outer surfaces will warm up and able to allow dangerous microbes to grow. Thus, thrawing procedure must follow properly to prevent lots growth of the microorganisms.
31.1. Advantages of freezing
31.1.1. Chemical reactions can occur in unfrozen water
31.1.2. Retard the growth of microorganisms
31.1.3. Inhibit enzyme activity
31.1.4. Coliforms are easily destroyed by heat and may die during freezing and frozen storage of foods.
31.1.5. Simple procedures. Adds convenience to food preparation.
32. Bacteria in log phase more sensitive to temperature than others phase.
33. Types of Freezing
33.1. AIR FREEZING – Products frozen by either “still” or “blast” forced air
33.1.1. - Cheapest (investment) - “still” slowest, more changes in product - “blast” faster, more commonly used
33.2. Individual quick freezing (IQF) - Products is fluidized with powerful of the vertical airflow that flow from beneath belt.
33.2.1. Advantages: High air velocity, shorter period of freezing periods, prevent decomposition of foods
33.3. Immersion Freezing: Known as the process of freezing by contact with a cooled liquid. The food is immersed in low temperature salt solution (NACl) to achieve a quick reduction in temperature.
33.3.1. Advantage: There is intimate contact between the food or package and refrigerant, so resistance to heat transfer is minimized.
33.4. Plate Freezing: Known as the process of freezing by contact with a cooled solid. Products that have regular shape materials or blocks are insert between metal plates.
33.4.1. Advantage: 1) Faster temperature reduction and freezing time particularly suited to hot offal and hot boned meat. 2) Lower refrigeration capacity requirements due to the absence of high capacity fans in the freezer.
34. Thawing (in general)
34.1. Thawing is a method used to melt or to soften the meat before cooking and consumption.
34.2. Thawing is also known as defrosting
34.3. Through thawing, it can help in restoring the features of the meat so that it could be as close to its fresh condition
34.4. Thawing can deteriorate the meat and for that, a proper way of doing this technique is crucial
34.5. it has a direct impact towards the meat's physicochemical and its structural properties
34.6. two commonly known thawing methods
34.6.1. atmospheric pressure
34.6.2. thawing in water
34.7. safe methods according to USDA FSIS
34.7.1. refrigerator, in cold water, and in the microwave
35. Chilling
35.1. - Temperature of foods maintained at 1-8 °C.
35.2. - Can be done by various equipment : continuous air cooler, ice bank cooler, plate hear exchanger, jacketed heat exchanger, ice implementation system, vaccum attribution system, and cryogenic chamber.
35.3. - Chilling rate is dependent on thermal conductivity, initial temperature of foods, density, moisture content, presence/absence of a lid on food storage vessel, presence of plastic bags as packaging, and size and weight of the food.
35.4. - Reduce the rate of biochemical and microbiological changes & extend shelf of fresh and processed food.
35.5. - This process reduce the initial temperature of the products and maintains the final temperature of products for a prolonged period of time.
36. FREEZING IN FOOD PRESERVATION
36.1. -Delays spoilage and keep food safe by preventing the growth of microorganism and slow down the enzyme activity which causing the food to spoil.
36.2. -Does not sterilize food as most microorganisms are still alive during frozen but inactive. (stop growth of microorganism and slow sown the chemical changes such enzymatic reactions)
36.3. -Extreme cold where food is frozen at or below -18°C.
36.4. -The principle of freezing basically 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. The immobilization of water to ice and the resulting concentration of dissolved solutes in unfrozen water lower the water activity of the food
36.5. METHODS
36.5.1. Quick/fast freezing
36.5.1.1. Direct/indirect contact of foods with refrigerant
36.5.1.2. Use of air blasts of frigid air blown over the foods being frozen
36.5.2. Slow freezing
36.5.2.1. essentially the type of freezing used in home freezer
36.6. ADVANTAGES
36.6.1. -Most food can be frozen
36.6.2. -Retained the nutrients, color and flavor
36.6.3. -Texture is better than other type of food preservation
36.6.4. -Simple and convenient
36.6.5. -Food can be kept longer if frozen
36.7. DISADVANTAGES
36.7.1. -Texture of some food is undesireable
36.7.2. -Storage space limited
36.7.3. -High cost in initial investment and maintaining the freezer
36.7.4. Alteration of organoleptic of foods
36.7.5. Temperature abuse
37. THAWING
37.1. -Thawing is naturally slower that freezing when conducted under comparable temperature differentials.
