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Home , Package testing, Shelf life

PACKAGED PRODUCT QUALITY AND

INTRODUCTION:-

The shelf life of a can be defined as the time period within which the food is safe to consume and has an acceptable quality to consumers. Just like any other food, frozen deteriorate during storage by different modes or mechanisms.

Packaging can become a shelf life limiting factor in its own right. For example, this may be as a result of migration of tainting compounds from the packaging into the food or the migration of food components into the packaging. Achieving a consensus on the definition of shelf life is never easy. Different groups within the food chain, i.e. consumers, retailers, distributors, manufacturers and growers, proffer subtly different perspectives of shelf life, reflecting the aspect of greatest importance and significance to them. For consumers, it is imperative that products are safe and the quality meets their expectations. Consumers will often actively seek the product on the shelf with the longest remaining shelf life as this is considered to be indicative of freshness. Consumer handling of products in terms of storage and use impacts on shelf life and is perhaps the biggest unknown for manufacturers when designing shelf life trials. For retailers, product quality must meet or exceed consumer expectations for repeat purchases. Product shelf life must be set to ensure that this is the over the entire product life, allowing sufficient product life for the distribution chain and retail turnover of product and some life for the consumer. Manufacturers, who are responsible for setting product shelf life must be able to justify the validity of the shelf life assigned. They are also under considerable pressure to produce products to meet the shelf life requirements of retailers and often this will dictate whether or not a product is stocked. Achieving the desired product shelf life is a powerful driver for product and packaging innovation to extend product life. Many new packaging materials such as packaging (MAP) have been developed to complement developments in new preservation techniques. The role of packaging in the maintenance and extension of shelf life cannot be over emphasised. The Institute of and Technology (IFST) Guidelines (1993) provide a definition of shelf life: ‘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 declaration of nutritional .’ This definition encapsulates most perspectives and leaves some flexibility, i.e. ‘desired...characteristics’, in assigning product shelf life. This is essential because once considerations of safety have been met, quality is generally a commercial consideration dependent upon the marketing strategy of the companies. The shelf life of a product is best determined as a part of the product development cycle. As the packaging may be one of the means by which shelf life limiting processes are controlled, or the packaging per se may limit the product shelf life, it is also important that the packaging requirements for the product are considered early during product development. Shelf life testing is carried out by holding representative samples of the final product under conditions likely to mimic those that the product will encounter from manufacture to consumption. Once the microbiological safety of the product has been determined, quality issues can be considered. This may be based on microbial numbers, chemical specifications or sensory assessment. In most cases it is likely to be a combination of these. For products with long shelf lives it is desirable to have indirect or predictive methods for determining shelf life. Increasing is the most common means of accelerating shelf life, but other parameters such as humidity, shaking or exposure to light, known to affect product stability can be used. Such tests are often product specific and based on a considerable knowledge of the product and its response under the accelerating conditions. The danger with this approach is that chemical reactions or microbiological growth is initiated, that would not take place under normal storage conditions. Another approach to accelerated shelf life testing is predictive modelling, where mathematical models are used to predict either the shelf life or the level of a shelf life limiting attribute as a function of the composition of the product. FACTORS AFFECTING PRODUCT QUALITY AND SHELF LIFE

For many foods, the product shelf life is limited by specific or key attributes that can be predicted at the time of product development. This is either on the basis of experience with similar products or observations of them, or from a consideration of • 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 is likely to result in. Intrinsic factors are the properties resulting from the make-up of the final product and include the following: • (aw) (available water) • PH/total acidity; type of acid • Natural micro flora and surviving microbiological counts in final product • Availability of oxygen • Redox potential (Eh) • Natural biochemistry/chemistry of the product • Added (e.g. salt, spices, • Product formulation • Packaging interactions (e.g. tin pickup, migration). Selection of raw materials is important for controlling intrinsic factors, since subsequent processing can rarely compensate for poor- quality raw materials. 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

PACKAGE PROPERTIES:-

Foods can be classified according to the degree of protection required. The advantage of this sort of analysis is that attention can be focused on the key requirements of the package such as maximum moisture gain or O2 uptake. This then enables calculations to be made to determine whether or not a particular packaging material would provide the necessary barrier required to give the desired product shelf life. In the case of metal cans and , these can be regarded as essentially impermeable to the passage of gases, odors and water vapor, while -based packaging materials can be regarded as permeable. This then leaves plastics-based packaging materials that provide varying degrees of protection, depending largely on the nature of the polymers used in their manufacture.

