Effect of temperature on microbial fermentation and control

the effect oftemperature on fermentation The vast majority of the bacteria used inmicrobial fermentation are medium-temperature bacteria, such as mold, line bacteria and general bacteriaTheir optimum growth temperature is generally 20 to 40 degrees CelsiusIn the fermentation process, it is necessary to maintain the appropriate temperature in order to make the growth of bacteria and the production of metabolites go smoothlytemperature has a great influence on fermentationIt will affect the rate of various enzyme reactions, change the synthesis direction of bacterial metabolites, affect the metabolic regulation mechanism of microorganisms, affect the physical and chemical properties of fermentation fluid, and then affect the dynamic properties of fermentation and the biosynthesis of productsthe effect of the temperature on the speed of the chemical reaction is commonly expressed by a temperature coefficient (Q10) (multiple of the increase in the speed of the chemical reaction for every 10 degrees C)In different temperature ranges, the value of Q10 is different, generally 2 to 3The relationship between the speed of enzyme reaction and temperature change is also fully consistent with this law, that is, within a certain range, as the temperature increases, the enzyme reaction rate also increases, but there is a suitable temperature, beyond this temperature, the catalytic vitality of the enzyme will decreaseThe effects of temperature on the enzyme reaction of bacterial growth and the enzyme reaction of metabolite synthesis are often differentsomeone looked at the effects of different temperatures (13 to 35 degrees C) on the growth rate, respiratory strength and penicillin production rate of penicillin, and as a result, the effect of temperature on these three metabolisms was differentAccording to the Alenius equation, the activation energy of penicillin growth e-34kJ/mol, the respiratory activation energy E-71kJ/mol, the activation energy of penicillin synthesis E s 112kJ/molFrom these data, we know that: penicillin generation rate on the temperature of the most sensitive, small temperature changes, will cause the generation rate to produce a significant change, deviation from the most appropriate temperature will cause the product yield of a more obvious decline, which indicates the importance of secondary metabolic fermentation temperature controlTherefore, the effect of temperature on the growth and anabolic growth of bacteria is extremely complex and its effect on fermentation needs to be examinedtemperature can also change the synthesis direction of bacterial metabolitesFor example, in the high concentration of Cl-and-low-concentration Cl-medium, the higher the fermentation temperature of the tetracycline nRRLB-1287, the higher the fermentation temperature, the more conducive to the synthesis of tetracycline, the increase of kinythromycin synthesized at 30 degrees C, only the production of tetracycline at 35 degrees C, and the synthesis of kinycin almost stoppedtemperature changes also affect the proportion of components of multi-component secondary metabolitesFor example, the ratio of aflatoxin G1 to B1 produced by fermentation at 20 degrees C, 25 degrees C and 30 degrees C is 3:1, 1:2, 1:1, respectivelyAlso, when aflatoxin is fermented at 10 to 20 degrees C, it is beneficial to the synthesis of penicillin, and at 28 degrees C it is beneficial to the synthesis of aflatoxin AThese examples show that temperature changes affect not only the rate of enzyme reaction, but also the synthesis direction of the product (which, of course, is also the enzyme reaction)It is reported that temperature can also affect the metabolic regulation mechanism of microorganisms, the end product in the amino acid biosynthesis pathway to the feedback inhibition of the first synthase, at a low temperature of 20 degrees C than at the normal growth temperature of 37 degrees C inhibition is more seriousin addition to the above direct impact, the temperature also has an impact on the physical properties of the fermentation liquid, such as the viscosity of the fermentation liquid, the solubility and transfer rate of oxygen in the fermentation liquid, the decomposition and absorption rate of certain substrates, etc., are affected by temperature changes, which affect the fermentation dynamics and the biosynthesis of the products, the factors that affect the change of fermentation temperaturein the fermentation process, there are both the factors that produce heat energy, but also the factors of loss of heat energy, and thus cause the change of fermentation temperatureHeat production factors are biothermal (Q biological) and stirring heat (Q stirring), and heat dissipation factors are evaporative heat (Q evaporation), radiant heat (Q radiation) and heat display (Q-positive)The resulting heat energy less lost heat, the resulting net heat is fermentation heat (Q fermentation, kJ/ (m3.h), i.eQ fermentation, Q biological and Q stirring-Q evaporation-Q-Q radiationThis is the main factor of the change of fermentation temperatureThese heat production and cooling factors are summarized below1, biothermal (Q biological)produce bacteria in the growth and reproduction process of heat, called biothermalThe nutrient matrix is broken down and metabolized by the bacteria to produce a large amount of heat, some used to synthesize the high-energy compound ATP, to supply the energy needed for anabolic, the excess heat is released in the form of heat energy, forming biothermal the size of biothermal heat varies with the composition of the bacteria and the medium Generally speaking, for a strain, under the same conditions, the more rich the media composition, the faster the nutrients are used, the greater the biothermal production The size of biothermal heat also varies with the incubation time: when the bacteria are in the spore germination and stagnation period, the biothermal heat produced is limited; Therefore, the fermentation heat released in the decimal period is the largest and is often used as the main basis for fermentation heat balance For example, tetracycline fermentation at 20 to 50h fermentation of the largest fermentation heat, the highest value of 29330kJ / (m3.h), the lowest value of other times is about 8380kJ / (m3,h), the average is 16760kJ / (m3.h) In addition, it was found that the biothermal heat of high-yield batches of antibiotics was higher than that of low-yield batches This shows that the metabolism of