Introduction of Fermented foodFermented foods are an extremely important part of humandiet and worldwide may contribute to as much as onethird of human diet. Different types of fermented food isused in butter, cheese, bread, fermented vegetables,fermented meats etc.The scope of food fermentation ranged from producingalcoholic beverages, fermented milk and vegetableproducts to genetically engineered super bugs to carry outefficient fermentation to treatment and utilization of wasteand overall producing nutritious and safe products withappealing qualities.
Fermented FoodDefinition:Fermented foods are those food produced bymodification of raw material of either animal orvegetable origin by the activities of microorganisms. Bacteria , yeast and moulds can be usedto produce a diverse range of products that differ inflavor, texture and stability from the original rawmaterial.OrFermented foods are those foods which are subjectedto action of microorganisms or enzymes to getdesirable biochemical changes and causesignificant modification to food.
Concept of fermentationIn biochemical sense the term fermentation refers to themetabolic process in which organic compounds(particularlycarbohydrates) are broken down to release energy withoutthe involvement of terminal electron acceptor such asoxygen. Partial oxidation of the substrate occurs so that onlyrelatively small amount of ATP energy is released comparedwith the energy generated if a terminal electron acceptor isinvolved. Partial oxidation of a carbohydrate can give rise toa variety of organic compounds. The compounds producedby microorganisms vary from organism to organism and areproduced via different metabolic pathways. The termfermentation can also be applied to any industrial processthat
Cont…Produces a material that is useful to humans and if theprocess depends on the activity of one or moremicroorganisms. These processes, known as industrialfermentations, are usually carried out on large scale andin vessels in which organism are normally grown inliquid media. Some industrial fermentations inbiochemical sense but the majority are aerobicprocesses in which the microorganisms use oxygen andmetabolize carbohydrates completely.Benefits of fermented foods : Fermented foods are anextremely valuable addition to human diet for variety ofreasons:
Benefits of fermented foods Increase in variety: Fermented foods increase thevariety of foods that are available, adding to our diet agroup of highly nutritious products with uniquecharacteristics. There are, for example, about 1000different types of cheeses. Use as ingredients: Fermented foods form importantingredients for a wide variety of dishes and are oftenused 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 fermentationprocess may improve the nutritional quality of rawmaterial. Here are some examples:
Cont.. Tape fermentation double the protein content of cassavaand increases the level of essential amino acids. The presence of yeasts in fermented food will increasethe vitamin B content. Anti nutritional factors such as phytase, glucosinolatesand lectins may be removed by fermentation process. Fermentation may produce an increase in theavailability of minerals. Preservation: Fermentation often preserves a rawmaterial, improving safety with regard to food bornepathogens and increasing shelf life; compare the shelfof raw milk(only a few days) with the shelf life ofyoghurt (several weeks).
Cont… Health benefits : Some fermented foods are said tohave definite health benefits although the scientificevidences for this is limited. Reports suggested thatfermented milk products such as yoghurt can reduceserum cholesterol levels and help avoid cancers,particularly those associated with the colon. Bioyoghurts (AB and ABT yoghurts) are said to have arestorative effects on the gut micro flora, assistingrecovery of a normal balanced flora after oral antibiotictherapy. Improve digestibility: Some fermented food are mosteasily digested than the original raw material. Peoplewho can not digest lactose properly (show lactose intolerance) can often consume some types of fermenteddairy products(particularly
Cont…yoghurts) without harmful effects. Lactose in tolerance isdue to the absence of enzyme galactosidase in digestivejuices, which converts lactose to glucose and glactose.Ingestion of dairy products leaves unabsorbed lactose ingut which is fermented by normal gut flora givingflatulence, abdominal pain and dirrhoea. Thefermentation of milk converts the harmful lactose tomore easily digested lactate, and theβ galactosidase inliver starter culture organisms appears to assist in thedigestion of any residual lactose. Legume, e.gsoyabean, contain oligosaccharides such as stachyosewhich are fermented in the gut to give gas and theassociated socially embarrassing flatus.
