Fermentation (PDF)

FERMENTATION By G. S. Olavario What is fermentation? Fermentation is any metabolic process in which microorganisms’ activity creates a desirable change in food and beverages, whether it’s increasing flavor, preserving foodstuffs, providing health benefits, or more. The word “ferment” comes from...

FERMENTATION By G. S. Olavario What is fermentation? Fermentation is any metabolic process in which microorganisms’ activity creates a desirable change in food and beverages, whether it’s increasing flavor, preserving foodstuffs, providing health benefits, or more. The word “ferment” comes from the Latin verb “fervere,” which means “to boil.” Ironically, fermentation is possible without heat. Fermentation is an enzyme catalysed, metabolic process whereby organisms convert starch or sugar to alcohol or an acid anaerobically releasing energy. The science of fermentation is called “zymology”. How does fermentation work? Microorganisms survive using carbohydrates (sugars, such as glucose) for energy and fuel. Organic chemicals like adenosine triphosphate (ATP) deliver that energy to every part of a cell when needed. Microbes generate ATP using respiration. Aerobic respiration, which requires oxygen, is the most efficient way to do that. Aerobic respiration begins with glycolysis, where glucose is converted into pyruvic acid. When there’s enough oxygen present, aerobic respiration occurs. Fermentation is similar to anaerobic respiration—the kind that takes place when there isn’t enough oxygen present. However, fermentation leads to the production of different organic molecules like lactic acid, which also leads to ATP, unlike respiration, which uses pyruvic acid. Depending upon environmental conditions, individual cells and microbes have the ability to switch between the two different modes of energy production. Organisms commonly obtain energy anaerobically through fermentation, but some systems use sulfate as the final electron acceptor in the electron transport chain. Process of Fermentation In fermentation, the first process is the same as cellular respiration, which is the formation of pyruvic acid by glycolysis where net 2 ATP molecules are synthesized. In the next step, pyruvate is reduced to lactic acid, ethanol or other products. Here NAD+ is formed which is re-utilized back in the glycolysis process. Process of Fermentation Fermentation occurs in the absence of oxygen (anaerobic conditions), and in the presence of beneficial microorganisms (yeasts, molds, and bacteria) that obtain their energy through fermentation. If enough sugar is available, some yeast cells, such as Saccharomyces cerevisiae, prefer fermentation to aerobic respiration even when oxygen is abundant. During the fermentation process, these beneficial microbes break down sugars and starches into alcohols and acids, making food more nutritious and preserving it so people can store it for longer periods of time without it spoiling. Fermentation products provide enzymes necessary for digestion. This is important because humans are born with a finite number of enzymes, and they decrease with age. Fermented foods contain the enzymes required to break them down. Fermentation also aids in pre-digestion. During the fermentation process, the microbes feed on sugars and starches, breaking down food before anyone’s even consumed it. What Are the Advantages of Fermentation? Fermented foods are rich in probiotics, beneficial microorganisms that help maintain a healthy gut so it can extract nutrients from food. Probiotics aid the immune system because the gut produces antibiotic, anti-tumor, anti-viral, and antifungal substances, and pathogens don’t do well in the acidic environment fermented foods create. Fermentation also helps neutralize anti-nutrients like phytic acid, which occurs in grains, nuts, seeds, and legumes and can cause mineral deficiencies. Phytates also make starches, proteins, and fats less digestible, so neutralizing them is extremely beneficial. Fermentation can increase the vitamins and minerals in food and make them more available for absorption. Fermentation increases B and C vitamins and enhances folic acid, riboflavin, niacin, thiamin, and biotin. The probiotics, enzymes, and lactic acid in fermented foods facilitate the absorption of these vitamins and minerals into the body. What Are the Advantages of Fermentation? Fermentation is suitable for all kinds of environments. It is one of the oldest metabolic processes which is common to prokaryotes and eukaryotes. Fermentation is widely used in various industries. Using suitable microorganisms and specified conditions different kinds of fermentation products are formed namely:- Wine Beer Biofuels Yoghurt Pickles Bread Sour foods containing lactic acid Certain antibiotics and What Are the Advantages of Fermentation? Fermentation can make food nutritious, digestible and flavoured. There are many benefits of consuming fermented food. It improves digestion and helps to maintain intestinal bacteria It has an anti-cancer effect. Improves immune system Reduces lactose intolerance Other than the food industry, there are many other areas where the fermentation process is