Paper 6 Food Biotechnology F06FB25 Fermentation of Fish and Meat 6.25.1 Introduction This module deals with the method of preserving fish and meat so as to retain their colour, flavour and texture and also to extend the shelf-life of the product. One of the well established preservation methods is fermentation which involving the use of beneficial microorganisms. These organisms, mainly of lactic acid group produce lactic acid which lowers the ph, thereby preventing the growth of other food spoiling bacteria. Thus, this module will introduce the learner to the method and significance of fermenting fish and meat. 6.25.2 Objectives After completing this module, the learner will be able to understand the method of fermentation of fish for long term preservation comprehend the type and nutritive value of fermented fish products know the method of fermentation of meat and its products 6.25.3 Overview This module is part of the Food Biotechnology paper. It is designed to give an overview of the method of fermentation of fish and meat. The different strategies for preservation of fish and meat by fermentation method has been presented and explained. The student will be able to appreciate the necessity of fermenting both fish and meat and understand the benefits of adding microorganisms to the food items to prolong the shelf-life of the products. 6.25.4 Fermentation of fish Fish is an important source of protein in the daily diet. However, fish has the disadvantage that it spoils quickly. If fish is not boiled, salted, dried, smoked or preserved in some other way, it will quickly spoil. Fermented fish paste and sauces have a much more important place in the daily diet than salted or dried fish. Although fermented foods are a good source of protein, they can be consumed only in limited quantities, because of the high salt content of these products. Fermentation of fish is especially used in situations where drying of the fish is not possible, because the climate is too wet and where cooling and sterilization of the product is too expensive.
Preservation of fish by fermentation technology has been popular from time immemorial. Fermented fish paste and sauces are relished as condiment (flavoured salt) along with cooked rice in many of the South East Asian Countries. During the fermentation of fish, protein is broken down in the presence of a high salt concentration. The fish protein is mainly broken down by enzymes which come from the fish itself. These enzymes are mainly present in the gut. In the traditional fermentation methods in which the intestines are removed from the fish, fermentation will often be slower as there are fewer enzymes present in the flesh. 6.25.4.1 Types of fermented fish products 1. Products in which the fish retain substantially their original form or preserved as large chunks. 2. Products in which fish are reduced to a paste 3. Products in which fish are reduced to a liquid. Traditional fermented fish products are basically salt fermented products. Depending on the proportion of salt added, the products can also be classified into high salt (more than 20% of total weight), low salt (6 to 8%) and no salt products. The dominant flavour giving components of fermented fish products are proteins and their hydrolytic cleavage products such as peptides, peptones, amino acids, higher fatty acids and their esters; glycerides and their derivatives, monosodium glutamate, nucleotides and inosine monophosphate. 6.25.4.2 Nutritive value of fermented fish products Fermented fish sauces and pastes generally contain amino acids and polypeptides equivalent to about 10% protein. Amino acids occur in such foods without much change in composition and quality with fish and hence contribute towards nutrition just like fish protein. They are also good sources of calcium, iron and some B group vitamins. However, nutritional importance of these products is limited by its high salt content which restricts its bulk consumption. 6.25.4.3 Role of microorganisms in fermentation Microorganisms probably play no role in the breaking down of protein during fermentation. However, microorganisms which can tolerate salt do seem to contribute to the specific taste and smell of the fermented product. In some fermentation techniques, a fermentable source of carbohydrates such as boiled rice is added to the fermented fish product. This combination stimulates the growth of
lactic acid bacteria. Due to the formation of lactic acid, which is desirable in these products, the ph of the fish mixture is lowered making the product safer and easier to keep. 6.25.4.4 Salt The main role of salt in fermentation of fish is to draw liquid out of the fish and to control fermentation. Addition of high salt content prevents the spoilage due to bacteria and as a result, the numbers of bacteria present drops as quickly as possible during fermentation. However, on the other hand, the high salt concentrations also slow down the fermentation speed. 6.25.4.5 Traditional fermentation methods Here the fermentation process is allowed to take place by chance and is based on experience alone. Further there is no control measures applied over fermentation. As in most traditional methods, influx of air is restricted and salt roughly about one-third of the weight of fish is added for the fermentation to occur spontaneously. The method in which the process is done varies according to region. So, experience alone determines the outcome of fermentation such as if the product has a different colour or smell so that it is different from normal, it should not be eaten. Traditional fish products are classified into two groups: 1. Products which, in the presence of salt, are fermented by the enzymes present in the fish flesh or intestines; 2. Products which are fermented in the presence of boiled or roasted rice.