TABLE :-

Degree of Protection Required by Various Foods and Beverages (Assuming 1 Year Shelf Life at 25°C)

MAX. OTHER GAS MAX REQUIRES REQUIRE FOOD/BEVERAG AMOUN PROTECTIO WATER HIGH OIL D GOOD E T OF O2 N NEEDED GAIN RESISTANC BARRIER GAIN OR E TO LOSS VOLATIL E ORGANIC S

Canned and 1-5 NO 3% YES NO flesh foods LOSS

Baby foods 1-5 NO 3%LOS YES YES S

Beers and wines 1-5 <20% co2 3% NO YES LOSSS

Instant coffee 1-5 NO 2% YES YES GAIN

Peanut 500-200 NO 10% YES NO GAIN

Fruit juices and 10-40 NO 3% NO YES LOSS

Dried foods 5-15 NO 1%GAI NO NO N

PREDICTING MICROBIAL SHELF LIFE

Microbial spoilage of foods is an economically significant problem for food manufacturers, retailers and consumers. Depending on the food, process and storage conditions, the microbiological shelf life can be determined by the growth of either spoilage or pathogenic microorganisms. In the case of spoilage microorganisms, the traditional method for determining microbiological shelf life involved storing the food at different and determining spoilage by sensory evaluation or microbial count. Where the microbiological shelf life is determined by the growth of pathogenic microorganisms, the traditional approach has been challenge testing of the food with the organism of concern, followed by storage at different temperatures and microbial analysis at intervals. For processes such as heat treatments, where the elimination of particular microorganisms is required (e.g., ), the use of inoculated packs is common. The primary step in the microbial shelf life determination of food is to identify the specific spoilage organisms (SSOs), defined as the fraction of the total microflora that are responsible for spoilage under the particular range of environmental conditions. The end of shelf life is when a certain level of deterioration is reached because of the SSOs, the microbial metabolic product. After determining the SSOs and the range of environmental conditions over which a particular SSO is responsible for spoilage, the next step is to decide the population level of the SSO at which time greatly depending on the initial contamination level. Hygienic control of food preparation and processing is required so that the end of shelf life is determined by the growth of spoilage organisms rather than of pathogens. The four key parameters log No, θlag, μmax and log Nc that describe the progress of microbial growth with time under certain defined conditions . The parameter log No is determined by the initial contamination level of the food, which is dictated by raw materials and food manufacturing conditions, whereas log Nc represents the critical or maximum cell density attainable under given conditions. Lag time (θlag) and maximum specific growth rate (μmax), depending on environmental conditions, directly affect the time to reach a certain critical level of microbial density corresponding to acceptable quality. The limit of microbial growth determining shelf life differs with food type, packaging and storage conditions SSO counts of 106–108 organisms g−1 or cm−2 are commonly used as a convenient upper limit of quality. When dealing with pathogenic such as Bacillus cereus and Staphylococcus aureus, a limit of 105 organisms g−1 has been used for of the food supply system for prepared foods. The time to reach the limit based on pathogen growth should be clearly understood as the minimum requirement for shelf life control. The time (θs) to reach a critical limit cell density of Nc is the shelf life and can be calculated using

