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Agricultural crops are processed for many different reasons. These range from the removal of anti-nutritional components and increasing the storage life of the final product to adding value to increase both employment and income generating opportunities. Fermentation is one of the most ancient and most important food processing technologies. However scientists and policy makers have neglected this area, particularly traditional fermented products from developing countries.
Fermented foods: an ancient tradition
Fermentation is one of the oldest forms of food preservation technologies in the world. Indigenous fermented foods such as bread, cheese and wine, have been prepared and consumed for thousands of years and are strongly linked to culture and tradition, especially in rural households and village communities.
The development of fermentation technologies is lost in the mists of history. Anthropologists have suggested that it was the production of alcohol that motivated primitive people to settle down and become agriculturists. Some even think the consumption of fermented food is pre-human (Stanton, 1985). The first fermented foods consumed probably were fermented fruits. Hunter-gatherers would have consumed fresh fruits but at times of scarcity would have eaten rotten and fermented fruits. Repeated consumption would have led to the development of the taste for fermented fruits. There is reliable information that fermented drinks were being produced over 7,000 years ago in Babylon (now Iraq), 5,000 years ago in Egypt, 4,000 years ago in Mexico and 3,500 years ago in Sudan (Dirar, 1993), (Pedersen, 1979).
Bread-making probably originated in Egypt over 3,500 years ago (Sugihara, 1985). Several triangular loaves of bread have been found in ancient tombs. Fermentation of milk started in many places with evidence of fermented products in use in Babylon over 5,000 years ago. There is also evidence of fermented meat products being produced for King Nebuchadnezer of Babylon. China is thought to be the birth-place of fermented vegetables and the use of Aspergillus and Rhizopus moulds to make food. The book called "Shu-Ching" written in the Chou dynasty in China (1121-256 BC) refers to the use of "chu" a fermented grain product (Yokotsuka, 1985).
Knowledge about traditional fermentation technologies has been handed down from parent to child, for centuries. These fermented products have been adapted over generations; some products and practices no doubt fell by the wayside. Those that remain today have not only survived the test of time but also more importantly are appropriate to the technical, social and economic conditions of the region.
Fermented foods are culturally and economically important
Fermentation is a relatively efficient, low energy preservation process which increases the shelf life and decreases the need for refrigeration or other form of food preservation technology. It is therefore a highly appropriate technique for use in developing countries and remote areas where access to sophisticated equipment is limited. Fermented foods are popular throughout the world and in some regions make a significant contribution to the diet of millions of individuals.
In Asia the preparation of fermented foods is a widespread tradition. The fermented products supply protein, minerals and other nutrients that add variety and nutritional fortification to otherwise starchy, bland diets. For instance Soy sauce is consumed throughout the world and is a fundamental ingredient in diets from Indonesia to Japan. Over one billion litres are produced each year in Japan alone. "Gundruk" which is a fermented and dried vegetable product is very important for ensuring food security for many Nepali communities especially in remote areas. It is served as a side dish with the main meal and is also used as an appetiser in the bland, starchy diet. The annual production of gundruk in Nepal is estimated at 2,000 tons. Gundruk is an important source of minerals particularly during the off-season when the diet consists primarily of starchy tubers and maize, which tend to be low in minerals. In Africa fermented cassava products (like gari and fufu) are a major component of the diet of more than 800 million people and in some areas these products constitute over 50% of the diet.
The need for research
Although fermentation of foods has been in use for thousands of year, it is likely that the microbial and enzymatic processes responsible for the transformations were largely unknown. It is only recently that there has been a development in the understanding of these processes and their adaptation for commercialisation. There is tremendous scope and potential for the use of micro-organisms towards meeting the growing world demand for food, through efficient utilisation of available natural food and feed stocks and the transformation of waste materials.
Because of the tremendously important role indigenous fermented fruits and vegetables play in food preservation and their potential to contribute to the growing food needs of the world, it is essential that the knowledge of their production is not lost. There is a danger that the introduction of 'western foods' with their glamorous image will displace these traditional foods.
This book presents an overview of the fermented fruit and vegetable products of Africa, Asia and Latin America. The book aims to introduce the reader to the vast wealth of knowledge, much of which is indigenous and undocumented and the importance attached to fermented fruits and vegetables in the diet. At the same time it is a practical handbook, allowing those who are interested to reproduce the products.
DESCRIPTION OF TERMS USED
Fermentation is the "slow decomposition process of organic substances induced by micro-organisms, or by complex nitrogenous substances (enzymes) of plant or animal origin" (Walker, 1988). It can be described as a biochemical change, which is brought about by the anaerobic or partially anaerobic oxidation of carbohydrates by either micro-organisms or enzymes. This is distinct from putrefaction, which is the degradation of protein materials.
