Food Processing Technology

1. Food Processing Technology Prepared by: Samer mudalal

2. 1.Introduction • Food science is a discipline concerned with all technical aspects of food, beginning with harvesting or slaughtering, and ending with its cooking and consumption. It is considered one of the agricultural sciences, and is usually considered distinct from the field of nutrition.

3. Some of the sub disciplines of food science include: • Food safety - the causes, prevention and communication dealing with foodborne illness • Food microbiology - the positive and negative interactions between micro-organisms and foods • Food preservation - the causes and prevention of quality degradation • Food engineering - the industrial processes used to manufacture food • Product development - the invention of new food products • Sensory analysis - the study of how food is perceived by the consumer's senses

4. Food chemistry - the molecular composition of food and the involvement of these molecules in chemical reactions • Food packaging - the study of how food is packaged to preserve the food after it has been processed. • Molecular gastronomy - the scientific investigation of processes in cooking, social & artistic gastronomical phenomena • Food technology - the technological aspects • Food physics - the physical aspects of foods (such as viscosity, creaminess, texture...)

5. aims of The food industries ( food processing) today 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.

6. Food processing divided into: • Unit operations combination of procedures to achieve the intended changes to the raw materials. • Unit operations are grouped together to form a process. The combination and sequence of operations determines the nature of the final product.

7. Consumer demand for foods • fewer synthetic additives, • fewer changes during processing. • ‘healthy’ or ‘natural’ image

8. This demands effect on food processing industry to launch food products: • Free from synthetic additives • low-fat, • sugar-free • low-salt • Supplemented with vitamins, minerals and probiotic cultures • Organic products

9. Motivation and changes of food industry • improved quality assurance and quality control • reduces production costs • Reduce wastage • increases production efficiency, • automation

10. Heat has important influences on food processing in a number of respects: • it is the most • convenient way of extending the shelf life of foods by destroying enzymic and • microbiological activity, or by removing water to inhibit deterioration; it changes the • nutritional and sensory qualities of foods; and generation of heat is a major processing • cost.

11. Unit operations that take place at ambient temperature and involve minimum heating of foods • operations that heat foods to extend the shelf life or to alter the eating quality; • operations that remove heat from foods to extend the shelf life with minimal changes in nutritional qualities and sensory characteristics; the final part, is concerned with operations that are integral to a food process but aresupplementary to the main method of processing.

12. Food processing • Food processing is the set of methods and techniques used to transform raw ingredients into food or to transform food into other forms for consumption by humans or animals either in the home or by the food processing industry. Food processing typically takes clean, harvested crops or slaughtered and butchered animal products and uses these to produce attractive, marketable and often long-life food products. Similar process are used to produce animal feed.

13. Food processing methods • Removal of unwanted outer layers, such as potato peeling or the skinning of peaches. • Chopping or slicing e.g. diced carrots. • Mincing and macerating • Liquefaction, such as to produce fruit juice • Fermentation e.g. in beer breweries • Emulsification • Cooking, such as boiling, broiling, frying, steaming or grilling

14. Deep frying • Baking • Mixing • Addition of gas such as air entrainment for bread or gasification of soft drinks • Proofing • Spray drying • Pasteurization • Packaging

15. Chapter 3 .Dehydration • Dehydration (or drying) is defined as ‘the application of heat under controlled conditions to remove the majority of the water normally present in a food by evaporation’ (or in the case of freeze drying by sublimation). • The main purpose of dehydration is to extend the shelf life of foods by a reduction in water activity This inhibits microbial growth and enzyme activity, but the processing temperature is usually insufficient to cause their inactivation.

16. Drying causes deterioration of both the eating quality and the nutritional value of the food. • Examples of commercially important dried foods are coffee, milk, raisins, and other fruits, pasta, flours (including bakery mixes), beans, nuts, breakfast cereals, tea and spices.

17. There are a large number of factors that control the rate at which foods dry, which can be grouped into the following categories • those related to the processing conditions • those related to the nature of the food • those related to the drier design.

18. 2.1.Drying using heated air • There are three inter-related factors that control the capacity of air to remove moisture from a food: 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. • The amount of water vapour in air is expressed as either absolute humidity2 or relative humidity3 (RH) (in per cent). • Psychrometry is the study of inter-related properties of air–water vapour systems.

20. Heat from drying air is absorbed by food and provides the latent heat needed to evaporate water from the surface. The temperature of the air, measured by a thermometer bulb, is termed the dry-bulb temperature. If the thermometer bulb is surrounded by a wet cloth, heat is removed by evaporation of water from the cloth and the temperature falls. This lower temperature is called the wet-bulb temperature. The difference between the two temperatures is used to find the relative humidity of air on the psychrometric chart • Adiabatic cooling lines are the parallel straight lines sloping across the chart, which show how absolute humidity decreases as the air temperature increases.