Cont..The oligosaccharides are broken down to readilydigestible monosaccharides and disaccharides duringmould fermentations of legumes, thus removing theproblem.Detoxification of raw materials: The fermentationprocess may remove toxic chemicals present in the rawmaterial. Cassava fermentation for example, removes acynogenic (cyanide producing) glycoside; cassava istoxic if eaten raw.
Table 1 History and origins of some fermented foodsFood Approximate yearof introductionRegionMushroomsSoy sauceWineFermented milkCheeseBeerBreadFermented MeatsSourdough breadFish saucePickled vegetablesTea4000 BC3000 BC3000 BC3000 BC2000 BC2000 BC1500 BC1500 BC1000 BC1000 BC1000 BC200 BCChinaChina, Korea, JapanNorth Africa, EuropeMiddle EastMiddle EastNorth Africa, ChinaEgypt, EuropeMiddle EastEuropeSoutheast Asia, North AfricaChina, EuropeChina
Table 2 Worldwide production of some fermented foodsFood Quantity (t) Beverage Quantity (hl)CheeseYoghurtMushroomsFish sauceDried stockfish15 million3 million1.5 million300 000250 000BeerWine1000 million350 million
Table 3 Individual consumption of some fermented foods: average perperson per yearFood CountryAnnualconsumptionBeer (I)Wine (I)Yoghurt (I)Kimchi (kg)Tempeh (kg)Soy sauce (I)Cheese (kg)Miso (kg)GermanyItaly, PortugalArgentinaFinlandNetherlandsKoreaIndonesiaJapanUKJapan13090704025221810107
Cont…Microflora in fermented foods: By tradition, lacticacid bacteria are the commonly usedmicroorganism for preservation of foods. Theirimportance is associated mainly with their safemetabolic activity while growing in food utilizingavailable sugar for the production of organic acidsand other metabolites. Their common occurrence inthe foods and feeds coupled with their long liveduse contributes to their natural acceptance asGRAS (Generally regarded as safe) for humanconsumption.
Cont..There are many kinds of fermented foods in which thedominating processes and end products are contributedby a mixture of endogenous enzymes and othermicroorganisms like yeast and mould. Very often, amixed culture originating from the native micro flora ofthe raw materials is in action in most of the foodfermentation processes. However, in an industrial scalea particular defined starter culture, which has beendeveloped under controlled conditions, is firstpreference so that the qualities of finished productcould be consistently maintained day after day.
Cont…Modern methods of gene technology makes it possiblefor the microbiologist to design and develop startercultures with specific qualities. Many microbiologistsstudies deal with identification of organisms isolatedfrom various fermented foods. Lactic acid bacteriaisolated from tomatoes that are naturally fermentedunder partial anaerobic conditions. These areLeuonostoc mesenteroides, Lactobacillus brevis andStreptococcous sp.In Asia mainly moulds of the genera Aspergillus,Rhizopus,
Cont..Mucor, Actinomucor. Amyomyces, Neurospora andMonascus are used in the manufacture of fermentedfoods.In Europe, mould ripened foods are primarily cheese andmeats, usually using a Penicillium species. Gari madeby fermenting cassava slurry was found to containBacillus, Aspergillus and Penicillium spp. aspredominant organisms.Lactic acid bacteria: Major group of Fermentative organisms. This group is comprised of 11 genera of gram-positivebacteria:
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 preciseboundaries all members share the property of producinglactic acid from hexoses. As fermenting organisms, they lack functional heme-linked electron transport systems or cytochromes, theydo not have a functional Krebs cycle.