used. Methane is produced by fermentation in sewage treatment plants and freshwater Types of Fermentation Lactic acid fermentation. Yeast strains and bacteria convert starches or sugars into lactic acid, requiring no heat in preparation. These anaerobic chemical reactions, pyruvic acid uses nicotinamide adenine dinucleotide + hydrogen (NADH) to form lactic acid and NAD+. (Lactic acid fermentation also occurs in human muscle cells. During strenuous activity, muscles can expend adenosine triphosphate (ATP) faster than oxygen can be supplied to muscle cells, resulting in lactic acid buildup and sore muscles. In this scenario, glycolysis, which breaks down a glucose molecule into two pyruvate molecules and doesn’t use oxygen, produces ATP.) Lactic acid bacteria are vital to producing and preserving inexpensive, wholesome foods, which is especially important in feeding impoverished populations. This method makes sauerkraut, pickles, kimchi, yogurt, and sourdough bread. Lactic Acid Fermentation Lactic acid is formed from pyruvate produced in glycolysis. NAD+ is generated from NADH. Enzyme lactate dehydrogenase catalyses this reaction. Lactobacillus bacteria prepare curd from milk via this type of fermentation. During intense exercise when oxygen supply is inadequate, muscles derive energy by producing lactic acid, which gets accumulated in the cells causing fatigue. Types of Fermentation Homo fermentation: only one type of product formation Hetero fermentation: more than one product formed Types of Fermentation Ethanol fermentation/alcohol fermentation. Yeasts break pyruvate molecules—the output of the metabolism of glucose (C6H12O6) known as glycolysis—in starches or sugars down into alcohol and carbon dioxide molecules. Alcoholic fermentation produces wine and beer. Alcohol Fermentation This is used in the industrial production of wine, beer, biofuel, etc. The end product is alcohol and CO2. Pyruvic acid breaks down into acetaldehyde and CO2 is released. In the next step, ethanol is formed from acetaldehyde. NAD+ is also formed from NADH, utilized in glycolysis. Yeast and some bacteria carry out this type of fermentation. Enzyme pyruvic acid decarboxylase and  Types of Fermentation Acetic acid fermentation. Starches and sugars from grains and fruit ferment into sour tasting vinegar and condiments. Examples include apple cider vinegar, wine vinegar, and kombucha. Vinegar is produced by this process. This is a two-step process. The first step is the formation of ethyl alcohol from sugar anaerobically using yeast. In the second step, ethyl alcohol is further oxidized to form acetic acid using acetobacter bacteria. Microbial oxidation of alcohol to acid is an aerobic process. Key Microorganisms in Food Fermentation  Lactic Acid Bacteria (LAB) Lactic acid bacteria (LAB) are bacteria that are common to the dairy industry; it is assumed that LAB are organisms that produce lactic acid as the principle byproduct of sugar fermentations. LAB are generally more tolerant of low pH environments than are other bacteria associated with milk and dairy products. LAB are common in nature and are often associated with plant materials. They can also be found as part of the resident microflora of humans and other mammals (e.g., oral cavity, GI track, etc.). LAB are most known in the dairy industry for their use in “starter” cultures and dairy fermentations. As starter cultures, they are added to milk and allowed to grow under controlled conditions in order to produce acid and/or modify the flavor and texture for the desired characteristics of a cheese or cultured product. LAB can also cause milk to “sour” while some strains may produce gas in cultured products or cheese that will influence package appearance and cause product flavor defects. Lactobacillus species: These bacteria are involved in lactic acid fermentation, which is critical for the production of yogurt, sauerkraut, and pickles. They convert lactose and other sugars into lactic acid, lowering the pH and creating an inhospitable environment for spoilage organisms. The genera of lactic acid bacteria Lactics are classified by the fermentation pathway used to ferment glucose and by their cell morphology. Lactobacill us are rod shaped organisms that can be either hetero- or homofermentative. They are widespread and can be isolated from many plant and animal sources. Lactobacilli are more tolerant to acid than the other genera of lactic acid bacteria and this property makes them important in the final phases of many food fermentations when other organisms are inhibited by the low pH. The genera of lactic acid bacteria Leuconostoc are ovoid cocci, often in chains. All bacteria of this genus have a heterofermentative mode of metabolism. When grown in media containing sucrose, copious amounts of a slimy polysaccharide (dextran) are produced. Dextran has found uses in medicine as a plasma extender and in biotechnology. The genera of lactic acid bacteria Pediococcus are cocci often found in pairs and tetrads that are strictly homofermentative. Their habitat is restricted mainly to plants. P. cerevisiae has been used as a starter culture for the fermentation of some sausages with great