pat244g - dasar pengolahan dan pengawetan (3
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PAT244G - DASAR PENGOLAHAN DAN PENGAWETAN (3 SKS) - 20122 - (Prodi -
41231)
Aturan
• Rapi dan sopan : pakaian berkerah dilarang pakai sandal
• Celana panjang wajar• Terlambat kuliah 20 menit • Kuliah Jika hujan, ditunda -- dispensasi
untuk 10 km >
Sistem Penilaian• Ujian Mid 60 • Tugas ; 30 - 15 dan 15• 1. Saudara membuat ringkasan 3 artikel pengolahan pangan. Pembuatan
tape kualitas dan jenis ketela pohon Proses Pembuatan tape Pemasaran, Potensi menjadi produk lain. Bika ambon, sumber ditulis 2 minggu 28 maret 2013,lewat nilai dipotong. Bisa dikirim lewat email.
• Kehadiran : 10 POINT
• Praktikum :100 % , laporan, ujian pratikum, pre tes , post tes : tidak ada susulan
Food processing has three major aims:
• 1.To make food safe (microbiologically, chemically).
• 2.To provide products of the highest quality (flavor, color, texture)
• 3.To make food into forms that are convenient (ease of use)
GOALS FOR PRESERVATION
• Safe -microbiologically, chemically and physically
• Convenience• Long shelf life• Good appearance• Good texture• Good flavor• Nutritious
Why Preserve / Process Foods?
• Prevent deterioration & spoilage• Destroy spoilage microorganisms & enzymes• Improve quality attributes– Change the form of the food
FOOD DETERIORATION AND FOOD SAFETY
1. CHEMICAL 2. ENZYMATIC 3. PHYSICAL
4. MICROBIOLOGICAL
A. THE GOOD
B. THE BAD
C. AND THE UGLY
SAFETY
• Ensuring the safety of food involves careful control of the process from the farm to the consumer.
• Safety includes control of both chemical and microbiological characteristics of the product.
• Most processing emphasize on microbial control. Often has as its objective the elimination of organisms or prevention of their growth.
• FOOD SPOILAGE – PROCESS THAT MAKES FOOD INEDIBLE
• FOOD FERMENTATION – PROCESS THAT CHANGES THE FOOD’S SENSORY CHARACTERISTICS AND INCREASES THE SHELF–LIFE OF THE ORIGINAL FOOD
• FOOD BORNE ILLNESS – INFECTIONS OR POISONING DUE TO THESE MICROORGANISMS
• MICROORGANISMS – SMALL ORGANISMS INVISIBLE TO THE NAKED EYE.
MICROBIOLOGICAL GROWTH IS DEPENDENT UPON SEVERAL
FACTORS.
1. pH – MEASURE OF ACIDITY ACIDIC < 7.0 > ALKALINEGROWTH BETTER NEAR NEUTRALITY
2. MOISTURE CONTENT – Aw MEASURE OF FREE WATER. MORE DRY <1.00(MAX) GROW BETTER NEAR 1.00
3. TEMPERATURE –
MOST ORGANISMS GROW BEST AT AMBIENT TEMPERATURES (600 – 800 F)
4. PRESENCE OR ABSENCE OF OXYGEN
WITH O2 – AEROBIC.
WITHOUT O2 – ANAEROBIC.
TYPES
1. BACTERIA – A VARIETY OF UNICELLULAR ORGANISMS THAT GROW UNDER A VARIETY
OF CONDITIONS • TYPICALLY FAST GROWERS UNDER THE RIGHT CONDITIONS.
