Biotechnology PM 504 PDF Lecture Notes

Biotechnology PM 504  Fermented Foods 1 2 3 Fermentation is the Fermented foods are foods This process preserves the food, biochemical change in that have been through a and le...

Biotechnology PM 504  Fermented Foods 1 2 3 Fermentation is the Fermented foods are foods This process preserves the food, biochemical change in that have been through a and leads to production of the organic substances process of lactofermentation beneficial enzymes, B-vitamins, produced as a result of in which natural bacteria Omega-3 fatty acids, and various action of microbial feed on the sugar and starch strains of probiotics enzymes. in the food, thereby creating lactic acid.  Fermented foods and fermented drinks like Kefir and Kombucha introduce probiotic bacteria into the digestive system. Probiotics have also been shown to help slow or reverse some diseases, improve bowel health, aid digestion, and improve immunity. Probiotics help maintain a balance of gut bacteria and digestive enzymes, thereby improving absorption of food. BENEFITS OF FERMENTED FOODS Fermented foods are cheaper source of nutrients as compared to health foods which can be expensive. Fermented foods such as sauerkraut, pickles, beets and other foods involve Lactofermentation that allows the storage of these foods for longer periods of time without losing the nutrients.  Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Raw milk kept at room temperature is liable to microbial spoilage and on prolonged storage spontaneously becomes sour due to the activity FERMENTED DAIRY PRODUCTS of lactic acid bacteria flora of these bacteria may develop, which can be transferred deliberately to fresh milk in order to maintain or even strengthen it. A fermented milk product has been defined by the international Dairy Federation as the milk product prepared from skimmed milk with or without the use of specific microbial cultures.  Various types of fermented milks and derived products have been developed in various parts of the world The nature of these products depends on the type of milk used, pre-treatment of the milk, temperature and the conditions of fermentation and on the subsequent technological treatments. FERMENTED DAIRY PRODUCTS Most fermented dairy products are produced by activities of lactic acid bacteria, yeasts and molds are also involved many times. These microorganisms can be propagated as multiple-strain starter cultures consisting of a defined mixture of pure cultures or as mixed- strain starter cultures consisting of an undefined mixture of different types of bacteria.  Fermented milk products are produced from homogenized or pasteurized milk with the help of starters containing lactic acid bacteria. Some of these products are enriched with different types of dairy products (whey powder, milk FERMENTED DAIRY PRODUCTS powder, buttermilk powder.) before fermentation. The use of different starters in manufacturing various types of products gives each product a specific texture and a characteristic taste. Fermentation temperature and time vary by product. The fermented milk products can be grouped into different categories: 1 2 3 Moderately sour type Sour and very high sour Acid-cum alcohol in addition with pleasant aroma types to lactic acid e. g. cultured milk. e. g. curd, yogurt. e. g. kumiss and kefir.  Microorganisms Involved in fermentation process Fermented dairy products are made from milk of almost all domesticated milch animals. During fermentation, certain physical and chemical changes occur in the milk due to the growth and fermentative activities of lactic acid bacteria used as starter cultures. General steps involved in preparation of fermented dairy products. The growing interest of consumers towards therapeutic products has led to incorporation of probiotic cultures in different milk products. As a consequence, probiotic cultures are being increasingly incorporated in yogurts and fermented milk products. The most important dominant group for fermentation is lactic acid bacteria which is accepted as GRAS (generally regarded as safe) for human consumption The probiotic bacteria used in commercial products are mainly members of the genera Lactobacillus and Bifidobacterium Nutritional Benefits of Fermented Milk Products (i) Lactic acid bacteria such as L. acidophilus, Streptococcus thermophilus and Brevibacterium bifidum have been found to interfere with the colonization and proliferation of food borne pathogens, thus protecting from gastrointestinal infections (ii) Lactic acid bacteria have been found to exert anticarcinogenic effect by different potential mechanisms by which lactic acid bacteria exert antitumor effects have been suggested such as changes in faecal enzymes thought to be involved in colon