21. Mechanism of drying • The third factor that controls the rate of drying, in addition to air temperature and humidity, is the air velocity. When hot air is blown over a wet food, water vapor diffuses through a boundary film of air surrounding the food and is carried away by the moving air • A water vapour pressure gradient is established from the moist interior of the food to the dry air. This gradient provides the ‘driving force’ for water removal from the food.

22. The boundary film acts as a barrier to both heat transfer and water vapor removal during drying. The thickness of the film is determined primarily by the air velocity; if the velocity is low, the boundary film is thicker and this reduces both the heat transfer coefficient and the rate of removal of water vapor. Water vapor leaves the surface of the food and increases the humidity of the surrounding air, to cause a reduction in the water vapour pressure gradient and hence the rate of drying. Therefore the faster the air, the thinner the boundary film and hence the faster the rate of drying.

24. (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.

25. Follow: factors affecting on drying • The composition and structure of the food has an influence on the mechanism of moisture removal. For example, the orientation of fibres in vegetables (e.g. celery) and protein strands in meat allow more rapid moisture movement along their length than across the structure. • The amount of food placed into a drier in relation to its capacity (in a given drier, faster drying is achieved with smaller quantities of food).

26. 2.2 Drying using heated surfaces • Slurries of food are deposited on a heated steel drum. Heat is conducted from the hot surface, through the food, and moisture is evaporated from the exposed surface. The main resistance to heat transfer is the thermal conductivity of the food • Additional resistance arises if the partly dried food lifts off the hot surface, forming a barrier layer of air between the food and the drum. Knowledge of the rheological properties of the food is therefore necessary to determine the thickness of the layer and the way in which it is applied to the heated surface

27. 2.3 Types of Driers 2.3.1 Hot-air driers • Bin 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 • Cabinet driers (tray driers) 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.

28. Tunnel driers • Layers of food are dried on trays, which are stacked on trucks programmed to move semi continuously through an insulated tunnel, having one or more types of air flow • Typically a 20m tunnel contains 12–15 trucks with a total capacity of 5000 kg of food.

29. Conveyor driers (belt driers) • Continuous conveyor driers are up to 20m long and 3m wide. Food is dried on a mesh belt in beds 5–15 cm deep. The air flow is initially directed upwards through the bed of food and then downwards in later stages to prevent dried food from blowing out of the bed.

30. (a) Conveyor drier and (b) three-stage conveyor drier.

31. Fluidized-bed driers • The main features of a fluidised-bed drier are a distributor to evenly distribute the air at a uniform velocity around the bed of material; a plenum chamber below the distributor to produce an homogenous region of air and prevent localised high velocities; and a disengagement or ‘freeboard’ region above the bed to allow disentrainment of particles thrown up by the air. • Air from the fluidised bed is usually fed into cyclones to separate out fine particles, which are then added back to the product or agglomerated. Above the distributor, mesh trays contain a bed of particulate foods up to 15 cdeep. Hot air is blown through the bed, causing the food to become suspended and vigorously agitated (fluidised), exposing the maximum surface area of food for drying

33. 2.4 Drying Effect on foods • All products undergo changes during drying and storage that reduce their quality compared to the fresh material and the aim of improved drying technologies is to minimize these changes while maximizing process efficiency. • The main changes to dried foods are to the texture and loss of flavor or aroma, but changes in color and nutritional value are also significant in some foods.

34. 2.4.1 Texture • Changes to the texture of solid foods are an important cause of quality deterioration, The loss of texture in these products is caused by gelatinization of starch, crystallization of cellulose , and localized variations in the moisture content during drying, which set up internal stresses. • These rupture, crack, compress and permanently distort the relatively rigid cells, to give the food a shrunken shrivelled appearance. On rehydration the product absorbs water more slowly and does not regain the firm texture of the fresh material. There are substantial variations in the degree of shrinkage and rehydration with different foods

35. In general, rapid drying and high temperatures cause greater changes to the texture of foods than do moderate rates of drying and lower temperatures. As water is removed during drying, solutes move from the interior of the food to the surface. The mechanism and rate of movement are specific for each solute and depend on the type of food and the drying conditions used • Evaporation of water causes concentration of solutes at the surface. High air temperatures (particularly with fruits, fish and meats), cause complex chemical and physical changes to solutes at the surface, and the formation of a hard impermeable skin. This is termed case hardening and it reduces the rate of drying to produce a food with a dry surface and a moist interior It is minimised by controlling the drying conditions to prevent excessively high moisture gradients between the interior and the surface of the food.

