Microbes in Household Products

Many everyday foods and drinks are produced with the help of microbes. Lactic acid bacteria (LAB) such as Lactobacillus acidophilus, L. lactis and Streptococcus lactis act as probiotics — live organisms that, when consumed, help restore and maintain a healthy gut flora and suppress disease-causing microbes; prebiotics, by contrast, are dietary fibres that nourish these beneficial microbes rather than being microbes themselves. When a small starter of curd is added to warm milk, its LAB multiply below about 40 degrees C and ferment the milk sugar, digesting the milk protein casein and turning milk into curd, which is more nutritious than milk because of the organic acids and vitamins generated in the process. Yogurt is produced similarly by Streptococcus thermophilus and Lactobacillus bulgaricus, which coagulate casein and convert lactose to lactic acid, with acetaldehyde giving yogurt its characteristic flavour. Cheese-making acidifies milk and adds the enzyme rennet to coagulate casein into curds, which are pressed into cheese using starter bacteria such as Lactococcus, Lactobacillus or Streptococcus — Swiss cheese gets its characteristic large holes from carbon dioxide released by Propionibacterium shermanii, while paneer (a fresh cheese common in South Asia) is coagulated directly with an acid such as lemon juice or vinegar. Idli and dosa batter is fermented by the bacterium Leuconostoc mesenteroides, while bread dough is leavened by the yeast Saccharomyces cerevisiae (Baker's yeast), whose fermentation of glucose to ethanol and carbon dioxide makes the baked bread porous and soft …