θs = θlag + 1/ μmax ln Nc/No

ACCELERATED SHELF LIFE TESTING

BASIC PRINCIPLES:-

The basic assumption underlying accelerated shelf life testing (ASLT) is that the principles of Chemical kinetics can be applied to quantify the effects which extrinsic factors such as temperature, humidity, gas atmosphere and light have on the rate of deteriorative reactions. By subjecting the food to controlled environments in which one or more of the extrinsic factors is maintained at a higher than normal level, the rates of deterioration will be accelerated, resulting in a shorter than normal time to product failure. Because the effects of extrinsic factors on deterioration can be quantified, the magnitude of the acceleration can be calculated and the “true” shelf life of the product under normal conditions calculated. Thus, a shelf life test that would normally take a year can be completed in about a 1–2 months if the storage temperature is raised from 20°C to 40°C. The need for ASLT of food products is simple—because many foods have shelf lives of at least 1 year, evaluating the effect on shelf life of a change in product formulation (e.g., a new antioxidant or thickener), the process (e.g., a different time/temperature sterilization regime) or the packaging (e.g., a new polymeric film) would require shelf life trials lasting at least as long as the required shelf life of the product. Companies cannot afford to wait for such long periods before knowing whether or not the new product/process/packaging will provide an adequate shelf life, because other decisions (e.g., to construct a new factory, order new equipment or arrange contracts for the supply of new packaging material) have lead times of months or years. Some way of speeding up the time required to determine the shelf life of a product is necessary, and ASLT has been developed for that reason. Such procedures have long been used in the pharmaceutical industry where shelf life and efficacy of drugs are closely related. However, the use of ASLT in the food industry is not as widespread as it might be, due in part to the lack of basic data on the effect of extrinsic factors on the rates of deteriorative reactions, in part to ignorance of the methodology required, and in part to skepticism of the advantages to be gained from using ASLT procedure. The logarithm of shelf life versus temperature and the inverse of absolute temperature. If only a small range of temperature is considered, then the former shelf life plot generally fits the data for food products. For a given extent of deterioration and reaction order, the rate constant is inversely proportional to the time to reach some degree of quality loss. Thus, by taking the ratio of the shelf life between any two temperatures 10°C apart, the Q10 of the reaction can be found. This can be expressed by the extension of Equation, assuming a linear shelf life plot:

Q10 = Kt+ 10/ Kt = θst/ θst+10 Where

θst is the shelf life at temperature T°C θst+10 is the shelf life at temperature [ T+10]C

ASLT PROCEDURES

The following procedure should be adopted in designing a shelf life test for a food product :-

1. Determine the microbiological safety and quality parameters for the product.

2. Select the key critical descriptor(s) or IoFs that will cause quality loss and, thus, consumer unacceptability in the food, and decide what tests (sensory and/or instrumental) should be performed on the product during the trial.

3. Select the package to be used. Often, a range of packaging materials will be tested so that the most cost-effective material can be selected.

4. Select the extrinsic factors that are to be accelerated and it is usually necessary to select at least two. 5. Using a plot determine how long the product must be held at each test temperature. If no Q10 values are known, then an open-ended ASLT will have to be conducted using a minimum of three test temperatures.

6. Determine the frequency of the tests. A good rule of thumb is that the time interval between tests at any temperature below the highest temperature should be no longer than

f2=f1Q10 ΔT /10 where f1 is the time between tests (e.g., days, weeks) at the highest test temperature T1 f2 is the time between tests at any lower temperature T2 ΔT is the difference in degrees Celsius between T1 and T2 Thus, if a product is held at 40°C and tested once a month, then at 30°C with a Q10 of 3, the product should be tested at least every

f 2 = 1× 3 ( 10/10 ) = 3 months

More frequent testing is desirable, especially if the Q10 is not accurately known, because at least six data points are needed to minimize statistical errors, otherwise the confidence in θs is significantly diminished.

7. Calculate the number of samples that must be stored at each test condition, including those Samples that will be held as controls.

8. Begin the ASLTs, plotting the data as they come to hand so that, if necessary, the frequency of sampling can be increased or decreased as appropriate.

9. From each test storage condition, estimate k or θs and construct appropriate shelf life plots from which to estimate the potential shelf life of the product under normal storage conditions. Provided that the shelf life plots indicate that the product shelf life is at least as long as that desired by the company, then the product has a chance of performing satisfactorily in the marketplace.