• NOT ALL ARE SPOILAGE AND DISEASE ORGANISMS i.e. FERMENTATION
• DISEASE PRODUCING ORGANISMS TYPICALLY MORE SENSITIVE TO ADVERSE GROWTH CONDITIONS
WIDE VARIETY
1. SOME BACTERIA GROW AT:
• REFRIGERATOR TEMPERATURES (PSYCHROPHILES) 450 F (7.20 C) TO 860 F (300 C); PSYCHROTROPHS
SOME BACTERIA GROW AT (cont.):
• ROOM TEMPERATURE (MESOPHILES); 680 F (200 C) – 1100 F (43.30 C)
• HIGHER TEMPERATURES (THERMOPHILES;1130 C – 1550 C)
2. SOME FORM SPORES THAT CAN SURVIVE ADVERSE CONDITIONS
3. SOME CAN GROW IN HIGH ACID FOODS
FOOD INFECTIONS
• INGESTED BACTERIA CAUSING ILLNESS
FOOD INFECTIONS
1. CLOSTRIDIUM PERFRINGENS – FORMS SPORES AND ANAEROBIC.
• SYMPTOMS: DIARRHEA, ABDOMINAL PAIN, HEADACHE, 8 TO 24 HRS INCUBATION.
• SOURCES: MEATS AND GRAVIES.
• PREVENTION: PROPER COOLING OF FOOD.
2. E.COLI – ALL TYPES OF FOOD. AVOID PRACTICES WHICH CAN CONTAMINATE FOOD.
• DIARRHEA, VOMITING. 18–24 HRS. RENAL FAILURE IN CHILDREN (0157:H7).
• PROPER COOKING OF GROUND BEEF, APPLE CIDER, PREVENTION OF CROSS CONTAMINATION (RAW FOOD AND FOOD HANDLERS).
3. SALMONELLA – SALMONELLOSIS • SYMPTOMS: DIARRHEA, ABDOMINAL CRAMPS, VOMITING, FEVER. CAN LAST TWO OR THREE DAYS. INCUBATION, 12 TO 36 HRS.
• SOURCES: EGGS (2.6–7%) AND MEATS (30% POULTRY ESTIMATED). MILK. CARRIERS (REMEMBER TYPHOID MARY).
• PREVENTION: REFRIGERATION, PROPER FOOD HANDLING PRACTICES, AVOID FOOD CONTACT WITH PESTS. HEATING FOODS (POULTRY, STUFFING, ETC.) TO AT LEAST 1650 F (65.50 C). PASTEURIZE EGGS 1400 F (600 C) FOR 3–4 MIN. PRIOR TO FREEZING OR DRYING. COOK ALL EGGS (WHITES AND YOLKS SHOULD BE SOLID: USDA). SALMONELLA–FREE PETS. GOOD PERSONAL HYGIENE.
4. LISTERIA – (LISTERIA MONOCYTOGENES)
• WIDELY DISTRIBUTED IN NATURE. GROWS AT REFRIGERATOR TEMPERATURES ONLY 100 TO 1000 CELLS REQUIRED.
(LISTERIA cont.)
• SYMPTOMS: WIDE VARIETY OF ILLNESSES, 1 DAY TO WEEKS AFTER INGESTION. MILD FLU–LIKE FOR HEALTHY PEOPLE. ELDERLY, PREGNANT WOMEN, INFANTS, IMMUNOCOMPRIOMISED: MENINGITIS, MISCARRIAGE, PERINATAL SEPTICEMIA.
(LISTERIA cont.)
• SOURCES: COLESLAW, RAW MILK, SOFT CHEESE ($66 MILLION), SEAFOOD, MEATS.
• PREVENTION: ENVIRONMENTAL SANITATION, PROPER PASTEURIZATION, CHLORINATED WATER, CONTROL AIRFLOW THROUGH PLANTS. USDA INSPECTION/REPORTING PROGRAM.
5. CAMPYLOBACTER JEJUNI.
• SYMPTOMS: IN 2–5 DAYS NAUSEA, CRAMS, HEADACHE, DIARRHEA FEVER: COMPLICATIONS MENINGITIS, SYSTEMIC INFECTION
(CAMPYLOBACTER JEJUNI cont.)
• SOURCES: FECAL MATERIAL, RAW MILK, EGGS, POULTRY, MEAT, CAKE ICING.
