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CLOSE THIS BOOKAppropriate Food Packaging (Tool)
2 Types of food and prevention of deterioration
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENT2.1 Food products that are suitable for small-scale processing
VIEW THE DOCUMENT2.2 Types of deterioration
VIEW THE DOCUMENT2.3 Extension of shelf-life
VIEW THE DOCUMENT2.4 Summary of the chapter

Appropriate Food Packaging (Tool)

2 Types of food and prevention of deterioration

In this chapter, one of the main reasons for packaging foods that was introduced in Chapter 1 - prevention of deterioration during storage - is covered in more detail. First the types of foods that are commonly produced by small to medium-scale processors are briefly described. This is followed by the main ways in which these foods spoil, together with other hazards that foods face during storage and distribution. The role of packaging in protecting foods against a variety of hazards is then described and the typical extension of shelf-life that arises from correct packaging is shown.

2.1 Food products that are suitable for small-scale processing

Some processed foods are not suitable for manufacture on a small scale and others have no local or regional demand. The factors that determine whether a food is suitable for production in a particular location are complex and inter-related. They are also specific to each production site. However broad guidelines on how to select the types of food that can be produced are as follows.

The selection of the type of food to process depends in part on the level of skill and experience of the staff that will do the production. Care should be taken with all low-acid wet foods, including meat products (especially sausages, burgers and pies), vegetable products, milk products (except yoghurt, butter and ghee) due to the risk of food poisoning. These foods require strict hygienic processing and an understanding by the operators of the risks involved. They should not be produced by inexperienced or untrained people.

Other products require the use of expensive high-technology equipment that is not generally affordable or repairable by small-scale producers. Examples include any low-acid canned foods (for example, canned meats, fish, vegetables, milk), hot-extruded snackfoods, carbonated (fizzy) drinks, homogenized or UHT (Ultra-Heat Treated) milk, solvent-extracted cooking oils and irradiated foods (the last is not legal in some countries). Some foods (for example, some baked goods and sugar confectionery) require a degree of flair, skill, imagination and experience to produce interesting and appealing products. Again these would normally only be produced by trained or experienced staff.

It can be seen from the above considerations that packaging is only one of the many factors that should be taken into account when setting up a business to process foods for sale. However because of problems of availability of packaging materials in many developing countries the problem of packaging assumes great importance. The methods used to select a product and the scale of production may need to be modified to take this into account. For example, the authors know of at least one food business in Africa in which the entrepreneur first found an available source of packaging materials and then designed a product that would suit it.

With these considerations in mind it is possible to analyse the factors that influence the likely success of a small food business and plan carefully to overcome any constraints. Typical questions that should be asked during the planning stage are shown in Table 2-1. In all cases, for a small business to be successful there should be:

- a good demand for the food, either locally or as exports to neighbouring areas or countries,
- supply of raw materials, ingredients and packaging materials,
- affordable, easily operated, maintained and repaired equipment,
- suitable infrastructure and facilities for processing and distribution of the selected food under hygienic conditions.

These considerations are shown as a 'decision tree' in Figure 2-1.


Figure

Questions to ask

How to find the answer

Who is the product aimed at?

Conduct a market survey

What is the demand for the processed food?

Conduct a market survey

Is there a health hazard associated with the food?

Consult a food technologist

What type of packaging is most suitable for the processor, distributor, retailer and consumer?

Conduct surveys, ask each group

Are all raw materials, ingredients and packaging materials available in sufficient quantities and at a low enough price when they are required?

Consult farmers, and suppliers to obtain prices, order sizes and plan ordering schedule

What is the expected scale of production?

Calculate from market surveys and resource availability

What is the expected profitability at the planned scale of production

Do a feasibility study

How much money is available to Invest in equipment and materials?

Consult suppliers or technical advisors

How will the food be sold

Have detailed discussions with potential distributors and retailers

What are the relevant regulations

Consult government authorities to find details of business registration, taxes(Ministry of Small Industries or equivalent) and food regulations, Ministry of Health, Food Standards

Table 2-1: Typical questions that should be asked during the planning stage

Taking these and other factors into account, Table 2-2 shows the foods that are commonly seen as suitable for production at the small scale. Short shelf-life products are those that are expected to be eaten within a few days of production. In general the following short shelf-life products are suitable for small-scale production because there is a good opportunity to add value to low-cost raw materials. There is often a good demand for such products and there are fewer packaging and distribution problems than occur with some other foods.