36. 2.4.2 Flavor and aroma • Heat not only vaporises water during drying but also causes loss of volatile components from the food and as a result most dried foods have less flavour than the original material. The extent of volatile loss depends on the temperature and moisture content of the food and on the vapour pressure of the volatiles and their solubility in water vapour. • Volatiles which have a high relative volatility and diffusivity are lost at an early stage in drying. Foods that have a high economic value due to their characteristic flavours (for example herbs and spices) are dried at low temperatures

37. Flavour changes, due to oxidative or hydrolytic enzymes are prevented in fruits by the use of sulphur dioxide, ascorbic acid or citric acid, by pasteurisation of milk or fruit juices and by blanching of vegetables. Other methods which are used to retain flavours in dried foods include: • recovery of volatiles and their return to the product during drying

38. mixing recovered volatiles with flavour fixing compounds, which are then granulated and added back to the dried product (for example dried meat powders) • addition of enzymes, or activation of naturally occurring enzymes, to produce flavours from flavour precursors in the food (for example onion and garlic are dried under conditions that protect the enzymes that release characteristic flavours).

39. 2.4.3 Colour • There are a number of causes of colour loss or change in dried foods; drying changes the surface characteristics of a food and hence alters its reflectivity and colour. In fruits and vegetables, chemical changes to carotenoid and chlorophyll pigments are caused by heat and oxidation during drying and residual polyphenoloxidase enzyme activity causes browning during storage.

40. This is prevented by blanching or treatment of fruits with ascorbic acid or sulphur dioxide. For moderately sulphured fruits and vegetables the rate of darkening during storage is inversely proportional to the residual sulphur dioxide content. However, sulphur dioxide bleaches anthocyanins, and residual sulphur dioxide is also linked to health concerns. Its use in dried products is now restricted in many countries.

41. The rate of Maillard browning in stored milk and fruit products depends on the water activity of the food and the temperature of storage. The rate of darkening increases markedly at high drying temperatures, when the moisture content of the product exceeds 4–5%, and at storage temperatures above 38ºC

42. 2.4.4 Nutritional value • Large differences in reported data on the nutritional value of dried foods are due to wide variations in the preparation procedures, the drying temperature and time, and the storage conditions. In fruits and vegetables, losses during preparation usually exceed those caused by the drying operation • For example Escher and Neukom (1970) showed that losses of vitamin C during preparation of apple flakes were 8% during slicing, 62% from blanching, 10% from pureeing and 5% from drum drying

43. Vitamins have different solubilities in water and as drying proceeds, some (for example riboflavin) become supersaturated and precipitate from solution, so losses are small . Others, for example ascorbic acid, are soluble until the moisture content of the food falls to very low levels and these react with solutes at higher rates as drying proceeds. Vitamin C is also sensitive to heat and oxidation and short drying times, low temperatures, low moisture and oxygen levels during storage are therefore necessary to avoid large losses.

44. Vitamin losses in selected dried foods

45. 2.4.5 Rehydration • Water that is removed from a food during dehydration cannot be replaced in the same way when the food is rehydrated (that is, rehydration is not the reverse of drying); loss of cellular osmotic pressure, changes in cell membrane permeability, solute migration, crystallisation of polysaccharides and coagulation of cellular proteins all contribute to texture changes and volatile losses and are each irreversible

46. Chapter 4. Blanching • Blanching serves a variety of functions, one of the main ones being to destroy enzymatic activity in vegetables and some fruits, prior to further processing by heat. As such, it is not intended as a sole method of preservation but as a pre-treatment which is normally carried out between the preparation of the raw material and later operations (particularly heat sterilisation, dehydration and freezing. Blanching is also combined with peeling and/or cleaning of food, to achieve savings in energy consumption, space and equipment costs

47. A few processed vegetables, for example onions and green peppers, do not require blanching to prevent enzyme activity during storage, but the majority suffer considerable loss in quality if blanching is omitted or if they are under-blanched. 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.

48. The factors which influence blanching time are: • type of fruit or vegetable • size of the pieces of food • blanching temperature • method of heating.

49. 3.1 Theory • The maximum processing temperature in freezing and dehydration is insufficient to inactivate enzymes. If the food is not blanched, undesirable changes in sensory characteristics and nutritional properties take place during storage. In canning, the time taken to reach sterilizing temperatures, particularly in large cans, may be sufficient to allow enzyme activity to take place. It is therefore necessary to blanch foods prior to these preservation operations.

50. 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.