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Fermented food

  1. 1. Introduction of Fermented food Fermented foods are an extremely important part of human diet and worldwide may contribute to as much as one third of human diet. Different types of fermented food is used in butter, cheese, bread, fermented vegetables, fermented meats etc. The scope of food fermentation ranged from producing alcoholic beverages, fermented milk and vegetable products to genetically engineered super bugs to carry out efficient fermentation to treatment and utilization of waste and overall producing nutritious and safe products with appealing qualities.
  2. 2. Fermented Food Definition: Fermented foods are those food produced by modification of raw material of either animal or vegetable origin by the activities of micro organisms. Bacteria , yeast and moulds can be used to produce a diverse range of products that differ in flavor, texture and stability from the original raw material. Or Fermented foods are those foods which are subjected to action of microorganisms or enzymes to get desirable biochemical changes and cause significant modification to food.
  3. 3. Concept of fermentation In biochemical sense the term fermentation refers to the metabolic process in which organic compounds(particularly carbohydrates) are broken down to release energy without the involvement of terminal electron acceptor such as oxygen. Partial oxidation of the substrate occurs so that only relatively small amount of ATP energy is released compared with the energy generated if a terminal electron acceptor is involved. Partial oxidation of a carbohydrate can give rise to a variety of organic compounds. The compounds produced by microorganisms vary from organism to organism and are produced via different metabolic pathways. The term fermentation can also be applied to any industrial process that
  4. 4. Cont… Produces a material that is useful to humans and if the process depends on the activity of one or more microorganisms. These processes, known as industrial fermentations, are usually carried out on large scale and in vessels in which organism are normally grown in liquid media. Some industrial fermentations in biochemical sense but the majority are aerobic processes in which the microorganisms use oxygen and metabolize carbohydrates completely. Benefits of fermented foods : Fermented foods are an extremely valuable addition to human diet for variety of reasons:
  5. 5. Benefits of fermented foods  Increase in variety: Fermented foods increase the variety of foods that are available, adding to our diet a group of highly nutritious products with unique characteristics. There are, for example, about 1000 different types of cheeses.  Use as ingredients: Fermented foods form important ingredients for a wide variety of dishes and are often used to impact special flavors, e.g pepperoni in pizzas, yogurts in curries, cheeses in a whole range of dishes, including soups, and soy sauce in stir fry dishes.  Improvement in nutritional quality: The fermentation process may improve the nutritional quality of raw material. Here are some examples:
  6. 6. Cont..  Tape fermentation double the protein content of cassava and increases the level of essential amino acids.  The presence of yeasts in fermented food will increase the vitamin B content.  Anti nutritional factors such as phytase, glucosinolates and lectins may be removed by fermentation process.  Fermentation may produce an increase in the availability of minerals.  Preservation: Fermentation often preserves a raw material, improving safety with regard to food borne pathogens and increasing shelf life; compare the shelf of raw milk(only a few days) with the shelf life of yoghurt (several weeks).
  7. 7. Cont…  Health benefits : Some fermented foods are said to have definite health benefits although the scientific evidences for this is limited. Reports suggested that fermented milk products such as yoghurt can reduce serum cholesterol levels and help avoid cancers, particularly those associated with the colon. Bio yoghurts (AB and ABT yoghurts) are said to have a restorative effects on the gut micro flora, assisting recovery of a normal balanced flora after oral antibiotic therapy.  Improve digestibility: Some fermented food are most easily digested than the original raw material. People who can not digest lactose properly (show lactose in tolerance) can often consume some types of fermented dairy products(particularly
  8. 8. Cont… yoghurts) without harmful effects. Lactose in tolerance is due to the absence of enzyme galactosidase in digestive juices, which converts lactose to glucose and glactose. Ingestion of dairy products leaves unabsorbed lactose in gut which is fermented by normal gut flora giving flatulence, abdominal pain and dirrhoea. The fermentation of milk converts the harmful lactose to more easily digested lactate, and theβ galactosidase in liver starter culture organisms appears to assist in the digestion of any residual lactose. Legume, e.g soyabean, contain oligosaccharides such as stachyose which are fermented in the gut to give gas and the associated socially embarrassing flatus.
  9. 9. Cont.. The oligosaccharides are broken down to readily digestible monosaccharides and disaccharides during mould fermentations of legumes, thus removing the problem. Detoxification of raw materials: The fermentation process may remove toxic chemicals present in the raw material. Cassava fermentation for example, removes a cynogenic (cyanide producing) glycoside; cassava is toxic if eaten raw.