Table 2-2

2.2 Types of deterioration

The section above indicated the types of food that can tee processed on a small scale. The reasons for their selection are mostly concerned with the demand from customers (the popularity of a food) and the feasibility of small-scale production. If it is decided that there is a good demand for a food and that production is feasible, it is then necessary to make sure that processing adequately preserves the food for its expected shelf-life. An understanding of the various factors that cause food to deteriorate is helpful to ensure that the correct processing and packaging is selected. In this section the causes of deterioration of foods are first described and then the different roles of processing and packaging in preservation of the food are described.
The main causes of deterioration of foods are as follows:

- micro-organisms,
- enzymes,
- chemical changes due to water, heat, metals, air or light,
- contamination by soils, stones, insects etc.
- physical (or mechanical) damage.

2.2.1 Micro-organisms

All fresh foods have micro-organisms on their surfaces, often in enormous numbers, and these can grow rapidly to spoil foods. A main purpose of processing foods is to destroy unwanted micro-organisms. Packaging prevents recontamination and together processing and packaging prevent micro-organisms from spoiling the product during distribution and storage (that is to give the food the shelf-life that is expected).

Micro-organisms may be divided into general groups such as bacteria, yeasts or moulds, each of which may be further divided into sub-groups. Of the many microorganisms, the main types of interest are those that cause food spoilage and those that cause food poisoning.

When food is processed correctly, the number of spoilage micro-organisms and their activity is reduced and controlled at known levels. It is when there is a failure in processing conditions or packaging materials that spoilage micro-organisms can have an effect on the food. They can result in the food going mouldy, developing an off-smell or fermenting. The different types of spoilage depend to a large extent on the nature of the food and in particular its acidity and its moisture content.

Food poisoning is mostly caused by bacteria. These are also controlled by the acidity and moisture content of a food as shown in Table 2-3.

Food poisoning micro-organisms may grow in low-acid foods. Heat processing to 121°C for 15-50 minutes in jars or cans is required to destroy these micro-organisms.

Such heating requires the use of pressure cooking and detailed technical knowledge. For these reasons it is strongly advised that these foods are not produced by small-scale processors, especially as a first venture.


Acidic or dry products

Low-acid products

Will support the

Moulds and yeasts

Many types of

growth of:


bacteria (including



food poisoning types)



and moulds

Production errors

Surface mould

Food poisoning

can cause:

growth or

especially from


fermentation. Low

canned


risk of health

vegetables or fish,


hazard

meat products

Examples of the

Fruit juices,


product:

yoghurt, jam dried



fruit


Table 2-3: Microbial growth on different foods

2.2.2 Enzymes

Enzymes are naturally occurring proteins that act on foods to cause changes in flavour, colour or texture. There are many hundreds of different enzymes but some of the more important spoilage changes include softening of fruits, rancidity of oils, browning of cut fruit or root crops and loss of green colour in vegetables. In general enzymes are either destroyed by heating or prevented from acting by changing the acidity or water content of the food.

2.2.3 Water

Enzymes and micro-organisms can only spoil foods if water is present. If the water is removed or made unavailable they cannot act. Different foods have different water contents (Table 2.4). Some, for example grains, are relatively dry when harvested and these can be easily preserved by removing the remaining water by drying. Other fresh foods such as fruits, vegetables and meat have a much higher water content and this should be made unavailable by either drying or concentration (water removed) or by freezing (water held as ice, which together with the low temperature, prevents micro-organisms and enzymes from acting).

However, removing water only prevents the action of enzymes and micro-organisms, it does not destroy them They can act again when water returns, for example during re-hydration of dried food, thawing of frozen food. Foods are therefore often heated (blanched) to destroy some of the enzymes and micro-organisms before drying or freezing.