37.2. -The maximum temperature differential permissible during thawing is much less than that which is conduct able during freezing.
37.3. - The time-temperature pattern characteristic of thawing is potentially more damaging than that of freezing. During thawing, the temperature rises rapidly to near the melting point and remains there throughout the long course of thawing, thus affording considerable opportunity for chemical reactions, recrystallization, and even microbial growth if thawing is extremely slow.
38. The time-temperature pattern characteristic of thawing is potentially more damaging than that of freezing. During thawing, the temperature rises rapidly to near the melting point and remains there throughout the long course of thawing, thus affording considerable opportunity for chemical reactions, recrystallization, and even microbial growth if thawing is extremely slow.
38.1. - Chilling rate is dependent on thermal conductivity, initial temperature of foods, density, moisture content, presence/absence of a lid on food storage vessel, presence of plastic bags as packaging, and size and weight of the food.
38.2. Chilling-control microbial growth and toxin production; temperature are usually 10-15 or 0-15 degree celsius; involve cooling by isce or refrigeration. Affected by temperature of chilling, relative humidity,air velocity,composition of the atmosphere in storeroom .
39. EFFECTS OF LOW-TEMPERATURE
39.1. FREEZING - can cause sublethal and lethal injury to microbial cells. For examples, DNA strand breaking, ribosomal RNA degradation and activation or inactivation of some enzymes.
39.2. CHILLING - produces cold shock leading to death and injury to cells. Membrane cells may damaged due to phase changes occur in membrane lipids. Because of that also, hyrophilic pores are created and allow the leaking out of cytoplasmic contents through the pores.
39.3. REFRIGERATION - prolong the shelf life of the food. During the process of refrigeration and storage there is a loss of essential nutrients. Also, their is some loss of colour, flavour and texture.
40. Chilled food managemant
40.1. 1.
40.1.1. 1. keep the most perishable foods, like cooked meats, in the coldest part of the fridge
40.1.2. 2. return perishable foods to the fridge or freezer as soon as possible after use
40.1.3. 3. remember to keep raw food below ready-to-eat food in the fridge, or use and separate fridges for raw and ready-to-eat food, if possible
40.1.4. 5. wrap or cover all raw or uncooked foods so that they can't touch or drip on other foods and contaminate them
41. Low Temperature
41.1. used to preserve food by inhibiting microbial growth
41.2. Preservation can be done through freezing which can be divided in 2 ways< slow freezing and quick freezing. Freezing cant kill microbes but it can stop the growth of microorganisms. Physchrophilic bacteria able to grown in cold condition
42. refrigeration below 5 celcius.
43. refrigeration below 5 celcius retards the growth of many foodborne pathogens effectively.
43.1. cooling rate is important in controlling growth of microorganisms.
43.2. refrigerated foods have limited shelf life because of microbial growth.
43.3. refrigerated foods have limited shelf life because of microbial growth.
43.4. there are 4 distinct low-temperature methods for the preservation of foods: room-temperature storage, chilling, refrigeration and freezing
44. Slow freezing process
44.1. sharp freezing, −4 to −29 degree celcius.
45. Flavobacterium
46. -18 degree celcius for 3-72hours
47. Nutrients of food is not affected
48. Little change in flcour, texture, colour and shape
49. <5°C to prevent growth of most FP bacteria
49.1. C.botulism
49.2. V. parahaemolyticus
49.3. Y. enterocolitica
49.4. L.monocytogens
50. 7. Slows down autolysis affect of enzyme on the food
51. depend on relative humidity , they can be
51.1. psychrophilic (cold adapted) - able to grow at or below 0 degree C, but unable to grow above 20 degree C
51.1.1. adaptations including cold-shock proteins, polyunsaturated branched-chain FA in membrane plasma & more efficient enzymes
51.2. psychrotolerant - able to grow at 0 degree C but grow well above 20 degree C
51.2.1. Pseudomonas Fluorescens
51.2.2. Pseudomonas Maltophilia
52. 2. Extreme cold (below -18 degree Celcius(-28 degree Celcius)
53. Chill temperature delays both bio-chemical and bacteriological changes. The deteriorative changes are retarded when low temperature is maintained
54. Chilling-control microbial growth and toxin production; temperature are usually 10-15 or 0-15 degree celsius; involve cooling by isce or refrigeration. Affected by temperature of chilling, relative humidity,air velocity,composition of the atmosphere in storeroom .
