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Yogurt or yogurt is usually a dairy product produced by bacterial fermentation of milk. The bacteria used to make milk healing properties are known as "yogurt cultures". Ferment of lactose by these bacteria produces lactic acid, which acts on milk protein to give yogurt its texture as well as characteristic tang. Worldwide, cow's milk is most commonly used to make yogurt, but milk from water ox , goats, ewes, mares, camels, and yaks is also used in various parts of the world .
Dairy products yogurt is produced using a culture of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus bacteria. In addition, other lactobacilli and bifidobacteria are also sometimes added during or after culturing yogurt.
How milk was first cultured into yogurt stays a enigma . Analysis of the L. delbrueckii subsp. bulgaricus genome points that the bacteria may have started on top of a plant. Milk may have grown spontaneously and unintentionally tainted through contact with plants, or bacteria may are instead transferred via the udder of domestic milk-producing animals. Until the 1900s, yogurt was a staple in dietings of people in the Russian Empire (and especially Central China and the Caucasus Mountains), Western Asia, South Eastern Europe Balkan Mountains , Central Europe, and Bharat. Stamen Grigorov (18781945), a Bulgarian student of medicine in Geneva , first studied the microflora of the Bulgarian yogurt. In 1905, he described it as consists of a spherical and a rod-like lactic acid bacteria. In 1907, the rod-like bacterium was called Bacillus bulgaricus (now Lactobacillus delbrueckii subsp. bulgaricus). The Russian Nobel laureate biologist Ilya Ilyich Mechnikov (also seen as lie Metchnikoff), from the Institut Pasteur in Paris, was influenced by Grigorov's work and hypothesized that regular consumption of yogurt was responsible for the unusually long lifes time of Bulgarian provincials . Considering Lactobacillus to be essential permanently health, Mechnikov worked to popularize yogurt as a foodstuff throughout Europe.
Yoghourt is nutritionally rich in protein , calcium, riboflavin , pyridoxine and cobalamin . It has nutritional benefits beyond those of milk. Men and women who are lactose-intolerant can generally tolerate yogurt better than other dairy products, because the lactose in the milk is changed over to glucose and galactose, and partly fermented to lactic acid, by the bacterial culture.
yogurt is very interesting from the morphologic viewpoint , because if has a high water content and so far is solid. Electron microscopy brings out some peculiarites in the evolution of yogurt structure. The varieties which take place in milk when yogurt is formed, involve particles so small that they can not be observed by light microscopy. Milk placed under an optical microscope reveals only fat globules - but nothing else. Electron microscopy, all the same , shows the prevalent milk proteins, i.e., casein, as minute globules, about a hundred nm in diameter (1 nanometer = 1x10-9 m). They are called casein micelles. Evenly doted in the milk and separated from each other by a distance of three micelle diameters in fresh milk, they are subject to Brownian motion and thus they don't really settle at the bottom of the container. Electron microscopy makes it possible even to study the surface of the casein micelles. In fresh or boiled milk, the surfaces of the casein micelles are non-reactive. When two casein micelles collide, they recoil and stay entire. This situation changes, however, when the casein micelles are destabilized. Lactic acid produced by bacteria such as Lactobacillus delbrueckii susp. bulgaricus, and Streptococcus salivarius subsp. thermophilus increases the acidity of the milk and destabilizes the micelles. After a certain acidity is reached, the micelles stick together. Discovered by naked eye, the milk can be viewed to "coagulate " or " clabber ".
