QUALITY CONTROL AND SIGNIFICANCE OF TESTING
Sunder Packages Quality Control means the control of “goodness” or the “Excellence” of a product. In this ever-changing pattern of producing and making things, if “Quality” of a product is not maintained then it is difficult for the product to survive. Selection of raw materials to the assessment of finished product; this entire chain of functions is effectively linked through quality control. Unless a job is thoroughly and continuously checked for quality, at the strategic stages, it is never possible to always get a good quality finished product. Quality control increases output and reduces breakdown. It seeks to ensure that the finished products conform to the specified standards of performance, utility and reliability. Hence, in any field today, quality control has become an indispensable tool of modern management.
Total quality control can be divided into two components as follows:
- Product quality control
- Packaging quality control
Packaging quality control involves three main stages namely:
- Quality control on incoming raw materials
- Quality control on in-process materials and
- Quality control on finished products
The quality control is a system encompassing specifications, inspections, analysis and recommendations. It should be regarded as an inbuilt characteristic of a package and the quality implications should begin right at the procurement stage. It is important because a substandard material creates immense problems at the production stage resulting in a large amount of defects. A correct approach is that the quality aspects should be considered at the designing stage itself. While developing a package, a proper approach would be to take into account the limits within which the material is expected to perform should be defined. It is important to strike a balance between cost of product and packaging material, understand production costs and material performance so as to arrive at an optimum cost. Therefore, true quality control should be inherent in the material and its adaptability to the operations becomes only a measure of quality control, which measures it as a routine shop floor operation. Checking and controlling of quality for any packaging material is a prelude to ensure that the performance of the packaging material is up to the mark. Therefore, before specifying any standard, it becomes essential to study the various parameters that control the performance of a packaging material at various stages of its existence.
A large number of parameters are important when one has to identify the type of tests to be selected and their significance with the end use requirements. The tests selected should be simple and quick to perform as well as have proven results in numerical values, which are easy to read and interpret. These quality control tests are carried out for comparative purposes, between similar materials or for assessment of a given material against a specific requirement or for investigational purposes with regard to performance of a material or a container.
Testing becomes necessary even in case of established materials and applications as all men and machines are fallible and liable to vary in performance and hence the need to detect the unacceptable deviations, as quality control measure is of paramount importance.
Due to increasing consumer protection legislation and higher safety standards,more testing is needed. Very often investigation testing is needed for:
- A new product – Established packaging for a new product formulation
- A new material – New plastic film for existing product
- A new application – Over-wrap film for shrink packaging
It is less costly to change/ modify material / design at the development stage by generating adequate data by testing, than at a later stage due to under or over designing.
In packaging, it is the performance required by the product to be packaged in its particular marketing environment. In order to carry this matching of properties against requirements, it is necessary to know what the various properties actually mean in practice and to have some method of quantifying them. Testing is also important for other reasons like evaluating a new product. Test results also help in making changes in new materials and processing variables specifications to be setup.
Testing is also essential for establishment of proper specifications for procurement and quality control of incoming material. The packaging specification is an effective information about all properties and special features of packaging materials and packages. The properties of packaging materials play an important role to establish optimum packaging specification.
Properties of packaging materials like plastics, paper are affected by variables like temperature and humidity. Their sensitively to temperature, light and humidity is due to their chemical nature. It is, therefore, necessary that test pieces should be subjected to standard pre-conditioning to bring them into an equilibrium state within a specified atmosphere.
The plastic packaging materials are broadly classified as flexible, which covers films, laminates, woven fabrics; semi-rigid, which cover extruded and lamitubes and rigid packages, which include moulded, blow moulded, centered and thermoformed products as well as material handling products such as crates, pallets etc.
There is a wide range of properties to be considered while selecting plastic materials for a particular purpose. The tests for plastic packages can be classified into three broad groups.
This group covers basically the physical strength and performance properties of packages on converting or packaging equipment. The different properties are thickness, tensile & elongation, heat seal strength, bond strength, hot tack, shrinkage, flex resistance co-efficient of friction, pin holes, de-lamination, identification, leakage test, dart impact, seam strength, environmental stress crack resistance, closure leakage test, adhesion test, torque test.