carcinogenesis, cellular uptake of mutagenic compounds, reducing the mutagenicity of chemical mutagens and suppression of tumors by improved immune response (iii) Milk supplemented with cells of L. acidophilus helps in digestion of lactose for people suffering lactose intolerance because the lactic acid bacteria used to make yogurt produce lactase and digest the lactose. lactose in yogurt is better digested than lactose in other dairy foods by lactase-deficient individuals because of intra intestinal activity of yogurt microbial β-galactosidase. Nutritional Benefits of Fermented Milk Products (iv) Yogurt and other fermented foods are believed to have immunostimulatory effects due to their bacterial components. Milk components such as whey protein, calcium, certain vitamins and trace elements are also capable of influencing immune system. (v) Fermented milk products have been reported to have hypercholesteremic effect it was found that L. acidophilus exhibits the ability to lower serum cholesterol levels. It has been reported that consumption of certain lactobacilli, or products made from them, may reduce blood pressure in mildly hypertensive people. (vi) Probiotics may help prevent allergic reactions such as food allergies by reinforcing the barrier function of the intestinal wall, thereby possibly preventing the absorption of some antigens.  Fermentation Process The processes used to turn milk into different fermented foods involves adding lactic-acid producing microorganisms, Industrial process of Kefir production. such as bacteria and yeast, which ingest lactose and release lactic acid, thereby increasing milk acidity, which allows the production of kefir, yogurt, cheese and sour cream among other fermented foods. Kefir has various essential vitamins, minerals, amino acids and enzymes, particularly phosphorus, magnesium, calcium and vitamins B2, B12, D, K The immunological antitumoral and hypocholesterolemic effects of kefir have been investigated Fermentation Process Cream and Sour Cream: Cream is high fat, liquid milk product, which is separated from whole milk and contains not less than 18 percent fat. a more proactive process is used in which the lactic-acid- producing bacteria Streptococcus lactis is used as starter culture and the product is held at 22°C until the acidity is at least 0.5 percent. Cheeses: Cheese may be the most popular fermented milk product which is rich in protein, vitamin A and saturated fat. Both soft and hard cheeses are produced by culturing milk for an extended period of time and the composition of cheese varies with the fraction of milk used. Certain types of cheeses can be made simply by straining the moisture out of curd or yogurt. When cheese is made from whey, most of the fats stay in the curd while vitamins and minerals are drained off in whey General procedure of cheese making. Fermentation Process Cheese produced when milk is coagulated by rennin (example cheddar cheese) is a good source of calcium and phosphorus which is lost in whey when coagulation is brought about by adding acid to produce soft cheese (such as cottage cheese). Moisture content of soft cheese varies from 40-75 per cent while that of hard cheese is 30-40 per cent. This leads to longer shelf life of hard cheese as compared to soft cheese. Acidophilus milk is another type of fermented dairy product where Lactobacillus acidophilus is used as the bacterial culture. Low fat or skim milk is cultured with L. acidophilus and incubated at 38°C in order to form soft curds. This bacterium establishes itself in the intestinal tract where it inhibits the activities of harmful gas- producing organisms and thus can help patients with diarrhea and intestinal gas. acidophilus milk has a harsh acid taste an alternative was development of sweet acidophilus milk The bacteria in sweet acidophilus milk are grown separately and then added to pasteurized milk. This milk is stored at 40º F to keep the bacteria inactive. When the milk is consumed, the beneficial bacteria become active in the warm stomach and intestinal tract. Fermentation Process Bonny Clabber is a wild-cultured dairy food in that it requires no starter; rather, its probiotic properties come directly from the natural flora in the milk. Raw whole milk is kept at room temperature until the milk solids naturally separate from the whey, thereby, developing a thick and yogurt-like consistency. Filmjölk is a Swedish cultured dairy food that is mildly sour, tangy flavored because of the action of Lactococcus lactis and Leuconostoc mesenteroides. These bacteria make the milk slightly acidic, and that acidic environment coagulates the milk‘s natural proteins turning the milk into sour, thick Filmjölk Buttermilk is traditionally made from the milk reserved from making