Fermentation

Introduction

Fermentation is the process of chemical breakdown of any organic substanceby different bacteria like yeast etc. It is defined as” the process of incomplete oxidation of sugar, espicially glucose, into alcohol and carbondioxide.” This process is done in the absence of air, so it an anaerobic process. In other it is the process in which gulcose is breakdown into pyruvic acid by glucolysis which is again degarded enzymetically to alcohol and carbon dioxide.

Fermentation is the only one biotechnology we have been following from our anccient time. This technique was started by our forfather and still we are following this process but in modern way. In ancient time people use to make alcohol from the different grains and fruits. Alcohol is the first biological product produced. Now fermentation is done commercially for the production of alcohol.

Yeast and its types

Different bacteria and fungi are used for the process of fermentation and yeast is one of the popular fungi used for this process. Saccharomyces cerevisae is a microscopic fungus. Louis pasture was the first person to report the activity of yeast in the process of fermentation in the nineteenth century. Now yeast is used industrially for the production of different products that are consumed by both animals and human. There are two types of yeast. They are mentioned below:

• Baker’s yeast- Saccharomyces cerevisae and Tourlopsis are included in these types of yeast which are grown on molasses. Some of these types of yeast are as follows:

1. These types of yeasts are used for flavoring the food.
2. As these types of yeasts are rich in protein, vitamins, etc. they are used as the supplementary nutrients.
3. These yeast Helps in the ferment and raise dough in bread making process.

• Alcohol (Brewer) yeast-These are the type of yeast which is mostly used for the production of several types of alcoholic beverages. Usually these types of yeast are grown in the carbohydrate, mostly in sucrose.

Table: Alcoholic liquor

How and why do microorganisms make alcohol?

Due to the consumption of the sugar such as glucose and fructose yeast is able to maintain the stoke ATP (Adenosine Tri-phosphate). Sugarcane juice contains sucrose, which is the type of sugar composed of one glucose molecule attached to the molecule of fructose. When the yeast grown in the oxygenated medium is bring in contact to the sugar, than the sugar is break down into a smaller and smaller molecule step by step and finally carbon dioxide and energy is obtained. When the sugar is bring in contact with the yeast which is not grown in the oxygenated medium than a series of chemical process will be completed and as a result ethanol or fuel alcohol is obtained.

Through the glucolysis process glucose can be splitted up into two molecules of pyruvic acids which are enzymetically degraded into alcohol and carbon dioxide by fermentation process. The yeast which help in fermentation of alcohol contain two essential enzymes, they are: pyruvate decarboxylase and alcohol dehydrogenase. Pyruvic acid is converted into acetaldehyde in presence of pyruvate decarboxylase and acetaldehyde is further converted into ethanol in presence of alcohol dehydrogena se by NADH.

Manufacture of alcohol in industrial scale

Molasses is the raw material used in the preparation of alcohol in the industries which is thick and dark syrup drained out form the refining process of raw sugar.

In the process of manufacture of alcohol in industries, molasses mash is adjusted to the desired sugar concentration and temperature by adding water and by adding measured quantity of acid or base wanted pH of the alcohol can be obtained. Molasses is kept in the fermentation tank known as bioreactor. In the bioreactor molasses mash is uniformly mixed with yeast (Saccharomyces) which is called starter. The well mixed mash and starter spatter and false to the bottom of tank. Soon the fermentation becomes vigorous and large amount of carbon dioxide is evolved. Within fifty hours or less the fermentation process is completed. Then after fermented molasses is distilled and alcohol is separated as well as other volatile constituents. The produce alcohol is purified by the means of rectifying columns and store in the container.

Fermentation process

Fermentation is done with one of the following method

• Batch process: In this process, nutrients medium as well fermenting organisms like yeast are kept in the bioreactor until the maximum products is produced. After each charge the medium with organism as well as product is removed. Then the tank is cleaned and the new and fresh batch is store.
• Continuous process: In this process, the product is taken of at regular time interval and the new medium is bring in contact to a bioreactor.
• Immobilized fermentation process: Living yeasts are immobilized in calcium alginate beads. In the bioreactor the beads with living cells are placed along with nutrient medium. In compression to the batch technique it is 20 times faster for the fermentation.