EXAMPLES OF ASLT PROCEDURES

• Dehydrated Products

In dehydrated vegetables, lipid and hydrolytic oxidation, together with nonenzymic browning and (in the case of green vegetables) chlorophyll degradation, are the major modes of deterioration. In dehydrated fruit, the major mode of deterioration is nonenzymic browning. Samaniego used temperatures of 30°C and 40°C to accelerate deterioration in sliced green beans and onion flakes and found that, for example, at 40°C, the shelf life of onions was 11 times shorter, and at 30°C, 3.5 times shorter than at 20°C when the aw was 0.56. • Frozen Foods

Plots of HQL or PSL versus time such curves suggest that accelerated tests could be used for predicting the shelf life of frozen foods with a considerable degree of accuracy. The shape of TTT curves for a wide range of products has been determined, and for any specific set of conditions (e.g., a particular product, process or package), a more detailed TTT curve could be determined. Then, accelerated tests could be carried out at temperatures as warm as −10 or even −8°C. As a result, the shelf life of a that would normally be stored at −18°C could be predicted in a few weeks or months at these higher temperatures. Although mold growth has been recorded down to −17°C, no evidence of microbiological growth on meat products has been found at or below −8°C, and therefore −8°C is generally recommended as the warmest temperature for ASLT of meat. Due cognizance must be taken of those frozen products such as frozen bacon, which exhibit so-called reverse stability where the keeping quality is poorer at −25°C than at −5°C. In ASLT of frozen foods, the formation of ice has to be considered. As ice forms, the concentration of the unfrozen aqueous phase increases and influences reaction rates because they depend on both temperature and concentration. Below about −7°C, the relative change in concentration of the unfrozen aqueous phase is small, but storage at temperatures above −7°C should be avoided. In the temperature range between 0°C and −7°C, the overall observed rate of reaction may increase, stay relatively constant or decrease depending on the specific system. Consequently, there is no generally applicable method to estimate low temperature shelf life from measurements made above −7°C

• Canned Foods

It is generally assumed that if good manufacturing practices are followed, microbial deterioration of canned foods will not be a problem. If there is thermophilic spoilage when canned foods are stored at elevated temperatures, then this is more than likely due to inadequate cooling of the cans following thermal processing. Microbial spoilage at ambient temperatures is generally the result of “leaker” spoilage, so-called because the microorganisms are drawn into the can during cooling; chlorination of cooling water according to good manufacturing practice will avoid this problem.

• Oxygen-Sensitive Products

In all the classical ASLT methods, temperature is the dominant acceleration factor used, and its effect on the rate of lipid oxidation is best analyzed in terms of the overall activation energy EA for lipid oxidation. An inherent assumption in these tests is that EA is the same in both the presence and absence of , although indications are that it is in fact considerably lower in the latter case. Although high O2 pressures can be used to accelerate reactions involving oxidation, it is not used very often since oxidation reactions typically become independent of the O2 concentration above a certain level which varies with temperature and other conditions.

PROBLEMS IN THE USE OF ASLT CONDITIONS

The potential problems and theoretical errors that can arise in the use of ASLT conditions have been described as follows:

1. Errors in analytical or sensory evaluation. Generally, any analytical measure should be done with a variability of less than ±10% to minimize prediction errors.

2. As temperature rises, phase changes may occur (e.g., solid fat becomes liquid), which can accelerate certain reactions, with the result that at the lower temperature the actual shelf life will be longer than estimated.

3. Carbohydrates in the amorphous state may crystallize out at higher temperatures, with the result that the estimated shelf life is shorter than the actual shelf life at ambient conditions.

4. Freezing “control” samples can result in reactants being concentrated in the unfrozen liquid, creating a higher rate at the reduced temperature and, thus, confounding estimates

5. If two reactions with different Q10 values cause quality loss in a food, the reaction with the higher Q10 may predominate at higher temperatures while at normal storage temperatures the reaction with the lower Q10 may predominate, thus confounding the estimation.

6. The aw of dry foods can increase with temperature, causing an increase in reaction rate for products of low aw in sealed packages. This results in overprediction of “true” shelf life at the lower temperature.

7. The solubility of gases (especially O2 in fat or water) decreases by almost 25% for each 10°C rise in temperature. Thus, an oxidative reaction such as loss of vitamin C or linoleic acid can decrease in rate if O2 availability is the limiting factor. Therefore, at the higher temperature, the rate will be less than theoretical, which in turn will result in an underprediction of “true” shelf life at the normal storage temperature.

8. If the product is not placed in a totally impermeable pouch, then storage in high temperature/ low humidity cabinets will generally enhance moisture loss, and this should decrease the rate of quality loss compared to no moisture change. This will result in a shorter estimated shelf life at the lower temperature.

