Salt tolerant / halophilic bacteria of Serratia, Micrococcus, Bacillus, Alcaligenes, Pseudo.
Molds (if acidity increases growth favours)
Souring by volatile acid production by Bacilli or to putrefaction
As on fish spoilage
Acinetobacter, Moraxella, Vibrio, Increases in Pseudo, increases Flavobacterium, Micrococcus, Bacillus
Chilling Pseudo, Acinetobacter, Moraxella
Near freezing spoilage occurs by Pseudomonas,Acinetobacter, Moraxella, Flavobacterium, Micrococcus.
Spoilage called as sourcing (Proteolytic)
At high Temperature souring may be result of
Fermentation of sugars by coliforms, Streptococcus, Lactobacillus, yeast to produce acids and a sour odor.
Pink oysters Asporogenous yeast
Others are Pseu, Serratia, Proteus, Clostridium growth occurs.
9.Explain about preservation of food using high temperatue.
principles of food preservation
1.Prevention or delay of microbial decomposition: By keeping out microorganisms (asepsis).
By removal of microorganisms (filtration).
By hindering the growth and activity of microorganisms.
Eg; by low temperature, drying, anaerobic conditions, chemicals.
By killing the microorganisms.
Eg; by heat or radiation.
2. Prevention or delay of self-decomposition of food:
By destruction or inactivation of food enzyme. Eg; blanching.
By prevention or delay of purely chemical reactions. Eg; prevention of oxidation by means of an antioxidant.
3.Prevention of damage because of insects, animals, mechanical causes etc.,
METHODS OF PRESERVATION: Asepsis
Removal of microorganisms.
Maintenance of anaerobic conditions eg: in a sealed, evacuated container.
Use of high temperature.
Use of low temperature.
Use of chemical preservative.
Mechanical destruction of microorganisms grinding, high pressure.
ASEPSIS: It refers Combination of two or more of the above methods.
to keeping out of microorganisms.
Inner tissues of healthy plants and animals are free of microorganisms, if they are present leads to initiate the spoilage.
If there is protective covering the spoilage may be delayed or prevented. Eg; shells of nuts, skins of fruits and vegetables, husks of ear corn, shells of egg, skin or membranes or fat on meat or fish.
The food technologists are concerned with bioburden of microorganisms where they consider both kinds and numbers of microorganisms in food.
Packaging of foods is a widely used application of asepsis. Eg; loose carton or wrapping.
Dairy industry concentration is made during milking process, handling.
Canning industry sealing can prevent contamination.
Meat packaging industry sanitary methods of slaughter, handling and processing reduce the load and thus improve the keeping quality of meat or meat products. Intestinal flora must be removed in animals.
REMOVAL OF MICROORGANISMS:
Removal of microorganisms may be by;
The liquid is filtered through a previously sterilized bacterioproof filter made of sintered glass,
Diatomaceous earth, unglazed porcelain, membrane pads or similar material and the liquid is forced through by positive or negative pressure. Eg; fruit juices, beer, soft drinks, wine and water.
2) CENTRIFUGATION: (SEDIMENTATION)
It is not very effective. Sedimentation is used in the treatment of drinking water. When centrifugation (clarification) is applied to milk, the main purpose is not to remove bacteria but to take out other suspended materials, although centrifugation at high speeds removes most of the spores.
It can act as surface sterilization. Eg; removal of soil microorganisms on the surface is by washing in fruits, vegetables, (cabbage, cucumber) etc. Washing foods may be dangerous if the water adds spoilage organisms or increases the moisture so that the growth of spoilage organisms is encouraged.
Removal of the spoiled particles of a food or discarding spoiled samples is important. Eg; Trimming the outer leaves of cabbage heads is recommended for the manufacture of sauerkraut.
Medium acid foods pH (between 5.3 and 4.5). Eg; spinach, beets, pumpkin.
Acid foods pH (between 4.5 and 3.7). Eg; tomatoes,pears,pineapple.
High acid foods pH (3.7 and below). Eg; berries,sauerkraut. Heat sensitive.
Due to increased concentration they can be easily destroyed.
Antiseptic or germicidal substances in the substrate aid heat in the destruction of organisms.
H2O2 + heat is used to reduce the bacterial content and is the basis of a process of milk.
HEAT RESISTANCE OF MICROORGANISM AND THEIR SPORES:
THERMAL DEATH TIME:
It is defined as the time it takes at a certain temperature to kill a stated number of organisms under specified conditions. It is also referred to as the absolute thermal death time to distinguish it from the majority thermal death time for killing most of the cells or spores present.
THERMAL DEATH TIME:
Expressed as the rate of killing.
THERMAL DEATH POINT:
It is the temperature necessary to kill the entire organism in 10 minutes.
HEAT RESISTANCE OF YEASTS AND YEAST SPORES:
The resistance of yeasts and their spores to moist heat varies with the species and even the strain, with the substrate in which they are heated.
Vegetative cell of ascospores 5 – 100c for destruction.
Spores of yeasts 600c for 10 –15 min but few are resistant.