Along with the alcohol carbon dioxide is produced as the bye product which is collected separately. Yeast cells are also isolate from fermented product and a part of yeast is kept further inoculation. The remaining yeasts used as the feeds for animals when they are dried and washed.

Fermentation process involves two broad groups

• Upstream process: All the process involve in the process of fermentation before starting the fermenter such as sterilization of the fermenter, preparation and sterilization of culture medium and growth of the suitable inoculum are called upstream process.
• Downstream process: All the process involves after the fermentation process is known as the downstream process. This process includes different process such as distillation, centrifuging, filtration and solvent extraction. Mostly this process involves the purification.

Bioreactor and its types

Bioreactor is defined as the vessel or a container which is designed is such a way that can provide an optimum environment in which microorganisms or their enzymes interact with a substrate to produce the required product. There are two types of bioreactor which are mention below:

• Open type: It is the type bioreactor which allows continuous process where substrate can be placed inside from one end and product is taken out from another end.
• Closed type: It is the type of bioreactor in which fermentation is done batch wise. During the fermentation process microbes are grown in nutrients placed in vessel. The stirred-tank fermentation is scientifically designed and has different ranges of capacity from one unit laboratory unit to production-scale vessel of huge capacity. Its vessel is cooled by a water jacket. The required amount of acid or alkali is added whereas air is pumped into bottom of the liquid. After each fermentation batch vessel should be sterilized by passing through steam lines.

Other fermented alcoholic beverages

Now a day different alcoholic beverages are produced in industries. People in all over the world consume different fermented alcoholic beverages. Some of the alcoholic beverages are described below:

1. Wine: Wine is the product made by the normal alcoholic fermentation of different juice of ripe fruits such as grapes, apple, oranges, cherries, apricots, pears and other. The prepared wine is named after the name of fruits like apple wine, cherry wine, etc.
2. Whiskey: It is the alcoholic beverage prepared by an alcohol distillate from the fermented mash of grains. After the several distillation of mash the low wines can be obtained. When the low wine is further distilled it result the high wines. When the water and high wine is mixed, its forms straight whisky. Firstly when the whisky is prepared it is colorless and the color was developed during aging process.
3. Rum: It is the alcoholic product produced by the distillation of fermented juice of sugarcane syrup, sugarcane molasses or other sugarcane by-products. After the alcohol is produced, flavor and color is added. The flavor and aroma improve with aging. Rum contains about 41% of alcohol.
4. Brandy: When the wine is distilled than brandy is obtained. It is also produce by the distillation of remounted fruits juice. Cognac is the best brandy which is made in Franch. It contains about 65-70 % of alcohol in it.
5. Gin: When fermented mash or raw grain is distilled, gin is obtained. The finest gin is distilled from a malt of barley and rye. The flavor of gin and any medicinal value are due to oil of juniper.

Application of fermentation in industries

Fermentation has different application in the industrial sector. Some of them are as follows:

1. Different organic acid are produced in industry with the help of fermantation. Lactic acid is produced in industries using thermophilic lactic acid bacteria.
2. Anino acid is produced commercially in large number by using fermentation process. Fermentation process helps to produce twelve amino acid out of twenty naturally occuring amino acid.
3. Vitamins can be also synthesis by the fermentation process.
4. Different enzymes can be synthesis during the peocess of fermentation.The bulks of enzymes used comercially are obtained frommicrobial sources and are produced by fermentation process.

Refernce

Arvind K. Keshari,Kamak K. adhikari. A Text Book of Higher Secondary Biology. Kathmandu: Vidyarthi Pustak Bhandar, 2014.

Agrawal, sarita. principle of biology. 2nd edition . kathmandu: Asmita book Publication, 2068 ,2069

Mehta, Krishna Ram. Principle of biology. 2nd edition. kathmandu: Asmita, 2068,2069.

Jorden, S.L. principle of biology. 2nd edition . Kathmandu: Asmita book Publication, 2068.2069.