bacteria is very strong when antibiotics are synthesized the size of biothermal strains corresponds to the respiratory strength of the bacteria, the greater the intensity of breathing, the greater the biothermal production In tetracycline fermentation, the changes are consistent, and the peak of biothermal heat is also the peak of carbon utilization It has been proved that under certain conditions, fermentation heat is proportional to the oxygen intake of the bacteria, i.e Q fermentation is 0.12 2, stir heat (Q stirring) the heat generated by the friction between the liquid and between the liquid and the equipment caused by the rotation of the fermentation tank mixer, i.e the heat is stirred The stirring heat can be calculated according to the under-type approximation 3, evaporative heat (Q evaporation) air into the fermentation tank and fermentation liquid wide contact before discharge, causing the energy required for evaporation of water, that is, evaporation heat The evaporative heat of water and the partial heat (Q-show) of the exhaust gas due to temperature differences are scattered to the outside world Q evaporation and Q are variable because the temperature and humidity of the incoming air vary with the climate and control conditions of the outside world 4, radiant heat (Q radiation) due to the temperature difference between the outer wall of the tank and the atmosphere, the part of the heat in the fermentation liquid radiates to the atmosphere through the tank, that is, the heat of radiation heat The size of the radiation heat depends on the difference between the temperature in the tank and the outside temperature, the greater the difference and the more heat dissipation Because Q bio, Q evaporation and Q-show, especially Q organisms in the fermentation process is changed over time, so fermentation heat also changes with time in the whole fermentation process, causing the fermentation temperature to fluctuate frequently In order to make fermentation can be carried out at a certain temperature, it is necessary to try to control it three, temperature control 1, the most suitable temperature choice the most suitable fermentation temperature is suitable for the growth of bacteria, but also suitable for the synthesis of metabolites temperature However, the optimum growth temperature is often inconsistent with the optimum production temperature All microorganisms have the most suitable temperature range under certain conditions The microbial species are different, the enzyme system is different, and the temperature required is different The same microorganism, culture conditions are different, the most suitable temperature is different If the optimal growth temperature of glutamate-producing bacteria is 30 to 34 degrees C, and the temperature of glutamate is 36 to 37 degrees C In the pre-bacterial growth stage of glutamate fermentation and seed culture stage, the optimum temperature of the bacteria growth should be met If the temperature is too high, the bacteria are prone to aging In the middle and late fermentation of the bacteria growth has stopped, in order to accumulate a large amount of glutamate, the need to raise the temperature appropriately Also such as the fermentation of primary metabolites lactic acid, the most suitable growth temperature of lactic acid streptococcus is 34 degrees C, while the most acid-producing temperature is 30 degrees C, but the fastest fermentation speed of the temperature of up to 40 degrees C This is especially true in sub-metabolite fermentation, such as in a medium with 2% lactose, 2% corn syrup and an inorganic salt, the most suitable growth temperature of the bacteria is measured at 30 degrees C, while the optimum temperature of penicillin synthesis is only 24.7 degrees C Therefore, the most suitable fermentation temperature can be selected the most suitable fermentation temperature varies with the bacteria species, the media composition, the culture condition and the growth stage of the bacteria Theoretically, the whole fermentation process should not only select one culture temperature, but should be based on the fermentation of different stages, choose different culture temperature In the growth stage, the optimum growth temperature should be selected, and the most suitable temperature should be selected during the product generation stage Fermentation temperature can be controlled according to different strains and different products someone tested the temperature-altering fermentation of penicillin, the temperature change process is, at first 5h, maintained at 30 degrees C, later reduced to 25 degrees C culture 35h, and then down to 20 degrees C culture 85h, and finally increased to 25 degrees C, culture 40h can Under these conditions, the yield of penicillin was 14.7% higher than that of the constant temperature culture at 25 degrees C Also such as tetracycline fermentation, in the middle and late to maintain a slightly lower temperature, can extend the production period of the product, 24h before the tank, culture temperature increase dating 2 to 3 degrees C, can make the last day of the fermentation unit increase rate increased by more than 50% All these indicate the good results of variable temperature fermentation However, in industrial fermentation, because of the large volume of fermentation liquid, the lifting temperature is more difficult, so in the whole fermentation process, often use a more suitable constant culture temperature, so that the product yield is the highest, or under possible conditions for variable temperature fermentation In the actual production, in order to obtain high fermentation efficiency and obtain satisfactory product yield, the second or third level management temperature is often used 2, temperature control industrial production, the large fermentation tank used in the fermentation process generally do not need to be heated, because of the fermentation release of a large number of fermentation heat, and the need to cool more Using an automatically controlled or manually adjusted valve, cooling water is transferred into the mezzanine or serpentine tube of the fermentation tank, cooled by heat exchange, and maintained a constant fermentation If the temperature is higher (especially the summer temperature in the south of China), the surface water temperature as cooling water is high, resulting in a very poor cooling effect, can not reach the predetermined temperature, the use of frozen salt water for recycling cooling, in order to quickly drop to the most suitable