Besides the above, tests which are carried out for ascertaining the quality of the packaging material or its conformity to laid down specifications, there are some other studies which are of great significance while developing packaging systems or selecting packaging materials for food products. These are:
- Extractability / migration test
- Shelf-life Determination and Compatibility test
They are discussed later in the chapter.
Appendix Table 1 at the end of the article, gives significant tests for plastic packaging materials and packages.
Universal Testing Machine ,Dart Impact Tester ,Differential Scanning Calorimeter
Some of the important tests and test equipment of plastic packages are discussed below:
1) Name of the test
Standard No Equipment used Units used for results
2) Name of the test :
Standard No Equipment used Units used for results Significance
: Caliper / Thickness
: To check conformity of thickness to desired specification. It is an important property affecting mechanical properties, sealability, barrier properties, performance, etc.
Tensile Strength and % Elongation
: It is a mechanical property significant in high-speed operations. By knowing the amount of deformation (strain) introduced by a given load (stress), it is possible to predict the response of the material under end-use conditions. Tensile strength is the maximum tensile stress, which a material can sustain and is taken to be the maximum load exerted in the film specimen during the test divided by the original cross section of the specimen. Elongation is usually measured at the point at which the film breaks and is expressed as the percentage of change of the original length of the specimen between the grips of the testing machine. Its importance is a measure of the film’s ability to stretch. During the unwinding operation, elongation is an important property. Too low an elongation is dangerous as any sudden imbalance in the unwinding operation could lead to breaking of the film. A certain amount of tension is necessary during the unwinding operation so that films with low yield strength are in danger of being stressed beyond their yield point.
- Climatic conditions
: Hot Tack Strength
: Universal testing machine (INSTRON)
: It is the critical factor in selecting sealant layers in applications such as vertical form / fill / seal lines where liquids and other substances may contaminate the seal area. Testing is done while the seal is still hot.
: As a result of manufacturing process, internal stresses are locked into the film and this can be released by heating. For any given type of film the temperature at which shrinkage will begin are related to processing techniques.
: Flex Resistance
: Gelbo flex tester
: No. of Cycles
: This test determines the resistance of flexible packaging materials to flex-formed pin holes. The resistance to repeated flexure or creasing is important. Some films are highly resistant whereas others will fail by pinhole or total fracture after bending only a few times. In essence, the resistance to bending is measured by repeatedly folding the film backwards and forwards at a given rate. The number of cycles to failure is recorded as the flex resistance. With tough and flexible polymer films, even a large number of flexings may be worth running the test on various thicknesses since a thicker film may show failure at a relatively low number of flexings. Even if failure does not occur, certain properties of the film may be seriously impaired. Permeability
In certain applications, high clarity and minimal haze or frostiness is desirable. This is the case in many packaging applications where good clarity enhances and the polymer structure diffuses light as it passes through film and cause hazy appearance. The hazemeter is setup to transmit a beam of light, which is diffused or scattered from its original path. The results are reported in terms of percentage haze. The lower haze, the better the clarity of the film.
Specular gloss correlates to the shine or sparkle of film. This trait can influence desirability of consumers to purchase the product packed in it. Gloss in film can be optimised by adjustment of extrusion parameters. Once processing conditions are perfect, changing resins to a higher melt index and higher density at constant molecular weight distribution, will yield in better gloss.
The list of different tests and their relevant IS, ISO, ASTM, BS, TAPPI Standards are given in Appendix Table 2 at the end of the article.
Shelf-life and Compatibility Studies
The term “Shelf-life” is generally understood to be the duration of that period between packing a product and using it, for which the quality of the product remains acceptable to the product user. An attempt to predict this period from data on the product, the package, the distribution and storage conditions is appropriate, where, alternative packaging materials are available which contribute positively (but to different levels) to the extension of shelf-life of the packed food product.
Shelf-life prediction is appropriate or required when the package is permeable or semi- permeable to atmospheric agents like water-vapour or/and oxygen. In the case of
impermeable containers such as tinplate containers and glass jars, it is not necessary to predict shelf-life. However, in such cases it is to be assumed that the seams and the closures of the packs are perfect. Metal containers, glass bottles, aluminium foil are used mainly for their being an absolute barrier against moisture vapour and gases. However, compatibility of metal containers with specific food items need to be ascertained and wherever necessary, suitable lacquer coatings may need to be provided to achieve product- package compatibility. The lining materials/wads of the closures/caps in glass jars also should be compatible with the packed food product.
