Lecture 3 Shelf Life PDF

1. Introduction 2. Factors influencing shelf life of foods 3. Measuring shelf life and spoilage of foods What is shelf life ? When to conduct shelf life study? What are end of shelf life parameters? Is the shelf life of food related to food safety? What are factor affects the shelf life of the...

1. Introduction 2. Factors influencing shelf life of foods 3. Measuring shelf life and spoilage of foods What is shelf life ? When to conduct shelf life study? What are end of shelf life parameters? Is the shelf life of food related to food safety? What are factor affects the shelf life of the product? 4 Shelf life of food products Introduction Shelf life is a guide for the consumer of the period of time that food can be kept before it starts to deteriorate, provided any stated storage conditions have been followed The shelf life of a product begins from the time the food is prepared or manufactured Its length is dependent on many factors including the types of ingredients, manufacturing process, type of packaging and how the food is stored.  Introduction………….cont It is indicated by labelling the product with a date mark For consumers, shelf life is imperative that products are safe and the quality meets their expectations For retailers, product quality must meet or exceed consumer expectations for repeat purchases Manufacturers, who are responsible for setting product shelf life, must be able to justify the validity of the shelf life assigned  Introduction………….cont When to conduct shelf life study  New product launch  New packaging  Collect data for validation  Change in ingredient  Aspects of QA/QC program End off shelf life parameters An acceptable self life allow the following desired characteristics of products to be retained  Sensory Chemical  Functional Microbial  physical 7 Is the shelf life of food related to food safety? Shelf life testing describes how long a food will retain its quality during storage Shelf life is the period of time during which the food product will remain safe; be certain to retain desired sensory, chemical, physical and microbiological characteristics; and comply with any label declaration of nutritional data Controlling the pathogen content (safety) of foods should be achieved by using a Hazard Analysis Critical Control Point (HACCP) system 8 What is HACCP HACCP is a system that allows you to deal with important food safety issues yourself 9 1: Identify hazards Microbiological Hazard Chemical Hazards Physical Hazards 10 Microbiological Hazard Any bacterium, virus, or protozoan that is capable of causing illness and that grows or may be carried on food Well-known examples of bacteria are Campylobacter, Listeria and Salmonella Giardia is an example of a protozoan that may be food borne It is important to have some understanding of the risks associated with different types of microbiological hazards. 11 Chemical Hazards Examples include excessive or toxic Vitamins amounts of: Minerals heavy metals Preservatives Chemicals Disinfectants Pesticides detergents and cleaning compounds. Herbicides Some hazards may be naturally present Insecticides such as in green potatoes 12 Physical Hazards Objects that get into food, or are already present in food, may cause illness, injury or distress to the person eating it Some examples are glass, metal fragments etc Other contaminants such as hair or insects may be offensive but not necessarily a danger to health They should nonetheless be considered and controlled 13 2: Determine critical control points Control points are the points in the food processing chain where it is possible to control or remove hazards Critical control points are the control points in the processing chain where it is essential to a hazard, usually because there is no later step at which to establish control 14 3. Establish Critical Limits The next step in the development of a HACCP plan is to establish critical limits for each critical control point. Critical limits (CL) are the parameters that indicate whether the control measure at the CCP is in or out of control. The FDA has listed factors that could be used in the critical limit determination and their corresponding preventive controls. 15 These factors for establishing critical controls and limits include the following:  correct temperature,  time of processing,  solid content,  titratable acidity level,  moisture level,  preservatives,  water activity,  salt concentration, and others 16 4. Establish Monitoring Procedures Once critical limits are set for each CCP during the HACCP plan development, procedures must be established to monitor the CCPs to determine whether the critical limits are being met. Monitoring procedures usually involve either a measurement or an observation. If the critical limit is a numerical value, then monitoring usually involves a measurement. If the critical limit is defined as the presence or absence of an attribute, then the monitoring procedure may involve observation. 