Precautions for the preparation of microbial fermentation medium

pay attention to the nutrient ratio and C/N ratiosuch as: sugar content should be suitable for microbial growth to be good, sugar too much to inhibit microbial growthThe general microorganism suitable C/N is 25:1 (the ratio of element C/N, also refers to the ratio of reduced sugar content in the medium to the crude protein content)nutrient concentration and matching ratio is appropriatewhen the concentration of nutrients in the medium is appropriate, microorganisms can grow well, nutrient concentration is too low can not meet the normal growth needs of microorganisms, when the concentration is too high may inhibit microbial growth, such as high concentrations of sugar, inorganic salts, heavy metal ions, not only can not maintain and promote the growth of microorganisms, but play a role in anti-bacterial or anti-bacterial, the concentration ratio between the nutrients in the medium also directly affects the growth and reproduction of microorganisms and/or the formation and accumulation of metabolites, in which the carbon-nitrogen ratio (C/N) has a greater impactStrictly speaking, the carbon-nitrogen ratio refers to the ratio of carbon to nitrogen in the medium, and sometimes to the ratio of reduced sugar to crude protein in the mediumFor example, in the process of producing glutamate using microbial fermentation, when the medium carbon nitrogen ratio is 4/l, the bacteria multiply in large quantities and accumulate less glutamate; For example, in the production process of antibiotic fermentation, the coordination of bacterial growth and the synthesis of antibiotics can be controlled by controlling the ratio between the quick-acting nitrogen (or carbon) source in the medium and the source of the late-acting nitrogen (or carbon)control pH conditionsthe pH of the medium must be controlled within a certain range to meet the growth and reproduction of different types of microorganisms or produce metabolitesThe most appropriate pH conditions for the growth and reproduction of various microorganisms or the production of metabolites vary, in general, bacteria and linebacteria are suitable for growth in the pH7 to 7.5 range, yeast and mold usually grow in the pH4.5 to 6 rangeIt is worth noting that in the process of microbial growth and reproduction and metabolites, due to the decomposition and utilization of nutrients and the formation and accumulation of metabolites, will lead to changes in the medium pH, if the culture pH conditions are not controlled, often lead to a decrease in microbial growth rate or/and a decrease in the production of metabolitesTherefore, in order to maintain the relative constant pH of the medium, a pH buffer is usually added to the medium, and the commonly used buffer is a mixture of one-hydrogen and dihydrophosphates (e.gKH2PO4 and K2HPO4)The K2HPO4 solution is alkaline, the KH2PO4 solution is acidic, and the pH of the equivalent mixture of the two substances is 6.8When the accumulation of acid in the medium leads to an increase in the concentration of H plus, the combination of H plus and weak alkaline salts to form a weak acidic compound, the medium pH will not be excessively reduced, if the oh-concentration in the medium increases, OH-combined with weak acidic salts to form a weak alkaline compound, the medium pH will not be excessively elevatedbut the KH2PO4 and K2HPO44 buffer systems can only be regulated within a certain pH range (pH6.4 to 7.2) Some microorganisms, such as lactic acid bacteria can produce a large number of acids, the buffer system is difficult to act as a buffer, at this time can be added to the medium insoluble carbonate (such as CaCO3) to adjust, CaCO3 is insoluble in water, will not make the medium pH excessive rise, but it can constantly neutralize the acid produced by microorganisms, while releasing CO2, the medium pH control within a certain range there are some natural buffering systems in the medium, such as amino acids, peptides, proteins are both sex estots, but also play the role of buffer the choice of the source of raw materials in the preparation of mediums should be used as cheap and easy-to-access raw materials as the medium composition, especially in the fermentation industry, the amount of medium is very large, the use of low-cost raw materials more reflectits its economic value For example, in the industrial production of microbial single-cell proteins, molasses (waste liquid containing sucrose in the sugar industry), whey (waste liquid containing lactose in the dairy industry), soy products industrial waste liquid and black waste liquid (the paper industry contains sugar and hexaccharide sulphate pulp) are often used as raw materials for the culture medium For example, methane fermentation in industry mainly uses waste water and waste slag as raw materials, while in rural China, the use of human and animal waste and grass for raw material fermentation to produce methane as fuel In addition, a large number of agricultural and sideline products or products, such as drum skin, rice bran, corn syrup, yeast paste, wine, bean cake, peanut cake, protein, etc are commonly used fermentation industry raw materials sterilizing treatment must avoid contamination of the equipment and workplaces used to obtain pure microbial culture For the medium, it is more necessary to carry out strict sterilization The medium is generally used for autoclave sterilization, and the medium is generally maintained at 1.05 kg/cm2, 121.3 degrees C to maintain 15 to 30min to achieve the purpose of sterilization In the process of autoclave sterilization, long-term high temperature will cause some heat-resistant substances to be destroyed, such as the formation of sugar saccharine, caramel, so the sugary medium is often in 0.56kg / cm2, 112.6 degrees C15 to 30min sterilization, some of the sugar requirements of the medium, sugar can be filtered out of the interval or sterilization, and other sterilized ingredients Mixing; long-term high temperature salso causes phosphates, carbonates and certain cations (especially calcium, magnesium, iron ions) combined to form insoluble complex to produce precipitation, therefore, in the preparation of synthetic media for observation and quantitative determination of microbial growth, it is often necessary to add a small amount of chelating agent in the medium, to avoid precipitation in the medium, commonly used chelating agent is ethylamine tetraacetic acid (EDTA) The composition of calcium, magnesium, iron plasma and phosphate, carbonate, respectively, to be sterilized, and then mixed to avoid the formation of precipitation;