Though polymeric packaging materials are not absolute barriers against moisture vapour and gases, they have been found to be increasingly useful due to various advantages like light weight, easy to carry, easy to transport, handle and stock.
The most important function of the package is to contain the
product and providde protection against changes in quality caused by adverse effects of surrounding environment. The selected packaging material has to be compatible with the product to be packed and should provide specific protection to maintain shelf-life i.e. quality preservation as well as economic considerations and competitive packaging. All these are taken into consideration in design and selection of a packaging system.
Shelf-life determinations help in:
- Selection of a package for a new product, which could
be optimum i.e. provide the desired shelf-life period at the most economic cost.
- Selection of an alternative package for an already marketed product, either to extend the shelf-life or to reduce the cost by using newer materials.
- Government requirement for open dating, declaration of “Best before date” assures the consumer of wholesome, nutritious, safe food.
Food Degradation Factors
For shelf-life determination studies, it is important to understand the mechanisms of food deterioration or degradation, and the factors for the same. From the time a food product is manufactured and packed, the process of degradation commences. Protective plastic packaging slows-down some of the reactions due to the action of light, moisture, atmospheric oxygen, etc. There are many identified food degradation mechanisms, the major ones being, the gradual loss of colour, texture, flavour and nutrients. Such deteriorative changes could be due to:
Storage studies can also be carried out at cyclic conditions. For the purpose of creating the storage conditions, humidity cabinets or environmental walk-in-chambers are used at IIP.
During the exposure period, the packages are withdrawn at fixed intervals of time to assess the quality of the product as per the product quality attributes laid down earlier. This is continued till the product becomes commercially unacceptable i.e. degradation occurs of the primary product quality attribute. To assess the product quality, organoleptic testing or sensory evaluation is also required to be carried out. The details of sensory evaluation are discussed later in the chapter.
When the packages are withdrawn, besides assessment of the product, checks are also made on the packaging material/package to observe for any softening/delamination/cracking, opening of seals, discolouration, surface stickiness etc. These checks help to establish the product-package compatibility, which is of prime importance for any packed product.
The results obtained on the assessment of the product quality and the package are tabulated and analysed for overall acceptability. Based on the analysis, shelf-life of the product in a particular package is determined. The ultimate selection of the packaging material or method would be governed by the marketing requirements and the economics of the packaging system.
Sensory Evaluation of Foods for Shelf-life Determination
A number of quality assurance procedures are used to examine and maintain the quality of a food product at different stages starting from receipt of the raw materials up to the finished product. These tests are physical, chemical, microbiological and sensory. Amongst all these methods, sensory evaluation is of paramount importance. The sensory quality has to be included in product evaluation since it is the only integrated multi-dimensional measurement. The sensory evaluation procedures have been studied in considerable details with the result that this scientific discipline has come to be recognised as fairly objective in nature (Larmond, 1987). The inherent variability of sensory evaluation by human subjects can be generally overcome through appropriate selection and training procedures, coupled with application of statistical methods so as to take full advantage of the high sensitivity of human sense organs that even today surpass the most sophisticated instrumental means for flavour, texture and colour examination (Ogden, 1993).
A successful implementation of sensory evaluation programme for shelf-life determination requires proper laboratory facilities, trained sensory panels and adoption of appropriate sensory methods. card comprising of different attributes, often the total score is taken as the “overall acceptability” of the product.
Different sensory tests coupled with relevant statistical methodologies make sensory evaluation an important tool for shelf-life determination.
Several successful attempts have been made to develop shelf-life prediction models for various food products, each relying heavily on a sound sensory evaluation technique.
A study conducted by IIP on shelf-life of “Rabri” using 9-point Hedonic Scale method for Sensory Evaluation is summarised at the end of the chapter.
Shelf-life Prediction by Formulae
Prediction of shelf-life of moisture sensitive products is carried out by using equations/ formulae. These are based on various theories by different people. The most simple one is described here. The prediction of shelf-life based on formulae, requires the determination of the moisture absorption isotherm of the food product.
