Food Processing Course Notes PDF

© 2024 Antonio Khabbaz Course: Food Processing Code: NUT320 CRN: 10680 Instructor: Antonio KHABBAZ Lectures: Mon 08:00-09:40 [email protected] 1 1 2...

© 2024 Antonio Khabbaz Course: Food Processing Code: NUT320 CRN: 10680 Instructor: Antonio KHABBAZ Lectures: Mon 08:00-09:40 [email protected] 1 1 2 1  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Properties of liquids, solids and gases Liquids, gases and some solids (for example powders and particulate materials) are termed ‘fluids’ and can flow without disintegration when a pressure is applied to them. In contrast, solids deform when pressure is applied to them. [email protected] 3 3 ❑ Properties of foods and processing theory Properties of liquids, solids and gases The transition from solid to fluid and back is known as a phase transition and this is important in many types of food processing Example of processes: -Evaporation -Distillation -Dehydration [email protected] 4 4 2  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Properties of liquids, solids and gases [email protected] 5 5 ❑ Properties of foods and processing theory Density and specific gravity A knowledge of the density of foods is important in separation processes, and differences in density can have important effects on the operation of size reduction and mixing equipment. The density of a material is equal to its mass divided by its volume and has units of kg/m^3. [email protected] 6 6 3  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Density and specific gravity The density of liquids is a straightforward measure of mass/volume at a particular temperature, but for particulate solids and powders there are two forms of density: -The density of the individual pieces and -The density of the bulk of material, which also includes the air spaces between the pieces (called bulk density) [email protected] 7 7 ❑ Properties of foods and processing theory Density and specific gravity The density of liquids can be expressed as specific gravity (SG), a dimensionless number, which is found by dividing the mass (or density) of a liquid by the mass (or density) of an equal volume of pure water at the same temperature. SG = mass of liquid/mass water (same volume) [email protected] 8 8 4  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Density and specific gravity The density of gases depends on their pressure and temperature. Pressure is often expressed as ‘gauge pressure’ when it is above atmospheric pressure, or as ‘gauge vacuum’ when it is below atmospheric pressure. When air is incorporated into liquids (for example cake batters, ice cream, whipped cream) it creates a foam and the density is reduced. The amount of air that is incorporated is referred to as the over-run. [email protected] 9 9 ❑ Properties of foods and processing theory Viscosity Viscosity is an important characteristic of liquid foods in many areas of food processing. For example, the characteristic mouth feel of food products such as tomato ketchup, cream, syrup and yoghurt is dependent on their consistency or viscosity. The viscosity of many liquids' changes during heating, cooling, concentration, etc. [email protected] 10 10 5  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Newtonian and non-Newtonian fluids Newtonian liquids do not change viscosity when force is applied. Examples include water, most oils, gases, and simple solutions of sugars and salts. [email protected] 11 11 ❑ Properties of foods and processing theory Newtonian and non-Newtonian fluids Many liquid foods are non-Newtonian, including emulsions and suspensions, and concentrated solutions that contain starches, pectin, gums and proteins. These liquids often display Newtonian properties at low concentrations but as the concentration of the solution is increased, the viscosity increases rapidly and there is a transition to non- Newtonian properties [email protected] 12 12 6  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Newtonian and non-Newtonian fluids [email protected] 13 13 ❑ Properties of foods and processing theory Surface activity A large number of foods comprise two or more immiscible components, which have a boundary between the phases [email protected] 14 14 7  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Surface activity Emulsions Chemicals that reduce the surface tension in the surface of a liquid are termed surface active and are known as ‘surfactants’, ‘emulsifying agents’ or ‘detergents’. By reducing the surface tension, they permit new surfaces to be produced more easily when energy is put into the system (for example by homogenizers). [email protected] 15 15 ❑ Properties of foods and processing theory Surface activity Emulsions Surface active agents contain molecules which are polar (or ‘hydrophilic’) at one end and non-polar (or ‘lipophilic’) at the other end. In emulsions, the molecules of emulsifying agents become oriented at the surfaces of droplets, with the polar end in the aqueous phase and the non-polar end in the oil phase. [email protected] 16 16 8  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Surface activity Foams Foams are two-phase systems which have gas bubbles dispersed in a liquid or a solid, separated from each other by a thin film. In food foams, the structure of the foam may be stabilized by freezing (ice cream), by gelation (setting gelatin in marshmallow), by heating (cakes, meringues) or by the addition of stabilizers such as proteins or gums. [email protected] 17 17 ❑ Properties of foods and processing theory Rheology and texture Rheology is the science of deformation of objects under the influence of applied forces. When a material is stressed, it deforms, and the rate and type of deformation characterize its rheological properties. [email protected] 18 18 9  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Rheology and texture The texture of foods has a substantial influence on consumers’ perception of ‘quality’ and during chewing (or ‘mastication’). Information on the changes in texture of a food is transmitted to the brain from sensors in the mouth, from the sense of hearing and from memory, to build up an image of the textural properties of the food. [email protected] 19 19 ❑ Properties of foods and processing theory Rheology and texture This may be seen as taking place in a number of stages: 1.an initial assessment of hardness, ability to fracture and consistency during the first bite. 2.a perception of chewiness, adhesiveness and gumminess during chewing, the moistness and greasiness of the food, together with