All about shelflife

October 16 1K.J.Karthika, Department of R& B

K.J.Karthika

Final year P.G scholar

Department of Rasashastra and Bhaishajya Kalpana

GAVC Tripunithura


Introduction•The present life style put forth the necessity of bulk productionof articles right from a stationary, to food and medicine.

• It is necessary to maket healthy and edible items.

• It is necessary to implement measures to prolong thedeterioration.

•In Ayurveda the concept of shelf life is highlighted by AcharyaSharangadhara while elaborating सवीर्यता अवधि of medicinalpreparations.

October 16 K.J.Karthika, Department of R& B 3

Definition•Shelf-life is the period of time over which a foodmaintains its safety and/or quality under reasonablyforeseeable conditions of distribution, storage and use.

•Validating product shelf-life is obtaining anddocumenting any evidence that proves that the shelf-lifeof a food is accurate and that the food will maintain itssafety and/or quality until the end of that shelf-life.


Scope- To apply appropriate date marking.It describes:• how shelf life is defined;• the causes of food deterioration and spoilage;• why food may become unsafe during storage;• how to decide whether a ‘best-before’ or ‘use-by’ datemark is required;• the information needed to work out what the shelf life is;and•how to ensure the safety of chilled foods.


Importantterminology•‘Best-before’ The date until which a food retains its specificproperties when properly stored, i.e. quality characteristics such asappearance, odour, texture, flavour etc. .

•Chilled foods are those foods that require storage at 5˚C or less tomaintain their suitability and safety.

•Date marking is the system for packaged foods with a shelf life ofless than 2 years.

•Perishable food is unprocessed or processed food that has a shortshelf life at room temperature before showing signs of deteriorationor spoilage (often mould or bacterial growth seen as fur or slime),e.g. fruit or pre-packaged bread Chilling perishable foods can


•Shelf-stable food is food of a type that, because of its composition(low moisture, high salt or sugar content) does not require to bestored refrigerated e.g. spices, flour, dried pasta or which wouldnormally be stored refrigerated but which has been processed sothat it can be safely stored in a sealed container at roomtemperature for a usefully long shelf life e.g. canned fish and meat.

•Stated shelf life is the period of time, established under intendedconditions of distribution, storage, retail and use, that the foodwould remain safe and suitable.

•‘Use-by-date’ Used for food which from a microbiological point ofview, is highly perishable and therefore, likely after a short periodto constitute an immediate danger to human health. After the ‘use-by’ date has passed, a food is deemed unsafe and must not be soldor consumed


Legal requirementsand responsibilitiesfor shelf-life


General Food LawFood must not be placed on the market if it is unsafe, i.e. injurious tohealth, or unfit for consumption.

ResponsibilityGenerally, the manufacturer of a food (with some exceptions) isresponsible for setting and validating the shelf-life. However, thisresponsibility may also fall to secondary manufacturers (co-packers),re-packers, food caterers, food retail outlets etc. depending onspecific circumstances.

Microbiological CriteriaUnder Regulation (EC) No 2073/2005, food should “not containmicroorganisms their toxins and metabolites in quantities thatpresent an unacceptable risk for human health”. food manufacturedshould comply with specified microbiological criteria throughout thefoods shelf-life under reasonably foreseeable conditions ofdistribution, storage and use.


Labelling

The ‘date of minimum durability’ is labelled. The date of minimumdurability provides for two different indicators of food shelf-life:

• ‘Use-by’ date

• ‘Best-before’


Setting and validating shelf-life of food


•In estimating and setting shelf-life, the primary objectiveshould be food safety.

•Procedures based on HACCP and good hygiene practiceand should always take into account, reasonablyforeseeable conditions of distribution, storage and use ofthe food including consumer practices where applicable.

•Document all work related to estimating, setting andvalidating food shelf-life.

•The shelf-life of food ideally should be estimated duringproduct development and set before the food goes on saleto consumers.


Shelf life testing


Describe the food product

On-going monitoring and verification of shelf-life.

establish the characteristics of the food, foreseeing conditions of

storage, distribution and use and possibilities for contamination.

Consult available scientific literature regarding the survival and growth

characteristics of microorganisms of concern.

Use predictive microbiology to estimate shelf-life.

Label the food with a shelf-life declaration.

Apply a safety margin to shelf-life.