Moisture Absorption Isotherm
The water content of a foodstuff or other moisture-sensitive product, and the relative humidity (or water activity) with which it is in equilibrium, are linked by a characteristic curve for the product. If the product is placed in an atmosphere with which it is not in equilibrium, its
moisture content will alter to bring it to equilibrium. The final moisture content usually differs for a given relative humidity, depending on whether the product has lost or gained moisture to reach equilibrium.
The experimental technique to obtain the water isotherm has been standardized following the COST 90 project of the European Cooperation in Scientific and Technical Research (Jowett, 1984). Saturated salt solutions are used in temperature-controlled enclosures to provide air of known relative humidity. Quantities of the product are exposed in these
enclosures until weight equilibrium is established.
Extractability/ Migration Studies
Plastics are a large comprehensive family of materials with very wide range of properties to meet almost every requirement of the packaging industry. Plastics being synthetic materials can be tailor-made to cater to a specific need or combination of performance requirements. “Plastics are an essential and enduring form of packaging”. It is no coincidence that around 50% of food in Europe is packed in plastics, whereas in India it is estimated to be around 15% to 25%.
Different types of plastics used in food packaging are polyethylenes (LDPE, HDPE, HM- HDPE, LLDPE), Polypropylene, Poly Vinyl Chloride, Polyester, Polyamides, Ethylene Acrylic Acid (EAA), Ionomers, Polycarbonate and their co-polymers. These materials may be used in different forms such as monofilms, co-extruded films, laminates, wrappers, pouches, injection/ thermoformed containers, blow moulded/stretch blow moulded jerry cans/ containers and bottles, drums, woven and knitted sacks, etc.
Plastics, in addition to the basic polymers derived from the petroleum industry, also contain some chemical components or additives, which are added in a small amount during manufacture and processing to impart desired properties to the polymer or to aid in their processing. These may be anti-oxidants, anti-blocking agents, anti-static agents, stabilisers, plasticizers, pigments, fillers, antislip agents, etc. The plastic packaging materials may also contain small amounts of monomers, oligomers, catalysts, polymerisation residues etc. These substances are generally low molecular weight components.
The polymers themselves, being of very high molecular weight, are inert and of limited solubility in aqueous and fatty systems and are unlikely to be transferred into food to any significant extent (Crosby, 1981). Even if fragments were accidentally swallowed, they would not react with body fluids present in the digestive system.
The low molecular weight substances and additives possess high mobility and therefore there is a likelihood of their transfer (migration) from the packaging material into the package contents, thereby contaminating the food with a possible toxic hazard to the health of the consumer. Therefore, guidelines for proper use of plastics for food packaging applications have been realised and threshold limits have been laid down. This threshold approach has been found to be an excellent model, by which majority of plastics materials are evaluated, and on the basis of which food grade application certificates are issued.
For regulating the use of plastics in food packaging, most of the countries have formulated standards and codes for the manufacture and use of plastic materials in contact with foodstuffs, suitable to conditions and situations in the country. In our country, the Bureau of Indian Standards (BIS) has also formulated standards to regulate the positive list of constituents and their specifications for each of the plastics for its safe use in contact with foodstuffs, pharmaceuticals and drinking water.
Significant Tests for Plastic Packaging Materials/Packages
Pin holes Tearing Gauge variation Wrinkles Odour
of polymer Tensile strength Elongation at break
Dart impact Coefficient of friction
of polymer Identification
strength & % elongation
Dart Impact test Extractibility studies
Thickness Identification of polymer Heat shrinkage (MD, CD )
Thickness Identification of polymer Tensile strength Elongation at break
Thickness of each layer Identification of polymeric substrate Peel bond strength
Heat seal strength
Odour pick test
Extractability studies (food grade) Flex durability
Water vapour transmission rate Oxygen transmission rate
Heat shrinkage (Shrink films) Elongation at break
Tensile breaking load
Print quality Dent at nozzle
Dirt / Dust
Vacuum leakage test
Barrier properties (WVTR & OTR)
Workmanship & finish Thread condition Denting (Metal)
Identification of plastics
Environment Stress Crack Resistance Compatibility of wad to product Torque test
Pressure Sensitive Self-Adhesive Plastic Tape
Rough-cut edge Dent at core Dust deposition Easy peelable
Thickness of plastic films Thickness of adhesive Identification of plastic film Adhesion strength to steel Tensile breaking load
Flexible Intermediate Bulk Container (FIBC)
Size and weight Tensile strength Top lift