17 5. Creating corrective actions The corrective actions must be determined for each CCP in cases where the CL is not met. The specific corrective actions depend upon the process used and type of food produced. When there is a deviation from the critical limit, corrective actions are required to prevent potentially hazardous foods from reaching consumers. 18 6. Establish Verification Procedures This HACCP principle includes comprehensive verification activities of the hazard evaluation itself, identification procedures, monitoring, and authorized corrective actions. Over time, operations will change as much as raw materials will. This means that the appropriateness of your HACCP food safety plans may also vary. Any activity of verification aims to ensure that the current HACCP system is being followed by the whole team. You can use this principle as a way to evaluate whether modifications are needed in operations or if they are still effective. 19 7. Establish Recordkeeping and Documentation Procedures Records are written evidence documenting the operation of the HACCP system. All measurements taken at a CCP, and any corrective actions taken, should be documented and kept on file. These records can be used to trace the production history of a finished product. If any questions arise about the product, a review of records may be the only way to determine whether the product was produced in a safe manner according to the HACCP plan. 20 Factors Affecting Product Quality and Shelf Life Factors affect shelf life are the make-up of the product (intrinsic factors) the environment that it will encounter during its life (extrinsic factors) and the ‘shelf life limiting processes’ that this combination of intrinsic and extrinsic factors 21 Factors Affecting Product Quality and Shelf Life Intrinsic factors are the properties resulting from the make-up of the final product and include the following: water activity (available water) , pH/ total acidity; type of acid natural microflora and surviving microbiological counts in final product availability of oxygen natural biochemistry/chemistry of the product added preservatives, e.g. salt, spices, antioxidants product formulation, packaging interactions, e.g. tin pickup, migration 22 Factors Affecting Product Quality and Shelf Life Extrinsic factors are a result of the environment that the product encounters during life and include the following: time–temperature profile during processing temperature control during storage and distribution relative humidity (RH) during storage and distribution exposure to light (UV and IR) during storage and distribution composition of gas atmosphere within packaging consumer handling 23 Factors Influencing … There are a range of points in the food chain where manufacturers can influence the mix of intrinsic and extrinsic factors which affect shelf-life. These include: Raw material selection and quality Product formulation and assembly The processing environment Processing and preservation techniques Packaging 24 Factors Influencing … Product packaging can have significant effects on many of these extrinsic factors and many developments in packaging materials have been driven by the need to reduce the impact of these environmental factors and extend shelf life In some instances, the packaging alone may be effective in extending shelf life, e.g. by providing a complete light and oxygen barrier 25 Factors Influencing … The interaction of the intrinsic and extrinsic factors either inhibit or stimulate a number of changes which limit shelf life These changes in food can be classified as: Microbial Chemical Physical Moisture /water activity related Temperature-related deteriorative changes 26 Physical and Physico-chemical Processes Physical changes affecting shelf life can be brought about directly by physical damage or by physico-chemical processes resulting from the underlying food chemistry Physical damage During product life, particularly in storage, distribution and consumer handling, products are subjected to vibration on vehicles, compressive loads during stacking in warehouses and sudden jolts and knocks 27 Physical and Physico-chemical Processes Physical damage The formulation of the product must be sufficient to tolerate such shocks or extended periods of vibration, e.g. emulsions must be stable enough to withstand vibration, and the packaging must be able to withstand and protect against such forces For fragile products that are susceptible to crushing, such as breakfast cereals and biscuits, the outer carton provides protection from physical damage and from potential tampering 28 Physical and Physico-chemical Processes Fruit and vegetables that are susceptible to bruising require protection from rough handling and the outer packaging used for distribution purposes needs to withstand stacking to considerable heights and withstand high and variable humidity The design of packaging for this purpose should be based on the properties of the commodity in terms of the humidity level it can