Carry out laboratory testing, i.e. durability and/or challenge testing.


Product specification• Ready-to-eat status of the food• Ingredient list and specifications for each ingredient. ( Someretailers will request ingredient supplier details )• Processing parameters• Good manufacturing and hygiene practices• Product specific procedures based on HACCP• Quality control parameters and measures• Packaging details and specifications for all packaging• Labelling considerations, e.g. shelf-life declaration• Storage, distribution and retail display conditions• Instructions for use of the product as applicable• Details of microbiological and compositional specifications,including limits• Legislative requirements


Product characteristic


Factors determining food deterioration

Food deterioration

Intrinsic factors

Extrinsic factors

pH

microflora

Water activity

Microbiological quality of ingredients

Food assembly

Redox potential

Natural barriers

Nutritional contents

Antimicrobial contents Food formulation and

constituents


Extrinsic factors

packageing

Gas atmosphere

Temperature

Relative humidity Procedures based on HACCP

Consumer practises

Storage and distribution

Historical data

GMP

Food processing


Intrinsic characteristics


pH•The pH and acidity are very important intrinsic characteristicsaffecting the survival and growth of microorganisms in food. Scalefrom 0 – 14.

•The pH scale is logarithmic, meaning that each one point change inpH is ten times more acidic or less acidic. Maximum microbial growthpH at range 6-8

•pH can be variable with time due to microbial activity, productcomposition etc.Within some foods, there may also be a range ofdifferent pH. foods containing meat, fats or oils can be difficult toacidify uniformly .

• Organic acids such as acetic, sorbic, propionic and benzoic typicallycause disruption of the microbial cell membrane. Acetic acid, i.e.vinegar at levels greater than 0.1%, inhibits the growth of some foodborne pathogens .


Formulation pH

Bilvadilehyam 5.8- 6.7

Chyavanaprasha 3.82- 4.23

Kushmanda rasayana 4.0- 4.5

Avipathikara churna 5-6

Eladi churnam 5-7

Navayasa churnam 3-4

Apamarga kshara 10-11

Kaishora guggulu 4-4.5

Arka lavana 9-10

Darvi malahara(gel) 3.7-4.2


Water activity•Water activity (aw) refers to the free or available waterwithin a food which is not bound to food molecules, i.e.water which is available in foods to support microbialgrowth.

•Water activity has a scale from zero, i.e. (0% wateravailable) to one (100% water available).

•Water activity is not the same as the moisture content offoods. e.g. jams have high moisture contents but themoisture is bound to the sugar in the jam and unavailablefor microbial growth, giving jams a low water activity.


•Sugar and particularly salt are used to preserve foods bydecreasing the water activity by either binding free water andmaking it unavailable for microbial growth, e.g. sugar in jams, orby exerting osmotic pressure directly on microorganisms, e.g. saltused in brine for some cured meats.

•Food processing techniques such as drying, freezing, curing(salting, drying or smoking) and cooking will also influence thewater activity. This will impact on the ability of microorganisms togrow and subsequently, the safety and shelf-life of the food. Mostmicroorganisms cannot grow at water activity of less than 0.60with the majority growing at levels greater than 0.90.

•Like pH, the water activity of a food can be change with time dueto microbial activity, product composition and formulation.


Commodity Water activity

Distilled water 1.0

Fresh milk ≥ 0.98

Fruit and vegetable juices ≥ 0.98

Dried fruits, jams, honey and flours

≥ 0.60- 0.85

Dried vegetables, soups, breakfast cereals and milk powders

≥ 0.20 – 0.30

Coffee powder ≤ 0.20


Redox Potential•The redox potential (Eh) of a food determines which typeof microorganisms will grow in it, depending on whetherthey require oxygen for growth (aerobic) or not (anaerobic).

• measured in millivolts (mV) because when electrons movethey create an electric current, which can be measured .

• it should be referenced with the pH of the food, as redoxpotential is dependent on the pH of the food.

• Routine measurement of the redox potential in foods isquite simple and normally taken at a pH 7.0.


Microorganisms can be broadly classified into thefollowing groups based on their requirements for oxygenand redox potential of the food (measured in mV) :

• Aerobes require oxygen for growth and can grow at aredox potential between +300 to +500 mV

• Facultative anaerobes grow with or without oxygen andcan grow at a redox potential between +300 to -100 mV

• Anaerobes require no oxygen for growth and can grow ata redox potential between +100 to ≤ -250 mV

• Microaerophilic require limited oxygen for growth andcan grow at a redox potential between +100 to ≤ -250 mV.


