Physical and Chemical Requirements for Microbial Growth - Essay Example

Microbiology Number Department Physical and Chemical Requirements for Microbial Growth Microbial growth basically refers to a general increase in the number of microbial cells thus forming populations. For microbes to grow there are certain physical and chemical requirements that should essentially be in place. Chemical requirements for microbial growth include water and other mineral elements, gases and growth factors. Mineral elements include carbon, nitrogen, sulfur, phosphorous, oxygen, and trace elements. Carbon is the main source of energy in microbes and can be obtained from carbohydrates, fats, lipids, or proteins (Chaudhary, 2008, p. 345). Chemoautotrophs and photoautotrophs both obtain energy from carbon dioxide. Carbon is also a structural organic molecule in microbes. Nitrogen is essential in the production of RNA, DNA, amino acids and proteins in the microbe. Nitrogen fixing bacteria such as Azotobacter and Rhizobium obtain their nitrogen directly from the atmosphere. Phosphorous is equally important in the manufacture of phospholipids and synthesis of nucleic acids. Oxygen is useful in aerobic species for cellular respiration. Different microbes require different oxygen concentrations while others do not require oxygen at all, or strictly die in its presence (Chaudhary, 2008, p. 365). Trace elements such as zinc, copper and iron are used by microbes to synthesize important enzymes, while vitamins are also needed by some microbes. Physical conditions such as temperature, pH and osmotic pressure determine the rate or absence/ presence of growth. Different microbes have different optimum temperatures at which growth is maximum as well as minimum and maximum growth ranges. In the same wavelength, various microbes have different pH requirements. A majority of bacteria, for example, thrive well between 6.5-7.5 pH ranges, while moulds and yeasts do well between 5 and 6. Acidophiles do well in acidic conditions. Similarly, different microbes can grow in different osmotic pressures. While halophiles can live in high osmotic pressures, other organisms would shrink (lose their water) and die (Chaudhary, 2008, p. 400). Industrial Production of Yoghurt Yoghurt is a milk product (produced from bacterial fermentation) with at least 8.25% non-fat solids. The main ingredient in the industrial production of yoghurt is milk, with the type of milk used dependent on the type of yoghurt intended. Stabilizers such as starch, pectin, gums, gelatins and alginates are used to increase the firmness of the end product, keep the fruit mixed uniformly in the yoghurt and to avoid whey separation (Adams & Moss, 2008, p. 121). Variety is yielded from the use of various preparations of fruits, flavors and sweeteners as permitted by the CFR. The first step of industrial production entails adjustment of milk composition to produce the right content of solids and fats. Stabilizers are added at this point. Secondly, the mixture is pasteurized at 85ᵒC for half an hour, or, alternatively, at 95ᵒC for 10 minutes. Pasteurization sterilizes the product and allows formation of a stable gel that will not separate in storage conditions. The pasteurization product is then homogenized at 2000-2500 psi which ensures thorough mixing of the ingredients and enhances final product’s consistency. After homogenization, the product is cooled to an ideal temperature for growth of starter cultures, that is, to around 42ᵒC (Adams & Moss, 2008, p. 132). Starter cultures are then added to the cooled product. The main starter cultures commonly employed in the production of yoghurt are Streptococcus thermophilus and Lactobacillus bulgaricus (Adams & Moss, 2008, p. 134). These starter cultures ferment lactose into lactic acid which lowers pH allowing the product to form a gel or clot. This fermentation also yields the characteristic flavor associated with yoghurt. Probiotic cultures, such as Lactobacillus casei and Lactobacilus acidophilus, are added to aid the digestion of lactose, function of the gastrointestinal tract and to boosts the immune system. Fermentation is allowed till a pH of 4.5 is achieved. This can take a long time. Afterwards, the yoghurt is cooled to 7ᵒC to halt the fermentation. Depending on the type of yoghurt, flavors and fruits are added, and the yoghurt packaged. Role of Microbes in the Nitrogen Cycle The nitrogen cycle is the process through which nitrogen is transformed into various chemical forms in different spheres of the earth. The most important processes in the cycle are fixation, ammonification, nitrification and denitrification. Most of the world’s nitrogen is found in the atmosphere. Nitrogen fixation allows this free atmospheric nitrogen to be useful to plants. Fixation occasionally occurs through lightning, but is predominantly accomplished by symbiotic or free living bacteria, which use their enzymes to transform this nitrogen into essential forms. Symbiotic bacteria, such as Rhizobium, commonly inhabit root nodules of leguminous plants such as alfalfa and beans forming mutualistic associations with them. Azotobacter is an example of free living bacteria. Other examples of free living nitrogen fixing bacteria include Klebsiella, Cyanobacteria, Beijerinckia, Clostridium, Desulfovibrio, purple sulfur bacteria, non-purple sulfur bacteria and green sulfur bacteria (Chaudhary, 2008, p. 78). Still, during the nitrogen cycle, microbes play an important role in aiding decomposition of dead plants and animals producing organic nitrogen in its wake. The organic nitrogen is further acted upon by bacteria or fungi to yield ammonium in the process of mineralization/ ammonification. Nitrification, converts this ammonium into nitrates, and is performed by nitrifying bacteria and other soil-borne bacteria. In this process, bacteria such as Nitrosomonas convert ammonium into nitrites then others like Nitrobacter oxidize the nitrites into nitrates. Denitrification then ensues in which these nitrates are converted back into nitrogen gas. Denitrification occurs in anaerobic conditions and is carried out by facultative anaerobes, such as Clostridium and Pseudomonas (Chaudhary, 2008, p. 80). Role of Microbes in the Spoilage of Jam Spoilage of foods such as jam means that the food loses its nutritional value, flavor and texture and becomes dangerous for consumption. There are three types of microbes that cause spoilage of jam. These are yeasts, moulds and bacteria. Yeasts evoke fermentation as they metabolize in the contaminated jam (general microbial contamination can occur if product is left unsealed, leaks or during processing if not all microbes are killed). False yeasts are common in jam spoilage as they prefer such high sugar and acid environments. True yeast, if present, will also act on the jam to yield Carbon IV Oxide and alcohol. Moulds can also invade the surface of the jam and the insides of the tin. These moulds can cause disease (when consumed especially in persons allergic to moulds), vomiting and nausea (Waites, 2001, p. 67). These moulds, just like yeasts, do well in the acidic environment of the un-canned/ contaminated jam. Bacteria predominantly leads to the spoilage of jam, and often results in serious food poisoning. If the can containing the jam is left unsealed, after use, Enteiobactea aeroqans bacteria can invade it and cause spoilage. Bacterial spoilage can also occur from the action of spore forming bacteria such as Bacillus and Clostridium that are heat resistant and survive sterilization techniques in the industry, or are acquired through cooling or leaks. Spoilage of the jam is enhanced by temperatures and oxygen levels that favor microbial growth (Waites, 2001, p. 24). References Adams, M., & Moss, M., 2008, Food microbiology (3rd ed.), Cambridge: Royal Society of Chemistry; 121, 132, 134. Chaudhary, V., 2008, Microbial physiology and metabolism, New Delhi, India: Navyug & Distributors; 78, 80, 345, 365, 400. Waites, M., 2001, Industrial microbiology, Osney Mead, Oxford: Blackwell Science; 24, 67. Read More