withstand, the airflow allowed, the rate of respiration of the product and its susceptibility to bruising 29 Physical and Physico-chemical Processes Insect damage Insect infestation can occur at any point after manufacture, but is most likely during extended storage periods or during shipment Package pests are classified in two groups – penetrators and invaders Penetrators are capable of boring through one or more layers of flexible packaging materials Invaders are more common and enter packages through existing openings, usually created from poor seals, openings made by other insects or mechanical damage 30 Moisture migration Hygroscopic foods require protection from moisture take-up, which in dry products such as breakfast cereals and biscuits causes loss of texture, particularly crispness Protection or prevention of moisture loss is best achieved by maintaining the correct temperature and humidity in storage In chilled and frozen foods, water loss can result in quality loss; however, it is often the resulting weight loss that is of greater importance due to the high monetary value of the products sold on a weight basis 31 Physical and Physico-chemical Processes Moisture migration Most fruit and vegetables have an equilibrium humidity of 97–98% and will lose water if kept at humidity's less than this due to transpiration The rate of water loss is dependent on the difference between the water vapour pressure exerted by the produce and the water vapour pressure in the air, and air speed over the product Loss of as little as 5% moisture by weight causes FV to shrivel or wilt 32 Physical and Physico-chemical Processes Barrier to odour pick-up In practice, several commodities are sometimes stored or distributed in the same container or trailer Chocolate products because of the high fat content and sometimes bland flavour, if inadequately wrapped and stored next to strong smelling chemicals, such as cleaning fluids, or in shops close to strongly flavoured sweets, such as poorly wrapped mints, can result in unacceptable flavour pick-up 33 Physical and Physico-chemical Processes Flavour scalping If a chemical compound present in the food has a high affinity for the packaging material, it will tend to be absorbed into or adsorbed onto the packaging until equilibrium concentrations have been established in food and packaging This loss of food constituents to packaging is known as scalping Scalping does not result in a direct risk to the safety of the food, or in the introduction of unpleasant odours or flavour 34 Physical and Physico-chemical Processes However, the loss of volatile compounds that contribute to its characteristic flavour affects sensory quality Physical changes include mishandling of foods like bruising of fruits and vegetables during harvesting, moisture uptake in cookies, or recrystallisation of ice cream due to temperature fluctuations 35 CHEMICAL/BIOCHEMICAL PROCESSES Chemical reactions will proceed if reactants are available and if the activation energy threshold of the reaction is exceeded The rate of reaction is dependent on the concentration of reactants and on the temperature and/or other energy, e.g. light induced reactions A general assumption is that for every 10◦C rise in temperature, the rate of reaction doubles The most important chemical changes are associated with  enzyme reactions, oxidative reactions like lipid oxidation, and non enzymatic browning 36 CHEMICAL/BIOCHEMICAL PROCESSES Oxidation A number of chemical components of food react with oxygen affecting the colour, flavour, nutritional status and occasionally the physical characteristics of food Packaging is used to both exclude, control or contain oxygen at the level most suited for a particular product Foods containing a high percentage of fats, particularly unsaturated fats, are susceptible to oxidative rancidity and changes in flavour 37 CHEMICAL/BIOCHEMICAL PROCESSES Antioxidants naturally occurring or added either slow the rate of, or increase the lag time to the onset of, rancidity Three different chemical routes can initiate the oxidation of fatty acids:  the formation of free radicals in the presence of metal ion catalysts, such as iron, or heat, or light – termed the classical free radical route; photo oxidation in which photosensitisers, such as chlorophyll or myoglobin, affect the energetic state of oxygen; or an enzymic route catalysed by lipoxygenase 38 CHEMICAL/BIOCHEMICAL PROCESSES Oxidation Once oxygen has been introduced into the unsaturated fatty acids to form hydroperoxides by any of these routes, the subsequent breakdown of these colourless, odourless intermediates, proceeds along similar routes regardless of how oxidation was initiated It is the breakdown products of the hydroperoxides – the aldehydes, alcohols and ketones that are responsible for the characteristic ‘stale’, ‘rancid’ and ‘cardboard’ odours associated with lipid oxidation 39 Table 2.1 The estimated maximum oxygen tolerance of various foods Source: Salame 1986 40 