| Natamycin,as a polyene macrolide antibiotics,mainly produced by fermentation with Streptomyces natalensis,Streptomyces chattanovgensis and Streptomyces gilvosporeus.Due to its broad-spectrum,high efficiency,safety,non-toxicity,and no adverse effects on food flavor,natamycin has been widely used in the food industry.There is Quorum Sensing mechanism in Streptomyces natalensis,and the exogenously added PI factor autoinducer binds to the bacterial receptor protein to positively regulate the synthesis of natamycin.In this dissertation,Streptomyces natalensis are used as experimental material to explore the mechanism of PI factor-promoting natamycin synthesis and to optimize the factors that influence the induction of the fermentation system.Finally,scale-up culture was conducted on a 5L automatic fermenter.Production provides basic data.The main findings are as follows:The physiological and biochemical indexed and the activity of related enzymes in the related free radsystem are determined,the mechanism of the promotion of natamycin synthesis by PI factors was preliminarily explored.The results showed that PI factor could effectively promote the growth of Streptomyces nataliensis.The dry weight of the induced group was 1.49 times that of the blank group.The consumption of reducing sugar in the induced group is always higher than that in the blank group,until the end of fermentation,the original sugar content in the induced group is 48.7% of the blank group;the addition of PI factor will change the cell permeability of the fermentation broth,resulting in increased electrical conductivity;PI factor can increase the enzyme activity of POD,CAT,PPO and SOD,enhance the bacteria Body to own cell protection.The optimal values of the single factor affecting the fermentation conditions of natamycin with PI factors are 5% S.natrium inoculation,initial pH of the fermentation broth is 7,volume is 50 mL,and shaking speed is 200 r/min,the fermentation temperature is 29°C,the PI factor concentration is 200 nmol/L,and the PI factor addition time is 48 h.Based on the results of single-factor tests,three factors that have a greater effect on the synthesis of natamycin are screened out by the Plackett-Burman method.The main effects of each factor are as follows: PI factor concentration> initial pH of the fermentation broth> loading volume Then response surface experiment is used to design and establish a mathematical model to obtain the best level of each influencing factor.The factors are PI concentration 210nmol/L,initial pH 7,and liquid volume 50 mL.Under this condition,the fermentation yield of natamycin reached 5.456 g/L,which is 2.22 times that of the blank group.Through laboratory shaker fermentation simulation of automatic tank fermentation culture on industrial production,it is determined that the dissolved oxygen content is between 30% and 35%,which is the most suitable for fermentation of natamycin produced by Streptomyces natrium.The amount of dissolved oxygen in the fermentor is improved by controlling the stirring speed and the air flow rate.The stirring rate required for the bacteria in the logarithmic growth phase is 500 r/min,and the air flow rate is 6 L/min.The bacteria are in a large amount of natamycin synthesis phase.The required stirring speed of the body is 300r/min,and the air flow is about 3L/min.In the automatic tank expansion culture fermentation stage,when the concentration of glucose in the culture fluid drops to 2%,feeding is started every 6 hours,so that the concentration is maintained stable at about 2%,and sugar is stopped after 78 hours of fermentation.The fermentation cycle is 120 h.Natamycin production reached 3.214 g/L.The pH value in the 5L automatic fermenter is controlled by adding NaOH,and the feed is used to expand the fermentation.During the massive logarithmic growth phase of natamycin,controlling the pH around 5.8,the natamycin production reaches the highest,with the highest value being 3.456 g/L. |
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