Filter Fig 1. Fish Processing in the Indo-Pacific Area There are three kinds of fermented fish products: 1. the fish flesh is converted into fermented fish products; 2. the fish is converted into a paste; 3. the fish, whole or in pieces, retains as much as possible of its own structure We know that fermented fish products are an important protein supplement. They contain a number of essential amino acids which can form an important addition to the daily diet. For example, fish sauce contains a lot of the amino acid, lysine which is essential amino acid to be supplied in the diet. This amino acid is found in small quantities in rice. The quality of the resultant product depends on the fat content of the fish, the enzyme activity in the fish flesh, contaminations in the salt used and the temperature. Contaminated salt can be recognized by its slightly pink colour and can be purified by heating the salt on a metal sheet over a fire. 6.26.4.6 Fish used Many small kinds of fish are used in fermentation. Table 1 lists the different kinds of fish used in South East Asia for fermentation.
Table 1: Salt water and fresh water fish and crustaceans which are mainly used in the fermentation methods of South-East Asia Product group Species Salt water fish Anchovies, herring, deep-bodied herring, Fimbriated herring, mackerel, round scad, slipmouth Freshwater fish Carp, catfish, climbing perch, gourami, mudfish Shellfish and Shrimp, mussels, oysters, ctopus crustaceans 6.25.4.7 Production of fish sauce as fermented product First, the fish are washed and left intact. Then they are packed with large quantities of salt in earthenware or wood containers. Usually 1 kg of salt is used for 3 to 4 kg of fish. The containers are filled to the rim so that no air is present and sealed so as to create an anaerobic environment. The fish protein is broken down as a result of activity of the enzymes present in the fish. After several months, a clear, amber coloured liquid will have been formed, which is then separated from the residue by squeezing it out. Sometimes, a fish sauce can also be made during the preparation of fish paste. Fermentation of fish sauce takes longer than that of fish paste; because all the flesh must be broken down to create a clear liquid. 6.25.4.8 Fish paste and whole fish A considerable part of the protein consumption in a number of Asian countries emerges from the consumption of fish paste, which is of greater importance from a nutritional point of view than fish sauces. There are two kinds of fish pastes used in South-East Asia: 1. fish-salt mixtures 2. products which are fermented in the presence of cooked or roasted rice on which yeasts and moulds are present. The general method of preparation of fish pastes is the same as that described for fish sauces. Only the fermentation time is shorter as not all of the fish flesh needs to be broken down. Fish paste must be mixed regularly to keep the salt evenly distributed. As a supplement to fish sauces and fish pastes, entire fish are also fermented in South- East Asia. The intestines and gills are removed from mackerel after which the fish are washed in drinking water. The fish are mixed with salt (1 kg of salt to 3 kg of fish) and put into jars.
Dried fruit pulp or tamarind (a tropical fruit) is added to the salt and fish to lower the ph. The fish are kept covered with brine with the help of weighted mats and are fermented for 2 to 4 months. They are transferred to wooden barrels and care is taken to keep them covered with brine. The fermented fish can be kept for one year. 6.25.5 Fermentation of Meat Meat is the most valuable livestock product. Meat is composed of protein and amino acids, minerals, fats and fatty acids, vitamins and other bioactive components, and small quantities of carbohydrates. From the nutritional point of view, meat s importance is derived from its high quality protein, containing all essential amino acids and it s highly bioavailable minerals and vitamins. Meat fermentation is a low energy preservation method, which results in unique and distinctive properties in meat such as flavour and palatability, colour, microbiological safety, tenderness and a host of other desirable properties of this specialized meat. A raw meat is often converted to fermented product by inoculation of cultured or wild microorganisms which lower the ph. Lactic acid accounts for the antimicrobial properties of fermented meat (Fig 2). This originates from the natural conversion of glycogen reserves in the meat and the added sugar during product fermentation. The acidification of the finished product upon addition of lactic acid and addition of salt which also lowers water activity on drying is the crux of fermentation. Both natural and controlled fermentations involve lactic acid bacteria.