CHEMICAL/BIOCHEMICAL PROCESSES Oxidation Reduction of the concentration of oxygen (both dissolved and in the headspace) to below 1%, removal of factors that initiate oxidation and the use of antioxidants are strategies employed to extend shelf life where rancidity is a shelf life limiting factor UV light from either natural or retail display cabinets can cause other changes that limit shelf life 41 CHEMICAL/BIOCHEMICAL PROCESSES Oxidation Vitamins A, B2, B6, B12 and folic acid are particularly susceptible to light; beers and lagers are susceptible to light-induced oxidation resulting in flavour and colour changes Incorporation of chemicals that absorb UV light into clear packaging materials, particularly glass beverage bottles can help to extend the shelf life of products 42 CHEMICAL/BIOCHEMICAL PROCESSES Enzyme activity Fruits and vegetables are living commodities and their rate of respiration affects shelf life – generally, the greater the rate of respiration, the shorter the shelf life Immature products, such as peas and beans, have much higher respiration rates and shorter shelf life than products that are mature storage organs, such as potatoes and onions 43 CHEMICAL/BIOCHEMICAL PROCESSES Enzyme activity Ethylene is a plant hormone that accelerates senescence and the ripening process It is a colourless gas with a sweet ether-like odour The effect of ethylene is commodity dependent but also dependent on temperature, exposure time and concentration Table 2.2 Effect of ethylene on the quality of fruit and vegetables 44 Factors Influencing … Microbiological microbial changes with respect to shelf life growth rate, pathogenicity and  production of toxins are very relevant issues 45 Factors Influencing … Growth of a specific microorganism during storage depends on several factors, the most important being: the initial microbial loading at the start of storage; the physicochemical properties of the food, such as moisture content, pH, presence of preservatives; the processing method used in the production of the food; and the external environment of the food, such as the surrounding gas composition and storage temperature 46 Table Minimum growth conditions for selected microorganisms 3.Measuring shelf life and spoilage of food  3.Measuring shelf life and spoilage of food  Foods can be broadly classified into perishability categories.  Three categories are chosen, based on normal processing, distribution, and handling conditions:  Perishable foods of less than 30 days shelf life in which the major problem is high temperature abuse  Semi perishable foods of greater than 30 days but less than 6 months’ shelf life.  Long shelf-life foods-these are foods of greater than 6 months’ shelf life. In some cases, they have been described as nonperishable foods. 3. Measuring shelf life and spoilage of food  Any packaged food with a shelf life of less than two years be labelled with a date mark  One of the following options must be used for date marking: a) “Use by” date: this is used for highly perishable foods that will present a safety risk if consumed after this date. A food must not be sold if it is past its “Use by” date, not should it be consumed. b) “Best before” date: this is used for foods other than those specified above. It is not illegal to sell food that has reached its “Best before” date 3. Measuring shelf life and spoilage of food  Foods are diverse, complex and active systems in which microbiological, enzymatic and physicochemical reactions are simultaneously taking place  Designing a shelf life test is a synthetic approach that requires sufficient understanding of all food-related disciplines, namely  Food Engineering, food chemistry,  Food microbiology, analytical chemistry,  Physical chemistry, polymer science, and  Food regulations 3. Measuring shelf life and spoilage of food …  Shelf life testing consists basically of  Selecting the quality characteristics which deteriorate most rapidly in time and  The mathematical modeling of the change  The selection of quality characteristics, depends on the specific product and usually requires professional judgment 3. Measuring shelf life and spoilage of food …  No single test can possibly measure all deteriorative events  No single test can be universally applicable to all foods, all conditions of processing, or all stages of oxidative process  Hence, a more reliable evaluation can be obtained by using a combination of tests 3. Measuring shelf life and spoilage of food … Fig. A partially staggered design for shelf-life testing 3. Measuring shelf life and spoilage of food …  A major goal for the food scientist is the prediction of the change in quality of a particular food as a function of both  Time and  Environmental condition  In order to make useful predictions about shelf life, the research scientist needs information regarding  The potential major modes for loss of quality of the product,  The factors which control the initial quality or nutritional value during manufacture, 3. Measuring shelf