Environmental biology is one of the critical Biology Topics that involves understanding how humans impact the environment and how to address environmental issues.
Role of Microbes in Food Processing – Common Microbes Used in Food Processing
Microorganisms have been in use for thousands of years to obtain products like curd, wine, vinegar, bread, etc. During the recent two to three decades biotechnology has brought total revolution, advancement, sophistication, and exploitation of such organisms in various fields for the welfare of human beings. Biotechnology has helped to increase industrial production of alcohols, antibiotics, vitamins, household products, and hormones by developing new and more efficient strains of microorganisms. Such microorganisms with a greater ability to fix different nutrients and make them available for plants are being used as biofertilizers. A few important aspects are discussed in this chapter.
Microbes are tiny living things that are found all around us and are too small to be seen by the naked eye. They live in soil, water, and in the air. The human body is home to millions of these microbes too, it is also called microorganisms.
In Household Food Processing
A. Dairy Products
A dairy product is a food produced from the milk of mammals. These are usually high energy-yielding food products. A production plant for the processing of milk is called a dairy factory. The lactic acid bacteria (LAB) are used in the preparation of butter, cheese, curd etc. The curd is prepared from milk in two steps. LAB converts lactose sugar to glucose and then glucose to lactic acid. Lactic acid causes coagulation of milk protein casein. Milk is changed into curd, yogurt, and cheese. The names of a few products, raw materials used, and the microorganisms involved are as follows.
In India, curd is prepared by inoculating skimmed milk with Lactobacillus acidophilus. The optimum temperature for the formation of curd is about 40°C. Curd has a higher nutritive value than milk. It contains many organic acids and vitamins like Vitamin B12. LAB, present in curd also prevents the growth of disease-causing microbes in the digestive tract. Curd is churned to prepare lassi.
It is prepared by curdling milk by Streptococcus thermophilus and Lactobacillus bulgaricus. The appropriate temperature is between 40-46°C for a duration of four hours. Yogurt is sweetened and mixed with fruits.
It is prepared by using the bacteria Streptococcus lactis, S. cremoris, and Lactobacillus citrovorum. It is a yellowish, soft, solidified form of milk cream.
4. Butter Milk
It is prepared by acidulation of skimmed milk with Lactobacillus acidophilus, Streptococcus cremoris, S. lactis, and Leuconostoc sp., for 18 hours at 22°C.
Cheese is prepared from curd separated from whey. There are three types of cheese – soft which contains 50-80% moisture, semi-hard with 45% moisture and hard with less than 40% moisture. Curdling of cheese is done by using different strains of LAB to prepare different types of cheese. Along with the microbe, rennet is used which contains the enzyme rennin that can coagulate milk protein casein. Unripened cheese such as cottage cheese and cream cheese are not fermented by microorganisms.
Ripened cheese is prepared by dipping the unripened ones in brine and wiping and maturing it by further microbial activities. It takes about 1-16 months. Large holes in Swiss cheese are due to excess CO2 production by applying Propionibacterium shermanii, Roquefort cheese by Penicillium roqueforti, camembert cheese by Penicillium camembert (when only bacteria are used is called cheddar, fungi are used is called Roquefort and both are used is called camembert).
Cheese is a food derived from milk that is produced in a wide range of flavors, textures, and forms by coagulation of the milk protein casein. Production of cheese-
- 1st Stage: At first the milk is separated into curd and whey by inoculating the milk in carefully controlled with a starter culture containing the microorganisms like Streptococcus lactis or Lactobacillus lactis. As fermentation proceeds, lactic acid sours the milk and coagulates the milk protein into casein and acid kept at 50°C. Coagulation is increased by adding rennet which contains the enzyme rennin at 32°C for 30 minutes.
- 2nd Stage: The solid part of milk is known as curd and the liquid is whey. The curd is heated gently to separate the cheese from the whey. The liquid left in cheese is drained by it in cloth. Then it is salted pressed into the desired shape and mixed with cream for marketing.
The different products, raw materials, and microbes used are listed below:
|Products||Raw Materials||Microorganisms Involved|
|1. Curd||Cream and skimmed milk||Lactobacillus acidophilus.|
|2. Cheese (soft, hard, unripened, ripened)||Milk-curd||Streptococcus, Leuconostoc, Propionibacterium shermanii, Penicillium roqueforti, Penicillium camemberti.|
|3. Yoghurt||Milk, creamed milk||Streptococcus thermophilus, Lactobacillus bulgaricus.|
|4. Butter||Creamed milk||Leuconostoc citrovorum, Streptococcus lactis, S. cremoris.|
|5. Butter milk||Creamed milk||Lactobacillus acidophilus, Streptococcus lactis, Leuconostoc mesenteroides, Streptococcus cremoris.|
|6. Kefir||Fermented milk||Streptococcus lactis, Lactobacillus kefir, Candida kefir, Lactobacillus bulgaricus.|
|7. Koumis||Mare’s milk||Lactobacillus bulgaricus.|
|8. Taette||Milk||Streptococcus lactis varhollan dicus, Yeasts (Saccharomyces sp.)|
|9. Idli||Rice and pulse powders||Leuconostoc mesenteroides|
|10. Fish sauces||Small fish||Bacillus sp.|
|11. Kimchi||Cabbage and other vegetables||Lactic acid bacteria|
Apart from breastfed infants, the human consumption of dairy products is sourced primarily from the milk of cows; yet goats, sheep, yaks, horses, camels, and other mammals are also the other sources of dairy products consumed by humans.