•with pH and water activity the redox potential of foodscan be variable.

•do not use redox potential measurements solely toassess product safety due to the high variability of theredox potential and the often low accuracy in itsmeasurement.


Natural barriers•Some foods will have natural barriers or coveringsthat provide different levels of protection fromexternal contamination. E.g, shells, skins andmembranes commonly found on foods such as nuts,eggs, vegetables/fruit and fish.

•when food business operators remove naturalbarriers from foods, an appropriate method to reducemicroorganisms, e.g. washing, filtration, trimming etc.,is used


NutrientavailabilityAll microorganisms have basic nutritionalrequirements for growth and maintenance of basicmetabolic functions, e.g. protein, fat, sugars,minerals, vitamins etc.

Requirements vary depending on themicroorganism. Typically, bacteria have the highestnutritional requirements followed by yeasts andmoulds.


AntimicrobialSubstances• Some foods will contain antimicrobial substanceswhich retard or prevent the growth of microorganisms.e.g. allicin in garlic and onions and lysozyme in eggsand milk.

• Some antimicrobial are also created during foodprocessing, e.g. production of phenols during smokingor bacteriocins during fermentation.


Food additives•Food additives can be added to prolong the shelf life of food.

•Regulation (EC) No 1333/2008 harmonises the use of foodadditives in foods in the EU and defines food additives asfollows23:

•“substances not normally consumed as a food in itself and notnormally used as a characteristic ingredient of food, whether ornot it has nutritive value, the intentional addition of which to foodfor a technological purpose in the manufacture, processing,preparation, treatment, packaging, transport or storage of suchfood results, or may be reasonably expected to result, in it or itsby-products, becoming directly or indirectly a component of suchfoods”.


Microflora•All foods naturally contain different types and concentrations ofmicroorganisms, i.e. natural microflora.

•the types and concentrations of microorganisms in food can varywidely.

•The presence of certain microorganisms in foods may retard orprevent the growth of pathogens by outgrowing the pathogens,consuming available nutrients and/or producing substances in thefood which retard or prevent growth of pathogens, i.e.competitive inhibition.., e.g. lactic acid bacteria.

•some microorganisms are added for processing and technologicalreasons such as lactic acid bacteria which are added to milk tomake cheese and yogurt.


Microbiological quality ofingredients•The microbiological quality of ingredients will affect the safetyand shelf-life of foods.

•It is assumed that all ingredients are a potential source ofmicrobiological contamination. From the starting point ingredientswhich comply with legislative requirements for food safety andhygiene, particularly microbiological criteria is used whereapplicable.

•In the absence of specific criteria set in legislation, ingredientsshould comply with relevant Irish standards, Irish guidelines27-31or industry best practice guidance .


•Ingredients should sourced from a supplier previouslyapproved by the food business operator.

•Water entering premises which is not of potablequality or where quality is unreliable, e.g. from aprivate well, appropriate treatment should be appliedby the food business operator to the water to ensure itis of potable quality before use.


Food formulation,composition, structureand assembly•The formulation, composition, structure andassembly of food will influence food safety and shelf-life.

•Some foods can have non-uniform, heterogeneousinternal structures and thus intrinsic characteristicsvary within the structure of the food and food as awhole.


1. Manufacturing ErrorAn ingredient is removed or an incorrect quantity of ingredient isadded to the product.

2. Product Development ErrorIngredients within a product are in close proximity to each other,causing migration of some components, e.g. water, fats out of theproduct

3. Quality of IngredientsIngredients from two different suppliers have differentmicrobiological quality / Ingredients of differing microbiologicalquality are combined together

4. Reformulating and Producing Variants ofProductsAn ingredient is replaced with an alternate ingredient


Extrinsiccharacteristics


TemperatureThe safety and shelf-life of most foods particularly thoserequiring refrigeration, is very dependent on temperature.