life and spoilage of food …  The environmental conditions the food will be exposed to including temperature, relative humidity and light,  whether it is packaged in a semi-permeable container, and, if so, the permeability of that film to oxygen, water vapor, and light  The kinetics of the reactions leading to loss of quality or nutritional value as a function of the reaction phase conditions in the food and the external environment 3. Measuring shelf life and spoilage of food … Approaches to shelf-life estimation of food products  Selecting an appropriate, reliable approach to modeling quality loss of a food product is an important  First step in estimating shelf-life, and allows for the efficient design of appropriate shelf-life tests  Shelf-life predictions are based on fundamental principles of food quality loss modeling,  Primarily kinetic modeling of different deterioration mechanisms that occur in food systems 3. Measuring shelf life and spoilage of food …  Several established approaches can be utilized for gathering of shelf-life data of food products: 1. Literature values: Estimating shelf-life based on published data 2. Distribution turn over: Utilizing known distribution times for similar products on the market 3. Distribution abuse test: product is collected at supermarket sites and stored in the laboratory under home use condition 4. Using consumer complaints as the basis for determining whether a problem is occurring 5. Accelerated shelf-life testing (ASLT) 3. Measuring shelf life and spoilage of food …  Obtaining a reliable approach to modeling quality loss of a food product is based on defining an appropriate index that measures, or directly corresponds to, food quality  These indices include:  Sensory evaluation, as well as  Chemical, microbiological and  Physical testing through instrumental or classical methods 3. Measuring shelf life and spoilage of food … Shelf-Life Study Methods and Procedures  A shelf life study is an objective, methodical means to determine how long a food product can reasonably be expected to keep for, without any appreciable change in quality  A separate study needs to be carried out for each type of product  There are two main methods used to study shelf-life: 1) Direct method 2) Indirect method 3. Measuring shelf life and spoilage of food … Direct method  The most common and direct way of determining shelf-life is to carry out storage trials of the product under controlled conditions that mimic those it is likely to encounter during  storage,  distribution,  retail display and  consumer use 3. Measuring shelf life and spoilage of food … Direct method …  It involves storing the product under preselected conditions for a period of time longer than the expected shelf life and checking the product at regular intervals to see when it begins to spoil  The exact procedure is unique for each product Steps involved in Calculating Shelf Life by the Direct Method PRODUCT RELATED SPOILAGE Before product on market  Raw materials, Product make-up, PH,  Water activity, Oxygen availability identify what may cause the food  Chemical preservatives to spoil or become unsafe  PROCESS RELATED SPOILAGE  Processing  Packaging , storage Decide which tests to use Sensory Evaluation, chemical, microbiological, physical Plan the shelf life study  What tests need to be carried out  How long will the study run for Run the shelf life study  How many samples will be tested each time  How many samples will be needed for the whole study period Determine the shelf life  When will the study be run? usually summer Once product on market Store sample under the same conditions Based on information you have recorded and Continue to monitor shelf life observed, decide how long the product can be kept 3. Measuring shelf life and spoilage of food … Indirect method  Indirect methods attempt to predict the shelf life of a product without running a full length storage trial; hence, they can be useful for products with long shelf lives  The most common indirect method is accelerated shelf life testing (ASLT) 3. Measuring shelf life and spoilage of food … Accelerated shelf-life testing  Shelf life testing is frequently a time-consuming process  To achieve shelf-life predictions in a shorter length of time, accelerated testing can be used  In accelerated shelf life study, the trial period is shortened by deliberately increasing the rate of deterioration  ASLT is applicable to any deterioration process that has a valid kinetic model  That process may be chemical, physical, biochemical or microbial 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures: 1. Evaluate the microbiological safety factors for the proposed food product and process 2. Determine which biological and physico-chemical reactions will significantly affect shelf life and hence can be used as quality loss indices 3. Select the package to be used for the shelf life test 4. Define the test’s storage temperatures 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures: 5. From