Bread is a staple food prepared by baking a dough of flour and water. It is popular around the world and is one of the world’s oldest foods. Bread is made from flour obtained by grinding cereal grains usually wheat. Strains of Saccharomyces cerevisiae grown on molasses are used as Baker’s yeast. The yeast is available in the form of powder or cake. A small quantity of yeast is added to wheat flour and kneaded. The kneaded flour is kept at a warm temperature for a few hours. It swells up. The process is called leavening. The puffed-up appearance is due to the production of CO2.
Actually, yeast produces three types of enzymes – amylase, maltase, and zymase. Amylase converts a small quantity of starch to maltose. Maltase converts it to glucose. Glucose is changed to ethyl alcohol and car¬bon dioxide by zymase. The leavened dough is baked. It produces soft and spongy bread. The sponginess is due to the expulsion of carbon dioxide and alcohol. Eventually, combinations of different flours and different proportions of ingredients, have resulted in the wide variety of types, shapes, and textures of bread available around the world. It may be leavened by a number of different processes ranging from the use of naturally occurring microbes to high-pressure artificial aeration during preparation and baking. A wide variety of additives may be used, from fruit and nuts to various fats, and chemical additives designed to improve flavour, texture, and colour.
Bread may be served in different forms at any meal of the day, eaten as a snack, and is even used as an ingredient in other culinary preparations. As a basic food worldwide, bread has come to take on significance beyond mere nutrition, evolving into a fixture in religious rituals, secular, cultural life, and language.
C. Dosa, Uppma and Idli
Indian food reflects an amalgamation of the cuisines of many diverse regions. There is great variety in Indian cuisines and popular breakfast foods vary from region to region. The popular foods for breakfast in South India are dosa, idli and uppma. Raw materials used are rice and black gram. These two are soaked overnight, washed, mixed, and ground. The mixture is allowed to undergo fermentation with Leuconostoc and Streptococcus species of bacteria. For idli, the dough is spread in small discs. When the batter has risen enough, it is cooked by steaming.
D. Other Foods
This is a type of food in Indonesia produced from soybean seeds. Water-soaked seeds are ground and inoculated with the spores of Rhizopus. The mixture is then incubated for 20-24 hrs at 32°C. After incubation, the product is added with salt and fried in oil before eating.
It is a Japanese food prepared from soybean seeds. In China, it is called Sofu. It is a cheese-like substance developed by the fermentation of soybean seeds by Mucor sp. The soaked soybean seeds are ground and added with Mg or Ca salts and the mass is incubated at 14°C for one month after inoculating with Mucor.
3. Soya Sauce
It is a brown, salty, and tangy sauce produced from a mixed substrate consisting of soybeans and wheat. This is a representative product that has mould activity in two stage fermentation process – Koji stage – the moulder starter used is often called koji. Moromi stage – a mashing process in which conditions are made so as not to allow moulds to grow.
Poi is a type of fermented food from Hawaiian islands. It is prepared from the Taro plant. The plants are steamed, ground, and kept for 1-6 days for fermentation. In the first few hours, Pseudomonas and other microbes dominate, but they are successively replaced by Streptococcus, Lactobacillus, and Leuconostoc, and finally, Geotrichum candidum and different yeasts dominate. Due to the presence of ethanol and different acids like acetic acid, lactic acid, etc., a suitable flavour and texture develop in the product.
Uses of Microbes in Non-Dairy Products:
|Domestic Food||Source Raw Materials||Microorganisms Involved|
|1. Tandoori roti, Kulcha, Nan||Flour, Wheat||Saccharomyces cerevisiae|
|2. Kasundi (Mustard Sauce)||Mustard paste, green mango||Leuconostoc mesenteroides|
|3. Idli||Rice, Lentil Pulse||L. mesenteroides, Streptococcus faecalis|
|4. Soya Souce||Soybean, Wheat||Aspergillus oryzae|
|5. Tofu||Coagulate soya milk||A. oryzae, Mucor sp.|
E. Single Cell Protein (SCP)
The term refers to protein obtained from the large-scale growth of cells of microorganisms such as bacteria, yeasts, and other fungi and algae. The protein may be used for human consumption or animal feed. It may also be a useful source of minerals, vitamins, fats, and carbohydrates. The common SCP are obtained from Spirulina, yeast, and Fusarium graminearum. The mushrooms, where fruit bodies are eaten as food are also considered in this group. Besides high protein content SCP is useful in reducing environmental pollution by managing industrial and agricultural wastes. The SCP industries have developed in different corners of the world in recent years.
Advantages of using Single-Cell Protein:
The advantages of using single-cell protein as a food substitute/supplement are:
- High yield.
- The protein content of microbial cells is high.
- The selected microorganisms yield proteins enriched with all essential amino acids.
- High vitamin content.
- The medium of growth for single-cell protein organisms may be industrial wastes or byproducts.
- e.g., bacterial cells that thrive on hydrocarbon wastes from the petroleum industry may be a good source of protein.
Disadvantages of using Single-Cell Protein:
- Consumers’ acceptability issue.
- Nucleic acid content of some microbial cells might cause intestinal problems.
- Source of all essential amino acids.
The term toddy is applied to sweet exudation obtained by tapping young unopened spadix of coconut. The term is also applied to a refreshing drink produced by fermentation of coconut water. Palm sugar or jaggery is obtained from boiling sweet exudation. Fresh exudates undergo fermentation within a few hours by naturally occurring yeasts to form beverages containing about 6% alcohol. If fermentation continues for more than 24 hours, toddy becomes unpalatable as alcohol is changed to vinegar.