Cont… Energy is obtained by substrate-level phosphorylationwhile oxidising carbohydrates. The lactic acid bacteria can be divided into two groupsbased on the end products of glucose metabolism. Those that produce lactic acid as the major or soleproduct of glucose fermentation are designatedhomofermentative. Those that produce equal amounts of lactic acid,ethanol and CO2 are termed heterofermentative. The homolactics are able to extract about twice as muchenergy from a given quantity of glucose as theheterolactics.
Cont… All members of Pediococcus, Lactococcus,Streptococcus, Vagococcus, along with somelactobacilli are homofermenters. Carnobacterium, Oenococcus, Enterococcus,Lactosphaera, Weissells and Lecconostoc and someLactobacilli are heterofermenters The heterolactics are more important than thehomolactics in producing flavour and aromacomponents such as acetylaldehyde and diacetyl.
Cont…Lactic Acid Bacteria – Growth: The lactic acid bacteria are mesophiles: they generally grow over a temperature range ofabout 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. Thoughsome as low as 3.2 and as high as 9.6.
Cont..Starter Cultures : Traditionally the fermenting organisms came from thenatural micro flora or a portion of the previousfermentation. In many cases the natural micro flora is eitherinefficient, uncontrollable, and unpredictable, or isdestroyed during preparation of the sample prior tofermentation (e.g. pasteurization). A starter culture can provide particular characteristics ina more controlled and predictable fermentation.
Cont… Lactic starters always include bacteria that convertsugars to lactic acid, usually: Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris or Lactococccus lactis subsp. lactis biovardiacetylactis. Where flavour and aroma compounds such as diacetylare desired the lactic acid starter will includeheterofermentative organisms such as: Leuconostoc citrovorum or Leuconostoc dextranicum.
Cont… The primary function of lactic starters is the productionof lactic acid from sugars Other functions of starter cultures may include thefollowing:○ 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
Cont… Food scientists frequently use the ability of bacterial cells togrow and form colonies on solid media to: isolate bacteria from foods, to determine what types and how many bacteria are present. Streak platesA single bacterial colonyA single bacterial colony
Cont..The streak plate technique : Bacteria are “streaked "over the surface of an agar plateso 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 ofcontaminating micro-organisms
The Streak PlateTechnique
Nutritional value of fermentedfoodsThere is a significant increase in the soluble fraction offood during fermentation. The quantity and quality offood proteins is expressed by biological value, andoften the content of water soluble vitamins is increased,while the anti nutritional factors show a decline duringfermentation. Fermentation also results in a lowerproportion of dry matter in food and concentrations ofvitamins, minerals and protein appear to increase whenmeasured on dry weight basis.Single as well as mixed culture fermentation of pearlmillet flour with yeast and lactobacilli significantlyincreased the total amount of soluble sugars, reducingand non reducing sugar content of anti nutritionalfactors to a safe level in comparison
Cont…With other methods of processing.Proteins: The protein efficiency ratio (PER) of wheatincreases on fermentation, partly due to increase inavailability of lysine. A mixture of wheat and soyabeansin equal amounts provides and improved pattern ofamino acids. The fermentation process raises the PERvalue of mixture to a level which is comparable to thatof casein.Fermentation may not increase the content of protein andamino acids unless ammonia or urea is added asnitrogen source to the fermentation media. The relativenutritional value (RNV) of maize increased from 65%to 81% when it is germinated, and
Cont…fermentation of flour made of the germinated maize givesa further increase in RNV to 87 % .Vitamins: During fermentation certain microorganismsproduce vitamins at higher rate than others do.Fermented milk products in general show an increase infolic acid content and slight decrease in vitamin B12while other B vitamins are affected only slightly incomparison to raw milk. The levels of vitamin b12,riboflavin and folacin are increased by lactic acidfermentation of maize flour, while the level ofpyridoxin is decreased.
Cont…Minerals: The mineral content is not affected byfermentation unless some salts are added to the productduring fermentation or by leaching when liquid portionis separated from the fermented food. Some times,when fermentation is carried out in metal containerssome minerals are solublised by the fermented product,which may cause an increase in mineral content.Phytate content in bread is lowered when the amount ofyeast or the fermentation time is raised.