Fresh food

Water content (%)

Shelf-life at room


temperature (days)


Fruits

80 - 95

1 - 30

Meat/Fish

55 - 70

2 - 7

Vegetables

75 - 90

2 - 20

Grains

8 - 14

more than 175

Table 2-4: Water content of some foods

The normal moisture content of a processed food should be maintained during storage. This is a main function of packaging for some foods. If the moisture content falls below an acceptable level in moist foods, the food dries out, shrivels and is seen as spoiled by consumers. Similarly if the moisture content of a dry food is allowed to rise above an acceptable level it will first lose its crispness and become unacceptable to consumers, but it may also gain sufficient moisture to allow micro-organisms to grow and cause further spoilage. The acceptable range of moisture contents is different for each processed food and for some it is a critical factor. Table 2.5 shows some foods that require careful control of the moisture content by processing and packaging to maintain their quality.

2.2.4 Heat

Food

Moisture contents (%)

Cooking oil

trace

Sugar

trace

Snack foods

1 - 5

Biscuits

2 - 6

Sweets

trace -10

Dried fish

5-10

Flours

12 - 14

Dried fruit

15 - 25

Honey

18

Jam

30 - 32

Tomato paste

55 - 65

Table 2-5: Foods that require careful control of the moisture content

Higher temperatures increase the rate of spoilage by micro-organisms and enzymes, up to a maximum above which they are destroyed (Figure 2-2).


Figure

When foods are heated above 60°C most enzymes and micro-organisms are destroyed - the higher the temperature the faster they are destroyed. This is one of the easiest methods of preservation and includes boiling, frying, baking and pasteurization. However, cooked food can be easily re-contaminated if it is not properly packaged.

Heat can also spoil packaged food. It can melt fats, cause a loss of texture or flavour and cause more rapid changes such as development of rancidity in oils and movement of moisture within a food which in turn leads to spoilage.

2.2.5 Light

Sunlight contains ultra-violet (UV) rays which cause rapid deterioration of some foods (especially oils and fatty foods) or specific components of a food such as certain vitamins. UV can also cause packaging materials to fade or to become brittle and lose their properties (for example polythene in Section 3.2.2). In general all foods should be stored in the shade away from direct sunlight. Electric lights do not have the same effects on foods because they do not contain the UV component.

2.2.6 Air

Some foods, especially those that have a high fat content or those with delicate flavours and aromas, are susceptible to oxidation (attack by air which causes off flavours to develop, known as rancidity). Biscuits, cooking oils, dried fish and other fatly foods are liable to spoilage by rancidity. These foods should therefore be protected from contact with air by storing them in airtight containers.

2.2. 7 Contamination

Foods are often contaminated when harvested or slaughtered and most processing involves a cleaning stage to remove these contaminants. However foods may also be contaminated after processing and this is more serious because the contamination will not be removed before the customer buys the food. The main types of post-processing contamination and possible sources are shown in Table 2-6.

Contaminant

Possible source

Hair

Operators, animals

Dust, soil, stones

Workplace, equipment,


transport

Bacteria, moulds

Air, operators, animals,


insects, birds, dust

Excreta

Animals, insects, birds

Oil, grease

Equipment, transport

Wood, glass, paper, cloth,

Workplace, transport

leaves etc


Metal

Equipment, workplace,


transport

Insects

Air, workplace,


transport

Table 2-6: Types of post-processing contamination and possible sources

One of the main functions of packaging is to protect foods against contamination from the time it has been processed until it is consumed. It should be noted that the contamination described before is accidential contamination. Contamination that is done deliberately to increase profitability or from malice is named adulteration. Packaging that is intended to prevent or reveal adulteration is described briefly in Chapter 3.

2.2.8 Mechanical damage

Foods are frequently fragile and easily crushed, scratched, split or otherwise damaged during storage and distribution. Damage is caused in four ways:

- by pressure such as that caused by stacking or piling foods too high,
- by impact from hitting or dropping the food,
- by vibration from transport,
- by foods rubbing against each other or against container sides.