success. Streptococcus are cocci in chains that are distinguished from the Leuconostoc by their strictly homofermentative metabolism. These organisms can be isolated from oral cavities of animals, the intestinal tract, skin, and any foods that come in contact with these environments. While the other genera of lactic acid bacteria rarely cause disease, Streptococcus pyogenes is a common, troublesome pathogen, causing strep throat and rheumatic fever. The genera of lactic acid bacteria Enterococcus and Lactoco ccus are two recent taxonomic divisions of lactic acid bacteria. These were created to reorganize the large and divergent Streptococcus g enus into smaller, more related groups of bacteria. Enterococcus are gram-positive cocci that form pairs or chains. They are distributed widely in the environment, particularly in feces of vertebrates. Strains can grow in the presence of 6.5% NaCl and with 40% bile present. The genera of lactic acid bacteria Lactococcus includes strains that are gram-positive, spherical cells occurring in pairs or chains. They have a strictly homofermentative metabolism and are found in dairy and plant products. For centuries lactic acid bacteria have been used to produce fermented food products including pickles, sauerkraut, sausage, yogurt, cheese, buttermilk, soy sauce, and more. Some examples include Streptococcus thermophilus along with Lactobacillus bulgaricus that are used in the production of yogurt. Also, Lactococcus lactis and S. thermophilus are two strains often used as starter cultures in the production of cheese. Finally, Lactobacillus and Leuconost oc are useful in the fermentation of cabbage to sauerkraut.  YEAST The scientific name “Saccharomyces” is derived from the Greek word meaning “sugar fungus” while “cerevisiae” comes from Ceres the Roman Goddess of the growth of food plants and crops. Saccharomyces cerevisiae (S. cerevisiae) is a species of yeast or single-celled fungus microorganism known since early times for its fermentation properties and used in baking, brewing, and winemaking. Today, it is also used as a unique probiotic to support gut health as well as being used for a variety of other applications.  YEAST Saccharomyces cerevisiae is a unicellular fungus that reproduces by budding from a pre-existing cell, and which presents the main components of a typical eukaryotic cell. Its cell wall is a dynamic structure relatively rigid that provides cell protection, and osmotic support and determines cell shape. S. cerevisiae cells are round to ovoid and are approximately 5–10 micrometers in diameter.(2) All strains of S. cerevisiae can grow aerobically on glucose, maltose, and trehalose. However, they fail to grow on lactose and cellobiose. S. cerevisiae growth on other sugars varies. Galactose and fructose are shown to be two of the best fermenting sugars. The ability of S. cerevisiae to use different sugars can differ depending on whether it is grown aerobically or anaerobically. Some strains cannot grow anaerobically on sucrose and trehalose.(3) In nature, S. cerevisiae is most commonly found on the skin of ripe fruits, such as grapes. S. cerevisiae can also be found in the bark of some tree species, as well as on some insects. S. cerevisiae is one of the most intensively studied eukaryotic model organisms in molecular and cellular biology. The genera of lactic acid bacteria Lactococcus includes strains that are gram-positive, spherical cells occurring in pairs or chains. They have a strictly homofermentative metabolism and are found in dairy and plant products. For centuries lactic acid bacteria have been used to produce fermented food products including pickles, sauerkraut, sausage, yogurt, cheese, buttermilk, soy sauce, and more. Some examples include Streptococcus thermophilus along with Lactobacillus bulgaricus that are used in the production of yogurt. Also, Lactococcus lactis and S. thermophilus are two strains often used as starter cultures in the production of cheese. Finally, Lactobacillus and Leuconost oc are useful in the fermentation of cabbage to sauerkraut.  YEAST Saccharomyces cerevisiae’s use in baking During fermentation in bread-making, Saccharomyces cerevisiae as yeast produces carbon dioxide and modifies the physical properties of dough through the action of enzymes. First, the yeast ferments sugars which it directly assimilates and is naturally present in the flour. The second phase corresponds to the fermentation of sugar found in flour called maltose. Glucose is transformed by Saccharomyces cerevisiae into carbon dioxide (which gives volume to bread and the honeycomb shape of the crumb) and alcohol (evaporated when baked). Saccharomyces cerevisiae yeast also produces aromatic compounds that contribute to the aroma and taste of bread. Lastly, during baking, fermentation is activated by heat and ends when the temperature reaches 50°C.  