9. If high enough temperatures are used, proteins may become denatured, resulting in both increases or decreases in the reaction of certain amino acid side chains, leading to either under- or overprediction of “true” shelf life.

Therefore, in light of the preceding points, the use of ASLT to estimate actual shelf life can be severely limited except in the case of very simple chemical reactions. Consequently, food technologists should always confirm the ASLT results for a particular food by conducting shelf life tests. under actual environmental conditions. Once a relationship between ASLT and actual shelf life has been established for a particular food, then ASLT can be used for that food when process or package variables are to be evaluated.

Another point worth stressing is that ASLT where temperature is the accelerating factor, is really only applicable for foods marketed in temperate climates. In tropical climates, the ambient temperature is typically 30°C–40°C and even higher in warehouses, trucks, and so on. These temperatures correspond to those suggested for ASLTs in Section 12.5.2 and higher temperatures than these cannot be used for ASLT because this would lead to reactions that were not representative of how the foods would deteriorate under actual tropical conditions.

SHELF LIFE DEVICES

There is a continual loss of quality from the time they leave the food processor until they are consumed, even under ideal handling conditions. The goal of modern food distribution techniques is to minimize the extent of quality degradation so that the foods will reach the consumer’s table as close to their original state as possible. Of all the extrinsic factors that accelerate quality degradation, the one which has the greatest influence is temperature. This is well known by food technologists, and most countries have codes of practice that specify optimum storage temperatures for many foods, particularly those classed as perishable. Despite these specifications, problems of storage temperature abuse arise all too frequently. One difficulty when storage temperature abuse is suspected lies in detecting the extent of the quality degradation without sampling the food (i.e., disturbing the integrity of the package). An associated difficulty is that many of those involved in the distribution chain are not trained to make reliable judgments about the quality of the food. Thus, food processors require a simple way of indicating whether their products have been stored at undesirable temperatures, or better still, a means of indicating how much shelf life remains.

EVALUATION AND TESTING OF TRANSPORT WORTHINESS OF FILLED PACKAGES

Methods of evaluation

Evaluations may be carried out on complete packs (filled or empty), on pack components or materials, or on the product to be carried. Methods include:

(a) Visual examinations and estimates made from existing knowledge and experience. These are particularly relevant when the performance of similar packs or products is known, or when small numbers of items are to be dispatched.

(b) Non-reproducible tests, e.g. drop tests by hand in an office, tearing a tape between the fingers.

(c) Reproducible tests, usually (but not always) carried out in a .

(d) Field trials on larger numbers of packages over several routes.

(e) Observations of performance in actual distribution. The proof of any package lies in its performance, in the field for which it was designed, over a relatively long period of time; only in this way can we fully evaluate the package or the material from which it is made.

Classifying methods of evaluation in another way, there are basically four avenues of approach:

(1) Comparative testing-to compare the unknown pack, component, material or product with one whose performance is known. This is often the simplest approach and can determine not only whether the unknown is better or worse than the known but also provide a measure of the degree of difference.

(2) Assessment testing-to simulate the events likely to be experienced in service and deduce, from the results, what may happen.

(3) Investigational testing-to determine where the strengths or weaknesses of the packaged product lie.

(4) Observational testing-to observe and/or record the performance in field trial actual distribution.

Journey hazards

Distribution system:-

Distribution systems exist in great variety and complexity, but however great the complexity, they may be considered to be combinations of a number ofsimpler elements. These simple elements are (a) The transport of packages from one point to another, with or without change of mode of transport (transport is considered to include the loading and unloading operations) and

(b) Storage. Points to be remembered are that the size, shape and weight of the outer has a considerable effect on the hazards encountered during a journey, and that different methods of transport give different hazards. Once it leaves the packaging line the package, and the product within it, will be subjected to a series of drops and impacts, crushing forces and vibrations, climatic and other environmental effects, before it reaches the point where the product is available for use by the customer.

The effect of environment on packages

To design packages, and to develop test sequences, we need to know what effects various environmental factors have, and in particular the effect of these factors at different levels, The following notes discuss these with respect to drops, compression and vibration.