  10. 10. Table 1 History and origins of some fermented foods Food Approximate year of introduction Region Mushrooms Soy sauce Wine Fermented milk Cheese Beer Bread Fermented Meats Sourdough bread Fish sauce Pickled vegetables Tea 4000 BC 3000 BC 3000 BC 3000 BC 2000 BC 2000 BC 1500 BC 1500 BC 1000 BC 1000 BC 1000 BC 200 BC China China, Korea, Japan North Africa, Europe Middle East Middle East North Africa, China Egypt, Europe Middle East Europe Southeast Asia, North Africa China, Europe China
  11. 11. Table 2 Worldwide production of some fermented foods Food Quantity (t) Beverage Quantity (hl) Cheese Yoghurt Mushrooms Fish sauce Dried stockfish 15 million 3 million 1.5 million 300 000 250 000 Beer Wine 1000 million 350 million
  12. 12. Table 3 Individual consumption of some fermented foods: average per person per year Food Country Annual consumption Beer (I) Wine (I) Yoghurt (I) Kimchi (kg) Tempeh (kg) Soy sauce (I) Cheese (kg) Miso (kg) Germany Italy, Portugal Argentina Finland Netherlands Korea Indonesia Japan UK Japan 130 90 70 40 25 22 18 10 10 7
  13. 13. Cont… Microflora in fermented foods: By tradition, lactic acid bacteria are the commonly used microorganism for preservation of foods. Their importance is associated mainly with their safe metabolic activity while growing in food utilizing available sugar for the production of organic acids and other metabolites. Their common occurrence in the foods and feeds coupled with their long lived use contributes to their natural acceptance as GRAS (Generally regarded as safe) for human consumption.
  14. 14. Cont.. There are many kinds of fermented foods in which the dominating processes and end products are contributed by a mixture of endogenous enzymes and other microorganisms like yeast and mould. Very often, a mixed culture originating from the native micro flora of the raw materials is in action in most of the food fermentation processes. However, in an industrial scale a particular defined starter culture, which has been developed under controlled conditions, is first preference so that the qualities of finished product could be consistently maintained day after day.
  15. 15. Cont… Modern methods of gene technology makes it possible for the microbiologist to design and develop starter cultures with specific qualities. Many microbiologists studies deal with identification of organisms isolated from various fermented foods. Lactic acid bacteria isolated from tomatoes that are naturally fermented under partial anaerobic conditions. These are Leuonostoc mesenteroides, Lactobacillus brevis and Streptococcous sp. In Asia mainly moulds of the genera Aspergillus, Rhizopus,
  16. 16. Cont.. Mucor, Actinomucor. Amyomyces, Neurospora and Monascus are used in the manufacture of fermented foods. In Europe, mould ripened foods are primarily cheese and meats, usually using a Penicillium species. Gari made by fermenting cassava slurry was found to contain Bacillus, Aspergillus and Penicillium spp. as predominant organisms. Lactic acid bacteria:  Major group of Fermentative organisms.  This group is comprised of 11 genera of gram-positive bacteria:
  17. 17. Cont… ○ Carnobacterium, Oenococcus, Enterococcus, Pediococcus, Lactococcus, Streptococcus, Lactobacillus, Vagococcus, Lactosphaera, Weissells and Lecconostoc  Related to this group are genera such as Aerococcus, Microbacterium, and Propionbacterium.  While this is a loosely defined group with no precise boundaries all members share the property of producing lactic acid from hexoses.  As fermenting organisms, they lack functional heme- linked electron transport systems or cytochromes, they do not have a functional Krebs cycle.
  18. 18. Cont…  Energy is obtained by substrate-level phosphorylation while oxidising carbohydrates.  The lactic acid bacteria can be divided into two groups based on the end products of glucose metabolism.  Those that produce lactic acid as the major or sole product of glucose fermentation are designated homofermentative.  Those that produce equal amounts of lactic acid, ethanol and CO2 are termed heterofermentative.  The homolactics are able to extract about twice as much energy from a given quantity of glucose as the heterolactics.