54.1. decrease hazard from microbial pathogen
54.2. Chilling temperature: 0-8 degree Celsius
54.2.1. Some foods can store at this temperature to prevent freezing injuries.
55. 6. Vacuum Packing
55.1. Remove air from a packaging or wrapping so that it can be sealed tight and firm.
55.1.1. Advantages
55.1.1.1. 1. Reduced product loss.
55.1.1.2. 2. Increase shelf life of a product.
55.1.1.3. 3. Cost effective.
55.1.2. Disadvantages
55.1.2.1. 1. Difficult to be opened.
55.1.2.2. 2. loss of preservation once the pack has been opened
55.1.2.3. 3. additional labeling often needed
56. 2. A number of methods used to kept foods from microbial spoilage.
57. 3. membrane proteins are allowed to continue functioning
58. results in off-odours, slime production, discoloration
59. Characteristics: Gram negative rods, form yellow to orange color colonies
60. Refrigeration
60.1. 0-7 Degree Celcius
60.2. less or equal to 4 Degree celcius (commercial refrigerated storage
60.2.1. Act as one of the freezing method to preserve foods in low temperature.
60.3. Refrigeration
60.3.1. 0-7 Degree Celcius
60.3.2. less than 5 Degree celcius to prevent growth of most FP bacteria
60.3.2.1. C.botulism
60.3.2.2. V. parahaemolyticus
60.3.2.3. Y. enterocolitica
60.3.2.4. L.monocytogens
60.3.3. less or equal to 4 Degree celcius (commercial refrigerated storage
61. Advantages of Low Temperature Treatment
61.1. 2. Better sensor quality and nutrient retention
61.2. 1. It is a is a natural form of preservation.
61.3. 3. Natural colour and flavour can be retained.
61.4. 4. Texture usually better than other preservative methods
61.5. 5. Simple procedure
61.6. 6. Destroys or slows down ezymmatic activity
61.7. 7. To reduce or prevent the spoilage caused by microorganisms and/or chemical reaction.
62. Storage Stability of Frozen Foods
62.1. Storage life can be extended significantly as storage temperatures become colder.
63. Principles of Freezing
63.1. 1. Do not sterilize food
63.2. 4. Slows chemical change such as enzyme reactions
63.3. 5. Preservation of food achieved by combination of low temperature and reduced water activity
63.4. 6. The lower temperature slows down the rate of chemical reaction and water is also removed from the sphere of activity.
64. Methods used in low temperature food preservation
64.1. Room Temperature storage
64.1.1. 15-20 degree Celsius
64.2. Chilling
64.2.1. 10-15 degree celcius
64.3. Refrigeration
64.3.1. 0 - 7.2 degree celcius
64.4. Freezing
64.4.1. Slow freezing
65. How psychorotrophs continue functioning at low temperature
65.1. 1. Contain increased amounts of unsaturated fatty acid in their membrane lipids
65.1.1. Refrigeration
65.1.1.1. 0-7 Degree Celcius
65.1.1.2. less than 5 Degree celcius to prevent growth of most FP bacteria
65.1.1.2.1. C.botulism
65.1.1.2.2. V. parahaemolyticus
65.1.1.2.3. Y. enterocolitica
65.1.1.2.4. L.monocytogens
65.1.1.3. less or equal to 4 Degree celcius (commercial refrigerated storage
65.1.1.4. Refrigeration
65.1.1.4.1. 0-7 Degree Celcius
65.1.1.4.2. less than 5 Degree celcius to prevent growth of most FP bacteria
65.1.1.4.3. less or equal to 4 Degree celcius (commercial refrigerated storage
65.2. 2. unsaturated fatty acid help to retain membrane phospholipid fluidity
66. Use for fruit,vegetables,citric acid and fruit juices
67. Prevent or slow down food spoilage from bacteria and fungi
68. Purpose of low-temperature preservation: to reduces the microbial activity and enzyme activity thus prolongs shelf life of foods
68.1. Minimum growth of microorganisms depend by the inhibition of solute transport. The range of growth temperature for a microorganism determined by how well the microorganism can regulate membrane fluidity within a given low-temperature range.