• PREVENTION: THROUGH COOKING AND PROPER HANDLING OF RAW PRODUCTS. CAN'T GROW <300 C
6. YERSINIA ENTEROCOLITIA.- GROWS AT REFRIGERATOR TEMPERATURES.
• SYMPTOMS: 1–2 DAYS DIARRHEA, FEVER, and SEVERE ABDOMINAL PAIN IN LOWER RIGHT QUADRANT (SIMILAR TO APPENDICITIS)
SOURCES: WIDELY DISTRIBUTED IN NATURE. MILK CONTAMINATED BY CHOCOLATE SYRUP AFTER PASTEURIZATION, CONTAMINATED SPRING WATER, AND MEAT.
PREVENTION: PASTEURIZATION, WATER TREATMENT (CHLORINATE), ACIDIFY FOODS <4.6, SALT>5%.
FOOD POISONINGS (INTOXICATIONS)
• INGESTED TOXIN LEFT IN FOOD BY ORGANISM.
1. BOTULISM – CLOSTRIDIUM BOTULINUM. FORMS SPORES AND ANAEROBIC. TYPE A, B, AND E AFFECT HUMANS. TYPE E CAN GROW AT REFRIGERATOR TEMPERATURES [380 F (3.30 C)] ANTITOXIN TREATMENT AVAILABLE.
INFANT BOTULISM NOT CONSIDERED A FOODBORNE DISEASE.
SYMPTOMS: NEUROTOXIN CAUSING MUSCLE PARALYSIS AND DEATH. INABILITY TO TALK, DIFFICULTY IN SWALLOWING, DOUBLE VISION, NAUSEA, VOMITING, DIARRHEA, CONSTIPATION IN EARLY STAGES. SYMPTOMS START 12 – 36 HRS AFTER EATING. DEATH IN AROUND 7 DAYS (20% NOW; TURN OF THE CENTURY – 50 TO 60%).
SOURCE: SEEN TYPICALLY IN LOW ACID (LOW ACID) HOME CANNED FOODS (pH > 4.5), SALMON, TUNA, MUSHROOMS, POTATO SOUP, BEEF STEW, UNREFRIGERATED BAKED POTATOES, GARLIC IN OIL, AND SOME SMOKED FISH.
PREVENTION: CAN LOW ACID FOODS PROPERLY (HIGH TEMPERATURE, PRESSURE), ACIDIFY, COOK SUSPECTED FOODS PROPERLY [2120F(1000
C)]. STORE FISH BELOW 380 F.
2. STAPHYLOCCOCAL – STAPHYLOCOCCUS AUREUS
• TOXIN IS HEAT STABLE (WITHSTANDS BOILING 20–60 MINUTES. GROWS 440 F (6.70
C) 1120 F (44.40 C)
SYMPTOMS: VOMITING AND DIARRHEA FROM 1 TO 6 HRS AFTER EATING.
SOURCES: HAM (SALT TOLERANT –10%; HAMS USUALLY 2–3% SALT), CREAM OR CUSTARD FILLED BAKED PRODUCTS, POTATO SALAD, HUMANS (40%) NASAL PASSAGES, WOUNDS, COWS WITH MASTITIS, 1989 CHINESE CANNED MUSHROOMS.
PREVENTION: PROPER HANDLING PRACTICES, REFRIGERATION BELOW 40 F (4.40 C), ELIMINATE MILK FROM COWS WITH MASTITIS FROM HUMAN CONSUMPTION.
3. BACILLUS CEREUS – SPORE FORMER
SYMPTOMS: ABDOMINAL CRAMPS, WATERY DIARRHEA, SOME VOMITING.
SOURCES: IMPROPERLY COOLED FOODS, HOLDING TEMPERATURES AND IMPROPERLY REHEATED FOODS (RICE)
PREVENTION: PROPER COOLING AND RE-HEATING [1650 F (73.90 C)].
MISCELLANEOUS OTHERS:
TUBERCULOSIS –CORYNEBACTERIUM TUBERCULOSIS AND BRUCELLOSIS (UNDULANT FEVER) RAW MILK.
