Microbes in Food and Industry: Quick Revision

A brief note on Microbes in Food and Industry. Read it before a test. Try each question at the end before you open its answer.

Household food

• Curd: lactic acid bacteria, for example Lactobacillus. The starter is the inoculum. Lactose becomes lactic acid. Vitamin B12 increases.
• Bread dough: baker's yeast, Saccharomyces cerevisiae, makes carbon dioxide. Idli and dosa batter: bacteria make the gas.
• Toddy: fermented sap of palms.
• Swiss cheese: Propionibacterium sharmanii makes carbon dioxide, so large holes. Roquefort cheese: a specific fungus gives the flavour.

Industry

• Wine and beer: no distillation. Whisky, brandy and rum: the broth is distilled. The yeast is Saccharomyces cerevisiae.
• Citric acid: Aspergillus niger. Acetic acid: Acetobacter aceti. Butyric acid: Clostridium butylicum. Lactic acid: Lactobacillus.
• Lipases: detergents. Pectinases and proteases: clear juices. Streptokinase from Streptococcus: clot buster.

Medicines

• Penicillin: seen by Fleming in 1928 on a dish with Staphylococcus. Made a medicine by Chain and Florey. Nobel Prize in 1945.
• Cyclosporin A: Trichoderma polysporum, immunosuppressant after a transplant.
• Statins: Monascus purpureus, lower blood cholesterol, competitive inhibitors of the enzyme that makes cholesterol.

A worked example

A juice has 150 g of sugar in each litre. The yeast ferments all of it at the best possible yield of 0.5114 g of ethanol from each gram of sugar. What is the strength?

1. Ethanol: $150 \times 0.5114 = 76.7$ g.
2. Volume: $76.7 / 0.789 = 97.2$ mL, which is $9.7\%$ of a litre.

Practice with new numbers

A program to try

The program works out the ethanol and the strength of a drink from its sugar.

Mistakes to avoid

• Saying that wine and beer are distilled. They are not.
• Saying that curd is made by yeast. It is made by lactic acid bacteria.
• Mixing the acid and the microbe. Citric acid goes with the fungus. Acetic and butyric acid go with bacteria.
• Saying that cyclosporin A lowers cholesterol. The statins do that.

Check yourself

1. Which gas puffs up dough?

2. Which microbe gives the holes of Swiss cheese?

3. Which microbe makes acetic acid?

4. Who showed that penicillin works as a medicine?

Sources

• NCERT (2023). Biology, Textbook for Class XII, chapter 8, Microbes in Human Welfare.
• Walker G. M. and Stewart G. G. (2016). Saccharomyces cerevisiae in the production of fermented beverages. Beverages, 2(4), 30.