68.1.1. Dehydro freezing
68.1.2. Points to be Considered Before Freezing Food
68.1.2.1. Vegetables
68.1.2.1.1. Blanching vegetables before freezing reduces the number of microorganisms, removes some air from the tissues, makes them more compact and enhances their colour. This also inactivate enzymes otherwise that would cause dete-rioration in palatability, colour and ascor-bic acid content during storage.
68.1.2.2. Fruits
68.1.2.2.1. can cut directly into sugar syrup or sugar to prevent oxidation
68.2. Two methods
68.2.1. Chill storage
68.2.2. Characteristics of microorganisms
68.2.2.1. mesophilic microorganisms
68.3. Freezing : preserving food through the application and maintenance of extreme cold temperature (−4°C to −40°C)
68.3.1. effective- most of the water of the food tissue is changed from the liquid to the solid state, retards enzymatic action and stops microbial growth
68.3.1.1. Quick freezing process
68.3.1.1.1. quick freezing process range from −32 to −40 degree celcius. desirable for many products in terms of retention of palatability and nutritive value.
68.3.2. grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from 20 to 45 °C . It is not able to synthesize proteins in low temperatures because it is sensitive to low temperature. Some notable mesophiles include Listeria monocytogenes, Staphylococcus aureus, and Escherichia coli. Other examples of species of mesophiles are Clostridium kluyveri, Pseudomonas maltophilia, Thiobacillus novellus, Streptococcus pyogenes, and Streptococcus pneumoniae.
69. Thawing
69.1. The microbial spoilage by thawing can be caused by the microorganisms especially psychrophiles as it can happen if the thawing process are not done properly.
69.1.1. psychrophile is the type of organisms that are able to grow between the range of subzero to 20 degree celcius, with the optimum temperature range is 10-15 degree celcius.
69.2. the food can be thawed by naturally or by placing the food inside the boiling water. but, in this process, it may alter the chemical and physical composition of the food.
70. Chilling
70.1. Reduces the activity of microorganisms by reducing chemical reaction and action of enzymes.
70.1.1. less microbial growth and prevent spoilage of food.
70.2. Psychrophiles are cold-loving so they will grow in food when store at chilling temperature and capable causing spoilage in foods.
70.2.1. They having minimum temperature for growth at 0 degree Celsius or lower. They grow best in temperature range of 0-15 degree Celsius.
70.3. Psychrotrophs are not cold-loving but they can tolerate at cold temperature. But show low growth rate at chilling temperature.
70.3.1. They have optimal and maximal growth temperatures above 15 and 20°C, respectively. They capable grow at 7 degree Celsius or lower.
70.4. Temporary method for preservation of food.
70.4.1. Many food spoilage microorganisms will be inactivate at chilling temperature.
71. Method
71.1. room temperature
71.1.1. 15 °C-25 °C
71.1.1.1. preservation of food by inhibiting microbial growth
71.1.1.1.1. psychrotrophic microbes survive and grow
71.1.1.2. storage of non-perishable foods by lowering microbial growth
71.1.1.2.1. partial microbial activity takes place
71.2. chilling
71.2.1. from 0 °C-15 °C
71.3. refrigeration
71.3.1. from 0 °C-7 °C
71.4. freezing
71.4.1. <-17 °C, about -28 °C
71.4.1.1. storage of food by inhibiting microbes growth. generally microbiostatic.
71.4.1.1.1. foods are easily spoiled after thawing with the release of juice
71.4.1.2. preservation of food by inhibiting microbial growth
71.4.1.2.1. psychrotrophic microbes survive and grow
72. Principle of freezing
72.1. Thus, a food is protected, preserved from deteriorating influences such as temperature and water.
72.1.1. During freezing, the water in the food is separated out from other food components, and is frozen.
72.2. The lower temperature slows down the rate of chemical reaction and water is also removed from the sphere of activity.