an assessment of the size and geometry of individual pieces of food. 3.a perception of the rate at which the food breaks down while chewing, the types of pieces formed, the release or absorption of moisture and any coating of the mouth or tongue with food. [email protected] 20 20 10  © 2024 Antonio Khabbaz [email protected] 21 21 ❑ Properties of foods and processing theory Rheology and texture Food texture assessment including texture profiling by sensory methods using taste panels, quantitative descriptive analysis and experimental methods in which measurements of the forces needed to shear, penetrate, extrude, compress or cut a food are related to a textural characteristic. [email protected] 22 22 11  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory [email protected] 23 23 ❑ Properties of foods and processing theory [email protected] 24 24 12  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Material transfer The transfer of matter is an important aspect of a large number of food processing operations: it is a key factor in solvent extraction, distillation and membrane processing and it is an important factor in loss of nutrients during blanching. Mass transfer of gases and vapors is a primary factor in evaporation, dehydration, baking and roasting, frying, freeze drying, the cause of freezer burn during freezing and a cause of loss in food quality in chilled, MAP and packaged foods. [email protected] 25 25 ❑ Properties of foods and processing theory Material transfer The two factors that influence the rate of mass transfer are a driving force to move materials and a resistance to their flow. When considering dissolved solids in liquids, the driving force is a difference in the solid's concentration, whereas for gases and vapors, it is a difference in partial pressure or vapor pressure. The resistance arises from the medium through which the liquid, gas or vapor moves and any interactions between the medium and the material. [email protected] 26 26 13  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Mass balances The law of conversion of mass states that ‘the mass of material entering a process equals the mass of material leaving’. In general, a mass balance for a process takes the following form: mass of raw materials in = mass of products and wastes out + mass of stored materials + losses [Many mass balances are analyzed under steady-state conditions where the mass of stored materials and losses are equal to zero.] [email protected] 27 27 ❑ Properties of foods and processing theory Mass balances Mass balances are used to calculate the quantities of materials in different process streams, to design processes, to calculate recipe formulations, the composition after blending, process yields and separation efficiencies. [email protected] 28 28 14  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Mass balances Here the total mass balance is W+A = moist air + D The mass balance for air (Component balance) is A +moisture= moist air [email protected] 29 29 ❑ Properties of foods and processing theory Exercise Calculate the total mass balance and component mass balance for mixing ingredients to make 25 kg of beef sausages having a fat content of 30%, using fresh beef meat and beef fat. Typically, beef meat contains 18% protein, 12% fat and 68% water and beef fat contains 78% fat, 12% water and 5% protein. [email protected] 30 30 15  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Heat transfer Most unit operations in food processing involve the transfer of heat into or out of a food. There are three ways in which heat may be transferred: by radiation, by conduction and by convection. [email protected] 31 31 ❑ Properties of foods and processing theory Heat transfer Radiation, is the transfer of heat by electromagnetic waves, for example in an electric grill. Conduction is the movement of heat by direct transfer of molecular energy within solids (for example through metal containers or solid foods). Convection is the transfer of heat by groups of molecules that move as a result of differences in density (for example in heated air) or as a result of agitation (for example in stirred liquids). [email protected] 32 32 16  © 2024 Antonio Khabbaz ❑ Properties of foods and processing theory Sources of heat and methods of application to foods The cost of energy for heating has become one of the major considerations in the selection of processing methods and ultimately in the cost of the processed food and the profitability of the operation. Different fuels have specific advantages and limitations in terms of cost, safety, risk of contamination of the food, flexibility of use, and capital and operating costs for heat transfer equipment. [email protected] 33 33 ❑ Properties of foods and processing theory Sources of heat and methods of application to foods The following sources of energy are used in food processing: electricity gas (natural and liquid petroleum gas) liquid fuel oil. [email protected] 34 34 17  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Sources of heat and methods of application to foods The following sources of energy are used in food processing: electricity gas (natural and liquid petroleum gas) liquid fuel oil. [email protected] 34 ❑ Properties of foods and processing theory [email protected] 35 35 © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of heat on micro-organisms The preservative effect of heat processing is due to the denaturation of proteins, which destroys enzyme activity and enzyme-controlled metabolism in micro-organisms. The rate of destruction is a first-order reaction ; that is when food is heated to a temperature that is high enough to destroy contaminating micro-organisms, the same percentage die in a given time interval regardless of the numbers present initially. This is known as the logarithmic order of death and is described by a death rate curve. [email protected] 36 37 37 35 36 18  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory The time needed to destroy 90% of the micro-organisms (to reduce their numbers by a factor of 10) is referred to as the decimal reduction time or D value. Death rate curve [email protected] 38 [email protected] 35 37 © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of heat on micro-organisms There are two important implications arising from the decimal reduction time: first, the higher the number of micro-organisms present in a raw material, the longer it takes to reduce the numbers to a specified level. In commercial operation the number of microorganisms varies in each batch of