VIBRIO PARAHAEMOLYTICUS – FOUND IN OCEANS. REQUIRES 24% SALT. WITH OR WITHOUT OXYGEN OPTIMUM 86–1040 F (30-400 C)
SYMPTOMS: 15–17 HOURS AFTER INGESTION. DURATION 1–2 DAYS ABDOMINAL PAIN, NAUSEA, VOMITING WITH DIARRHEA, OCCASIONAL BLOOD AND MUCUS IN FECES. FEVER (1–20 F IN 60-70% OF THE CASES).
SOURCES: RAW FISH, MOLLUSKS AND SHELLFISH.
PREVENTION: COOKING, SANITATION, ABSTAIN FROM EATING RAW SQUID, OCTOPUS, CLAMS AND OYSTERS IN JULY, AUGUST, SEPTEMBER OR TIMES THAT COASTAL WATERS ARE WARM.
DISEASES FROM OTHER MICROORGANISMS
1. TRICHINOSIS – ROUNDWORM
SYMPTOMS: NAUSEA, VOMITING, DIARRHEA IN 1–4 DAYS IF HIGH DOSE. IF LOW DOSE NO SYMPTOMS UNTIL 7TH DAY. LARVAE CAN MIGRATE FROM THE INTESTINES INTO MUSCLES CAUSING HIGH FEVER [1040
F(400 C] AND SWELLING.
SOURCE: TYPICALLY TRANSMITTED THROUGH EATING PORK,(BEAR, PORK/DEER, UNDER COOKED SAUSAGE)
PREVENTION: COOK PORK TO INTERNAL TEMPERATURE OF AT LEAST 137 F (58.30 C), NO PINK COLOR,(NATIONAL LIVESTOCK AND MEAT BOARD – 770 C (1700 F), FRESH FROZEN PORK 520 F (–15 TO 28.90C) FOR A PERIOD OF 6–30 DAYS, ETC., CONTROL AND COOK FEED GIVEN TO HOGS.
2. HEPATITIS TYPE A – VIRUS.
CONTROL BY PROPER HANDLING PRACTICES.
NORWALK VIRUS – VOMITING
YEAST
1. LARGER THAN BACTERIA
2. MORE ADVANCED PHYSIOLOGICALLY
3. CAN GROW UNDER MORE ADVERSE CONDITIONS
4. TYPICALLY SPOILAGE OR FERMENTATIVE ORGANISMS
5. VERY HEAT SENSITIVE
MOLDS
1. ADVANCED PHYSIOLOGICALLY – CAN BE MULTICELLULAR
2. PRODUCE SPORES THAT ARE LESS HEAT RESISTANT THAN BACTERIAL SPORES
3. NEED OXYGEN TO GROW
MOLDS (cont.)
4. CAN GROW UNDER THE MOST ADVERSE CONDITIONS
– SLOW GROWTH
5. CAN BE SPOILAGE OR PATHOGENIC
OR DESIRABLE (BLUE CHEESE)
– TOXIN PRODUCTION (MYCOTOXINS)
AFLATOXIN – MOLD POISONING
• PRODUCED BY ASPERGILLUS FLAVUS
• TYPICALLY FOUND ON CEREAL GRAINS AT THE PROPER MOISTURE AND TEMPERATURE
– CORN – PEANUTS
AFLATOXIN (cont.)
• FATAL AT LARGE DOSES, TYPICALLY LIVER DAMAGE.