  19. 19. Cont…  All members of Pediococcus, Lactococcus, Streptococcus, Vagococcus, along with some lactobacilli are homofermenters.  Carnobacterium, Oenococcus, Enterococcus, Lactosphaera, Weissells and Lecconostoc and some Lactobacilli are heterofermenters  The heterolactics are more important than the homolactics in producing flavour and aroma components such as acetylaldehyde and diacetyl.
  20. 20. Cont… Lactic Acid Bacteria – Growth:  The lactic acid bacteria are mesophiles:  they generally grow over a temperature range of about 10 to 40oC,  an optimum between 25 and 35oC.  Some can grow below 5 and as high as 4oC.  Most can grow in the pH range from 4 to 8. Though some as low as 3.2 and as high as 9.6.
  21. 21. Cont.. Starter Cultures :  Traditionally the fermenting organisms came from the natural micro flora or a portion of the previous fermentation.  In many cases the natural micro flora is either inefficient, uncontrollable, and unpredictable, or is destroyed during preparation of the sample prior to fermentation (e.g. pasteurization).  A starter culture can provide particular characteristics in a more controlled and predictable fermentation.
  22. 22. Cont…  Lactic starters always include bacteria that convert sugars to lactic acid, usually:  Lactococcus lactis subsp. lactis,  Lactococcus lactis subsp. cremoris or  Lactococccus lactis subsp. lactis biovar diacetylactis.  Where flavour and aroma compounds such as diacetyl are desired the lactic acid starter will include heterofermentative organisms such as:  Leuconostoc citrovorum or  Leuconostoc dextranicum.
  23. 23. Cont…  The primary function of lactic starters is the production of lactic acid from sugars  Other functions of starter cultures may include the following: ○ flavour, aroma, and alcohol production ○ proteolytic and lipolytic activities ○ inhibition of undesirable organisms  A good starter CULTURE will:  Convert most of the sugars to lactic acid  Increase the lactic acid concentration to 0.8 to 1.2 % (Titratable acidity)  Drop the pH to between 4.3 to 4.5
  24. 24. Cont…  Food scientists frequently use the ability of bacterial cells to grow and form colonies on solid media to:  isolate bacteria from foods,  to determine what types and  how many bacteria are present.  Streak plates A single bacterial colony A single bacterial colony
  25. 25. Cont.. The streak plate technique :  Bacteria are “streaked "over the surface of an agar plate so as to obtain single colonies.  Obtaining single colonies is important as it enables;  the size,  shape and  colour of the individual colonies to be examined.  It can also highlight the presence of contaminating micro-organisms
  26. 26. The Streak Plate Technique
  27. 27. Nutritional value of fermented foods There is a significant increase in the soluble fraction of food during fermentation. The quantity and quality of food proteins is expressed by biological value, and often the content of water soluble vitamins is increased, while the anti nutritional factors show a decline during fermentation. Fermentation also results in a lower proportion of dry matter in food and concentrations of vitamins, minerals and protein appear to increase when measured on dry weight basis. Single as well as mixed culture fermentation of pearl millet flour with yeast and lactobacilli significantly increased the total amount of soluble sugars, reducing and non reducing sugar content of anti nutritional factors to a safe level in comparison
  28. 28. Cont… With other methods of processing. Proteins: The protein efficiency ratio (PER) of wheat increases on fermentation, partly due to increase in availability of lysine. A mixture of wheat and soyabeans in equal amounts provides and improved pattern of amino acids. The fermentation process raises the PER value of mixture to a level which is comparable to that of casein. Fermentation may not increase the content of protein and amino acids unless ammonia or urea is added as nitrogen source to the fermentation media. The relative nutritional value (RNV) of maize increased from 65% to 81% when it is germinated, and
  29. 29. Cont… fermentation of flour made of the germinated maize gives a further increase in RNV to 87 % . Vitamins: During fermentation certain microorganisms produce vitamins at higher rate than others do. Fermented milk products in general show an increase in folic acid content and slight decrease in vitamin B12 while other B vitamins are affected only slightly in comparison to raw milk. The levels of vitamin b12, riboflavin and folacin are increased by lactic acid fermentation of maize flour, while the level of pyridoxin is decreased.
  30. 30. Cont… Minerals: The mineral content is not affected by fermentation unless some salts are added to the product during fermentation or by leaching when liquid portion is separated from the fermented food. Some times, when fermentation is carried out in metal containers some minerals are solublised by the fermented product, which may cause an increase in mineral content. Phytate content in bread is lowered when the amount of yeast or the fermentation time is raised.