Fig 2 General steps in the meat fermentation process Most starter cultures, used today, consist of lactic acid bacteria and/or micrococci, selected for their metabolic activity which often improves flavour development. The reduction of ph and lowering of water activity are microbial hurdles in producing a safe product. Fermented sausages often have a long storage life due to added salt, nitrite, and/or nitrate, low ph due to lactic acid production by lactic acid bacteria organisms in the early stages of storage, and later drying which reduces the water activity. 6.25.5.1Definitions Guidelines proposed in the U.S (American meat Institute, 1982) for making fermented dry or semi-dry sausages include a definition for dry or semi-dry sausages. Dry sausages include chopped or ground meat products that due to bacterial action, reaches a ph of 5.3 or less. The drying removes 20% to 50% of the moisture resulting in a moisture-to-protein ratio (MP) of no greater than 2.3 to 1.0. Semi-dry sausages are similar, except that they have a 15 to 20% loss of moisture during processing. Semi-dry sausages also have a softer texture and a different flavour profile than dry sausages. However, because of the higher moisture content, semi-dry sausages are
more susceptible to spoilage and are usually fermented to a lower ph to produce a very tangy flavour. 6.25.5.2 Fermented sausages Fermented sausages are defined as a mixture of ground lean meat and minced fat, curing salts, sugar and spices which are embedded into a casing and subjected to fermentation and drying. The quality of fermented sausages is closely related to the ripening process that gives colour, flavour, aroma and firmness to the product. This is developed by a complex interaction of chemical and physical reactions associated with the fermentative action of the microbiological flora present in the sausage. Incubation of sausages at the optimum growth temperature for the lactic acid bacteria, coupled with reduced oxygen, causes exponential growth of the lactic acid bacteria which causes conversion of simple sugars into lactic acid and lowering of ph. The fermentation route is glycolysis for the homofermentative lactic acid. This produces a sharp tangy taste. In general, the higher the temperatures up to the optimum growth temperature, the shorter the fermentation. Rapid fermentation results in sulphides, ketones and methylbranched acids, while slow fermentation results in methyl branched alcohols, aldehydes and esters. 6.25.5.3 Starter cultures for Fermented Meat products Starter cultures are defined as preparations containing live microorganisms capable of developing desirable metabolic activity in meat. They are used to increase the microbiological safety, to maintain stability by inhibiting the growth of undesirable microorganisms and to improve the sensory characteristics of fermented sausages. Starter cultures are formed by mixing different types of microorganisms, where each one has specific function. Lactic bacteria are used in order to generate controlled and intense acidification which inhibits the growth of undesirable microorganisms, and provides increased safety and stability to the product. Table 1 shows the microorganism species most commonly used as starter cultures to fermented meat products Microorganism Genus and species Lactic acid bacteria Lactobacillus acidophilus, L. alimentarius, L. brevis, L. casei,
L. curvatus, L. fermentum, L. plantarum, L. pentosus, L. sakei Lactococcus lactis Pediococcus acidilactici, P. pentosaceus Actinobacteria Kocuria variansc Streptomyces griséus Bifidobacterium sp Staphylococcus S. xylosus, S. carnosus subsp. carnosus, S. carnosus subsp. utilis, S. equorum Halomanadaceae Halomonas elongata Enterobacter Aeromonas sp Mold Penicillium nalgiovense, P. chrysogeum, P. camemberti Yeast Debaryomyces hansenii, Candida famata Table 1. Microorganism species most commonly used as starter cultures to fermented meat products. Among the starter lactic acid bacteria, Lactobacillus brevis, L.planatarum, L.feremntum and Pedioccus pentosaceus have been characterized as probiotics. Strains of L.sakei and P.acidilactici have also been proposed as potential probiotic in meat products. Probiotic cultures can also be selected from the lactic acid bacteria in fermented meat products.
Facultative or obligate anaerobes which belong to the Gram-positive acid forming bacteria (primarily lactic acid) such as the genera Lactobacillus, Streptococcus, Pediococcus, Leuconostoc, Lactococcus and Enterococcus are used which can metabolize several saccharides into lactic acid, alcohols, aliphatic compounds, lipids and some amino acids. These organisms perform two functions in fermented sausages: reducing nitrate and nitrite into nitric oxide and when combined with myoglobin is responsible for cured colour, and by anaerobic glycolysis to produce lactic acid from glucose which reduces the ph. The sterile tissues of animals on slaughtering become contaminated by spoilage and pathogenic Gram-negative bacteria such as E.coli, Salmonella species, Pseudomonas sp. and Closteridium periferigens and also Gram-positive species. As a measure of preservation of meat, its water activity (aw) is reduced by adding salt or curing by the addition of nitrite or drying. Acid fermentation of meat is carried out to enhance the stability, texture, colour and flavour of the product by choosing appropriate starter cultures. In the manufacture of fermented meat products, starter cultures mainly of Pediococcus cervisiae, Lactoobacillus planatarum and Micrococcus are used. The majority of fermented products may be classified into dry sausages with a moisture content of 25 to 45% (aw ~0.91) and semi-dry sausages with a moisture content of ~ 50% (aw ~0.95). Meat curing compounds and starter culture are mixed and stuffed in casings at low temperature of about - 5 C and incubated at a temperature between 20 and 40 C for fermentation. The fermented product is dried at 10-20 C. Examples of dry fermented meat sausages include pepperoni and salami while bologna and summer sausages are semi dried fermented meat sausages. Fermented poultry sausages include dry as well as semi-dry turkey sausages. 6.25.6 Conclusion In this module, the method of preserving fish and meat by fermentation has been presented. This procedure involves the use of probiotic microorganisms mainly lactic acid bacteria group, which aims to lower the ph in the products by producing lactic acid as the end product in their metabolism. This helps to enhance flavour and texture in the processed foods and extend the shelf-life of the products.