• CARCINOGENIC AT LOW DOSES
• YEAST AND MOLD INHIBITORS • PROPIONATES, PHOSPHATES, SORBATES
MICROBIOLOGICAL PROCESS CONTROL
1. PERSONNEL STANDARDS – HAND WASHING – HEALTHY – HAIR COVERING, GLOVES – CLOTHING
2. INGREDIENT CONTROL (SENSITIVE) – PRODUCTS FROM ANIMALS – SPICES
– PRODUCTS THAT ARE IN CONTACT WITH THE SOIL
3. PLANT CLEANNESS
CLEAN: REMOVE POTENTIAL FOOD AND HIDING PLACES FOR MICROORGANISMS AND PLACES
FOR VECTORS SANITIZE: KILL MOST OR
ALL OF THE ORGANISMS ON SURFACES
4. PLANT AND EQUIPMENT DESIGN – PREVENT POTENTIAL PLACES FOR MICROBIAL GROWTH AND MICROBIAL VECTORS.
5. FOODS MUST BE PROPERLY REFRIGERATED.
6. FOODS MUST BE ADEQUATELY PROCESSED AND PROTECTED FROM RECONTAMINATION (CROSS–CONTAMINATION).
7. THE MANAGEMENT MUST STRESS PRODUCT SAFETY AND QUALITY.
Potentially Hazardous Foods (PHFs)
• Foods that contains in whole or in part of the following:– Milk or milk products
– Shell eggs
– Meats
– Poultry
– Fish
Potentially Hazardous Foods (PHFs)
– Shellfish– Edible crustaceans (shrimp, lobster, etc.)– Baked or boiled potatoes– Tofu or other soy products including textured soy
proteins– Plant foods that have been treated (beans)
Potentially Hazardous Foods (PHFs)
– Raw seed sprouts
– Sliced melons
– Unpasteurized fruit juices (apple)
FOOD SAFETY – YOU DON’T WANT A RECALL
• Regulatory agencies can issue public warnings.
• Recalls and seizures are not uncommon. They occur at a rate of about 400/year.
• It is one of the major responsibilities of all food processors to produce safe and wholesome food for the consuming public.
Procedures to Help Reduce Food-borne Illnesses
• Good Manufacturing Practices (GMPs)• Standard Operating Procedures (SOPs)• Sanitary Standard Operating Procedures
(SSOPs)• Hazard Analysis Critical Control Points
(HACCPs)• Management Support
Code of Federal Regulations Title 21 Part 110
• Current Good Manufacturing Practice in Manufacturing, Processing, Packing, or Holding Human Food (CGMP or GMP)
• See Appendix 1 for more detailed examples.
Good Manufacturing Practices
• Personal Hygiene• Quality Raw ingredients• Sanitary Storage • Processing • Packaging Areas
Outside the Plant
• Parking and roads paved and graded to drain.
• Building constructed to prevent pest entry.
Receiving
• Truck dock entries constructed to prevent bird
nests other pests from entering plant.
• Trucks clean inside, good condition, and tightly
constructed and refrigerated if appropriate.
Processing• Time-temperature, pH, aw processing
controls maintained in good condition and calibrated regularly with records retained.
• Proper cleaning and sanitizing of equipment and surrounding areas.
• Cleaning supplies stored in a separate area.
Packaging
• Good sanitation and housekeeping in the area.
• Cleanliness of packaging equipment.
• Packaging materials protected from contamination.
• Metal detectors in place.
FOOD SAFETY – YOU DON’T WANT A RECALL
• Regulatory agencies can issue public warnings.
• Recalls and seizures are not uncommon. They occur at a rate of about 400/year.
• It is one of the major responsibilities of all food processors to produce safe and wholesome food for the consuming public.
Procedures to Help Reduce Food-borne Illnesses
• Good Manufacturing Practices (GMPs)• Standard Operating Procedures (SOPs)• Sanitary Standard Operating Procedures
(SSOPs)• Hazard Analysis Critical Control Points
(HACCPs)• Management Support
QUALITY
• Quality of a food product involves maintenance (or improvement) of the key attributes of the product -including color, flavor and texture.
• To maintain quality it is important to control: – •microbiological spoilage– •enzymatic degradation– •chemical degradationT&
PROCESSING AND PRODUCT QUALITY
• The components of food product quality include: 1.Safety 2.Healthfulness 3.Flavor 4.Texture 5.Color 6.Shelf Life
CONVENIENCE
• Today's consumers want food products that are convenient to use and still have all the qualities of a fresh product.
PRESERVATION OF FOOD
• Raw Materials• Food Processing
–Ready to Eat (RTE) consumer products–Not ready to eat food products
(requirefurther preparation by the consumer)
Processing by application of heat
• Heat treatment remains one of the most important methods used in food processing, not only because of the desirable effects on eating quality (many foods are consumed in a cooked form and processes such as baking produce flavours that cannot be created by other means), but also because of the preservative effect on foods by the destruction of enzymes, micro-organisms, insects and parasites.