Asexual spore are more resistant than ordinary mycelia ( 600c) ie.,5 – 100c rise.
Aspergillus, Mucor, Penicillium are more resistant to heat.
Pasteurization kills spores and vegetative cells.
Sclerotia are difficult to kill by heat and they can survive at 90- 100 0c to spoil canned fruits. They can be killed at 1000min at 830c or 300 min at 850c.
Mold spores are resistant to dry heat.
3.HEAT RESISTANCE OF BACTERIA AND BACTERIAL SPORES:
Cocci are more resistant than rods.
Higher the optimal and maximal temperature of growth, greater the resistance to heat.
Capsule is difficult to kill.
Cells high in lipid content are harder to kill.
T0 WITH TIME
1000c for 1.7 min
1000c for 15-20 min
1000c for 100 – 330 min
1000c for 520 min
500c for 2- 3 min
600c for 4.3 min
4.HEAT RESISTANCE OF ENZYMES:
Enzymes are inactivated at 79.40c for 10 min.
Pasteurization of milk can be checked by the presence of bovine phosphatase. If this enzyme is observed then the process was not carried out properly is understood.
10.write a short notes on heat pentration in food substance.
The rate of penetration of heat into a food must be known in order to calculate the thermal process necessary for its preservation. Every part of the food in a can must have to obtain the adequate heat treatments to prevent spoilage may be by
1. Conduction – near the center (slow in food, rapid in metals)
2. Convection – heat passes from molecules to molecule.
When solid particles of food are suspended in a liquid, the particles heat by conduction and liquid heats by convection.
Factors involved are:
1. The material of which the container is made.
2. The size and shape of the container.
3. Initial temperature of the food.
4. Retort temperature.
5. Consistency of can contents and size and shape of pieces.
a. Pieces that retain their identity.
b. Pieces that cook apart and become mushy or viscous.
c. Pieces that layer.
6. Rotation and agitation.
a. Below 100C
b. At 100 C
c. Above 100 C
Pasteurization is a heat treatment that kills part but not all of the microorganisms present and usually involves the application of temperature below 100C.
1. When more vigorous heat treatments might harm the quality of the product. E.g.: market milk.
2. To kill pathogens. E.g. market milk.
3. Main spoilage organisms are not very heat resistant.
E.g.: yeast in fruit juices.
4. When process requires additional chilling.
5. When competing organisms are to be killed, allowing desired fermentations, usually by added starter organisms. E.g.: cheese making.
Preservative methods used to supplement pasteurization include;
3. Maintenance of anaerobic conditions.
4. Addition of high concentration of sugar. E.g.: sweet condensed milk.
5. Addition of chemical preservative. E.g.: Pickles
1.Pasteurization time and temperature:
1. Milk Low temperature / long time
LTH / [holding] 62.8C for 30 min
High temperature short time
[HTST] 71.7C for 15 sec
Ultra pasteurization 137.8 C for 2 sec
2. Ice cream mix LTH 71.7 C for 30 min
HTST 82.2 C for 16-20 sec
3. Grape wine 82 –85 C for 1 min
4. Fruit wine 62.8 C for 30 min
5. Beer 60 C for 15 min
6. Dried food 85 C for 30 –90 min
7. Bottled grade juice 76.6 C for 30 min
8. Bottled apple juice 60 C for 15 min
9. Bulk apple juice 85-87.8 C for 30-60 sec
10 Vinegar 65.6 C for 30 min
If pasteurization is not proper, then there is the presence of enzyme bovine phosphatase. Q fever may be transmitted by milk.
2. Heating at 100 C:
It is process where fresh vegetables before freezing or drying involves heating at about 100 C.
The internal temperature of break, cake or other bakery products approaches but never reaches 100 C as long as moisture is present.
Simmering is gentle boiling with the temperature about 100 C.
In meat, the internal temperature reaches only about 60 C in rare beef, up to 80C in well-done beef, 85 D in a pork roast.
The outside of the food very hot, but the center ordinarily does not reach 100 C.
Cook implies a specific time and temperature for a thermal process.
8. Warming up:
A small increase in temperature up to heating to 100 C.
3.Heating above 100C:
Milk can be heated to temperatures up to 150C by use of steam infection or steam infusion followed by flash evaporation of the condensed steam and rapid cooling. This is referred to as UHT processes.
Canning / appertization:
Canning is defined as the preservation of foods in sealed containers and usually implies heat treatment as the principal factor in the prevention of spoilage. Canning is the general term and is replaced by hermetically sealed containers. Nicolas appert has been called the “Father of canning”.
1. Initially glass vessels are used.
2. Later metals, plastics are used.
3. Corks were also used.
4. Recently cans are made of tin.
5. Enamels are coated on to flat sheets of plate before the manufacturer of cans to prevent or slow discoloration or corrosion.
6. Aluminum parts are used for products that do not require high vacuums or high -T processing. E.g.: Beer, foreign fruits, cheese.
7. Plastic flexible pouches or bags are used or plastic laminated with foil are employed mostly for packaging frozen, dried or unprocessed foods. They are also used for foods that can be packaged hot, although steam – pressure sterilization of foods in pouches has been accomplished.