Another main function of packaging is to minimise these types of physical damage to foods during transport and storage. This type of packaging is often known as a shipping container and these are described in more detail in Chapter 4. A summary of the different roles of processing and packaging to prevent deterioration described above is shown in Table 2-7. The factors that affect the shelf-life of foods and the protection offered by different packaging materials are shown in Table 2-8.


Table 2-7


Table 2-8

2.3 Extension of shelf-life

The section above describes the processing and packaging that is needed to preserve foods for their expected shelf-life. It also indicated that for different foods the importance of packaging can vary from simply keeping foods clean to being the main factor that controls the shelf-life. It was noted that for many foods the humidity of the climate in which the food is stored is one of the most important considerations.

In the following section the actual extension of shelf-life for different foods is shown for two types of climate. Readers should note that the data given is indicative only and that shelf-life will vary according to the local storage conditions used. Table 2-9 indicates the likely extension of shelf-life of the foods to be achieved by proper packaging.


Table 2-9

2.3.1 Short shelf-life products

Baked goods

Breads and cakes are normally sold by small-scale bakers within a day of baking to retain the fresh baked flavour and odour and the correct texture. Staling takes place rapidly at tropical temperatures and leads to a toughening of the crumb and, in some breads a softening of the crust. The changes happen in both humid and dry climates but additionally there may be drying out of some products in dry climates. Because of the short shelf-life packaging is mainly used to keep these products clean and it is not used as a barrier to moisture or air.

Clean paper (for example tissue paper) is an adequate packaging material, but old newspapers should not be used because the ink is poisonous. Plain or coated cellulose is likely to be too expensive for most small bakers and is not needed if the products are to be consumed on the day of production or the following day. Polythene bags are used by some bakers to give a 'more attractive' or 'professional' image. If polythene is used to wrap baked goods, care should be taken to allow them to cool to room temperature after baking. This will prevent moisture condensing on the inside of the bag and wetting the surface of the food. If this is allowed to happen it will result in mould growth at the wet spots as well as a loss of the required texture in these places.

Snackfoods

Many snackfoods are produced by small-scale entrepreneurs for immediate consumption as 'streetfoods' and these are rarely packaged except for a container to hold the pieces together and keep them clean. In particular some fried foods cannot be stored for more than a few hours because migration of oil softens the crisp crust of such foods and spoils their texture.

Others snackfoods are sold in packets with an expected shelf life of a few days to several weeks. These include puffed and toasted cereals and fried legumes/cereals in such products as 'Bombay mix'.

The main causes of spoilage are moisture pickup in humid climates, which leads to softening of the products within a few hours, and rancidity which develops over a few days or weeks depending on the type of oil used for frying and the storage conditions. Packaging should therefore be used to prevent moisture pickup in humid climates and also prevent air and light from reaching the product in both humid and dry climates to restrict the development of rancidity. As these products tend to be fragile the pack should also protect against crushing and other types of mechanical damage. It is usual to use a barrier film such as polypropylene for sealed bags of product and a cardboard box to protect against light and mechanical damage.

Dairy products

Pasteurized milk depends on both the heat treatment of pasteurization and post-processing cooling to maintain its shelf-life. Packaging should be sterilized to prevent contamination after processing but its main function is to contain the milk and keep it clean.

Spoilage is mostly due to micro-organisms that survive pasteurisation and these then cause the milk to sour after a few days. Spoilage may also be due to rancidity and loss of some vitamins, which is accelerated by sunlight. During distribution and storage the milk should therefore be kept cool and away from direct sunlight to achieve the expected shelf-life. Polythene bags are commonly used because they have lower costs than other packs. These are adequate if the milk is carried home by the customer and used straight away but they are less successful if the milk is distributed to retailers first. Reusable glass bottles with foil lids are used in some countries as a relatively low cost package. To be economical there should be a high rate of bottle return (usually above 90%) and particular care is needed to ensure that returned bottles are thoroughly cleaned and inspected (Section 3.1.1).