YEAST Brewer and winemakers’ “secret ingredient” In the absence of air, Saccharomyces cerevisiae cells transform sugars into carbon dioxide and alcohol. This process is what changes simple barley or wheat into beer and grapes into wine. In beer brewing, saccharomyces cerevisiae is sometimes referred to as a top-fermenting or top-cropping yeast. Yeast not only plays a major role in the fermentation process, in brewing but also the aromatic qualities of the end product. Different types of strains are often brewers’ “secret ingredient.” Depending on the temperatures used in fermentation, the same strain can produce different flavors. Saccharomyces cerevisiae is also the main strain used in winemaking. Yeast in winemaking is used for the fermentation process just like in brewing. As the yeast makes alcohol through feeding, it also produces fermentation aromas (fruity, peach, rose, etc.) and secondary aromas, known as varietal aromas, associated with specific grape varieties. These secondary aromas can only be revealed by using specific types of yeast during the fermentation process (vanilla spice or toasty notes).  YEAST Nutritional yeast = saccharomyces cerevisiae In recent years, many people have started consuming a specific type of yeast called nutritional yeast or also known as NOOCH. In fact, most nutritional yeasts are made with the yeast strain Saccharomyces cerevisiae. It can be used in dietary supplements, seasonings, and functional foods. Nutritional yeast can also provide appealing nutritional contributions. It is a valuable source of protein. These proteins contain all the essential amino acids that people should get in a healthy diet. Source of dietary fiber, Saccharomyces cerevisiae yeast also contains several vitamins like thiamine (B1), riboflavin (B2), niacin (B3), Pyridoxine (B6), and folic acid (B9). This makes nutritional yeast a potentially interesting source of vitamins for all, including vegans and vegetarians.  MOLDS There are relatively few molds in fermented food and beverages, including Actinomycetes, Mucor, Rhizopus, Amylomyces, Monascus, Neurospora, Aspergillu s, and Penicillium. The main role of these molds in fermented food is to produce a variety of enzymes. For example, protease (acidic, neutral, alkaline), amylase, glutamidase, pectinase, hemicellulase, and cellulase can use starch, oligosaccharide and monosaccharide as carbon source, and protein, amino acid and urea as nitrogen source. Maltose can effectively induce Asp. oryzae to secrete various hydrolytic enzymes, such as Asp. oryzae to secrete α-amylase, Asp. Niger, and Asp. nigrum to produce Glucoamylase and so on. Starchy raw materials are degraded into small molecular sugars such as dextrin, maltose and glucose under the action of amylase and glucoamylase. On the one hand, they promote the growth of bacteria, yeasts and other microorganisms, and further metabolize to produce alcohols, organic acids and other flavor substances. On the other hand, some monosaccharides, oligosaccharides, and polysaccharides that can’t be decomposed increase the nutritional value of the products. Protein raw materials are decomposed into peptides, amino acids and other functional and flavor substances by protease. At the same time, these small molecular substances also contribute to the growth and metabolism of bacteria and yeast. Stages and Conditions for Successful Fermentation Inoculation and Lag Phase: Introduce the initial stage of fermentation where microorganisms are introduced to the substrate (e.g., milk, dough). Discuss the lag phase where microorganisms adapt to the environment before active fermentation begins. Exponential Growth Phase: Explain the phase where microorganisms rapidly multiply and metabolize substrates, leading to significant biochemical changes. Emphasize the importance of maintaining optimal conditions (temperature, pH, oxygen levels) for this phase. Stationary and Decline Phases: Describe the stages where the growth rate slows due to nutrient depletion and waste accumulation, eventually leading to the stabilization of the product's characteristics. Environmental Conditions: Detail the specific environmental conditions required for different types of fermentation, such as anaerobic conditions for alcoholic fermentation and controlled temperatures for lactic acid fermentation. Nutritional and Sensory Changes in Fermented Foods Nutritional Enhancements: Discuss how fermentation can increase the bioavailability of nutrients, produce vitamins (e.g., B-vitamins), and reduce anti-nutritional factors in foods. Use examples like increased folate in fermented vegetables and improved protein digestibility in fermented dairy. Sensory Changes: Analyze how fermentation impacts the flavor, texture, and aroma of food products. Explain how lactic acid contributes to the tangy taste of yogurt and how alcohol and carbon dioxide influence the texture of bread. Case Studies: Present case studies of specific fermented foods (e.g., yogurt, sauerkraut) to illustrate how fermentation enhances both nutritional and sensory qualities. 1. Feldmann, Horst (2010). Yeast. Molecular and Cell bio. Wiley-Blackwell. Pg. 2. ISBN 978-3527326099. 2. https://www.researchgate.net/publication/2222445 79_Brewer’s_Saccharomyces_yeast_biomass_charact eristics_and_potential_applications https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9041 164/ Add a Slide Title - 7 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4261 876/ Add a Slide Title - 8