E.g.: Jams, dried food products.
8. Tin cans were first used by Peter Durand.
Food has sulphur and tin has Fe combine to form FeS. Standard enamel is used for cans for highly colored fruits and berries or for beets to prevent the fading of colour caused by tin plate. Enamels are coated with Zno, so that the white ZnSo4 is formed instead of dark FeS, When low acid, sulfur – bearing foods such as corn as canned and darkening of the interior of the can be avoided.
Meat, fat-containing foods should not be stored in cans containing Zno as they split the fats. Special enamels may be employed for certain products. E.g.: milk, meat, wine, beer, soups and some fruit juices.
Food => Remove the spoiled food by trimming => wash with sterile water (Surface sterilization)
Blanching / steam sterilization and cooling
Blanching sets the colour, softens the tissues and kills some microbes
Add sugar / salt solution
Evacuated before sealing
Usually by heating headspace / unfilled part of the container by mechanical means.
Canned food (commercially sterile or practically sterile or bacterially inactive)
2. HC7 / Heat cool fill method.
3. Steam pressure E.g. Tomato juice may be presterilised at 121 C to 132 C to kill spores of B. coagulants before canning and then the sealed cans of juice are given a milder heating.
4. SC / Sterilizing and closing.
5. PFC / Pressure filler cooker.
E.g.: apple slices, food is dried to about half its original weight before canning.
7. Direct gas flame.
8. Steam injection.
9. Flash 18
10. Addition of preservation / irradiation / chemicals.
Pressurized packaged foods / aerosols:
They are packed under pressure of a propellant gas, usually
1. Co2 => inhibits many microbes => aerobic bacteria and molds not lactic acid bacteria. E.g. B. coagulans, Strep. facelis or yeasts.
2. N2 => inhibit anaerobes not aerobes.
3. Nitrous oxide = represses fungi.
E.g.: whipped cream, beverage toppings, salad dressings, oils, and jellies.
The cans may be cooled by
1. Immersion in cold water.
2. Spray of water.
3. Large cans are cooled slowly to avoid strain or breakage.
4. By means of air currents.
Canning in the home:
2. Steam pressure
3. Micro over
4. Cold pack method => not for vegetables and meats.
11.write short notes on preservation of food using low temperatue?
preservation by use of low temperature
Low temperature preservation is used commonly to retard chemical reactions and action of food enzymes. Therefore there is a gradual decrease in the activity of microorganism and also the spoilage of food.
The growth and metabolic reaction of microorganisms depend upon the enzymes and the rate of enzyme reactions directly affected by temperature.
During low temperature metabolic activity is arrested. Food enzymes are inactivated.
Low temperature methods:
1. Chilling / cold storage.
2. Freezing / frozen storage.
3. Freeze during / Lyophilization.
Chilling / cold storage:
1. It involves cooling by ice or by mechanical refrigeration.
2. It is used to prevent the growth and reduce the metabolic activity of microbe.
3. Temperature is 0 –15C.
4. Ice crystals can be used to store fish, meat during transportation.
5. Use of mechanical refrigerator. E.g. food storage in industry.
Lower the temperature of storage, the greater the cost. The temperature is selected on the basis of
1. Kind of food.
3. Condition of storage. Certain foods have an optimal storage temperature or range of temperature well above the freezing point and may be damaged by lower temperature.
E.g.: banana should be kept in the refrigerator, best at about 13.3 to 16.7C.
The optimal Rh depends on the temperature, composition of the atmosphere, ray treatments.
Low RH => loss of moisture and hence weight, witting and softening of vegetables and shrinkage of fruits.
High RH => growth of spoilage microorganisms.
E.g.: yeast => 90 –92%
Molds => 85 –90%
Changes in RH and T during storage may cause sweating or precipitation of moisture on the food, so favors microbial spoilage. E.g.: slime on the moist surface of sausage.
To prevent the development of stale odors and flavors, and maintain uniform RH throughout the room. It adequate ventilation is not provided; food in local areas of high humidity may undergo microbial decomposition.
4. Composition of storage atmosphere:
It is controlled by the introduction of Co2, ozone or other gases called as gas storage.
1. Food remains unspoiled for a longer period.
2. Rh may be maintained.
3. Keeping quality is maintained.
4. Higher storage temperature can be used without shortening the keeping time of food eg. Optimal CO2 concentration.
Eggs 2.5 %, Beef 10%, Bacon 100%, Apples concentration of O2 and CO2 is significant.
5. Irradiation :
UV lamps have been installed in rooms for the storage of meat & cheese.
Freezing / Frozen storage :
The selection & preparation of foods for freezing – fruits & vegetables are selected on the basis of their suitability for freezing & their maturity & are washed, trimming, cut vegetables are scalded/ blanched & fruits may be packed in a syrup.
Meats are selected to minimize enzymatic & microbial changes. Most foods are packaged before freezing, but some foods in small pieces. E.g. Strawberries may be frozen before package.
Scalding or blanching is done:
Inactivation of plant enzymes that involve toughness.