Shelf Life Testing PDF

Shelf life The time when a product no longer maintains the expected quality to the consumer Quality loss should be without compromising safety Safety is not the only quality attribute that should be considered in determining shelf life – Increased microbial growth may compromise flavor,...

Shelf life The time when a product no longer maintains the expected quality to the consumer Quality loss should be without compromising safety Safety is not the only quality attribute that should be considered in determining shelf life – Increased microbial growth may compromise flavor, and color without the food becoming unsafe – If a nutritional claim is part of the product concept, a loss in nutrition may determine when the shelf life end point has occurred Shelf life can be determined by the change in quality factors of the product e.g. appearance, texture, odor Shelf life and product quality are HIGHLY related !!  Factors controlling shelf life The shelf life of a food is controlled by 3 factors: – Product characteristics including formulation and processing parameters (intrinsic factors) pH, water activity, enzymes, microorganisms, concentration of reactive compounds Can be controlled by selection of raw materials and ingredients as well as the choice of processing parameters – Properties of the package Can have a significant effect on extrinsic factors  indirectly affect the rates of deteriorative reactions – Environment to which the product is exposed during distribution and storage (extrinsic factors) Temperature, relative humidity, light, total pressure and partial pressure of difference gases, and mechanical stresses including consumer handling Can affect the rates of deteriorative reactions that occur during the shelf life of a product The shelf life of a food can be altered by changing its composition and formulation, processing parameters, packaging system, or environment to which it is exposed  Factors controlling shelf life: Product characteristics Perishability (based on the changes that can occur during storage) Perishable foods (very short shelf life) – chill (0-70C) or freezer temperature (-12 to -180C) if they are to be kept for more than short period – Milk, fresh meat, poultry, fish, minimally processed foods, fresh fruits and vegetables Semiperishable foods (short-to-medium shelf life) – Contain natural inhibitors (e.g. some cheeses, root vegetables, eggs) – received some type of mild preservation treatment (e.g. pasteurized milk, smoked hams, pickled vegetables) – Greater tolerance to environmental conditions and abuse during distribution and handling Nonperishable (medium-to-long shelf life) – Shelf stable foods – Low-moisture content unprocessed foods (cereal grains and nuts, some confectionary products) – Heat-sterilized product (e.g. canned foods), preservatives (e.g. soft drinks), dry mixes (e.g. cake mixes), reduced water content (e.g. raisins and crackers) – They only retain this status if the integrity of package that contains them remain intact – There is still limit to their shelf lives due to deteriorative chemical reactions that proceed at room temperature independently of the nature of the package, and permeation through the package of gases, odors, and water vapor  Product characteristics Bulk density – For packages of similar shape, equal weights of products of different bulk densities will have different free space volumes  package areas and package behaviour will differ – The bulk density of food powders can be affected by processing and packaging E.g. milk and coffee are instantized by treating individual particles so that they form free-flowing agglomerates or aggregates  relatively few points of contact Free space volume is important on the rate of oxidation – If a food is packaged in air, a large free space volume is undesirable – If the product is packaged in an inert gas, a large free space volume acts as a large “sink” to minimize the effects of oxygen transferred through the package – A large package surface area and a low food bulk density result in greater oxygen transmission  Product characteristics Concentration effects – Because most of the chemical compounds in packaged food product have little opportunity to move, the concentration differences among those compounds will increase as the reactions proceed – Several different deteriorative reactions may proceed simultaneously – a lag and a log phase with very different rate constants of microbial growth – difficult to obtain kinetic data useful for predictive purposes  suggestion: sensory panels to determine the acceptability of the food  Factors controlling shelf life: Package properties Foods can be classified according to the degree of protection required – Protect from O2, other gases, water gain, water loss, oil resistance, barrier to volatile organics – Metal cans and glass containers : regarded as essentially impermeable; – paper-based : permeable – plastics-based : provide varying degrees of protection, (depending largely on the nature of the polymers) Important package properties: – Water vapor transfer – Gas and odor transfer REVISE……………… Thermal properties – Thermal conductivity Different thermal conductivity may affect the heating or cooling rate in heat processes, e.g. pasteurization or sterilization of packaged food.. Metallic materials have high thermal conductivity due to the electron mobility in metallic bonds. Organic materials, e.g. plastics and wood products, have low thermal conductivity due to their atomic and intermolecular bonds. Still air (200C) has k of 0.02 W m-1 0C-1  very low thermal conductivity Thus.. corrugated board and expanded polystyrene are better insulating materials than solid board and homogenous plastics (at the same thickness).  Factors controlling shelf life: Distribution environment Climatic – The deterioration in product quality of packaged foods is often closely related to the transfer of mass and heat through the package – Packaged foods may gain or lose moisture; they will also reflect the temperature of their environment since most packages are not good thermal insulators  distribution environment has an important influence on the rate of deterioration of the food Mass transfer – Concerns: exchange of water vapor, oxygen, volatile aromas, transmission of nitrogen and carbon dioxide – The difference in partial pressure of the vapor or gas across the package barrier will control the rate and extent of permeation – transfer can also occur due to the presence of pinholes in the material, channel in seals and closures, or cracks that result from flexing of the package material during filling and handling – Water vapor transfer depends on the partial pressure difference across the package barrier, and on the nature of the barrier itself Heat transfer – The temperature to which the product is exposed during the time from production to consumption is important – Food products are exposed to fluctuating temperature environments  the fluctuation is important to be known for an accurate estimation of shelf life  Factors contributing to shelf life Microbial growth – Increased microbial growth can result in unsafe product if the growth is food borne pathogens and toxins – It can also change flavor, appearance, odor and texture of the product – Microbial changes can be measured during the shelf life. When designing tests, environmental factors, product concept and desired attributes should be considered – Preservation methods against microbial growth: low pH (