Impacts

Impacts may be from dropping or by shocks from other goods coming into dynamic contact during handling, etc. The drop hazard has been investigated more than most other hazards, and Table gives an indication of the heights of drop which packages may experience in various handling systems. The drop hazard is usually studied by drop recorders placed in packages, which are similar in all respects, including weight, to normal packs. The instrument inside the package is calibrated by dropping on to a standard floor before the package is despatched with a normal consignment of similar packages. There are several types of instrument, from single drop counters (which only record that the package has been dropped above a certain height) to sophisticated equipment that records impacts in the three major axes of the package with a time base and provides a means of estimating the actual height and attitude of fall at . Such data obtained from instruments or observations often have to be interpreted to make a realistic, and not too complicated, test sequence. For example, how do three 100-mm drops followed by one 900-mm drop compare with four 300-mm drops in terms of the damaging effect on a case and/or itscontents? In both the total impact energy is the same, but will the effect be different? For several types of content, and for sacks and fibreboard cases, have been performed in which the package was dropped from constant height until a specified amount of damage was caused. Results of most such tests can be fitted by an expression of following type:

(No. of drops from height h2 to cause specific damage)/ (No. of drops from height hI to cause some damage) i.e N2/N1=(h1/h2)a

where the exponent a is usually between 2 and 3. If a = 2, and 36 drops from 150 mm produce failure, then 36 x (150/300)2, i.e. 9, drops from 300 mm will produce the same failure. In other words, 9 drops from 300 mm produce the same effect on the package as 36 drops from 150 mm. Thus, if a package has a series of drops, the cumulative effect is proportional to

(h1/h2)a + (h2/h1)a + (h3/h1)a + ………. +( hn/h1)a where hl is the height ofthe first drop of the package, h2 the second, and so on.

In addition to a knowledge of the drop heights likely in transport and distribution, the value of the goods, the number being transported in each consignment and other factors will also have a bearing on the degree of safety that a manufacturer may wish to apply.

Table - Typical heights from which packages may be dropped

Weight range (kg) Type of handling Typical drop height(m)

1-10 1 man throwing 1.0-1.2

10-50 1 man carrying 0.8-1.0

35-200 2 man handling 0.5-0.7

150-400 Handled by light equipment 0.4-0.6

Crushing

Crushing is generally caused by stacking loads and these may occur in warehousing or in transit. In the latter instance the packaged product is also subject to vibration from the vehicle at the same time. As far as warehousing is concerned it is usual to assume that the load is evenly distributed in a stack of cases whether or not these are palletized. Under such conditions the maximum load will be experienced by the bottom layer of cases and each individual case in that layer will be supporting a load equivalent to the weight of one case multiplied by the number of layers

W=(H/h-1)w

Where H = stack height, h = package height, w = package weight and W = the load to be supported. As might be expected, the effects of the time the stack will exist must be taken into account by the use of a safety factor. The assessment is more complex when the stack is vibrated at the same time, as it is during transport, but in general the height ofthe stack is limited here by the height of the transport vehicle and this is rarely greater than 2.5 m in road, rail and air transport. Stack heights in ships, however, can be much greater where deep hold storage is concerned. The load which a fibreboard case, for example, will support in a stack is not the same as its compression strength P measured under standard conditions. It is affected by several factors:

(a) The length of time the load is applied (b) The moisture content of the board (c) The way the load is applied to the case (i.e. profile and stacking pattern) (d) Previous handling of the package (e) Support provided by fittings and contents.

The compression strength determined by the standard method and needed by a batch of cases will be given by P = (n - 1) Wabcdef, where a-e are factors corresponding to items (a)-(e) above, and f is a factor to allow for the variability in strength of a consignment of cases, so that a weak case from the batch placed at the bottom of a stack is unlikely to collapse. All factors except e are greater than 1; if the case is required to take all the load, then e will be 1, otherwise it will be less than 1. Thus the required compression strength of the case is normally greater than the compressive load by a factor which usually lies between 1.5 and 5. The factors for moisture content, time of loading and, to a lesser extent, stacking pattern, are known fairly accurately but those for previous handling and internal support depend much more on the individual package and distribution system. Hence, actual stacking tests are often included in .