Microorganisms’ ability to grow at different temperatures isbroad and includes those microorganisms which are:

• Psychrotrophic, i.e. optimum temperature 20°C to 30°C, butmany can survive and grow at or below 5°C

• Mesophilic, i.e. optimum temperature 30°C to 40°C, but manycan survive and grow between 20°C to 40°C

• Thermophilic, i.e. optimum temperature 55°C to 65°C, butmany can survive and grow at 45°C but not less than 30°C


•The control of temperature during all stages of foodmanufacture, storage, distribution and use should becarefully considered, measured and documented byfood business operators as it can significantly affectshelf-life.

•Research has shown that domestic refrigerators oftenoperate at a higher temperature than 5°C.Recommended temperatures for distribution, cateringand retail in Ireland are ≤ 5°C.


Gas atmosphereThe gas atmosphere and its composition which surround afood will affect shelf-life.

How to alter gas atmosphere?

1.Modified atmosphere packaging (MAP)/gas flushing: Theair surrounding the food packaging is removed and the packis sealed, leaving a small residual air content in the pack.

2.Vacuum packing (VP): the air surrounding the foodpackaging is also removed but replaced with a gas or mixtureof gases such as oxygen, carbon dioxide or nitrogen, beforesealing.


Other factors influencing gas atmosphere:-

•The specific concentrations of gases•The packaging material and equipment used.•Nature of material packed.

e.g; permeability of packaging and actively respiring fruitand vegetables can affect the composition of gases in thepack during shelf-life which in turn, can affect microbialgrowth and product safety.

Under current legislation, foods which have their shelf-life extended by means of packaging gases must belabelled “packaged in a protective atmosphere”.


•It is also recommended that the labelling carries a clearstatement that the shelf-life is no longer valid once foodpackaging is opened.

• MAP and VP packaged food should also carryinstructions for use that include how soon the food mustbe consumed after the pack is opened and the storagetemperature for the opened product.


Relative humidity•Relative humidity is the concentration of moisture in theatmosphere surrounding a food.

•There is an exchange of moisture between a food and itsatmosphere which continues until the food is in equilibrium withthe surrounding atmosphere.

•Relative humidity can affect the water activity of foods. If dryproducts like cereals are held at high humidity, the water activitywill increase.

•The relative humidity is also associated with the storage anddistribution temperature of foods. For lower storage temperatures,a higher relative humidity is required to ensure that productcharacteristics are maintained.


Packaging•Help to control both the gas atmosphere and relativehumidity of foods which will affect food safety andshelf-life.

•The choice and use of packaging often requiresspecialized equipment, materials and trainedpersonnel.

•Food business operators should seek expert advicefrom an appropriate packaging supplier before using aspecific packaging technology to ensure the safety oftheir food and compliance with legislation.


Food processing•The variety and nature of food processing variesenormously depending on the food being manufactured.

•processing is designed to improve food palatability,safety and shelf-life.

• Common technology such as heat treatment, i.e.cooking, pasteurization etc. will improve food safety andextend shelf-life by destroying dangerous pathogens andreducing numbers of other microorganisms.


•Typically, heat treatments are mild and will not destroy allmicroorganisms, their spores or toxins, but rather willdestroy or reduce numbers of specific microorganisms.

•Variations in heat resistance have been observed in manypathogens and the intrinsic characteristics of the foodsuch as salt and fat concentration, pH and presence ofcompetitive microorganisms etc. have also been shown tohave an effect.

•Heat treatments should be sufficient to ensure heatpenetration at the centre or thickest part of a food andreduce the number of target pathogens by 6 log cycles, i.e.a six-fold reduction in pathogen numbers, e.g. from 1million per gram to 1 per gram.


•Other processing technologies such as high pressureprocessing, smoking, fermentation, curing, drying, chilling,freezing etc. may alter the intrinsic or extrinsic propertiesof the food to retard or select for the growth of specificmicroorganisms.

• Some forms of food processing such as natural smokingmay also result in the formation of antimicrobialsubstances in foods which can retard microbial growth.


Storage,distribution and use•How a food is stored, distributed and used by consumers willaffect food safety and shelf-life.

•Food experience temperature variation due to season of theyear or abuse during storage, distribution and use which cansignificantly affect food safety and shelf-life.

•Recommended temperatures for distribution, catering and retailare ≤ 5°C.Many domestic refrigerators have been shown tooperate at high temperatures around 10°C which can significantlyaffect the safety and shelf-life of food products.

