MICROBIAL ACTIVITIES IN FOODS
Microbial flora associated with foods have a broad complement of enzymes that bring about fermentative proteolytic and lipolytic changes.Proteolytic organisms break down proteins and other nitrogenous compounds resulting in putrid & rotten odour & flavor.
Lipolytic organisms hydrolyze lipids giving rise to free fatty acids resulting in rancidity. These changes are undesirable in foods .
Fermentation produces flavor & textural changes also increases its nutritional quality.
Fermentation by certain molds, break down the indigestible protective coating as they are rich in cellulose splitting enzymes.
These enzymes convert cellulose simple sugars thereby increasing Nutritive value.
FERMENTATION
Fermentation is a metabolic process that consumes sugar in the absence of oxygen. The products are organic acids, gases, or alcohol.It occurs in yeast and bacteria.
The term fermentation means breakdown of carbohydrates material by microorganisms under anaerobic condition.
The list of foods produced by fermentation is extremely long and includes cheese, curd, butter, all alcoholic beverages. pickles, vinegar, bread, idli, soya sauce, coffee, tea, cocoa etc.
FERMENTATION
Yeast : Bread, Beer, Wine, distilled liquorsYeast + Bacteria: Vinegar
Bacteria: Fermented milk
FERMENTATION & ROLE OF LACTIC ACID BACTERIA
Fermentation is one of the oldest ways of food preservation. This is made possible by the use of Lactic Acid Bacteria or LAB that plays the major role in this process. Even with the absence of oxygen, it drives the reactions of converting the carbohydrate to lactic acid with addition of carbon dioxide .It also contributes to smell, taste, texture and colour of the foods. Without LAB, fermentation of sourdough bread, soybean, all fermented kinds of milk, beer, and pickles cannot be carried out. Since they are microaerophilic, which do not utilize oxygen, it cannot cause extreme changes in the food.
Lactic acid bacteria have been used to ferment or culture foods for at least 4000 years. They are used in particular in fermented milk products from all over the world, including yoghurt, cheese, butter, buttermilk, kefir and koumiss.
Lactic acid bacteria refers to a large group of beneficial bacteria that have similar properties and all produce lactic acid as an end product of the fermentation process. They are widespread in nature and are also found in our digestive systems. Although they are best known for their role in the preparation of fermented dairy products, they are also used for pickling of vegetables, baking, winemaking, curing fish, meats and sausages.
The manufacture of fermented milk products,involves a microbial process by which the milk sugar, lactose is converted to lactic acid. As the acid accumulates, the structure of the milk protein changes (curdling) and thus the texture of the product. Other variables such as temperature and the composition of the milk, also contribute to the particular features of different products.
The Lactic acid also gives fermented milk their slightly tart taste. Additional characteristic flavours and aromas are often the results of other products of lactic acid bacteria. For example, acetaldehyde, provides the characteristic aroma of yoghurt, while diacetyl imparts a buttery taste to other fermented milk. Additional micro-organisms such as yeasts can also be included in the culture to provide unique tastes. For example, alcohol and carbon dioxide produced by yeasts contribute to the refreshing, frothy taste of kefir, koumiss and Leben. Other manufacturing techniques such as removing the whey or adding flavours, also contribute to the large variety of available products.
For yoghurt, the manufacturer depends on a symbiotic relationship between two bacteria, Streptococcus thermophilus and Lactobacillus bulgaricus, where each species of bacterium stimulates the growth of the other. This interaction results in a shortened fermentation time and a product with different characteristics than one fermented with a single species.
With yoghurt and other fermented milk, there are considerable opportunities for exploiting lactic acid bacteria as probiotic cultures. These supplements and help our normal gut bacteria to function more efficiently. The worldwide market for these products continues to increase in response to the demands of an increasingly health-conscious public.
Lactic acid bacteria are therefore excellent ambassadors for an often maligned microbial world. They are not only of major economic significance but are also of value in maintaining and promoting human health.
FERMENTATION IN FOODS
Fermentation in Dairy Foods
Milk has been used to produce fermented milk products as far back as 10,000 B.C. in different regions all over the world. The many benefits of fermented milk products include enhanced digestibility, new and unique flavours, added probiotics, vitamins and minerals, and preservation products for a food that normally has a very short shelf life.Fermenting Process
The processes used to turn milk into different fermented foods involves adding lactic-acid-producing microorganisms, such as bacteria and yeast, which ingest lactose, or milk sugar, and release lactic acid as waste. This result is a rise in milk acidity, which allows the production of kefir, yogurt, cheese and sour cream among other fermented foods.Kefir
Kefir is a fermented yoghurt-like drink that dates back centuries to the shepherds of the Caucasus Mountains. The word “kefir” is derived from the Turkish word “Keif,” which means “good feeling”; a benefit this drink is said to provide for those who consume it. Kefir is produced with starter grains, known as kefir grains, which contain active microorganisms consisting of 83 to 90 percent lactic acid bacteria and 10 to 17 percent yeast. Kefir incorporates various essential vitamins, minerals, amino acids and enzymes, particularly phosphorus, magnesium, calcium and vitamins B2, B12, D, K and A.Yogurt
A staple of the Middle Eastern diet for thousands of years, yoghurt is a fermented food that holds the same level of protein and fat as the milk from which it is produced. It is also a source of calcium and vitamins B2, B6 and B12. Yogurt, like other fermented milk products, is primarily cultured from cows milk but can be made from goat’s milk. Microorganisms can also be used to ferment non-dairy milk, including coconut milk, almond milk and soy milk, into yoghurt.Cheese
Cheese may be the most popular fermented milk product, using more than one-third of all milk produced in the United States each year for its production. Both soft and hard types of cheeses are produced by culturing milk for an extended period of time. Certain types of cheeses can be made simply by straining the moisture out of sour cream or yogurt. Some other types of cheese, however, require additional steps in the culturing and fermentation process. Over 2,000 varieties of cheeses exist, with some of the most notable being cheddar, feta, cream, goat and blue.Sour Cream
The original process for making sour cream was to simply let cream sour on its own. Today, a more proactive process is used: the lactic-acid-producing bacteria Streptococcus lactis. The flavour of sour cream is mild and tangy and the texture is thick and smooth. With a fat content somewhere between 10 to 14 percent, sour cream has significantly fewer calories than mayonnaise – a food sour cream can replace in many applications. Sour cream also works well in baking recipes for cookies cakes, bread and pies.Fermentation in Vegetables
Fermented vegetables begins with Lacto-fermentation, a method of food preservation that also enhances the nutrient content of the food. The action of the bacteria makes the minerals in cultured foods more readily available to the body. The bacteria also produce vitamins and enzymes that are beneficial for digestion.In eastern Himalayan regions of India, a wide range of fermented vegetable products are prepared for bioprocessing the perishable vegetable for storage and further consumption. Lactic acid fermentation vegetables such as gundruk, sinki, and khalpi are fermented vegetable products of Nepal, Sikkim, and Bhutan.