The vibration hazard

This can cause loosening of fastenings and components of items such as closures, abrasion of surfaces of items or print on packages, of cushioning materials, and, when combined with compression loads, more rapid failure of fibreboard cases at lower compression loads during transit. Generally, there is a lack of quantitative data on the effects of vibration on packages. An exception is the effect of compressive load and vibration on corrugated fibreboard cases. Vibration damage may take two forms. First, failure due to resonance and second, failure due to fatigue. All structures will vibrate; each has its own natural or resonant frequency which will depend on its mass and stiffness. When the frequency to which the packaged item is subjected is small, compared with its natural frequency, the effect is slight. Also when the exciting frequency is large (three or more times the natural frequency), the item does not have time to react and again the effect is small. It is when the exciting frequency is close to the natural frequency that effects become serious because in this range the exciting force pushes the vibrating part of the item at exactly the right time and in the right direction. This is analogous to a child's swing, where if the swing is pushed at the right moment the child goes higher or similarly when the hand is passed through water in a bath, back and forth at the right rate the water will soon be over the ends of the bath and on to the floor. At lower or higher rates these effects do not happen. In packaging we are only concerned with the vibrations that occur in transport systems and these are generally covered by testing [4J over the 1-100 Hz frequency range. Damage is most likely from vibrations in the frequency band 1-15 Hz because for many packages the resonant frequency of the packaged products falls into this range.

Package test equipment

Mechanical testing:-

Even when the climatic hazard is not regarded as relevant, package testing must be performed under standard conditions (see ISO 2206 or BS 4826 pt. 2). All packages should be tested in a controlled atmosphere, generally 23°e, 50% r.h.

Equipment to impact the package.

The variables here are the intensity of impact, which is dependent on distribution system, size of pack, etc., and the position of impact, which is selected from most likely or most vulnerable points. In drop-test equipment, impact intensity is varied by adjusting the drop height.

The equipment is of three basic types: (a) drop arm (convenient but limited capacity)

(b) sling and quick release (time-consuming) and

(c) releasetrap platform (erection time is long, difficult to operate).

All these have a specified floor as dropping surface. They can all be used as part of a sequence, or as single tests, such as the Bruceton Staircase technique to establish the critical drop height. Details are found in ASTM D 775 and D 997, ISO 2248 and BS 4826 pt. 4. In the inclined plane technique, the impact is varied by the speed at the moment of impact. The equipment consists of a 'dolly' running down a plane at 10° to the horizontal to impact a buffer across the track. This is generally used by impacting the faces and edges only as part of a test sequence, but suffers because of poor reproducibility between different (ASTM D 880, ISO 2244 and BS 4826 pt. 5). In the rolling test, the intensity of impact is fixed by the dimensions of the pack. No equipment is needed except a standard floor. It is used for packs in the 36-90 kg (about 80- 200 lb) range, and principally tests the efficacy of fittings (see ISO 2876 and BS 4826 pt. 11). In therevolving technique, impact and sequence depend entirely on pack dimensions, etc. The equipment is a 2- or 4-m (7- or 14-ft) drum fitted with baffles, which is used for comparative testing of packs of the same weight and shape. This is not much favoured now, since it cannot be used for comparing packs of different sizes and weight and it has a poor reproducibility .

Equipment to vibrate the package.

The variables here are frequency, amplitude, time, overload, and whether or not the pack is fixed to the platform. Equipment is of two types: fixed-amplitude, small frequency variation machines with overload (LAB), or variable-frequency and amplitude electrohydraulic-type machines. LAB machines are used in testing fatigue effects on packaging, fittings and abrasion of the product in normal test sequences. Electrohydraulic-type machines are used in testing effects of resonance frequencies on packaging and contents . The ISO and British Standards are both concerned with the fixed amplitude vibrators, but an International Standard for the more sophisticated vibration machines is under consideration.

Equipment to compress the package.

The variables here are the weight of the stack load, the method of supporting the load, and the time of stacking. The Stacking test requires a platform, weights, and a deflection recorder, and is used as part of a test sequence. The compression test controlling the rate of loading and measuring the load/deflection) is used to give quantitative results in short time .

Climatic testing

Cabinets and chambers.

