Food processing

1. Introduction

Food processing, preservation, and packaging are important activities to prevent food loss, and to increase food palatability, transportability, and shelf life and thereby ensuring sufficient availability of food yearround. Improperly stored food can cause foodborne diseases if consumed and result in revenue loss. An estimated 15% of food produced is lost post-harvest. The different traditional and modern preservation techniques help to maintain food quality and safety during storage.

Processing includes mechanical, chemical, and thermal methods to transform raw ingredients into food or other intermediate products. Processing increases the variety of food products available and makes them more convenient to the consumer. Some commonly used food processing methods are chopping or slicing, mincing, liquefaction, fermentation, emulsification, cooking, mixing, and gasification, such as adding gas to bread or soft drinks.

Various factors, such as contamination by microorganisms, insect infestation, enzyme degradation, physical damage, and chemical changes, such as oxidation, can cause food spoilage. The process of food degradation that eventually leads to spoilage starts immediately after harvest or slaughter due to enzymes in the plant cells and animal tissues, mechanical damage caused during harvesting and post-harvest handling, and presence of bacteria, molds and yeasts. Preservation is the process of handling and treating food to prevent its spoilage by controling the growth of microbes, avoiding oxidation of fats (rancidity), and stopping enzyme activity to maintain the nutritional value, texture, and flavor of the food. Some traditional food preservation methods are drying, heating, cooling, fermenting, pickling, boiling, and adding sugar or salt.

Food storage is an important part of food preservation, as improper storage or transport conditions can adversely affect nutrient content, changes in color, texture, and flavor. Besides avoiding physical damage and contamination, careful control of the storage environment including factors like storage temperature and atmospheric gases (oxygen, carbon dioxide, and ethylene) can extend fresh food storag.

Negative aspects of food processing have arisen with the development of so-called ultra processed foods, which usually contain artificial ingredients to change color, texture, flavor and odor as well as ingredients like preservatives and sweeteners. Many of these products are low in nutrients and fibre but high in sugar (which is one of the cheapest preservatives), salt, and fat and therefore calorie-dense. They are pleasant to eat and often lead to overconsumption and obesity. A five-year study of over 100,000 people found that every 10 % increase in consumption of ultra processed food was associated with a 12 % higher risk for cancer.

2. Food processing as a business

Food processing is a scientific and technological activity that covers more than just food preparation and cooking. 

It involves the application of scientific principles to slow down the natural processes of food decay caused by micro-organisms, enzymes in the food, or environmental factors such as heat, moisture and sunlight. 

Every country or region has its own traditional methods or recipes to process and preserve food, which are handed down through the generations. Examples from Asia include fruit 'leathers' (dried sheets of fruit paste that have an appearance of thin leather), fruit pastes, pickles and chutneys. In Africa and Latin America, a wide range of dried chips, dried and powdered leaves, fruit beers and other fermented fruit and vegetable products are traditionally produced. In most developing countries food processing is also a method of generating employment and family incomes. Under these circumstances, producers must compete with others in the same country and with imported products. In many cases homemade products are inadequate to compete with the industrial products with respect to packaging and presentation of the foods. Nevertheless, products made with traditional processing methods might be tasty and healthy alternatives.

However, the selection of suitable products for small scale manufacture and the processes chosen to make them, require very careful consideration. It is not sufficient to assume that alone from a seasonal surplus of a raw material a viable processing venture can be created. There must be a demand for the processed food which is clearly identified before a business is set up. Otherwise the most likely result is to produce a processed commodity that no-one wants to buy with substantial financial losses to those involved.

In general the types of products that are suitable for small scale production are those for which there is a high demand, and a higher value can be added by processing. Typically fruits and vegetables have a low price when in their raw state, but can be processed into a range of snackfoods, dried foods, juices, pickles, chutneys etc., which have a considerably higher value.

Another important point to consider before venturing into a food processing business is the safety of the food products that are produced. Careful control of processing conditions and attention to hygiene are therefore essential when processing foods.

Source: Guidelines for small-scale fruit and vegetable processors. (FAO Agricultural Services Bulletin - 127)

3. The effect of different processing methods on micriobial activity

4. Examples for processed foods

1. Crisps

Starchy fruits, like potatoes, cassava, cocoyam, jackfruit, breadfruit, plantain, and banana, etc. can be fried and eaten as snackfoods.

Heat during frying destroys enzymes and micro-organisms and if sufficient moisture is removed and the product is packaged, it can have a shelf life of several weeks. Care needs to be taken to avoid oxidation (rancidity) of the frying oil during storage of the product.

2. Dried food

Typical dried foods include fruits, fruit leathers, fish, biltong (venison or beef), pasta, vegetables, and herbs. Drying removes most of the water from produce, thereby reducing microbial activity and extending the shelf life. Airdrying and solar drying are low-cost alternatives to oven driers. In some cases the food is first treated with sugar or salt to increase the drying effect. Some dried foods are used for convenience, others are attractive snacks. Airtight storage and protection from breakage/crushing during packaging, storage and transport might be necessary.