Fermentation in Indian Foods
India is traditionally rich in fermented foods. In the Indian sub-continent, fermented food using local food crops and other biological resources are very common.Fermented foods such as idli and dahi were described as early as 700 BC. At present, there are hundreds of fermented foods with different base materials and preparation methodology. Each fermented food is associated with a unique group of microbiota, which increases the level of proteins, vitamins, essential amino acids and fatty acids
Foods like idlis, dosas, dhoklas, wadas and kadhi are some of the lactobacillus fermented cereals and legumes that are commonly consumed in India. The fermented foods increase the absorption of vital minerals from the gastrointestinal tract, thus preventing mineral deficiencies. Bread, fish sauce, wine and beer are some of the yeast-based fermented food beverages.
Indian fermented foods are consumed by the local population not just as a diet but as traditional medicine too. Many of the foods were observed to have a beneficial effect during ailment by the local people and they are used as a special diet or medicine for ages. Fermented food idli is easily digested and often used as food for infant and invalids. Fermented milk dahi can be used to cure intestinal disease such as diarrhoea; intake of dahi has anti-cholesteric, anticarcinogenic, anti-diabetic, angiotensin-converting enzyme inhibition effect and anti-atopic dermatitis effect.
Fermentation in Bakery Products
Fermentation is a baking process in which yeasted dough rises and increases in volume and flavour is developed. Fermentation occurs when yeast converts sugar present in flour such as starch into carbon dioxide and ethyl alcohol. CO2 gas is trapped by gluten proteins the flour which causes the dough to rise. Fermentation results in a light and airy crumb.Fermentation influences product volume, shape, crust colour, and crumb cell structure.
Fermentation in Alcoholic Beverages
Fermented beverages are produced through the process of fermentation. Fermentation in the case of alcoholic beverages refers to a metabolic process by which yeast converts sugar to ethanol. Yeast is a type of fungus used in the fermentation of alcohol. In order for fermentation to take place, you begin with some type of carbohydrate that is needed to feed the yeast. The type of carbohydrate used determines what the final product will be.Let’s look at some examples. Beer is produced by fermenting grain. Wine or hard cider is produced by fermenting fruit. Mead is produced by fermenting honey. Milk and tree or plant sap can be used to produce fermented beverages as well.
There is a limit to the alcoholic content of fermented beverages because yeast cannot survive in alcohol. Once the concentration of ethanol produced by the fermentation process reaches about 15%, the yeast will die and fermentation process will end.
In order to produce beverages above the concentration of ethanol achieved through fermentation, a distillation process is used. Distillation of alcoholic beverages is the process by which water is removed from a mixture of ethanol and water.
Vinegar
Vinegar is a food product made by acetic acid bacteria that can ferment the alcohol in alcoholic liquids to acetic acid.Vinegar has been used for cooking and in the household and different industries due to its mildly acidic nature for many centuries. It is one of the foods together with beer, wine, bread and fermented dairy products, that is the result of fermentation by microorganisms and has been around for thousands of years. It is a mixture of acetic acid (most often 5%) and water.
The fermentation is performed usually by acetic acid bacteria, from the genus Acetobacter, from the alcohol in a variety of sources (e.g., apple cider, wine, potatoes, fermented grain). Acetobacter bacteria are Gram-negative aerobic rods. They are naturally present in environments where alcohol is being produced and can be isolated from damaged fruit, apple cider, etc. In these liquids, the bacteria form a film on the surface, since they are aerobic and need good oxygen supply.
This film, called the mother of vinegar, can be used as a starter culture of acetic fermentation in fresh alcohol liquids. Mother of vinegar can also be found in unpasteurized store brand vinegar. Acetic acid bacteria are transmitted in nature by vectors like fruit flies and Vinegar Eels.
This acetic acid fermentation needs oxygenation. If left at room temperature alcohol-containing solution with Acetobacter will be converted to vinegar in months. The industrial process can be completed within hours since air is bubbled and mixed through the solution.
Vinegar can also be an undesired product in wine production. If the temperature in the fermentation vessel is too high, the Acetobacter will outgrow the yeasts and the produced alcohol will be converted to vinegar.