Cheese preparationDefinition: In simple term cheese is the curd of milkseparated from the whey and pressed in to solid mass. Itis defined as a product made from the curd obtainedfrom the milk by coagulating the casein with the help ofrennet or similar enzymes in the presence of lactic acidproduced by added or adventious microorganisms, fromwhich part of moisture has been removed by cutting,cooking and/ or pressing, which has been shaped in andthen ripened by holding it for sometime at suitabletemperatures and humilities.Types of cheeses: The classification of cheese is basedon a number of factors like raw material, type ofconsistency, appearance(interior and exterior), fatcontent, moisture content
Cont..and ripening methods. However, the most commonly usedcriteria are the moisture content of the finished product andmode 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 differentbacteria like Lactococci, Lactobacilli, Pedococci,Propionibacteria, and brevibacteria etc.
Cont… Mold ripened: Ripening is brought about by moldspecies like Penicillium. Unripened: Ripening is not done.Basic processes involved in cheese production : Thecheese production involves the following three mainstepsA. Coagulum formationB. Separation of curd from whey, andC. Ripening of cheeseCoagulum Formation: Milk coagulation occurs due todistinct activities
Cont.. Inoculation with bacterial cultures e.g. Streptococcuslactis 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 caseinand caseino macro peptides. This cleavage occurs atspecific peptide bonds between phenylalanine atposition105 and meithonine at position 106 and leads tocoagulation of α andβ caseins and k casein hydrolysisproducts.k- casein stabilizes the colloidal nature of milk. The Nterminal
Cont..Region of k- casein is hydrophobic and it associates withthe lipophilic regions of α andβ casein, which areinsoluble. The C- terminal region of k-casein ishydrophilic and associates with water molecules. Thusan intact k casein molecule keeps the insoluble α andβcasein in suspension and prevents their coagulation.Hydrolysis of k casein by rennet separates itshydrophobic and hydrophilic regions and thereby ,eliminates its protective influence. As a result the α andβ caseins plus the k casein hydrolysis productsparticipate and form the coagulum. Calcium is essentialfor coagulation, and the process is very temperaturedependent.
Cont…Separation of curd: The coagulum is heated to 37 C andcooled. This eliminates rennet activity and separates, to someextent, the watery fluid called whey. The curd is separatedfrom whey, salted, and mixed with proteases and/ or lipases;alternatively, bricks of cheese may be inoculated withspecific strains of fungi, e.g. Penicillium camembertii, etc.The bricks are pressed to remove excess moisture to enableproper ripening.Ripening : Ripening procedures will vary with the type ofcheese produced. The cheese bricks are inoculated withspecific strain of fungi (P. roquefortii and P. camembertii)for the development of appropriate flavours through proteaseand lipase activities. Alternatively , protease and lipase maybe used for this purpose
Cont.. Protease from B. amyloliquefaciens are used toenhance flavors in cheddar cheese. Protease hydrolyze proteins to produce peptides ofvariable sizes. Peptides having terminal acidic aminoacids residues produce meaty appetizing flavors. Buthydrophobic amino acids residues located nonterminally produce bitter flavors; the flavors arestrongest in medium sized peptides are absent in longerpeptides and they decrease with decrease in peptidesize. Therefore, the kind and degree of flavor in cheesecan be controlled by regulating protein hydrolysis.
Common Cheese Making StepsCutting and CookingMilling and Salting Forming and Pressing Curing or RipeningDraining, Matting and WashingStarter and Rennet Addition
Terms Coagulation- Change from a fluid to a thickened mass;curdle; congeal. Whey- The watery part of milk that separates after themilk sours and thickens. Brine- Water strongly saturated with salt. Rennin- A stomach enzyme that coagulates casein and isused to commercially curdle milk in the making of cheese.But now microbial rennin are used.