cultured butter using a starter culture and making whole-milk then adding lactic acid bacteria, particularly Streptococcus lactis or Lactobacillus bulgaricus. Dried buttermilk is used in baking. After inoculation with starter cultures, the product is incubated at 20-22°C. Yogurt is a fermented dairy food that requires a heat source in order to culture properly. Made by culturing milk with a variety of lactic acid producing, thermophilic bacteria. well known strains of bacteria in yogurt are Lactobacillus bulgaricus and Streptococcus thermophilus Any type of milk such as whole milk, low fat or skim milk can be used for yogurt production. Inoculated milk is incubated at 42-46°C until desired flavor, acidity and consistency are attained. FERMENTED VEGETABLES Sauerkraut: Cabbage contains a large number of lactic acid bacteria that can ferment and produce sauerkraut with salt alone. Sauerkraut is a clean, uncontaminated product, obtained by characteristic natural fermentation of shredded cabbage by lactic acid bacteria in the presence of not less than 2 % and not more than 3% salt. In order To obtain product of the highest quality, all the bacterial strains must carry out fermentation in a certain sequence. This fermentation can be broadly categorized as having successive stages, including an initial heterofermentative stage followed by a homofermentative stage Graph showing increase in lactic acid content with time during Sauerkraut fermentation. Sauerkraut Fermentation Leuconostoc mesenteroides: These bacterial strains initiate the fermentation, first producing around 0.25 to 0.3% lactic acid. They are heterofermenters and thus produce different compounds such as lactic acid, acetic acid, ethyl alcohol, carbon dioxide, mannitol, as end products. Mannitol produced is a bitter flavored compound which is metabolized later during the process by Lactobacillus plantarum. All the acids, in combination with alcohol form aromatic esters and contribute to the characteristic flavor of sauerkraut at optimum temperature. However, if the temperature is higher than 72° F (22° C), bacteria might not grow and that may lead to off-flavor of sauerkraut. In about 2 days, Leuconostoc mesenteroides produces about 0.3% lactic acid. decrease in pH is detrimental to the growth of bacterial species and restricts their growth. Lactobacillus plantarum: Once the growth of L. mesenteroides stops, L. plantarum takes over the production of lactic acid and continues the fermentation until an acidity level of 1.5 to 2% is achieved at temperatures higher than 72° F (22° C) and can also grow at higher acidity levels. Cabbage should contain up to 3.5% sugar. The sweeter the raw cabbage, the better is the sauerkraut obtained. L. brevis continues fermenting until an acidity level of 2.5 - 3% is obtained. Cabbage fermentation comes to the end, when the entire sugar has been exhausted by the bacterial culture. Sauerkraut Fermentation Any change to the above cycles of lactic acid production will alter the taste and quality of sauerkraut as long as the proper amount of salt is added and the recommended temperatures are maintained, the three bacteria strains will ferment Time temperature relationship for Sauerkraut fermentation: cabbage in the proper sequence giving a sound product. During fermentation, glucose is converted to about 50% lactic acid, 25% acetic acid and ethyl alcohol, and 25% carbon dioxide. Effect of Fermentation Temperature The best quality sauerkraut is produced when the temperature is maintained at 65-72° F (18-22° C). Temperatures of 45.5° F (7.5° C) to 65° F (18° C) favor the growth and metabolism of L. mesenteroides. Temperatures higher than 72° F (22° C) favor the growth of Lactobacillus species. Generally, lower temperatures produce higher quality sauerkraut due to slower metabolism at 45.5° F (7.5° C), bacterial growth is slowed down so, that the complete fermentation takes longer duration, sometimes even six months. In contrast, higher temperatures produce sauerkraut in 7-10 days. But the product produced is of lower quality and can have off flavor, aroma and texture. because high temperatures lead to faster metabolism and fermentation, which does not allow some types of lactic acid bacteria to grow all. As more lactic acid is produced, the sauerkraut becomes more acidic. Once the sugar supply is exhausted, lactic acid bacteria stop growing. Control of Bacteria Sauerkraut is made by lactic acid bacteria that break sugar into lactic acid, carbon dioxide and some alcohol. Cabbage contains water, sugar and many nutrients and thus is a perfect media for all types of bacteria to grow. Heat treatment kills undesirable bacteria, but it also kills lactic acid bacteria, so this method cannot be used for bacterial control in Sauerkraut