  31. 31. Cheese preparation Definition: In simple term cheese is the curd of milk separated from the whey and pressed in to solid mass. It is defined as a product made from the curd obtained from the milk by coagulating the casein with the help of rennet or similar enzymes in the presence of lactic acid produced by added or adventious microorganisms, from which part of moisture has been removed by cutting, cooking and/ or pressing, which has been shaped in and then ripened by holding it for sometime at suitable temperatures and humilities. Types of cheeses: The classification of cheese is based on a number of factors like raw material, type of consistency, appearance(interior and exterior), fat content, moisture content
  32. 32. Cont.. and ripening methods. However, the most commonly used criteria are the moisture content of the finished product and mode of ripening. i) Types based on moisture content:  Very hard(maximum 34% moisture)  Hard (maximum 39% moisture)  Semi hard/ semi soft (39-50% moisture)  Soft (50-80% moisture) ii) Type based on mode of ripening  Bacteria ripened: Ripening is brought about by different bacteria like Lactococci, Lactobacilli, Pedococci, Propionibacteria, and brevibacteria etc.
  33. 33. Cont…  Mold ripened: Ripening is brought about by mold species like Penicillium.  Unripened: Ripening is not done. Basic processes involved in cheese production : The cheese production involves the following three main steps A. Coagulum formation B. Separation of curd from whey, and C. Ripening of cheese Coagulum Formation: Milk coagulation occurs due to distinct activities
  34. 34. Cont..  Inoculation with bacterial cultures e.g. Streptococcus lactis or S. cremoris(for incubating at 31 C) or S. thermophilus combined with Lactobacillus lactis, L. bulgaricus or L. helveticus (for incubation at 50C) results in lactose degradation to produce lactic acid, which lowers the pH to about 4.6.  Incubation with rennet cleaves k casein into para casein and caseino macro peptides. This cleavage occurs at specific peptide bonds between phenylalanine at position105 and meithonine at position 106 and leads to coagulation of α andβ caseins and k casein hydrolysis products. k- casein stabilizes the colloidal nature of milk. The N terminal
  35. 35. Cont.. Region of k- casein is hydrophobic and it associates with the lipophilic regions of α andβ casein, which are insoluble. The C- terminal region of k-casein is hydrophilic and associates with water molecules. Thus an intact k casein molecule keeps the insoluble α andβ casein in suspension and prevents their coagulation. Hydrolysis of k casein by rennet separates its hydrophobic and hydrophilic regions and thereby , eliminates its protective influence. As a result the α and β caseins plus the k casein hydrolysis products participate and form the coagulum. Calcium is essential for coagulation, and the process is very temperature dependent.
  36. 36. Cont… Separation of curd: The coagulum is heated to 37 C and cooled. This eliminates rennet activity and separates, to some extent, the watery fluid called whey. The curd is separated from whey, salted, and mixed with proteases and/ or lipases; alternatively, bricks of cheese may be inoculated with specific strains of fungi, e.g. Penicillium camembertii, etc. The bricks are pressed to remove excess moisture to enable proper ripening. Ripening : Ripening procedures will vary with the type of cheese produced. The cheese bricks are inoculated with specific strain of fungi (P. roquefortii and P. camembertii) for the development of appropriate flavours through protease and lipase activities. Alternatively , protease and lipase may be used for this purpose
  37. 37. Cont..  Protease from B. amyloliquefaciens are used to enhance flavors in cheddar cheese.  Protease hydrolyze proteins to produce peptides of variable sizes. Peptides having terminal acidic amino acids residues produce meaty appetizing flavors. But hydrophobic amino acids residues located non terminally produce bitter flavors; the flavors are strongest in medium sized peptides are absent in longer peptides and they decrease with decrease in peptide size. Therefore, the kind and degree of flavor in cheese can be controlled by regulating protein hydrolysis.
  38. 38. Common Cheese Making Steps Cutting and Cooking Milling and Salting Forming and Pressing Curing or Ripening Draining, Matting and Washing Starter and Rennet Addition
  39. 39. Terms  Coagulation- Change from a fluid to a thickened mass; curdle; congeal.  Whey- The watery part of milk that separates after the milk sours and thickens.  Brine- Water strongly saturated with salt.  Rennin- A stomach enzyme that coagulates casein and is used to commercially curdle milk in the making of cheese. But now microbial rennin are used.
  40. 40. THANKS