Study of Lactic Acid Fermentation

Lactic acid has a long history of uses for fermentation and preservation of human foodstuffs. It was first discovered in sour milk by Scheele in 1780, who initially considered it a milk component. In 1789, Lavoisiernamed this milk component acid lactique, which became the possible origin of the current terminology for lactic acid. In 1857, however, Pasteur discovered that it was not a milk component, but a fermentation metabolite generated by certain microorganisms. At the beginning of the 20th century Ellie Metchnikoff (1845-1916, winner of the 1908 Nobel Prize for physiology) advocated the beneficial effects of lactic acid bacteria. He discovered that Bulgarians had average life span of 87 years and that the Bulgarian diet constituted mainly of cultured milk products. Thus, he hypothesized that the consumption of large quantities of live lactic acid bacteria in yogurt suppressed the multiplication of putrefactive bacteria in the large intestine, and prevented aging and shortening of life. This is the “theory of longevity by yogurt”. Lactic acid is considered as a very important chemical compound with significant applications in pharmaceutical, chemical industry and especially in the food industry. Worldwide demand for lactic acid is growing at a rate of approximately 12-15% a year.

Lactic acid production from agricultural crops such as wheat, corn and beet has recently received much attention because of the increasing demands for polylactic acid, which is used in biodegradable plastics. The production of such biodegradable polymer can replace non-degradable plastics and thus solve the environmental pollution problem. The increasing use of chemical synthesis plastics, which takes about hundred years to degrade, has cause environmental deterioration, with these waste plastic clogging landfills, strangling wildlife and littering beaches. The production of PLA will increase if new economic production routes are developed to increase annual lactic acid consumption. World demand for lactic acid is currently estimated at $150 million (100 000 tons). An annual growth of 8.6% of the lactic acid market is expected between 2010 and 2012. About 50% of the market is in food and beverage applications, which is a mature and stable market. For polylactic acid, the potential market has reached about 160 000 tons in 2003 and 390 000 tons in 2008.

This type of fermentation could nevertheless be important because the carbon sources are waste product that would otherwise be difficult and expensive to discard, rather than agricultural crops that could be put to other uses in the production of human food and animal feed. There are five chapters in the present thesis. Chapter first is introductory which shows an overview of the current status of many diverse and interesting aspects of modern fermentation technology. Chapter second is general experimental methods which shows instrumentation techniques followed in lactic acid fermentation technology. Chapter third parametric studies of lactic acid deals about optimization of right conditions for lactic acid fermentation by Lactobacillus bulgaricus NCIM-2359 Chapter fifth and sixth which is main parts of the thesis includes lactic acid fermentation by Lactobacillus bulgaricus NCIM-2359 exposed to some active organic molecules (AOM) and some chemical mutagens. Some of these compounds has been found useful and significant for higher yields of lactic acid. I am grateful to professors, research colleagues, parents, my wife and little babies for their moral support and encouragement for this venture.