These can be of two kinds: the injection type ( where relative humidity is maintained by a humidity-sensitive device controlling admission of moisture from an external source, and the non injectiontype (BS 3718), where relative humidity is maintained by circulating air over a selected saturated salt solution. The performance requirement limits for cabinets and chambers are as follows:-

Temperature variation (the difference in temperature between points within the working space at anyone moment) ± O.5degree celcius

Temperature fluctuation (changes in temperature within the working space at one point during 30 min)± 0.5.C

Long-term stability (difference in temperature at centre of working space over 72 h ± l°q.

Injection-type cabinets have an unlimited moisture supply; non-injection cabinets will not maintain conditions if the salt is no longer in solution (i.e. if all the water is evaporated). Non- injection systems are not suitable for large chambers, as these have a large temperature variation (at30°C, 90% r.h., a temperature variation of only 0.5°C causes a R.H change of 2.7%). It may be necessary to give the pack some preliminary mechanical handling testing before the climatic test, and it is important to examine seals, etc., to ensure the pack is properly formed and closed. In assessing overall performance of a package, the package is stored for a period (usually in a chamber) as part of a test sequence that includes simulation of other hazards. When testing fibreboard cases for compression strength under damp conditions, differences may arise through differences in R.H within the chamber. These may be corrected by measuring the moisture content of the board at the time of test.

SOME CLIMATIC TESTS ARE:-

1. RAIN TEST: - A stimulated rainfall of 4x1 inches per hour should be produced by a water spray nozzle designed to emit water in small droplets rather than a fine mist. The rainfall should be dispersed uniformly over the test area. Duration of the test is generally two hours.

2. SAND AND DUST TEST: - The purpose of sand and dust tests is to evaluate the resistance of a package to the penetration of sand and dust, to determine the erosive effects of blowing sand and dust, on exposed items and to determine the immediate effects as the malfunction of moving parts, by the presence of sand and dust. A standardized mixture of sand and dust of density 0.1 to 0.5gm/cu.ft is used to create an atmosphere for this. The temperature of this atmosphere is maintained at 77degree Fahrenheit for another 6 hours. A standard sand and dust velocity of 200 per min is maintained throughout the test unless an optional velocity of 2300 ft. per min. is specified.

3. SALT SPRAY TEST: - The purpose of the salt spray test is to evaluate the resistance of the package to by salt spray and to serve as a general standard for corrosion resistance. No correction exists between the test time and the natural exposure time. The package is exposed for 50 hours, to wet, dense fog generated by the automation of 20% water solution of Nacl .The solution shall maintained at a PH between 6.5 to 7.2, the temperature of the fog being maintained at 95 degree Fahrenheit.

4. RESISTANCE TESTS: - All materials used in the fabrication of shipping containers should be tested for fungus resistance.

10ml of distilled water containing approximately 0.005% dioctyl sodium sulfacuccinate is introduced directly into each culture. The culture is then raked with a sterile wire and agitated to insure a well sporated suspension. The test item is then placed in a humidity chamber and exposed to a relative humidity of 25% and a temperature of 86 degree Fahrenheit for 28 days, 25% or less of the samples or test items have fungus growth on more than4% of their exposed surface, the material is considered to be fungus nutrient. If 2% or less of the exposed surface is covered, the material is considered to be inert for fungus growth.

The foregoimg gives only a brief idea of a possible laboratory and fields tests. These tests gives the following coorelations to obtain a satisfactory picture on package performance.

1. A coorelation between the performance of the package in service and the laboratory transport test which reproduces in some degree the events which would happen to the package in the field.

2. A coorelation between the laboratory transport test on the package and tests on the empty container and any other component such as cushions etc. thus would enable the package maker to use simpler control tests on bulk production.

3. The third coorelation to be made is between the materials of construction and the containers.

In general, it might be said that all these tests would help to conclude:-

1. The overall durability of the container. 2. Any possible reduction in the cost of packaging 3. Improvements required in the design of the box to preclude damage in transmit 4. Adequacy of the cushioning used

In short, a series of tests would enable to determine the transport worthiness of the package.

REFERENCES:-

1. principles and practice, GORDON ROBERTSON , Third edition

2. Food packaging technology edited by RICHARD COLE

3.A handbook of food packaging 2nd edition by FRANK A. PAIN