Microbiology

Microbiology Study Guide

Low Temperatures The preservation of food is also done by reducing enzymes that restrict the metabolism activities of enzymes through treating food at low temperatures. Two types of freezing methods are used for successful preservation of food: slow freezing and quick freezing. Freezing helps to reduce the number, as well as activity, of the microbes, but does not kill all of them. Moreover, not all types of microbes can be killed using freezing techniques. Some species of microbes that remain unaffected by freezing are fungi and Psychrophillic bacteria including Pseudomonas, Alcaligenes, micrococcus, and flavobacterium . Chemicals Another important method to save food from contamination and to store it for a longer duration, is by using chemicals like propionic acid, sulfur dioxide, sorbic acid, and benzoic acid. It should be noted that these acids are not harmful for human consumption, as these can be easily metabolized by the human body. After adhering to some predetermined norms, even some antibiotics can be used for food preservation. For instance, meat is preserved using the antibiotic tetracycline. Such antibiotics are normally allowed since cooking these food items leads to elimination of the antibiotics. As studied in one of the previous sections, natural acids act as preservatives for many food items. For instance, lactic acid and acetic acid help to eliminate contamination in sauerkraut. Drying Sun drying is one of the methods by which the excess water from food items is evaporated, discouraging the growth of microbes in the food. In the chocolate and coffee industry, the cocoa and coffee beans are dried for longer preservation through belt, cabinet, and tunnel drying methods. Lyophilization, the process of freeze drying, helps eliminate moisture from food contents. Radiations Surface contamination is generally avoided with the help of ultraviolet radiations. For instance, the short wavelength light of the ultraviolet radiation is mostly used at meat processing units. As per state and federal laws by the U.S., various fruits, spices, and vegetables can be preserved using the ionized radiations of gamma rays. Microbial Determinations Themagnitude of the contamination caused by microbial actions can be studied and determined using microbial determinations. It is vital to determine the presence and quantum of these microorganisms in food items since these have the ability to cause many diseases, like staphylococcal food poisoning, typhoid fever, cholera, salmonellosis, gastroenteritis, and others. The Standard Plate Count This method is used to determine the presence and count of bacteria in food contents. The test is performed by testing the sample of food and diluting it in sterilized water containing 99 ml of sterile liquid. In order to determine the total count of bacteria per gram of food, the dilution factor is multiplied with the formed bacterial colonies.

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