• The other main advantages of heat processing are:• 1. relatively simple control of processing conditions• 2. capability to produce shelf-stable foods that do
not require refrigeration• 3. destruction of anti-nutritional factors (e.g. trypsin
inhibitor in some legumes)• 4. improvement in the availability of some nutrients
(e.g. improved digestibility of proteins, gelatinisation of starches and release of bound niacin).
Blanching
Blanching
To achieve adequate enzyme inactivation, food is heated rapidly to a pre-set temperature, held for a pre-set time and then cooled rapidly to near ambient temperatures. The factors which influence blanching time are:• type of fruit or vegetable• size of the pieces of food• blanching temperature• method of heating.
• Under-blanching may cause more damage to food than the absence of blanching does, because heat, which is sufficient to disrupt tissues and release enzymes, but not inactivate them, causes accelerated damage by mixing the enzymes and substrates. In addition, only some enzymes may be destroyed which causes increased activity of others and accelerated deterioration.
• Enzymes which cause a loss of eating and nutritional qualities in vegetables and fruits include lipoxygenase, polyphenoloxidase, polygalacturonase and chlorophyllase. Two heat-resistant enzymes which are found in most vegetables are catalase and peroxidase. Although they do not cause deterioration during storage, they are used as marker enzymes to determine the success of blanching. Peroxidase is the more heat resistant of the two, so the absence of residual peroxidase activity would indicate that other less heat-resistant enzymes are also destroyed.
The factors that control the rate of heating at the centre of the product are:• the temperature of the heating medium• the convective heat transfer coefficient• the size and shape of the pieces of food• the thermal conductivity of the food.
• If blanching is inadequate, a larger number of micro-organisms are present initially and this may result in a larger number of spoiled containers after processing. Freezing and drying do not substantially reduce the number of micro-organisms in unblanched foods and these are able to grow on thawing or rehydration.
• Blanching also softens vegetable tissues to facilitate filling into containers and removes air from intercellular spaces which increases the density of food and assists in the formation of a head-space vacuum in cans
Equipment• The two most widespread commercial methods of blanching involve
passing food through an atmosphere of saturated steam or a bath of hot water.
• The yield of food from the blanching operation is the most important factor in determining the commercial success of a particular method. In some methods the cooling stage may result in greater losses of product or nutrients than the blanching stage, and it is therefore important to consider both blanching and cooling when comparing different methods.
• Steam blanching results in higher nutrient retention provided that cooling is by cold-air or cold-water sprays. Cooling with running water (fluming) substantially increases leaching losses,2 but the product may gain weight by absorbing water and the overall yield is therefore increased. Air cooling causes weight loss of the product due to evaporation, and this may outweigh any advantages gained by nutrient retention (Bomben
• et al., 1975).
• There are also substantial differences in yield and nutrient retention due to differences in the type of food and differences in the method of preparation (for example slicing and peeling increase losses and reduce the yield).
• Recycling of water does not affect the product quality or yield but substantially reduces the volume of effluent produced. However, it is necessary to ensure adequate hygienic standards for both the product and equipment by preventing a build-up of bacteria in cooling water, and the improved hygiene control may result in additional costs which outweigh savings in energy and higher product yield.
1 Steam blanchers
• At its simplest a steam blancher consists of a mesh conveyor belt that carries food through a steam atmosphere in a tunnel. The residence time of the food is controlled by the speed of the conveyor and the length of the tunnel. Typically a tunnel is 15m long and 1–1.5m wide. The efficiency of energy consumption is 19% when water sprays are used at the inlet and outlet to condense escaping steam. Alternatively, food may enter and leave the blancher through rotary valves or hydrostatic seals to reduce steam losses and increase energy efficiency to 27%, or steam may be re-used by passing through Venturi valves. Energy efficiency is improved to 31% using combined hydrostatic and Venturi devices (Scott et al., 1981).