Yoghurt should be stored and distributed in a similar way to milk to give a longer shelf-life. Here however the higher acidity delays spoilage by micro-organisms and extends the shelf-life by several days compared to milk. As a result there is less need for cooling but the product should be protected from sunlight to prevent development of rancidity. Packaging is mostly to contain the yoghurt, keep it clean and insect free and keep out sunlight. Clay pots, and plastic pots are most commonly used. These may be unsealed or covered with a cloth or film. Plastic pots may also be heat-sealed with a foil lid.

2.3.2 Medium/long shelf-life products

Dried foods

The shelf-life of dried foods depends mostly on the relationship between the individual product and the humidity of the air during storage. Foods that are in equilibrium with the surrounding air will neither gain nor lose moisture and, provided that their moisture content is low enough to stop micro-organisms from growing, they will remain stable.

Foods that are traditionally dried in a particular area are suited to the local conditions and will remain stable for long periods with very simple packs to contain the food and keep it clean. However there are situations in which a dried food needs to have more elaborate protection if the humidity in an area changes (for example at the beginning or end of a rainy season), if the food is moved to another area which has a different air humidity, or finally if a new food is dried in a particular area. These are all reasons why packaging is needed to form a barrier to moisture.

Changes in humidity affect dried foods in one of two ways: if the humidity increases the food becomes more moist and this may then allow micro-organisms to grow and spoil the product. This also happens if the food is allowed to become wet from rain during storage. The food also becomes softer and the change in texture may also be seen as spoilage in some foods (for example snackfoods and biscuits). If the humidity falls this will cause the food to dry out further. For most foods this does not result in spoilage, but in some (for example some dried fruits) sugars may crystallize, the texture may harden excessively and the product may be seen as spoiled.

It can be seen from Table 2-9 that the benefits of packaging are substantial for some dried products, particularly in humid areas where the package should provide a barrier to moisture. Many dried foods are susceptible to rancidity and for these a barrier to air and light is needed. Many dried foods are also fragile and easily broken. They are therefore packed in cartons or boxes to give protection against mechanical damage. Products stored in dry areas do not benefit from an extension of shelf-life by packaging and the pack is simply used to contain the food and keep it clean.

Sugar preserves

These products are stable for long periods without packaging due to their high acidity and high sugar content. Packaging is mostly used to contain the product, keep it clean and prevent contamination from insects that are attracted to the sugar. Care needs to be taken that the temperature of the preserve is at 80 - 85 °C when it is filled into containers. If it is higher, steam from the product may condense on the inside of the lid and moisten the surface of the preserve. This dilutes the product and may allow mould growth If the temperature of filling is too low it is more difficult to pour the preserve and a partial vacuum will not form in the container headspace (Section 3.1.1).

Acid and fermented preserves

Here preservation is achieved by the combined effects of salt, acid and sugar. In acid preserves, added vinegar (acetic acid) is used whereas in fermented preserves lactic acid is formed by the bacteria used in the fermentation. The proportion of salt, acid and sugar can be changed within limits to suit local tastes, but any decrease in one should be compensated for by an increase in the others. Acetic acid (in acid preserves) is volatile and the container should therefore be airtight to prevent it escaping and allowing mould growth Fermented preserves contain lactic acid which is not volatile. Here the packaging does not have a major effect on the shelf life of the preserve and is simply used to contain the food and protect it from contamination.

Beverages and fermented beverages

Fruit juices and nectars which are intended for immediate consumption after opening rely on pasteurisation for their preservation. The package is therefore used to protect the juice from re-contamination by micro-organisms and maintain its shelf life. For squashes and cordials that are diluted with water before drinking, preservation is achieved by a high sugar content, by pasteurization and by added chemical preservatives. Here the package is opened and the contents are used over a long period, a little at a time. The package therefore has no preservative effect and is simply used to contain the food and keep it clean and free of insects that are attracted by the sugar.

Wines and spirits rely on a high alcohol content and a high acidity for preservation. However in these drinks the flavour components and the alcohol itself are both volatile and also able to react with air to produce off-flavours. The packaging should therefore be airtight. In some products, particularly wine and beers, there may be chemical changes caused by sunlight and the packaging in this case should also be lightproof. Glass is the preferred packaging for each type of product because it is inert. If necessary coloured glass can be used to protect against light. Other containers, such as metal or some plastic pots and bottles, may react with the beverage and create off-flavours.