The changes caused by fermentation can be both advantageous and disadvantageous. Fermentation, initiated by the action of micro-organisms occurs naturally and is often part of the process of decay, especially in fruits and vegetables. However, fermentation can be controlled to give beneficial results. Fermentation is a relatively efficient, low energy preservation process, which increases the shelf life and decreases the need for refrigeration or other form of food preservation technology. It is therefore a highly appropriate technique for use in developing countries and remote areas where access to sophisticated equipment is limited.
There are several definitions of "fruit", which makes classification and distinction between fruit and vegetable difficult. The everyday usage of the word "fruit" defines fruit as "The edible product of a plant or tree, consisting of the seed and its envelope, especially the latter when juicy and pulpy" (Little et al, 1973). The scientific definition of a fruit is "The structure that develops from the ovary of an angiosperm as the seeds mature, with (false fruit) or without (true fruit) associated structures" (Walker, 1988)
In terms of food processing, fruits are nearly all acidic and are therefore called high acid foods. The acidity naturally controls the type of organism that can grow in fruits, with yeasts and moulds being the only spoilage organisms likely to be found on fruit products. The acidity level of tropical fruits, such as banana, mango and papaya, decreases as the fruit ripens (Anon, 1993). With respect to food processing and preservation, it is probably this definition of a fruit that will be most useful.
A vegetable is "a plant cultivated for food, especially an edible herb or root used for human consumption"(Little et al, 1973). In general, vegetables tend to be less sweet than fruits and often require some form of processing to increase their edibility.
In terms of food processing, vegetables are classified as low acid foods due to their lower levels of acidity. Low acid foods are more prone to deterioration by micro-organisms and can in fact provide an ideal substrate for food poisoning organisms when in a moist environment. Low acid foods can be safely preserved by making them more acidic, either through pickling or salting or drying (Anon, 1993).
Agro-processing describes the transformation of agricultural produce into a different physical or chemical state. The term agro encompasses a wide range of food and non-food agricultural products. The term food processing applies only to products which are suitable for human consumption. Agro processing applies to any of the numerous activities that take place in the chain of events between harvest or slaughter of the raw material and production of the final product. It covers a range of processes with varying degrees of complexity and technical input to suit the individual situation. Different treatments range from the relatively simple processes of rice husking, drying and grinding to the more complex transformation of oilseeds into margarine and essential oil distillation.
Salt present in a brine is expressed as degrees "Salometer" which is a percent saturation of sodium chloride by weight. A saturated solution of pure sodium chloride (100 degrees Salometer) contains 26.359g per 100ml at 15.5 degrees C. Therefore a 10 degree Salometer contains 2.64% salt by weight.
Biotechnology can be described as the application of scientific and engineering principles to the processing of materials, for the provision of goods and services, through the use of biological systems and agents (Anon, 1992).
A complex carbohydrate is one that is composed of long branched chains of single sugar units (glucose, fructose or galactose). Examples of complex carbohydrates include starch and cellulose.
A reducing sugar is a sugar, which has reactive aldehyde or ketone groups. All simple sugars are reducing sugars. Sucrose, a common sugar, is not a reducing sugar.
Microbe and micro-organism are generic terms for the group of living organisms which are microscopic in size. Included in the definition are bacteria, viruses, moulds, yeasts and fungi.
An enzyme is a biological catalyst, which is used to facilitate and speed up reactions. It is a protein and requires a specific substrate to work on. Its working conditions are set within narrow limits for example, optimum temperature, pH conditions and oxygen concentration. At temperatures above 42° C, mammalian proteins (and therefore enzymes) are denatured. However, certain bacterial enzymes are tolerant of a more diverse temperature range.
Hydrolysis is the splitting or breaking down of complex molecules by the action of enzymes or acid. For example the hydrolysis of starch and cellulose both yield simple glucose units.
With reference to micro-organisms, one which requires oxygen for survival.
An anaerobic organism is one which does not require oxygen for survival.
A micro-organism which can adapt to exist with or without oxygen.
An organism which requires small amounts of oxygen for survival.
Water activity (a w )
Water exists in two states within a cell free and bound. Water activity is a measure of the amount of free water available for a potential reaction microbial or enzymic. Water activity is a measure of the free moisture in a product and is the quotient of the water vapour pressure of the substance divided by the vapour pressure of pure water at the same temperature. It is measured on a scale of 0 to 1.0 where 1.0 is the activity of pure water.
pH is a measure of the hydrogen ion concentration. It is measured on a scale of 1 to 14, where 1 represents a high concentration of hydrogen ions (acidic) and 14 represents a low concentration (alkaline). The optimum pH for most micro-organisms is near neutral (pH 7.0). However, certain species are acid tolerant . Foods with a pH of 4.6 or lower are termed high acid foods. If the pH is above 4.6, it is a low acid food and is more prone to bacterial and fungal spoilage.
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