fermentation. PH of fresh cabbage is at around pH 7.0. This neutral pH makes cabbage an ideal food for microorganisms as it contains water, sugar, proteins, minerals and all nutrients. Bacterial control is important at all stages of fermentation. Type and population of bacteria can be maintained by washing, applying salt and elimination of oxygen. Absence of Oxygen: Many microorganisms such as molds species need oxygen to survive. Absence of oxygen can thus help to inhibit the growth of such microorganisms. Oxygen elimination can be accomplished by a few methods such as packing the container tightly to full capacity with shredded cabbage, finely slicing the cabbage, this allows to pack more cabbage and disperse more air. keeping cabbage submerged in brine using weights, using water channel fermented crocks or air lock glass jars and eliminating oxygen which preserves vitamin C from oxidizing and losing its strength.  Health Benefits of Sauerkraut Sauerkraut is considered to be a rich source of vitamins C, B, and K. As a result of the fermentation process, the bioavailability of nutrients is increased which renders sauerkraut even more nutritious than the original cabbage. Low in calories and high in calcium and magnesium. Sauerkraut is a very good source of dietary fiber, folate, iron, potassium, copper and manganese. Acts as a good source of probiotics. Unpasteurized and uncooked sauerkraut contains live LAB which improves digestion and promote the growth of healthy flora in alimentary canal sauerkraut has been found to be high in the antioxidants such as lutein and zeaxanthin which are associated with preserving ocular health.  Spoilage of Sauerkraut Spoilage in sauerkraut causes undesirable color, off-odors, soft texture and unpleasant flavor and could result in a product that is unsafe to eat. if it has not fermented properly, it may not have become acidic enough to be preserved. If insufficient acid is formed, harmful microorganisms may grow. Sauerkraut may suffer from softness due to insufficient salt concentration, high temperatures during fermentation, uneven salt distribution or air pockets caused by improper packing, or wilted cabbage. Some yeasts may grow on surface of sauerkraut and lead to pink coloration due to higher than desired salt concentration, an uneven distribution of salt insufficient juice to cover the cabbage during fermentation exposure to air, high temperatures during fermentation, processing or storage, or by a long storage period. Fermented Olives Table olives are one of the main fermented vegetables in the world and can be processed as treated or natural. Green olives are obtained from olives harvested during the ripening cycle when they have reached normal size. Fresh green olives need to processed at the earliest as they undergo spoilage very quickly. As compared to natural fermented olives, treated green olives need to undergo an alkaline treatment before initiation of fermentation. Lactic acid bacteria (LAB) are the microorganisms responsible for the fermentation of treated olives In addition, yeasts also play a minor role and effect the flavor and aroma of table olives. Lactobacillus spp. has been consistently isolated from table olives. L. plantarum and L. pentosus are the predominant species in most fermentations. Fermented Olives Processing of Green Olives Green olives are processed in two principal ways: with fermentation (Spanish type) and without fermentation (Picholine or American type). Spanish or Sevillian Type The olives are treated in a diluted lye solution (sodium hydroxide) to eliminate and transform the oleuropein and sugars, to form organic acids that aid in subsequent fermentation, and to increase the permeability of the fruit the solution should cover the fruit completely. The olives remain in this solution until it has penetrated two thirds of the way through the flesh. The lye is then replaced by water and the product is washed repeatedly to remove any remaining residue. Fermentation was carried out in wooden casks in which the olives are covered with brine. More recently, larger containers which are coated with an inert material are used. The brine (9-10%) causes the release of the fruit cell juices, forming a culture medium suitable for fermentation. Fermented Olives The most dominant flora at the beginning of fermentation is the Gram-negative bacteria which are a consequence of contamination produced in the plant installations, and in the atmosphere. These bacteria disappear after a week and a half, making conditions conducive for the growth of LAB. At pH level of 6 and below, lactobacilli start multiplying rapidly, producing acid and inhibiting the growth of gram-negative bacteria. The brine attains a pH of 4.5 leading to a predominance of Lactobacillus plantarum