Microbiology Of Foods

Food microbiology is the study of all aspects of microbial actions on food and food products, both directly and indirectly related to the welfare of mankind. Topics included in food microbiology are history of food microbiology, number and kinds of microbes in foods, intrinsic and extrinsic parameters of foods, methodologies, food spoilage, food preservation, and food-borne pathogens.

All living things smaller than 0.1 mm in diameter are classified as microorganisms because they are too small to be seen by the naked eye. Although human beings suspected the existence of these microbes for a long time, the real beginning of the field of study of microorganisms started when Antonie van Leeuwenhoek (1632-1723), a Dutch amateur lens grinder, reported the observation using his lens of many animalcules. He reported his observations to the Royal Society of London and described the microbes accurately, including bacteria (rod, sphere, and spiral), protozoa, and yeasts. Because he did not train any students to follow his work, no one really mastered his technique of lens grinding for the observation of microbes. His work was confirmed by Robert Hooke in 1678 using a compound microscope. No noticeable advancement in microbiology occurred until the middle of the 1800s.

The first major development in microbiology centered around the controversy over the theory of spontaneous generation. In Greek mythology humans were able to create life. People believed that animals could originate from the soil, maggots could be produced by exposing meat to warm air, and so on. Francesco Redi (1626-1697) showed that when gauze was placed over ajar containing meat, no maggots formed because flies were not allowed to contact the meat. Gradually the idea of life being generated from nonliving things was discarded by those performing experiments on the subject. However, this topic still lingered in the minds of many.

With the discovery of microbes the controversy rekindled. People questioned where these microbes came from. One camp believed that microbes occurred spontaneously, and the other camp believed that microbes were developed from other microbes and that life cannot come from nonliving matter. In the process of proving or disproving the theory of spontaneous generation, several important issues concerning microorganisms were raised and' some experimental procedures were developed. John Needham in 1749 observed microorganisms in putrefying meat and explained this as evidence of spontaneous generation. Laz-zaro Spallanzani boiled beef broth, sealed the flasks, and observed that no microorganisms developed in the broth. The pro-spontaneous generation camp proposed that exclusion of air prevented spontaneous generation. The con-spontaneous generation camp indicated that microorganisms in the air were the source of contamination in faulty experiments. By heating the air or trapping the microorganisms with heat-treated cotton, no microorganism would develop in heated broth even if the air was allowed to come in contact with the broth. The pro-spontaneous generation camp insisted that heat destroyed some vital force that prevented the development of life forms. Finally Louis Pasteur, using his famous goosenecked flask, showed that even unheated air, when allowed to contact heated broth, will not result in the development of microorganisms as long as the particles in air were allowed to settle at the bottom of the U-shaped neck of the flask. Disproving the theory of spontaneous generation was essential for the development of microbiology because this allowed scientists to observe microbiological events in sterile media with known inoculated cultures free from the uncertainties of some unknown living agent that might spontaneously develop in the media.

With his disproving of the theory of spontaneous generation, Pasteur introduced the field of fermentations and food microbiology. Since ancient times people have produced wine, beer, bread, and other fermented products without knowing the exact reason for the development of such foods. Pasteur was involved with fermentation because of the occurrence of spoilage in wine at that time in France. He started the project by first proving that alcoholic fermentation of grapes, fruits, and grains was the result of organisms he called ferments. He showed that good wine batches had certain types of ferment and bad batches had other types of ferment. By heating juice at 63°C for 30 min he could kill the bad ferments, and after cooling the juice he could consistently produce satisfactory wine by inoculating ferments from good wine batches into the juice. Not only did he solve the problem of wine disease, but he also developed the process of pasteurization of food and drink. In the process of these studies he discovered that some organisms can grow in the absence of air. His work resulted in the scientific understanding of food fermentation and thus greatly improved the quality of fermented food products. The value of his study was that he showed the direct relationship between activities of a specific microorganism in the development of a specific product (i.e., good yeasts acting on pasteurized grape juice under proper conditions will result in wine).

The precise time at which humans started to realize the role of microbes in food products cannot be determined. However, it is safe to assert that humans noticed the results of microbial action such as spoilage of food and food poisoning early in the history of food-gathering and food-producing periods. Humans experienced and noticed the changes occurring in foods without knowing the reasons behind such activities until the development of the science of microbiology. The real beginning of food microbiology coincided with the development of microbiology, especially Pasteur's work on food fermentation processes. Early studies in food microbiology centered on dairy bacteriology. Only about 20 years ago did the field of food microbiology become a recognized field. Today it has a great impact on issues such as food safety, genetic engineering of new food products, methodologies in applied microbiology, food technology, and preservation technologies.

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