Sugar confectionery

The main cause of spoilage for most types of confectionery is moisture pickup which softens the sweet, dilutes the sugar at the surface and leads to yeast or mould growth. This is related to the humidity of the storage air and the effects of this are similar to those described above for dried foods. A barrier film such as cellulose or polypropylene is used to form sealed bags and cardboard carton used to protect softer confectionery from mechanical damage. Chocolate is an exception in that the high fat content makes it more susceptible to spoilage by high temperatures or by rancidity. High temperatures (above 35°C) cause movement of the cocoa butter or vegetable fats to the surface of the chocolate where they appear as a white 'bloom'. This is harmless but is unacceptable to most consumers and effectively spoils the food. Aluminium foil or metallized film is commonly used to reflect heat from chocolate and cardboard boxes provide additional heat insulation as well as protection from mechanical damage.

Syrups, honey, pastes, purees and oils

In each case these foods rely for preservation on their low moisture content and in some cases, high acidity. They are mostly stable at a wide range of air humidities and packaging is therefore used to contain the products and keep them clean. Some products such as cooking oils, peanut butter and other nut pastes, have a high fat content and are therefore likely to go rancid if storage conditions are incorrect. In these foods the shelf life is increased by using an airtight and lightproof container. Care is needed when packaging fatty products in some types of plastic pots or bottles as there is a risk of migration of chemicals from the plastic into the fat. This produces off-flavours and is a potential health hazard (Section 3.1.4).

Essences/flavours

The main economic value of these food components is their volatile flavours and aromas. They rely entirely on the package to contain these flavours and aromas, and because of the high value of these products it is often worthwhile to use a more expensive package. These products are also susceptible to rancidity and the package should be lightproof and airtight. Metal cans and glass bottles are the only suitable containers for these products.

Dairy products

Cheese, butter, ghee and khoa rely for their preservation on a reduced moisture content. The shelf-life is also extended by cool storage. Packaging does not contribute significantly to the extended shelf-life and is mostly used to keep the foods clean and free of contamination. Simple packages such as plastic film, waxed or greaseproof paper are commonly used. Polythene is commonly used in developing countries but this should be discouraged for long-term storage because of migration of chemicals from the plastic into the fatly food. Some cheeses are dipped into edible wax which provides a protective coating and extends the shelf-life.

Baked goods

Biscuits and some types of cake are preserved by their low moisture content and for a long shelf-life, they should not gain nor lose moisture. They are therefore subject to the same factors that are described for dried foods above. When packaged for the humid tropics they require a moisture barrier and because of their often high fat content, they should also be protected from rancidity by a lightproof and airtight package. Plastic films such as polypropylene or coated cellulose together with a cardboard carton to resist mechanical damage are satisfactory. In dry climates glass jars, metal boxes or plastic tubs are suitable for protecting these products from breaking and for preventing contamination. Polythene should not be used for long term storage due to migration of chemicals into the fats contained in these foods.

Frozen foods

In the context of this publication, the only frozen food being considered is ice cream and this should not be stored by small-scale producers for more than a day or so. It is usually kept in a freezing box and is sold directly to consumers. No packaging is therefore required other than to contain the product.

Smoked foods

Smoked fish and to a lesser extent, meats and vegetables, are preserved by their low moisture content, the chemicals from the smoke and by added salt. They are essentially dried foods and as such are subject to the same factors that are described above for dried foods.

A summary of the packaging options for the groups of food described above is shown in Table 2-10.


Table 2-10

2.4 Summary of the chapter

In Chapter 2 the reasons why some foods are more suitable than others for small-scale processing were first described. These included business and technical considerations and a list of suitable foods was drawn up, indicating the principle of preservation, expected shelf-life and packaging requirement for each food. The main causes of deterioration of these foods were then described and this was followed by the ability of different types of packaging to protect the foods and extend their shelf life. Finally the chapter concluded with a description of the packaging options that are available for processors to use when making the foods described. In the next chapter the properties and methods of use of individual packaging materials are described in detail.

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