and certain yeasts. Butyric fermentation may take place in some cases if pH changes a type of deterioration known as zapatería (cobbler’s) produces an unpleasant taste and odor at the end of the fermentation process Produced by bacteria belonging to the Clostridium and Propionibacterium genera which start multiplying at the onset of spring/summer season due to increase in temperature. The right combination of brine concentration and pH level (5% salt and 4.5 pH) helps to control fermentation processes. When properly fermented, olives keep for a long time. Fermented Olives Picholine Style French, Moroccan and Algerian olives belonging to Picholine variety Olives are first treated with 3-3.5 % lye solution in which they are left for 8 to 72 hours until the lye has penetrated three- quarters of the way through the flesh.. In order to remove their bitterness, they are washed repeatedly for one to two days, and then placed in a 5-6% brine solution for two days. They are then transferred to 7% brine solution. After 8-10 days they are ready for consumption. For increasing the keeping properties of olives, the concentration of brine can be increased to 8-10% or they need to be kept at low temperatures of 5º and 7º C, in a 3% brine solution.  Spoilage of Olives Soft pickles are produced as a result of contamination with some bacteria and yeasts Slime formation may occur due to low acid and salt. Darkening: Contact of green olives with air may lead to darkening of their color due to oxidation of polyphenols. Keeping olives in 1-2 % H2SO4 solution may be helpful in removing dark color. Blistering: Air spaces/ gas pockets may be produced beneath the surface of olives by gram negative bacteria such as Klebsiella, Escherichia due to high temperature and high alkaline conditions. This may be avoided by using 0.5 per cent lactic acid and 3-6 per cent salt and maintaining hygienic conditions. Off flavor: Development of disagreeable flavor may be a consequence of butyric acid formation which can be avoided by washing the olives and putting them in 7-8 per cent acid.  Spoilage of Olives Zapatera sickness: This may be caused due to formation of caprilic acid and butyric acid by propionibacterium and clostridium. It can be prevented by maintain the pH0.75%. Sodium nitrate is responsible for developing the characteristic color and flavor in cured meat. Addition of reducing sugars (e.g. glucose solids, dextrose) to the brine also helps in browning reactions during thermal processing to produce a desirable color and a caramel flavor in some products such as bacon.  Fermented Sausages The Processing of Fermented Sausages Sodium ascorbate or ascorbic acid (0.5–1%) is added in order to prevent oxidation and improve color stability by reducing metmyoglobin in meat to myoglobin, thus accelerating the overall curing reaction. addition, ascorbates and erythorbates have been shown to block the formation of carcinogenic N-nitrosamines in cooked cured meats The raw materials and additives, including microbial starters, are added for mixing and chopping, often under vacuum, in a mincer or cutter. Once ready, the batter is immediately stuffed under vacuum into natural, semisynthetic (collagen) or synthetic casings that are permeable to water and air, and both ends are clipped. The sausages are hung in racks and placed in natural or, mostly, air-conditioned fermentation chambers at high relative humidity.  Fermented Sausages The Processing of Fermented Sausages Ripening includes the activity of fermentative bacteria followed by drying for development of sensory characteristics. Some types of sausages are subjected to smoke (controlled combustion of oak wood at 300-600 °C) to minimize the production of polycyclic hydrocarbons. Smoke has antimicrobial and antioxidant effects, generates specific flavor and color components. Defects and Their Causes Fermented meat products may be associated with various defects due to improper fermentation or processing. Surface may be blurred, due to higher temperature of the fat comminution, blending and stuffing.  Fermented Sausages The sausages might be deformed due to too rapid drying or case-hardening. There might be discoloration of the product surface owing to too high smoking when the surface is wet; smoking or ripening. Discoloration of product from the inside can arise due to insufficient curing salt; insufficient oxygen removal during comminution and stuffing or too old (rancid) fat. White spots on surface of fermented meat products might be due to yeasts and molds because of inefficient drying or contamination of ripening room with yeasts and molds. Unacceptable acidic taste might occur in certain cases when the raw material has too high carbohydrate concentration or higher than necessary temperature.