raw material, but it is difficult to recalculate process times for each batch of food. [email protected] 40 ❑ Properties of foods and processing theory Effect of heat on micro-organisms Second, because microbial destruction takes place logarithmically, it is theoretically possible to destroy all cells only after heating for an infinite time. Processing therefore aims to reduce the number of surviving micro-organisms by a pre-determined amount. This gives rise to the concept of commercial sterility. Typical minimum time–temperature conditions needed to destroy Cl. Botulinum are 1.8 s at 141ºC. [email protected] 41 38 19  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of heat on micro-organisms The destruction of micro-organisms is temperature dependent; cells die more rapidly at higher temperatures. By collating D values at different temperatures, a thermal death time (TDT) curve is constructed. The slope of the TDT curve is termed the z value and is defined as the number of degrees Celsius required to bring about a ten-fold change in decimal reduction time. The D value and z value are used to characterize the heat resistance of a micro-organism and its temperature dependence respectively. [email protected] 42 ❑ Properties of foods and processing theory [email protected] 43 39 © 2023 Antonio Khabbaz [email protected] 44 ❑ Properties of foods and processing theory Effect of heat on micro-organisms There are many factors which determine the heat resistance of microorganisms, but general statements of the effect of a given variable on heat resistance are not always possible. [email protected] 45 40 20  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of heat on micro-organisms 1. Type of micro-organism. Different species and strains show wide variation in their heat resistance. Spores are much more heat resistant than vegetative cells. 2. Incubation conditions during cell growth or spore formation. [email protected] 46 ❑ Properties of foods and processing theory Effect of heat on micro-organisms 3. Conditions during heat treatment. The important conditions are: (a)pH of the food (pathogenic and spoilage bacteria are more heat resistant near to neutrality; yeasts and fungi are able to tolerate more acidic conditions but are less heat resistant than bacterial spores). (b)water activity of the food influences the heat resistance of vegetative cells; in addition, moist heat is more effective than dry heat for spore destruction. [email protected] 47 41 © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of heat on micro-organisms (c)composition of the food (proteins, fats and high concentration of sucrose increase the heat resistance of micro-organisms; the low concentration of sodium chloride used in most foods does not have a significant effect; the physical state of the food, particularly the presence of colloids, affects the heat resistance of vegetative cells). (d)the growth media and incubation conditions, used to assess recovery of microorganisms in heat resistance studies, affect the number of survivors observed. [email protected] 48 ❑ Properties of foods and processing theory Effect of heat on nutritional and sensory characteristics The destruction of many vitamins, aroma compounds and pigments by heat follows a similar first-order reaction to microbial destruction. In general, both values are higher than those of micro- organisms and enzymes. As a result, nutritional and sensory properties are better retained by the use of higher temperatures and shorter times during heat processing. [email protected] 49 42 21  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of heat on nutritional and sensory characteristics This concept forms the basis of individual quick blanching, high-temperature short-time (HTST) pasteurization, ultrahigh-temperature sterilization and HTST extrusion. [email protected] 50 ❑ Properties of foods and processing theory [email protected] 51 43 © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Water activity Deterioration of foods by micro-organisms can take place rapidly, whereas enzymic and chemical reactions take place more slowly during storage. In either case the water content is a very important factor controlling the rate of deterioration. It is the availability of water for microbial, enzymic or chemical activity that determines the shelf life of a food, and this is measured by the water activity (aw) of a food, also known as the Relative Vapor Pressure (RVP). [email protected] 52 ❑ Properties of foods and processing theory Water activity Examples of unit operations that reduce the availability of water in foods include those that physically remove water (dehydration, evaporation, freeze drying or freeze concentration and those that immobilize water in the food (for example by the use of humectants in ‘intermediate- moisture’ foods and by formation of ice crystals in freezing. [email protected] 53 44 22  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of Aw on foods Almost all microbial activities are inhibited below aw 0.6, most fungi are inhibited below aw 0.7, most yeasts are inhibited below aw 0.8 and most bacteria below aw 0.9. The interaction of aw with temperature, pH, oxygen and carbon dioxide, or chemical preservatives has an important effect on the inhibition of microbial growth. [email protected] 54 ❑ Properties of foods and processing theory [email protected] 55 27 45 © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory [email protected] 56 ❑ Properties of foods and processing theory [email protected] 57 46 23  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory [email protected] 58 ❑ Properties of foods and processing theory [email protected] 59 47 © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory [email protected] 60 ❑ Properties of foods and processing theory Effect of water activity on microbial, enzymic and chemical changes to foods. [email protected] 61 48 24  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz ❑ Properties of foods and processing theory Effect of water activity on microbial, enzymic and chemical changes to foods. [email protected] 62 Effects of processing on the sensory characteristics of foods [email protected] 63 49 © 2023 Antonio Khabbaz Flavor changes: Human tongue and back of the oral cavity enable to sense: -Sweetness -Sourness -Saltiness -Bitterness 64 64 Effects of processing on the sensory characteristics of foods [email protected] 65 50 25  © 2024 Antonio Khabbaz © 2023 Antonio Khabbaz Effects of processing on the sensory characteristics of foods [email protected] 66 51 26