Food Processing Technology. Prepared by: Samer mudalal. 1.Introduction.
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1. To extend the shelf life to allow time for distribution, sales and home storage.
2. To increase variety in the diet by providing a range of attractive flavours, colours, aromas and textures in food (collectively known as eating quality, sensory characteristics or organoleptic quality); .
3. To provide the nutrients required for health (termed nutritional quality of a food).
4. To generate income for the manufacturing company.
1. the amount of water vapor already carried by the air
2. the air temperature
3. the amount of air that passes over the food.
(a) and (b) Drying curves. The temperature and humidity of the drying air are constant and all heat is supplied to the food surface by convection.
2.3.1 Hot-air driers
Bin driers are large, cylindrical or rectangular containers fitted with a mesh base. Hot air passes up through a bed of food at relatively low velocities
These consist of an insulated cabinet fitted with shallow mesh or perforated trays, each of which contains a thin (2–6 cm deep) layer of food. Hot air is blown at 0.5–5ms1 through a system of ducts and baffles to promote uniform air distribution over and/or through each tray.
• type of fruit or vegetable
• size of the pieces of food
• blanching temperature
• method of heating.
Blanchers: (a) IQB steam blancher (after Timbers et al. (1984)); (b) blancher–cooler
(from Hallstrom et al. (1988)) and (c) counter-current blancher (after Wendt et al. (1983)).
Effect of blanching on cell tissues: S, starch gelatinised; CM, cytoplasmic membranes altered; CW, cell walls little altered; P, pectins modified; N, nucleus and cytoplasmic proteins denatured; C, chloroplasts and chromoplasts distorted.
Differences in both steam versus water blanching and air versus water cooling are significant at the 5% level Adapted from Cumming et al.
4.2.1 Pasteurization of packaged foods
Time–temperature relationships for pasteurization. The hatched area shows the range of times and temperatures used in commercial milk pasteurization.
Counter-current flow through plate heat exchanger: (a) one pass with four channels per medium; (b) two passes with two channels per pass and per medium
Vitamin losses during pasteurization of milk
•. the type of food
• the temperature of the oil
• the method of frying (shallow or deep-fat frying)
• the thickness of the food
• the required change in eating quality
Different conveyor arrangements: (a) delicate non-buoyant products (for example fish sticks); (b) breadcrumb-coated products; (c) dry buoyant bulk products (for example half-product snacks); (d) dual purpose (for example nuts and snacks).
Isotope irradiation plant: 1, irradiation chamber; 2, control room; 3, infeed conveyor; 4, outlet conveyor; 5, raw food store; 6, irradiated product store; 7, concrete shielding wall
Microbial destruction by irradiation: A, Pseudomonas sp.; B, Salmonella sp.; C, Bacillus cereus; D, Deinococcus radiodurans; E, typical virus.
Effect of irradiation on water-soluble vitamins in selected foods
2. 0ºC to +5ºC (pasteurised canned meat, milk, cream, yoghurt, prepared salads, sandwiches, baked goods, fresh pasta, fresh soups and sauces, pizzas, pastries and unbaked dough).
3. 0ºC to +8ºC (fully cooked meats and fish pies, cooked or uncooked cured meats, butter, margarine, hard cheese, cooked rice, fruit juices and soft fruits).
7.1.1 Fresh foods
1. thermophilic (minimum: 30–40ºC, optimum: 55–65ºC)
2. mesophilic (minimum: 5–10ºC, optimum: 30–40ºC)
3. psychrotrophic (minimum: 0–5ºC, optimum: 20–30ºC)
4. psychrophilic (minimum: 0–5ºC, optimum: 12–18ºC).
• the type of food
• the degree of microbial destruction or enzyme inactivation achieved by the process
• control of hygiene during processing and packaging
• the barrier properties of the package
• temperatures during processing, distribution and storage.
• mechanical refrigerators
• cryogenic systems.
• Refrigerant vapour passes from the evaporator to the compressor where the pressure is increased.
• The vapour then passes to the condenser where the high pressure is maintained and the vapour is condensed.
• The liquid passes through the expansion valve where the pressure is reduced to restart the refrigeration cycle.
• a low boiling point and high latent heat of vaporisation
• a dense vapour to reduce the size of the compressor
• low toxicity and non-flammable
• low miscibility with oil in the compressor
• low cost.
• fruits (strawberries, oranges, raspberries) either whole or pureed, or as juice concentrates
• vegetables (peas, green beans, sweet corn, spinach, and potatoes)
• fish fillets and sea foods (cod, plaice, shrimps and crab meat) including fish fingers, fish cakes or prepared dishes with an accompanying sauce
• meats (beef, lamb, poultry) as carcasses, boxed joints or cubes, and meat products (sausages, beefburgers, reformed steaks)
• baked goods (bread, cakes, fruit and meat pies)
• prepared foods (pizzas, desserts, ice cream, complete meals and cook–freeze dishes).
Freezers are broadly categorized into:
• mechanical refrigerators, which evaporate and compress a refrigerant in a continuous cycle and use cooled air, cooled liquid or cooled surfaces to remove heat from foods
• cryogenic freezers, which use solid or liquid carbon dioxide, liquid nitrogen (or until
recently, liquid Freon) directly in contact with the food.
Effect of freezing
• Degradation of pigments. Chloroplasts and chromoplasts are broken down and chlorophyll is slowly degraded to brown pheophytin even in blanched vegetables. In fruits, changes in pH due to precipitation of salts in concentrated solutions change the colour of anthocyanins.
• Oxidation of lipids. This reaction takes place slowly at -18ºC and causes off-odors and off-flavors.
• increased competition that forces manufacturers to produce a wider variety of products and more quickly
• escalating ارتفاعlabour costs and raw material costs
• increasingly stringentقاصي regulations that have resulted from increasing consumer demands for standardised, safe foods and international harmonisation الانسجامof legislation and standards.
• more consistent product quality (minor variations in processing that would causechanges to product quality are avoided)
• greater product stability and safety
• greater compliance with legal and customer specifications
• more efficient operation
• verification of correct inputs by operators (e.g. checking that operators specify thecorrect weight and types of ingredients)
• increased production rates (e.g. through optimization of equipment utilization)
• improved safety (automatic and rapid fail-safe procedures with operator warnings incase of, for example, a valve failure or excessive temperature rise).
• not suitable for processes in which manual skill is necessary or economically moreattractive
• higher set-up and maintenance costs
• increased risk, delays and cost if the automatic system fails
• the need for a precise understanding of the process for programming to achieve therequired product quality
• reliance on accurate sensors to precisely measure process conditions.
• sensors to detect process conditions and transmitters to send this information to the controller
• a controller to monitor and control a process
• actuators (for example a motor, solenoid or valve) to make changes to the process conditions
• a system of communication between a controller and actuators and transmitters
• an ‘interface’ for operators to communicate with the control system.
The pre-requisites for control of a process are sensors and instruments which measure specified process variables and transmit the information to a process controller.
• primary measurements (for example temperature, weight, flow rate and pressure)
• comparative measurements, obtained from comparison of primary measurements (for example specific gravity)
• inferredاستنتاجي measurements, where the value of an easily measured variable is assumed to be proportional to a phenomenon that is difficult to measure (for example hardness as a measure of texture)
• calculated measurements, found using qualitative and quantitative data from analytical instruments or mathematical models (for example biomass in a fermenter).