FOSC: Shelf life
Physical deterioritive changes
• Physical bruising • Moisture loss in fresh produce - wilting • Moisture gain in cereals and biscuits • Freezer burn in frozen foods • Hardening of semi moist products due to moisture loss • Instant coffee, tea and dried drink mixes become sticky and caked
What are predictive models
mathematical equations which use information from a database to predict bacterial growth under defined conditions. Most predictive models are specific to particular types of organisms.
Sensory Panels in measuring shelf life
measure changes in eating quality. Provide powerful info but are limited: If saftey is in doubt, time consuming, expensive, difficulties arise when masuring changes over time (inconsistent use of scales, change of panel, sample change).
Temperature Related deteriorative changes: Ice recrystalisation
occurs in icecream due to fluctuating temp.
Temperature Related deteriorative changes: Crystallisation
occurs in products with sugars at high temps
Chemical deteriorative changes in food: Exposure to light.
off flavour development in milk, colour loss in natural food colours
Chemical deteriorative changes in food: Lipid oxidation
oxygen attacking unsaturated fats causing rancid off-flavours (potato chips), colour changes in dried vegetables
Date marking style
uncoded, day, month, year - If not more than 3 months, day and monh only are of. If greater than 3 months, month and year only are ok.
Chemical deteriorative changes in food
lipid oxidation, enzymatic reaction, non-enzymatic browning, exposure to light.
Changes and K
Different reactions/processes have different Ea values. At different temp, spoilage will occur at different rates (K). K can be determined at different temps, allowing Ea and Ka to be obtained from the plot of In(k) vs 1/T. Can use this info to determine the shelf life at some lower temp. Technique has limitation but is useful.
What must manufacturers understand in order to prevent shelf life reduction
Food manufacturers must have an understanding of storage conditions, including constant & fluctuating environmental conditions and how these influence the product characteristics.
Reduction of shelf life through human error
Handling abuse can affect shelf life after factory. Temperature abuse most common in distribution, retail and domestic storage.
Labelling requirements
IFST (1993) states date marking requirements, these rules apply to all packaged food with shelf lives of less than 2 years. The standard requires a best before date unless the food needs to be eaten within a certain period for health and saftey reaons (requires use by date)
shelf life case study, soup, testing
Microbe testing: tested total bacteria, yeasts and moulds and bacillus Cereus. Showed the bacillus cereus and total bacteria within limits. Chemical testing, tested pH, showed a slight increase in pH (.1 for direct, .2 for abused). Physical Testing, tested seperation/ settling of particls, visual and smell factors, showed seperation of 1-2 ml and no settling colour/odour changes. Decided it satisfied shelf life requirements.
Temperature Related deteriorative changes: Destabalisation
Occurs in emulsion systems with fluctuating temperatures.
Other forms of accelerated shelf life determination
Other tests used depending on the main thing affecting shelf life e.g. Thickeners - less stable at low, but above 0 degrees, repeated cooling to 0 and returning to room temp will speed up synerisis. Emulsions - instability can be induced by shaking for several hours. Dried products - humidity can accelerate texture changes. Lipids - Oxygen concentration accelerates lipid oxidation/ off flavours.
Food stability map
Representation between water activity and relative reaction rate. Series of lines - represent microbiological changes (higher the curve, higher the rate), dependant of water activity.
Definition of stability (food)
Resistane to chemical chane or physical Disintegration
What are the three main criteria for shelf life asessment
Saftey, acceptable sensory characteristics and nutritional value.
Accelerated Shelf life determination (ASLD)
Technique aimed at increasing the reaction/deterioration rates (chemical, biochemical or even physical). Thus accelerate the shelf life. Commonly done by using elevated storage temperatures.
Indirect methods for shelf life testing
Techniques that enable the prediction of shelf life using models "predictive modelling", Capable of integrating changes in food manufacturing technology, distribution and retailing, Very useful when the shelf life is expected to be relatively long (e.g. canned foods, dried food)
Practical aspects of changes due to ASLD
Temperature will enhance both physical/chemical (e.g. flavour change, separation of emulsion) change rates, microbial growth (within a certain range), and the diffusion of oxygen through plastic packaging.
Use By date
The date which signifies the end of the estimated period if stored in accordance with any stated condition, after which the intact package of food should not be consumed because of health and saftey reasons.
Best Before Date
The date which signifies the end of the period suring which the intact package of food, if stored in compliance to any given conditions, will remain fully marketable and retain any specific qualitites for which expressed of implied claims have been made.
What is required for predictive modelling (2)
The properties of the product and packaging are required for the calculations. Information from modelling programmes needs to be verified by challenge testing or a shelf life trial.
What shelf lives must a food have.
a microbiological shelf life, a chemical shelf life, an organolepic shelf life.
Changes that occur due to different temp (ASLD)
can be any parameter that will affect consumer acceptance, including: • rancidity • texture changes • moisture loss • moisture gain • staling • flavour loss • light induced changes • enzymatic browning • chemical browning, and • microbial spoilage.
The sale of food past best before
can be sold after the best before date, not legal to sell if spoiled, rotten or unsafe.
Temperature Related deteriorative changes
can occur at both elevated and low temps. Increasing the temp ususally increases chemical reaction rate. Reactions = crystalisation/ recrystalisation, destabalisation. reduced temp = stale bread.
Chemical deteriorative changes in food: Enzymatic reactions
damaged cells release enzymes that enhance deterioration, e.g. in fruits and vegetables
What type of foods must be marked with a use by date
food that needs to be consumed within a certain period of time due to health and saftey reasons. Health reasons - special formulated foods e.g. special diet or multivitamin food. Saftey reasons - food may become microbiologically unsafe before it notecibly spoils. Does not apply to shelf stable or frozen foods. MAy apply to chilled ready to eat food.
The direct method steps of shelf life study
identify causes of food deterioration, decide required tests to use to measure deterioration, create a plan to study shelf-life, conduct the shelf-life study, determine the shelf life, monitor the shelf life periodically ( to verify study)
The sale of food past use buy
illegal to sell any food that has passed its use by date.
Interaction of intrinsic and extrinsic factors affecting shelf life.
interaction of factors either inhibit or stimulate a number of processes which limit shelf life. These processes are microbiological, chemical, physical and temperature related.
Arrhenius Eq:
relationship between rate of change (k) and change in temperature (T)
Chemical deteriorative changes in food: Non- enzymatic browning
sugars reacting with proteins, causing darkening, off flavours and a decrease in protein nutritional quality in dried dairy products, dried eggs and cake mixes
Instrumental measurement of Shelf life
temperature, temp-time monitoring, bulk density, viscosity, texture, pH, water activity, chemical markers.
Shelf life case study - soup, process
testing conducted on soup, simulation of hot filling under direct (4-6C) and abused (4-22) temp conditions. The tests were conducted over 42 days.
What is shelf life
the length of time a product will retain cetain expected characteristics (sensory, chemical, physical and microbe) related to quality. During this time the product will remain safe and comply with any label decleration of nutritional data when stored under the reccomended conditions.
extrinsic factors that affect shelf life
time - temp regime, temp of storage and distribution, humidity, exposure to light, environmental microbe count, composition of atmosphere within packaging, consumer handling.
What can predictive models be used for
to calculate the shelf life of a food. Information on the changes that occur in the product when it deteriorates,
How is shelf life decided
via direct or indirect method, where the aim is to find out under specified storage conditions the point in time (from manufacture) at which the food has become unsafe or unacceptable.
Intrinsic factors that affect food shelf life
water activity, pH and total acidity, redox potential, nutrients, natural microflora, natural biochemistry, use of preservitives.
