| In this study,we took Alternaria alternata as the tested microorganism,L-cysteine and chlorine dioxide was used respectively to Alternaria alternata under the condition of vitro and vivo.Observing the changes of spore germination,germ tube elongation and colony growth under microscope,and measuring colony growth of Alternaria spp.to explore the inhibitory effect of two reagents on Alternaria spp.Then selecting the optimal concentration of L-cysteine solution to treat the grapes inoculated with Alternaria alternate.To explore the inhibition effect of the two reagents on Alternaria alterniflora by observing the changes of fruit diseases,storage quality and related enzyme activities after them were inoculated with Alternaria spp.and treated with two chemical reagents.Then,we selected appropriate concentration of chlorine dioxide gas and L-cysteine solution to treat grape berries based on the previous experiment,at the same time,used polyethylene film bags with thickness of 0.02 mm is used to store fruits and place in the environment of 25? and 60%~65% humidity.Measuring the changes of texture,color,nutritional components,activity of peroxidase and polyphenol oxidase during storage to study on the effect of two preservatives on grape.And sum up the best plan which can effectively inhibit the grape Alternaria rot and maintain the fruit quality for a long time.The results are as follows:1.Used Alternaria alternate as the research objective.We treated the fungus with several different mass concentrations(400,600,800,1000,1200,1400,1600,1800,2000,2200,2400,2600,2800 and 3000 mg/L).we concluded that L-cysteine at high concentrations could significantly inhibit the mycelial growth,the rate of spore germination and germ tube elongation of fungus.Among them,2800mg/L L-cysteine treatment group had the best inhibition effect.On the 6th day,the inhibition rate of colony growth was 95.96%.Observing the shape of mycelium under microscope,We found that the density of mycelium in the treatment group was very small,and the mycelium was hollowed,blackened,coarsened and atrophied.But in the control group,the mycelium was thin and smooth the mycelium was thin and smooth.Then selecting the optimal concentration(1600,2000,2400 and 2800 mg/L)of L-cysteine solution to treat the grapes inoculated with Alternaria alternate and stored in incubator at 28?.The results show that the decay rate,fruit dropping rate and weight loss rate of grape fruits treated with 2800mg/L L-cysteine were significantly lower than those of the control group(p<0.05).2800mg/L L-cysteine can effectively reduce the accumulation of malondialdehyde in fruit.The MDA content is only 41.39 nmol/g after 15 days storage,which is significantly lower than other treatment groups.2800mg/L L-cysteine can also effectively maintain the activities of peroxidase(POD),polyphenol oxidase(PPO),catalase(CAT)and superoxide dismutase(SOD),so that it can enhance the resistance of fruit and enhance the resistance of fruit to disease.As a conclusion,2800mg/L L-cysteine treatment group can effectively inhibit the occurrence and expansion of Alternaria alternata rot,delay fruit aging and decay,and maintain good quality of fruit.2.Used different concentrations of chlorine dioxide were used to treat Alternaria for 10,20 and 30 minutes.It was found that chlorine dioxide gas could effectively reduce the colony growth,germ tube elongation and spore germination rate of Alternaria spp.And with the increase of concentration and time,the inhibition effect is better.Among them,when 9.0 ? g/L chlorine dioxide gas has treated for 30 minutes,it would has the best inhibition effect.Because it could effectively inhibit the tube elongation and spore germination,and the colony inhibition rate reached 100%.At the same time,the hyphae were not observed clearly under microscope after 24 h.Then selecting the optimal concentration(3.0?6.0?9.0?g/L)of chlorine dioxide gas to treat the grapes inoculated with Alternaria alternate and stored in incubator at 28?.By measuring the relevant indicators,the results showed that 9.0 ? g/L chlorine dioxide gas treatment group could effectively inhibit the decay rate,fruit drop rate and weight loss rate of grape fruit stem,delay the accumulation of malondialdehyde content in the fruit,and maintain high antioxidant activity.And 9.0?g/L chlorine dioxide gas could effectively inhibit the decrease of POD,PPO,CAT and SOD activities.At the 10 th day of storage,PPO activity was 1.67 times of the control group,POD activity was 2.10 times of the control group,CAT activity and SOD activity were significantly higher than other groups.As a result,when the fruit was treated with 9.0 ? g/L chlorine dioxide for 30 minutes.It can effectively delay the damage of grape fruits caused by Alternaria rot.3.The grape berries were fumigated with 9.0?g/L chlorine dioxide gas for 30 min and sprayed with 2800mg/L L-Cysteine ammonia solution respectively.The fruits were sealed with polyethylene film bags of 0.02 mm thickness and stored at the environment of temperature 25?and humidity 60%-65%.The results showed that compared with the control fruit,the L-Cysteine treatment group could effectively maintained the texture properties such as fruit hardness,elasticity,mastication,adhesion,cohesiveness,recovery and sensory quality such as fruit color during storage,and delayed the decrease of soluble solids,sugar,protein and Vc content.After 12 days,the content of soluble solids and soluble sugar were 1.04 and 1.17 times of that of the control group,and the content of soluble protein and ascorbic acid were significantly higher than that of other groups,and they were 1.12 and 1.87 times of that of the control group.In addition,2800mg/L L-cysteine can also effectively inhibit the increase of MDA content and PPO activity,and maintain high POD activity.In a word,2800mg/L L-cysteine can extend the shelf life of fruit to a certain extent,maintain the quality of texture,nutritional components and physiological and biochemical quality of fruit,and realize its commodity value to the maximum extent possible. |
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