•Scientific studies have shown a relatively poor understanding ofbasic food hygiene and food safety, particularly temperature


Good manufacturingand hygiene practices•Measures to control microorganisms in foods must becomplimented by measures to minimize the risk ofcontamination or recontamination from the foodprocessing environment.

• Good manufacturing practices (GMP) and hygienepractices (GHP) and the development andimplementation of procedures based on HACCP arefundamental in maintaining food safety and setting andvalidating food shelf-life.


Historical data•Historical data are an important component kept as apart of their on-going business.

•These data are recorded as part of legal obligations,routine monitoring and testing as part of quality controlprocedures and customer requirements.

•These data can be used to verify the correct operation offood business operator controls for safe production offoods.


Procedures based on HACCP

•All food business operators, with the exception of primaryproducers, are legally obliged to implement and maintain,permanent procedures based on HACCP3.

•It provide a structured systematic approach to food safety, whichinvolves identifying potential hazards and planning for theirmonitoring and control.

•the extrinsic and intrinsic factors of the food such as temperature,pH, etc may be identified as critical control points there byconsistently and systematically, reduce or prevent hazardsoccurring and ensure that the shelf-life is achieved.


Consultation ofscientific literature•When the intrinsic and extrinsic characteristics of thefood have been established, this information can be usedto compare the product with existing data on the survivaland growth of pathogens in scientific literature.

•Data on food safety, pathogens, manufacturing, shelf-lifeetc. are available from scientific journals, books, industryguides,etc.

•Additionally, the FSAI and other competent authorities,e.g. Department of Agriculture Food and the Marine(DAFM), the Health Service Executive (HSE) as well as


PredictiveMicrobiology•Predictive microbiology uses mathematical models andcomputer software to graphically describe the responsesof microorganisms to intrinsic or extrinsic characteristics.

•Initially useful to help estimate food safety and shelf-lifehaving established the food’s intrinsic and extrinsiccharacteristics.

•They are also useful when food with an established shelf-life is subject to a minor process or formulation change


•Data generated from predictive microbiological modelsshould only be used as a guide to the response ofmicroorganism(s) to a particular set of characteristics andshould be verified by a durability study or challenge test.Consultation with a competent body is stronglyrecommended before their use.

•predictive models can provide a cost effective, themodel’s predictions may not be accurate, due toinconsistent microbial responses and variations in thegrowth media.


Laboratory Testing•The next step in a shelf-life study is often the planningand design of laboratory testing of the food.

•microbiological tests are predominately used to makethe critical decisions regarding food safety, food qualityand shelf-life and are often carried out in conjunctionwith tests to establish safety.

•Two types of laboratory testing, durability studies andchallenge testing can be used in relation to shelf-life.


Durability studies•Durability study determines the growth ofmicroorganisms in the food as manufactured, underreasonably foreseeable conditions of distribution, storageand use.

•Before beginning a durability study, it should be properlydesigned and planned.

•If the durability study is specifically for L. monocytogenesin foods, the EC guidance should be followed .In all othercases, food business operators should follow the twelvegood practice steps outlined below:


1. Confirm the samples to be tested

2. Establish the study durationThe durability study should run up to and beyond the target shelf-life required by

the food business operator. For example, if the target shelf-life is 28 days, testingcould last 28 days plus seven days. Under some circumstances, a product mayexceed its qualifying criteria before its target shelf-life. At this point, testing shouldstop and the food business operator accepts the estimated shelf-life or continuewith product development and further testing until the desired shelf-life is achieved.

3. Establish the study conditionslaboratory testing to be carried out under realistic conditions. Foods should bestored at temperatures which reflect normal practice, even if these temperaturesare different to the recommended temperatures.storage time is divided into three stages, i.e.•distribution,•retails display•consumer storage with two thirds of the time at 6°C (representative of the 75thpercentile of the chill chain in Ireland) and one third at 8°C.


4. Establish the frequency of testing

•The frequency of should be based on experience withsimilar foods and the established characteristics of the food.

•For example, perishable food with a target shelf-life ofseven days may require testing at daily intervals while lessperishable foods may only require twice weekly or weeklytesting intervals.


5. Establish the number of samples to be tested

•It is important that a sufficient number of sample replicates aretested to account for product variability. This is because thedistribution of microorganisms in foods is typically not uniform.

•The size of the food business operator’s production batch will helpdetermine the number of samples required.