the desired shelf life at expected storage and handling temperatures, and based on available information on the most likely Q10, calculate testing time at each selected temperature  If no information is available on the expected Q10 value, minimum three testing temperatures should be used Note: Q10 is the increase in the rate of the reaction when the temperature is increased by 100C 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures:  This estimates the effect of temperature on the accelerated deterioration of shelf-life  In its simplest form, it can be expressed as the ratio of the rate of deterioration at a temperature of θ+10oC to that at a temperature of θ  Alternatively, it can be expressed as 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures: 6. Decide the type and frequency of tests to be conducted at each temperature.  At each storage condition, at least six data points are required to minimize statistical errors; otherwise, the statistical confidence in the obtained shelf life value is significantly reduced 7. Plot the data as it is collected to determine the reaction order and to decide whether test frequency should be altered 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures: 8. From each test storage condition, determine reaction order and rate, make the appropriate Arrhenius plot, and predict the shelf life at the desired actual storage condition 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures:  There are a number of approaches to ASLT but all are concerned with how to get reliable deterioration data in a short period, what model to use and how eventually to predict the actual shelf-life of the product 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures: 1. Initial Rate Approach  Conceptually, one of the simplest techniques for accelerating the shelf- life testing is the ‘initial rate approach’  It may be applicable to cases where the deterioration process can be monitored by an extremely accurate and sensitive analytical method 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures: 1. Initial Rate Approach…  This method should be capable of measuring minute changes in the extent of deterioration after a relatively short storage time at actual conditions  In such a case, it is possible to get the kinetic data of the initial rate of the deterioration process at a very early stage of the process 3. Measuring shelf life and spoilage of food …  The following steps outline the Accelerated Shelf Life Testing procedures: 1. Initial Rate Approach…  To predict the actual shelf-life, one needs only to know or to evaluate how the deterioration process behaves as a function of time  In chemical reactions that information is provided by the order of reaction (n)  In the case of monitoring the change in concentration (C) of a component of interest, the kinetic equation may be expressed as: 1. Initial Rate Approach… dC/dt = KCn Where K is the kinetic constant and t is time. For sake of simplicity, let us define an index of deterioration (D) that has the form: dD =dC /Cn = Kdt By doing that, the index of deterioration will be always linear with time and will have the following form: D - D0 = Kt 1. Initial Rate Approach… D - D0 = Kt where D0 is the initial level of the index of deterioration The product shelf-life (ts ) is therefore: ts = (D - D0)/K 3. Measuring shelf life and spoilage of food … 1. Initial Rate Approach…  Information about the order of reactions in many food systems is available in the literature  Most of the chemical deterioration reactions in foods follow either a zero or a first order kinetics  The value of the index of deterioration will be in these cases:  Zero order (n = 0) D = C  First order (n = 1) D =lnC 3. Measuring shelf life and spoilage of food … 1. Initial Rate Approach…  When the order of reaction is unknown, a simple accelerated test procedure may be used to evaluate it empirically  Such a method uses any convenient kinetically active factor to accelerate the deterioration process.  The initial rate method, when applicable, can provide an ideal accelerated shelf-life testing technique 3. Measuring shelf life and spoilage of food … 2. Kinetics model approach  The kinetic model approach is the most common method for accelerated shelf- life testing  The basic process involves the following steps: 1. Selection of the desired kinetically active factors for acceleration of the deterioration process 2. Running a kinetic study of the deterioration process at such levels of the accelerating factors that the rate of deterioration is fast enough 3. Measuring shelf life and spoilage of food … 2. Kinetics model approach …  The basic process involves the following steps: 3. By evaluating the parameters of the kinetic model, extrapolating the data to normal Storage conditions 4. Use the extrapolated data or the kinetic model to predict shelf-life at actual storage conditions Fig. Schematic diagram of data extrapolation in accelerated shelf-life testing 2. Kinetics model approach … Applying fundamental chemical kinetic principles, the rate of food quality change can in general be expressed as a function of composition and environmental factors. dQ/dt= F (Ci, Ej) Where:- Ci= Are composition factors of the food, such as concentration of reactive compounds, inorganic catalysts, enzymes, reaction inhibitors, pH, water activity, as well as microbial populations and Ej = Represents environmental factors, such as temperature, relative humidity, total pressure and partial pressure of different gases, light and mechanical stresses. 