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Fermentation is a slow decomposition of complex organic compound into simpler compounds by the action of enzymes. Enzymes are complex organic compounds, generally proteins. Examples of fermentation are souring of milk curd, bread making wine making, brewing. The word ‘Fermentation’ had been derived from Latin (‘Ferver’ means to ‘boil’). As during fermentation there is lot of frothing of liquid due to the evolution of carbon dioxide, it gives the appearance as if it is boiling. The science of fermentation is known as zymology. Fermentation takes place in the absence of oxygen (when the electron transport chain is unusable) and becomes the cell’s primary means of ATP (energy) production. Sugars like glucose, sucrose when fermented in presence of yeast cells are converted to ethyl alcohol.
During fermentation of starch, starch is first hydrolyzed to maltose by action of enzyme diastase. Diastase is obtained from germinated barley seeds. Fermentation is carried out at a temperature of 4-16°C (40-60°F). This is slow for most kinds of fermentation, but is beneficial for cider as it leads to slower fermentation with less loss of delicate aroma. Apple based juices with cranberry also make fine ciders; and many other fruit purees or flavorings can be used, such as grapes, cherry, raspberry. The cider is ready to drink after a three month fermentation period, though more often it is matured in the vats for up to 2 to 3 years.
History of Fermentation
Since fruits ferment naturally, fermentation precedes human history. Since ancient times, however, humans have been controlling the fermentation process. The earliest evidence of winemaking dates from eight thousand years ago in Georgia, in the Caucasus area. Seven thousand years ago jars containing the remains of wine have been excavated in the Zagros Mountains in Iran, which are now on display at the University of Pennsylvania. There is strong evidence that people were fermenting beverages in Babylon circa 5000 BC, ancient Egypt circa 3150 BC, pre-Hispanic Mexico circa 2000 BC, and Sudan circa 1500 BC. There is also evidence of leavened bread in ancient Egypt circa 1500 BC and of milk fermentation in Babylon circa 3000 BC. French chemist Louis Pasteur was the first known zymologist, when in 1854 he connected yeast to fermentation. Discovery of Fermentation
Louis Pasteur in 1860 demonstrated that fermentation is a purely physiological process carried out by living microorganism like yeast. Although showing fermentation to be the result of the action of living microorganisms was a breakthrough, it did not explain the basic nature of the fermentation process, or prove that it is caused by the microorganisms that appear to be always present. Many scientists, including Pasteur, had unsuccessfully attempted to extract the fermentation enzyme from yeast. Success came when in 1897 German chemist Eduard Buechner demonstrated that yeast extract could bring about alcoholic fermentation in the absence of any yeast cell. He proposed that fermenting activity of yeast is due to active catalysts of biochemical origin. These biochemicals are called enzymes. Enzymes are highly specific compound or a closely related group of compounds.
Importance of Fermentation
Enrichment of the diet through development of a diversity of flavors, aromas and textures in food substances. Preservation of substantial amounts of food through lactic acid, alcohol, acetic acids and alkaline fermentation. Biological enrichment of food substances with proteins, essential amino acids, fatty acids and vitamins. A decrease in cooking times and fuel requirements by production of hydrogen, methane etc.
Fruit and vegetable juices contain sugar such as sucrose, glucose and fructose. These sugars on fermentation in the presence of enzymes invertase and zymase give ethanol with the evolution of carbon dioxide. 279082516573500C12H22O11 Invertase C6H12O6 + C6H12O6 563880040703500Sucrose Glucose Fructose 315277515240000C6H12O6 + C6H12O6 zZymase 2C2H5OH + 2CO2 Glucose Fructose Ethanol .
Glucose is a reducing sugar and gives red coloured precipitates with Fehling’s solution, when warmed. When fermentation is complete, the reaction mixture stops giving any red colour or precipitate in Fehling’s solution. REQUIREMENTS
Conical Flasks (250ml), test tubes and water bath, apple juice, Orange juice, carrot juice, Fehling solution A, Fehling solution B, Pasteur salts and distilled water.
Take 5.0ml of apple juice in a clean 250 ml conical flask and dilute it with 50ml of distilled water. Add 2.0g of Baker’s yeast and 5.0ml of solution of Pasteur’s salts to the above conical flasks. Shake well the contents of the flask and maintain the temp of the reaction mixture between 35 degrees and 40 degrees C. After 10 minutes take 5 drops of the reaction mixture from the flask and add to a test tube containing 2ml of Fehling reagent. Place the testube in a boiling water bath for about 2 minutes and note the colour of the solution or the precipitate. Repeat the step 4 after every 10 minutes, when the reaction mixture stops giving any red colour with the Fehling agent, the completion of fermentation is indicated. Note the time taken for the completion of fermention.
Repeat the above experiment by taking 5.0 ml of carrot juice. Note: Pasteur’s salt solution
Pasteur’s Salt Solution is prepared by dissolving ammonium tartrate, 10.0gm; potassium phosphate 2.0gm ; calcium phosphate 0.2gm, and magnesium sulphate 0.2 gm dissolved in 860 ml of water.
Volume of fruit juice taken = 5.0 ml
Volume of distilled water added = 50.0 ml
Weight of Baker’s yeast added = 2.0gmVolume of solution of Pasteur’s salts = 5.0 ml TIME
(IN MINUTES) COLOUR OF REACTION MIXTURE ON REACTION WITH FEHLING SOLUTION IN CASE OF APPLE JUICE CARROT JUICE
The rate of fermentation of apple juice is than the rate of fermentation of carrot juice.