•In the absence of a specified sample number, it is recommendedthat at least three replicate samples from three separateproduction batches are tested at each interval during the durabilitystudy.

•The larger the number of replicates tested per interval, the greaterthe degree of confidence a food business operator can have in theestimated shelf-life.


6. Choose the Testing Laboratory

7. Establish the tests to be performed•The type of pathogen(s) which could be expected to be present in thefood will depend on the intrinsic and extrinsic characteristics of thefood.

•comply with any requirements of legislation on the microbiologicalcriteria of food products

•The decision to carry out specific microbiological tests should only bemade by a trained food microbiologist or in consultation with acompetent body.

•It is recommended that all microbiological tests are carried out using arecognized reference method. An alternative method, this methodmust be validated against the reference method.


8. Perform and document the durability study.

•Ensure all samples are stored under agreed storageconditions and tests are performed on the appropriatesamples at the appropriate time intervals.

•It is recommended that all sample details, conditions ofstorage, tests performed, procedures, results etc aredocumented.

•All documentation should be filed to allow it to bereadily available to the food business operator andcompetent authorities alike should they wish to reviewit.


9. Interpret the test results and set the shelf-life

•The results of durability studies reflect the naturalcontamination of food products.

•‘Absence’ results are not proof that the batch of food fromwhich the samples came is not contaminated.

• Due to the low probability of detecting pathogens in acontaminated batch, the low number of microbial cellsinitially present and their uneven distribution in the food.

•The interpretation of the test results should only be madeby a trained food microbiologist in consultation with thetesting laboratory.


•Using these results and other data recorded, assign anappropriate shelf-life which ensures food safety.

•If results appear unsatisfactory or inconsistent, furthertesting may be required.

• In some cases, if the estimated or target shelf-lifedetermined during product development is not achieved inthe durability study, the product may have to beredeveloped or modified.


10. Applying a margin of safety

•The shelf-life will never be an absolute value that terminates at anexact time and date. Rather, there will be a distribution of timesand dates around an average shelf-life.

•The margin of safety is determined and after examining allreasonably foreseeable conditions of processing, storage,distribution and use.

•It is not possible to define exact margins of safety for foodproducts as it will vary between products. However, possiblevariations in the characteristics of foods, e.g. pH or storagetemperature, should be taken into consideration when applying themargin of safety.

•The rationale behind an applied margin of safety should be andthe food product specification and labelling finalised.


11. Labeling of shelf-life

•Foods which are microbiologically perishable and mayconsequently, after a short period of time, pose a risk topublic health, will generally have their shelf-life indicatedby a ‘use-by’ date

•ready-to-eat foods, or after treatment, unlikely to besufficient to destroy pathogens and toxins or metaboliteswhich may be present, will also have their shelf-lifeindicated by a ‘use-by’ date.

•The ‘use-by’ date will indicate the date up until which theproduct can be safely consumed.


12. On-going monitoring and verification

- It is not necessary to repeat works carried out toestimate, and set food shelf-life unless production processis modified or changed.

-Verify product safety and shelf-life periodically as subtlechanges can arise in products over time.

-Samples of food products may also be taken by foodbusiness operators at different points in the distributionchain or as a result of customer complaints and tested toverify the foods safety and shelf-life.


Challenge testing•A new food product with a unique set of intrinsic andextrinsic characteristics developed will not have data on theeffect of these characteristics on specific in the scientificliterature.

•to evaluate the safety of the food using challenge testing isemployed.•

•Challenge testing determines if a pathogen(s) can growand/or survive in the food and if so, how fast it will grow, i.e.growth potential.

•Challenge testing will also establish and validate the safetyof foods over a set shelf-life.


•In a challenge test, a food is inoculated with several strains of aknown pathogen or non-pathogenic microorganism with similarcharacteristics, at a specific inoculation level.

•It is recommended to use at least three strains with known growthcharacteristics of which two should preferably be isolates from similarfoods and one should preferably be a human isolate.

•The food is then stored under reasonably foreseeable conditions ofdistribution and use by the laboratory and the survival and growth ofthe inoculated microorganisms is measured.

•it is important to note that challenge testing is highly specialised,complex, expensive and generally food product exclusive. Consultationwith a competent body or an appropriately experienced laboratory isstrongly recommended before deciding to use challenge testing.

All about shelflife

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Transcript of All about shelflife