2. Kinetics model approach …  The established methodology consists of:  Identifying the chemical and biological reactions that influence the quality and the safety of the food  Then, through a careful study of the food components and the process, the reactions judged to have the most critical impact on the deterioration rate, are determined 2. Kinetics model approach …  Excluding the effect of the environmental factors, Ej, by assuming them constant, at the most probable level or judging it negligible within their expected variation,  a simplified reaction scheme that expresses the effect of the concentration of the reactants, is developed 2. Kinetics model approach …  The ultimate objective is to model the change of the concentrations of constituents connected to food quality, as functions of time  In a simplified way, food degradation and shelf life loss is in practice represented by the loss of desirable quality factors A (e.g. nutrients, characteristic flavors) or the formation of undesirable factors B ( e.g. off flavors, discoloration) 2. Kinetics model approach …  The rates of loss of A and of formation of B (rA and rB) are expressed as: rA =-dcA/dt = -k [cA ]n rB = dcB/dt ]= k’ [cB ]n’  The quality factors [A] and [B] are usually quantifiable chemical, physical, microbiological or sensory parameters characteristic of the particular food system  Both k and k' are the apparent reaction rate constants and n and n' the reaction orders 2. Kinetics model approach … Effect of Environmental Factors on Kinetics of Food Deterioration  The above approach kinetically defines a food system by the underlying assumption that the environmental conditions are constant  Since most environmental factors do not remain constant the next logical step would be to expand the models to include them as variables, especially the ones that more strongly affect the reaction rates and are more prone to variations during the life of the food 2. Kinetics model approach … Effect of Environmental Factors on Kinetics of Food Deterioration  The practical approach is to model the effect into the apparent reaction rate constant, i.e. expressing k as a function of environmental factors, Ej: k =k(Ej) 2. Kinetics model approach … Temperature  The most prevalent and widely used model is the Arrhenius relation, derived from thermodynamic laws as well as statistical mechanics principles where: k = kA exp (-EA/RT)…………… for Zero order  with kA the Arrhenius equation constant and EA the excess energy barrier that factor A needs to overcome to proceed to degradation products (or B to form), generally referred to as activation energy 2. Kinetics model approach … Temperature  In practical terms it means that if values of k are available at different temperatures and ln k is plotted against the reciprocal absolute temperature, 1/T, a straight line is obtained with a slope of -EA/R and ln kA intercept ln k = ln kA - EA/RT …….. For first order 2. Kinetics model approach …  By studying a deterioration process and measuring the rate of loss at two or three temperatures (higher than storage temperature),  Then extrapolate on an Arrhenius plot with a straight line to predict the deterioration rate at the desired storage temperature Figure: Arrhenius plot 2. Kinetics model approach … Water Activity  The moisture content and water activity can influence the kinetic parameters (kA, EA), the concentrations of the reactants and in some cases even the apparent reaction order, n  Most relevant studies have modeled either kA as a function of aw related to the change of mobility of reactants due to aw dependent changes of viscosity, or EA as a function of aw 2. Kinetics model approach … Water Activity  The inverse relationship of EA with aw (increase in aw decreases EA and vice versa) could be theoretically explained by the proposed phenomenon of enthalpy-entropy compensation  The applicability of this theory and data that support it have been discussed by Labuza (1980a). 2. Kinetics model approach … The QA Concept  Despite the fact that aw is a thermodynamic term not directly linked with chemical kinetics, an empirical relation was found to exist between the rates of many chemical reactions and aw from the monolayer up to the reactivity maximum.  