Tipe steam blancher
1. Individual quick blancherIn the first stage the food is heated in a single layer to a sufficiently high temperature to inactivate enzymes. In the second stage (termed adiabatic holding) a deep bed of food is held for sufficient time to allow the temperature at the centre of each piece to increase to that needed for enzyme inactivation.
2. Batch fluidised-bed blanchers operate using a mixture of air and steam, moving at approximately 4.5ms1, which fluidises and heats the product simultaneously. The design of the blanching chamber promotes continuous and uniform circulation of the food until it is adequately blanched.
2 Hot-water blanchers
• There are a number of different designs of blancher, each of which holds the food in hot water at 70–100ºC for a specified time and then removes it to a dewatering-cooling section.
• In the widely used reel blancher, food enters a slowly rotating cylindrical mesh drum which is partly submerged in hot water. The food is moved through the drum by internal flights.
Effect on foods
• The heat received by a food during blanching inevitably causes some changes to sensory and nutritional qualities.
• In general, the time–temperature combination used for blanching is a compromise which ensures adequate enzyme inactivation but prevents excessive softening and loss of flavour in the food
Nutrients• Some minerals, water-soluble vitamins and other water-soluble
components are lost during blanching. Losses of vitamins are mostly due to leaching, thermal destruction and, to a lesser extent, oxidation. The extent of vitamin loss depends on a number of factors including:– the maturity of the food and variety– methods used in preparation of the food, particularly the extent of cutting,
slicing or dicing– the surface-area-to-volume ratio of the pieces of food– method of blanching– time and temperature of blanching (lower vitamin losses at higher
temperatures for shorter times)– the method of cooling– the ratio of water to food (in both water blanching and cooling).
Colour and flavour• Blanching brightens the colour of some foods by removing air
and dust on the surface and thus altering the wavelength of reflected light. The time and temperature of blanching also influence the change in food pigments according to their D value.
• Sodium carbonate (0.125% w/w) or calcium oxide are often added to blancher water to protect chlorophyll and to retain the colour of green vegetables, although the increase in pH may increase losses of ascorbic acid. Enzymic browning of cut apples and potatoes is prevented by holding the food in dilute (2% w/w) brine prior to blanching. When correctly blanched, most foods have no significant changes to flavour or aroma, but under-blanching can lead to the development of off-flavours during storage of dried or frozen foods
Texture
• One of the purposes of blanching is to soften the texture of vegetables to facilitate filling into containers prior to canning. However, when used for freezing or drying, the time–temperature conditions needed to achieve enzyme inactivation cause an excessive loss of texture in some types of food (for example certain varieties of potato) and in large pieces of food. Calcium chloride (1–2%) is therefore added to blancher water to form insoluble calcium pectate complexes and thus to maintain firmness in the tissues.
Pasteurisation
• Pasteurisation is a relatively mild heat treatment, in which food is heated to below 100ºC. In low acid foods (pH4.5, for example milk) it is used to minimise possible health hazards from pathogenic micro-organisms and to extend the shelf life of foods for several days. In acidic foods (pH4.5, for example bottled fruit) it is used to extend the shelf life for several months by destruction of spoilage micro-organisms (yeasts or moulds) and/or enzyme inactivation
Theory
• The sensible heat required to raise the temperature of a liquid during pasteurisation is found using:
Q = mc(ѳA – ѳB)
where Q (W) specific rate of heat transfer, m(kg s1) mass flow rate,c (kJ kg1 ºC1) specific heat capacity and (ƟA-ƟB) (ºC) temperature change.
• The extent of the heat treatment required to stabilise a food is determined by the D value of the most heat-resistant enzyme or micro-organism which may be present. As flavours, colours and vitamins are also characterised by D values, pasteurisation conditions can be optimised for retention of nutritional and sensory quality by the use of high-temperature short-time (HTST) conditions. For example in milk processing the lower-temperature longer-time process operating at 63ºC for 30 min (the holder process) causes greater changes to flavour and a slightly greater loss of vitamins than HTST processing at 71.8ºC for 15 s.