3. Canned food

Canning is the processes where food is filled into jars or cans and heated to destroy enzymes and micro-organisms. The filled jars or cans are closed with a lid and pasteurized ( at 90-100°C for 10-20 min) or sterilized (at 121°C for 15-40 min) so that an internal vacuum forms when cooling down, thereby tightening the seal. The sealed container then preserves the food by preventing re-contamination and excluding air and sometimes light. Canned foods are usually further preserved by addition of salt or brine (15 g salt/ltr), sugar or sugar syrup (200-600g sugar/ltr), pickling acid (usually lactic or acetic acid), or oil. Examples are jams, processed meat, pickles, canned fruits and vegetables, olives, and canned fish. 

4. Juices and juice concentrates are technically also examples of canned (bottled) foods. The juice is extracted from the fruits or vegetables and pasteurized. In some cases sugar or citric acid are added for increased preservation or to achieve the required taste (sweet-sour balance). For fruit concentrate the juice is either steam heated to evaporate the water present in the juice (between 50-80% of the water is removed) or ultra-filtered and then concentrated using reverse osmosis.

5. Nut butters

Nuts, almonds, and many oilseeds can be processed into nut butters. They are usually heated or roasted to increase the release of oil and sometimes the skins are removed either before (almonds) or after roasting (peanuts, hazelnuts, etc.). Sugar or salt can be added to taste. The nuts are then ground to the required smoothness and viscosity. No firther preservation is necessary, however stabilizers can be added to avoid the separation of solids and oil. If exposed to air, these butters become rancid. 

6. Chutneys and sauces

To process chutneys, ketchup or other sauces, usually a raw or combination of raw materials like unripe mangoes, tomatoes, chillies, etc. is processed (chopped or pulped) and mixed with spices, sugar, salt, vinegar or oil for further preservation, then bottled and pasteurized. Some sauces (e.g. ketchup) need to be boiled for extended periods to achieve the required taste and viscosity.

7. Fermented foods

A large veriety of indigenous and traditional fermented foods and beverages exist accross the globe. Vegetables are either fermented with salt or lactic acid, starchy foods are fermented into alcoholic beverages, protein-rich legumes are fermented e.g. into tofu or condiments. Fermentation is a naturally occuring process that changes the properties of the food and in such a way that microbial activity is disrupted. Foods are fermented to preserve them for longer periods and/or to change their taste and nutritional properties.

8. Vinegar

Fruit residues and peels can be left to ferment naturally first into alcohol and then into vinegar, by making use of a certain type of vinegar-forming bacteria (Acetobacteraceae).

9. Baked goods

Grains, like wheat, rye, oats, millet, rice, corn, etc. can be milled into flour or flakes and used to produce a large variety of different porridges, muslis, cookies, bread crumbs, and other baked goods. The dough for baked goods is often raised with yeast or sourdough (leaven), and mixed with salt, sugar, fats and other spices. The more moisture is removed during the baking process, the longer is the shelf life of the products.

10. Dairy products

Cow, goat, ewe (sheep), buffalo and yak milk is traditionally processed into a large variety of regional and traditional dairy products like butter, ghee, yoghurt, kefir, ice cream, paneer, fresh and hard cheeses, etc. Some of these products depend on culturing and coagulating the milk with different bacteria, rennet or acids as well as heating and ripening for some periods. In the process the pH and moisture level are reduced, making the dairy products less susceptible to rot and changing the taste and texture of the product. Raw milk is usually pasteurized, sterilized or processed into UHT milk to make it less perishable.

11. Processed meats

Raw meat is highly perishable and poses a serious health risk if consumed in a spoiled state. To extend its shelf life it is often processed into cured, smoked or cooked meats, like salami, ham, bacon, sausage, etc. The addition of salt and the cooking process reduces microbial activity. Meat is also cut into different bite-size shapes (cubes, mince, steaks, stripos, etc.) for convenience. Meat can be stored frozen for longer periods.

Cured meat and fish are produced by adding salt, nitrates, sugars, and nitrites to slow the oxidation process (reduce rancidity) and to reduce the moisture content using the osmosis dehydration process, which helps to reduce microbial damage. Curing also imparts a particular flavor to foods. Examples are salami and prosciutto.

12. Chocolate and candy

Candy and chocolate making has a long artisan tradition. It requires special techniques and equipment. Cocoa beans are finely ground at low heat to produce a very smoth chocolate paste that is then tempered into chocolate in many different forms. Marzipan, nougat and nuts are often added. Candy or caramel is made from boiled sugars (glucose and sucrose) and aromas, and in some cases starch. The high sugar content in these sweets serves as preservative.

Coating dried fruit with chocolateor, adding caramel to apples or other processed grain products, like popcorn, peanuts and tree nuts or nut and seed bars, is another form of food processing.

13. Convenience food

Convenience food is a modern addition to the processed food range. It consists of pre-cooked, per-prepared. assembled, and cooled or frozen foods, which can be cooked without further preparation, or re-heated or consumed directly. Among them are peeled, chopped, cut or sliced fresh vegtables or fruits, frozen pizzas, microwave meals, frozen vegetables, to-go sandwiches and many mor