The QA concept, which is similar to the Q10 concept, provides a method for modeling the effect of aw on chemical stability 2. Kinetics model approach … The QA Concept  The QA value represents the increase in reactivity (decrease in half- life) due to a 0.1-unit increase in aw; QA is mathematically defined as follows: 2. Kinetics model approach … The QA Concept  A QA value of 1.5 means that for each 0.1 aw increase, the reaction half- life will decrease by 33% or the rate will increase by 50%  By plotting the natural log of reaction half-life versus aw, QA can be calculated from the slope using the following equation: QA = e−0.1*slope  Using the QA value, the half-life (or shelf-life) can be estimated at any aw between the monolayer and the reactivity maximum. Shelf Life Prediction  Example of shelf life prediction #1  The shelf-life of a ghee product ends when the peroxide value reaches 0.6%. A food product development team needs to predict the product shelf-life at 22°C. Peroxide concentration change with time for the ghee was applied to zero order, first order and second order models. According to the fit, root mean square error was minimum for zero order model; both at 45 oC and 70 oC. Thus, the model-representing rate of change of peroxide value will be:  Example of shelf life prediction #1 Where: k = rate constant for peroxide formation (meq*kg-1*day-1), t = time (days), PVo = initial peroxide value estimated (meq/kg) and PV = peroxide value in meq/kg at time t  Example of shelf life prediction #1  Plot of [PV] versus time for each temperature yields K and PVo values.  The estimated PVo (from regression) for both temperatures is not significantly different form initial experimental values, which suggests model adequacy is satisfactory.  Regressions of lnk vs. 1/T were performed to obtain the Arrhenius parameters kA and EA/R. Example of shelf life prediction #1 Example of shelf life prediction #2 @22℃ k= 0.0026 PV= [Pvo]+kt t= (PV]-[PVo])/k (0.6-0.01)/0.0026 Shelf life, ts= 226 days= 7.5 months  Example of shelf life prediction #2  The shelf-life of an aspartame-sweetened product expires when 10% of the aspartame is lost. A food product development team needs to predict the product shelf-life at 20°C and aw 0.15. Table below lists aspartame stability data at three temperatures and three water activities, as collected by Bell (1989).  Example of shelf life prediction #2  From this data, a shelf-life plot can be constructed and the Q10 determined.  Similarly, the QA can be calculated from a QA plot.  The values for the Q10 and QA were determined to be 4.25 and 1.55, respectively.  Example of shelf life prediction #2  To predict the shelf-life, is, at 20°C and aw 0.15, the following equation is used: θs =(t10%, aw 0.34, 30°C )x(Q10)(30-T)/10x(QA )(0.34−aw )/0.1  *t10% loss = time to 10% loss of aspartame.  Aspartame degradation kinetics in low and intermediate moisture food systems.  Substituting in the shelf-life at aw 0.34 and 30°C, the Q10 and QA values, and the target environmental conditions (i.e., T = 20°C and aw = 0.15), the following solution results:  Table: Aspartame Stability Data Conditions Rate Constant (day-1) t 10% loss* (days) aW 0.34, 30°C 0.00548 19.2 aW 0.35, 37°C 0.01538 6.9 aW 0.42, 45°C 0.04828 2.2 aW 0.34, 30°C 0.00548 19.2 aW 0.57, 30°C 0.01574 6.7 aW 0.66, 30°C 0.02224 4.7  Example of shelf life prediction #2  Substituting in the shelf-life at aw 0.34 and 30°C, the Q10 and QA values, and the target environmental conditions (i.e., T = 20°C and aw = 0.15), the following solution results: θs =(19.2 days)×(4.25)10/10 × (1.55)0.19/0.1 = 188 days  Thus, using the kinetic data in Table, a shelf-life of 188 days was predicted for an aspartame-sweetened product at 20°C and aw 0.15.  Example of shelf life prediction #3 Browning of fruit Juice during storage ,product stored for 60 days and optical density measured at 10 days intervals, if browning reaction can be characterized by zero order kinetics calculate shelf life if optical density of 0.24 signifies end of shelf life day Optical density (Browning) 1 0 0.05 From scaterd plot digrame for zero order kinetics we get the 2 10 0.071 equation Y=0.002 x + 0.0501 by using day vers optical 3 20 0.081 density, 4 30 0.11 From this equation we get Slop=0.002=K 5 40 0.128 6 50.149 0.24-0.05/0.02 =95 days 7 60 0.17 ts = (D - D0)/K  Example of shelf life prediction #4 A reduction of Vitamin C in juice during storage the reaction is known to follow first order kinetics , data were obtained for ascorbic acid concentration for 18 days storage, determine rate constant, the manufacturer would like to declare vitamin C concentration of 15 mg/100ml on the label , for how would the claim be valid from the day of manufacture?  Example of shelf life prediction #4 Day Vc mg/100ml Lan (D) 0 50 Lan(50)=3.91203 3 40 Lan(40)=3.68 6 35 Lan(35) = 3.55 9 30 Lan(30)=3.40 12 25 Lan(25)=3.21 15 22 Lan(22) =3.09 18 20 Lan(20)=3.99 Ploat graph of ln(d) vers timeor day and we get the For shelf life for first order equation reaction y= 0.051x+3.8677, and R2= 0.9904 ts = ln(D0/D)/K = ln(50/15)/0.051 Slop = fist order rate constant (k)=0.051 =23.6 days Time to reach 15mg/100ml So the claim valid for 23.6days