Optimization Of Fermentation Medium Of Natamycin And Its Effects On The Preservation Of Chestnut

Chestnut is high yield in China and it has rich nutrition.But,it is difficult to store chestnut in natural conditions.So,the fresh-keeping of chestnut has attracted much attention in the world.Nowadays,as the income arise,more and more people has becoming pay attention to food safety problems.Besides,more and more relevant reports has been emerging.As well,people are becoming more prudently to choose food antiseptic substance.Traditional antiseptic substance has some defects,such as much dosage and low antimicrobial activity.Natamycin is macrolide antibiotic,which can inhibit the growth of fungi and the reproduction of mycotoxin.Natamycin is separated from the metabolite of actinomycetes,for instance,streptomyces natalensis.As a natural antiseptic,natamycin is widely used in the food field,but it's fermentation yield is low.As a result,it has great significance to optimize the fermentation medium of natamycin,as well as it's effect to store chestnut.In this article,the carbon and nitrogen source of fermentation medium are optimized firstly,then oxygen carrier is added to find the best recipe of fermentation medium.The effect of metal ions in the medium on the synthesis of natamycin is researched secondly.Finally,natamycin compound antiseptic substance on the effect of chestnut preservation is revealed.1.Optimize the carbon nitrogen source of fermentation medium by single factor tests.The results show that the best carbon source of natamycin fermentation medium is glucose,and the fermentation unit of natamycin is 1255 mg/L when glucose concentration is 45 g/L.Compared with control group,the yield was increased by 78.1 %.The best nitrogen source is yeast extract and beef extract,the yield of natamycin is 1851 mg/L when the ratio of yeast powder and beef extract is 1 :2.Compared with control group,54.25 % yield is increased.Adding different oxygen carriers to optimize fermentation medium shows that the soybean oil is the best oxygen carrier,the yield of natamycin is 1772 mg/L when 4 %?v/v?soybean oil be added.Compared with control group,43.9 % yield is increased.The orthogonal test showed that the influences of oxygen carrier to natamycin synthesis are various,the sequence is soybean oil,glucose,beef extract,and yeast extract from big influence to small.And response surface optimization experiment was carried out to get the best medium for 48 g/L glucose powder,4 g/L yeast extract,8.5 g/L beef extract,and 4.5 % soybean oil.The best medium make natamycin production reached 2210 mg/L,which is 3.2 times of natamycin production of control group.2.Add metal ions to research their influences on natamycin production.Results show that when adding a low concentration of K⁺,Ca²⁺,and Mg²⁺ solution,natamycin production was improved to a certain extent,but the production of target products can been inhibited as these metal ion concentration are increased.The natamycin biosynthesis amount has different degree of inhibition when Zn²⁺,Cu²⁺,Mn²⁺,Na+,Fe²⁺ are added into the solution respectively.3.In the experiment of preservation of Chinese chestnut,the screening of the insect resistance,preservative and coating agent was carried out.The results show that the best method is immerse chestnut 30 min in 55 degrees water,best aspetic is natamycin?0.5 g/Kg?and potassium sorbate?1.5 g/Kg?.The best coating agent is 1% pullulan.Under this condition,chestnut can be kept for 90 days in 15 ?,the mass losing-rate is 3 %,decay rate is 3 %,the content of polysaccharide keeps in 31.82 %,Compared with control group,the decay rating reduce 61 %.This method can inhibit the activity of polyphenol oxidase,the activity of peroxidase and phenylalnine ammonialyase increased.And,it improves the disease resistance and delay aging of chestnut.So,it is an effective way to store chestnut.