• Higher temperatures and shorter times (for example 88ºC for 1 s, 94ºC for 0.1 s or 100 ºC for 0.01 s for milk) are described as higher-heat shorter-time processing or ‘flash pasteurisation’.
D value decimal reduction time The time needed to destroy 90% of the micro-organisms (to reduce their numbers by a factor of 10) decimal reduction time example if we have 1000 microorganisms in food does it refer to 90% reduction to 100 then to 10 & finally to1 or does these refers to 3 log cycles
• Alkaline phosphatase is a naturally occurring enzyme in raw milk which has a similar D value to heat-resistant pathogens (Fig. 11.1).
• The direct estimation of pathogen numbers by microbiological methods is expensive and time consuming, and a simple test for phosphatase activity is therefore routinely used. If phosphatase activity is found, it is assumed that the heat treatment was inadequate to destroy the pathogenic bacteria
• Colour, flavour and aroma• In fruit juices the main cause of colour deterioration is
enzymic browning by polyphenoloxidase. This is promoted by the presence of oxygen, and fruit juices are therefore routinely deaerated prior to pasteurisation. The difference between the whiteness of raw milk and that of pasteurised milk is due to homogenisation, and pasteurisation alone has no measurable effect. Other pigments in plant and animal products are also mostly unaffected by pasteurisation. A small loss of volatile aroma compounds during pasteurisation of juices causes a reduction in quality and may also unmask other ‘cooked’ flavours.
Heat sterilisation
• Heat sterilisation is the unit operation in which foods are heated at a sufficiently high emperature and for a sufficiently long time to destroy microbial and enzyme activity. As a result, sterilised foods have a shelf life in excess of six months at ambient temperatures.
• The length of time required to sterilise a food is influenced by:– the heat resistance of micro-organisms or
enzymes likely to be present in the food– the heating conditions– the pH of the food– the size of the container– the physical state of the food.
• Heat resistance of micro-organisms• The factors that influence heat resistance of
micro-organisms or enzymes and their characterisation by D and z values
The z-value of an organism is the temperature, in degrees Fahrenheit or Celsius, that is required for the thermal destruction curve to move one log cycle.
Hubungan z dan D
• Example: if it takes an increase of 10°F to move the curve one log, then our z-value is 10. Given a D-value of 4.5 minutes at 150°F, the D-value can be calculated for 160°F by reducing the time by 1 log. The new D-value for 160°F given the z-value is 0.45 minutes. This means that each 10°F increase in temperature will reduce our D-value by 1 log. Conversely, a 10°F decrease in temperature will increase our D-value by 1 log. So, the D-value for a temperature of 140°F would be 45 minutes.
• In low-acid foods (pH>4.5), the heat resistant, spore forming micro-organism, Clostridium botulinum is the most dangerous pathogen likely to be present. Under anaerobic conditions inside a sealed container it can grow to produce a powerful exotoxin, botulin, which is sufficiently potent to be 65% fatal to humans. Cl. botulinum is ubiquitous in soil and it is therefore likely to be found in small numbers on any raw material that has contact with soil. Because of the extreme hazard from botulin, the destruction of this micro-organism is therefore a minimum requirement of heat sterilisation.
Rate of heat penetrationHeat is transferred from steam or pressurised water through the container and into the food. Generally the surface heat transfer coefficient (Chapter 1) is very high and is not a limiting factor in heat transfer. The following factors are important influences on the rate of heat penetration into a food:• Type of product. Liquid or particulate foods (for example peas in brine) in whichnatural convection currents are established heat faster than solid foods in which heat is transferred by conduction (for example meat pastes and corned beef).Thelow thermal conductivity of foods is a major limitation to heat transfer in conduction heating foods.• Size of the container. Heat penetration to the centre is faster in small containers than in large containers.• Agitation of the container. • Temperature of the retort. A higher temperature difference between the food and the heating medium causes faster heat penetration.• Shape of the container. Tall containers promote convection currents in convective heating foods.• Type of container. Heat penetration is faster through metal than through glass orplastics owing to differences in their thermal conductivity