72.3. The water is reabsorbed by the food components upon thawing and food is restored to its original quality.
72.4. When a food is frozen, the water undergoes transition from liquid to solid state and also in subsequent thawing.
72.4.1. When there is transition from solid to liquid state, there is a damaging effect on food.
72.4.2. The texture and the structure of the food may be affected to such an extent that it may become irreversible and upon thawing the food will not be restored to its original condition.
73. - Does not sterilize food. - Extreme cold (0°F or -18°C colder): - Stops growth of microorganisms and - Slows chemical changes, such as enzymatic and metabolic reaction. - 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. The immobilization of water to ice and the resulting concentration of dissolved solutes in unfrozen water lower the water activity (aw) of the food - Preservation is achieved by a combination of low temperatures, reduced water activity and, in some foods, pre-treatment by blanching.
74. Advantage Of chilling
74.1. Can extend the shelf life of food
74.2. Larger range of fresh and convenience food are offered to customers.
75. The use of low temperature
76. Why are some microorganisms able to grow at low temperature?
76.1. The example was Psychrophilic microorganisms that can adapt with low temperature because they have cytoplasmic membranes and enzymes that are likely to form rigidify during the low temperature. These will impact the membrane permeability due to enzymes needing certain conditions to be flexible. Also, it has the impaired protein folding and protein cold that denatures with the low temperature which could maintain its biological activities at low temperatures as it is below -20°C.
77. Dairy Product
77.1. Must store the milk below 4 degree celsius to protect the quality of milk and can inhibit the growth of bacteria.
77.2. This temperature is held through the warehousing, distribution, delivery and storage to keep the milk cool as it can last longer and safer.
77.3. Different kind of bacteria has different optimal growth temperature. Optimum growth temperature indicates the highest growth rate of that particular organism. Mesophilic bacteria grow best at room temperature approximately at 20°C to 45°C, thermophilic bacteria grow best at high temperature between 50°C to 80°C, while psychrotrophs grows at low temperature of 4°C to 25°C and psychrophiles survive at 0°C to 15°C. Preservation of food can be done in low temperature like chilling and freezing to inhibit microbial growth so the food can last longer. However, freezing can negatively affect its quality in terms of nutritional value, the flavor and color of foods. Freezing can completely kill most of harmful bacteria but some may survive as freezing only inactivate their activities. But the endospores and toxins produced by unwanted bacteria can survive at low temperature. Foodborne pathogen that can thrive in refrigerated food include Staphylococcus aureus, Listeria monocytogenes and Psudomonas spp. Hence, freezing food cannot be considered as completely killing all foodborne microorganisms.
78. Enzymatic and microbial changes slow at low temperature
78.1. Prevent growth of mesophiles
78.2. Lead to microflora dominated by psychropiles
78.3. Temperature changes, duration of storage, and cross contamination - increase microbial problems (from foodborne pathogen)
78.4. Physiological changes:- production of phenazine, carotenoid pigments, stimulation of extracellular polysaccharide production, lactic acid
78.5. Thermal stability of enzyme produced by psychrotropic microorganisms
79. Freezing based on using Liquid Gaseous
79.1. Liquid Nitrogen Freezing (LNF)
79.1.1. temperature: -110 Celcius
79.1.2. 10 cm frozen layer per hour
79.1.3. based on pure nitrogen gas
79.2. Liquid Carbon Dioxide Freezing (LCO2F)
79.2.1. temperature: -70 Celcius
79.2.2. 5-8cm frozen layer per hour.
79.2.3. based on carbon dioxide gas
80. Low temperature food preservation on microbes
80.1. methods
80.1.1. Freezing
80.1.1.1. storage below food's freezing point
80.1.1.2. water immobilization; high concentration of dissolved solutes; lower aW
80.1.2. refrigeration
80.1.2.1. store at temperature range 7.2 - 0 degree Celcius
80.1.2.2. slow down the spoilage
80.1.2.3. psychrophilic type microbes may grow
80.1.3. chilling
80.1.3.1. temperature range -1 - 8 degree Celcius
80.1.3.2. reduce rate of biochemical and microbiological changes