Pathogenic Mechanism Of Bacterial Soft Rot Of Mung Bean Sprouts And The Inhibitory Effect Of Chitosan On Soft Rot

Mung bean sprouts are one of the most popular sprout varieties in China.In recent years,the production of mung bean sprouts has shown a trend of large-scale and factory-oriented,but it has also caused soft rot,which accounts for more than 5%of the total output,and is difficult to control,causing huge economic losses and food safety risks.In order to solve the problem that has plagued the mung bean sprouts industry for a long time,this article has carried out research on the cause,mechanism and prevention methods of the soft rot phenomenon of mung bean sprouts.The research content mainly includes the isolation and identification of bacteria in soft rot mung bean sprouts,screening of key pathogens associated with soft rot,and exploring its physiological and biochemical characteristics and pathogenic mechanism.At the same time,according to the characteristics of the selected pathogens,the feasibility and optimal conditions of chitosan to prevent and cure mung bean sprouts soft rot were explored.The research results provide theoretical and technological support for the technological progress of the mung bean sprouts industry.The main contents are as follows:(1)Using Congo red staining method to isolate bacteria with pectin decomposition ability from rotten mung bean sprouts,and DNA extraction,PCR amplification and 16Sr DNA identification were performed on the isolated bacteria.The DNS method was used to determine the activity of pectinase produced by different strains,and the relationship between the phenomenon of soft rot and the activity of pectinase produced by the strain was discussed.The results shows:13 strains with pectin-decomposing ability were screened and judged as 6 strains,including 2 strains of Acinetobacter,3 strains of Pseudomonas,and 2 strains of Klebsiella,3strains of Paenibacillus,1 strain of Enterobacter,2 strains of Roseateles.The enzyme activity of different strains showed a trend of increasing first and then decreasing during the 9-day culture period,and generally reached the maximum on the 4th to 5th day.The inoculation culture test showed that the level of pectinase activity has a strong correlation with the onset of mung bean sprout soft rot and the degree of soft rot.Therefore,it is inferred that Paenibacillus is the key pathogen causing soft rot of mung bean sprout,and pectinase is the key pathogenic factor.(2)Carry out the physiological and biochemical analysis of Paenibacillus,and determine the effects of temperature,p H,carbon and nitrogen sources and different ion concentrations on the growth and enzyme production of Paenibacillus.The results show that Paenibacillus is a gram-negative bacterium with an optimal growth temperature of 28°C,which is more suitable for growth in an alkaline environment.In addition,natural heteropolysaccharide carbon sources(such as orange peel powder and pectin)or organic nitrogen sources(such as peptone)can induce Paenibacillus to produce higher activity pectinase.Zn²⁺can promote the growth of Paenibacillus at low concentrations(1 mmol/L),and inhibit the growth of Paenibacillus at high concentrations(100 mmol/L).Na⁺and Ca²⁺have the effect of inhibiting pectinase activity,and the effect is more obvious when the Paenibacillus grows for 48?96 h.(3)Through the soaking treatment of mung beans seeds,the effects of chitosan solution on the growth quality of mung bean sprouts and the growth curve and enzyme production of Paenibacillus was explored.The results showed that:Chitosan solution with a concentration lower than 0.50%(w/v)will not damage the germination of mung bean,and 0.01%chitosan can promote the growth of mung bean hypocotyls and roots,increase the content of ascorbic acid,and enhance the function of mung bean sprout cell membrane.The 0.05%chitosan treatment can reduce the activity of polygalacturonase,improve the soft rot of mung bean sprouts,and inhibit the formation of brown spots on the surface of mung bean sprouts tissue.When the Oxford cup method was used to determine the antibacterial effect of different concentrations of chitosan,the radius of inhibition zone formed by 0.25%(w/v)was the largest.When the growth curve of bacterial suspension was determined by absorbance value,it was determined that the minimum inhibitory concentration of chitosan against Paenibacillus was 1.25 mg/m L,and 0.50%chitosan treatment could achieve the effect of reducing the growth rate of Paenibacillus.