Study On The Defense Response To Invation Of Pathogen And Antagonistic Mechanism For Fresh-cut Apple

Fresh-cut fruits and vegetables are the ready-to-eat products that processed by washing, peeling, cutting or slicing, trimming, grading and packaging. Fresh-cut fruits and vegetables satisfied the demand of modern life with the advantages of natural, fresh, health and convenience. However, fresh-cut fruits and vegetables can easily cause microbial infection, which shorten the shelf-life seriously. In this pater, apple was used, and the defense response to invation of pathogen and antagonistic mechanism for fresh-cut apple was investigated. There are five parts:1. The growth trend of bacteria and change of sensory quality of fresh-cut apple during the storag at 20℃、10℃、and 4℃ was studied in the research. Then microorganism growth model was established in order to imitate the shelf-life of fresh-cut apple by using dilution-plate method and bubbing method. The results indicated that the Gompertz model could effectively imitate the dynamic change of number of bacteria during different storage temperatures, therefore could be used to to rapidly and accurately evaluate the total number of bacteria. For fresh-cuf apples to keep fresh and be away from serious browning and corruption, when the total number of bacteria was less than 104cfu/g,storage time can be 1 day at 20℃,3day at 10℃ and 7day at 4℃,through combing with sensory score and the Gompertz model of storaged fresh-cut apple,so safety of fresh-cut apple be guaranteed.2. The pathogenic molds which cause fresh-cut apple corruption were identified. According to morphological character method,28 strains of molds were isolated from fresh-cut apple, in which there were 7 Cladosporium strains,21 Penicillium strains. In the further,21 Penicillium strains were identified by the microscopic examination and cultivation characters in different media including CA, CYA, G25N. The results showed that 4 kinds of Penicillium were identified, including Penicillium echinulatum,Penicillium crustosum, Penicillium roqueforti, Penicillium chrysogenum.3. In this paper, yeasts from rotten apples were isolated, purified and identified. The results indicated that 4 strains of yeast were identified as Phaffia rohdozyma, Rhodotorula Harrison, Saccharomycodes Hansen, and Saccharomycodes Reess based on their colonial morphology and biology characteristics.4. Pathological reaction of fresh-cut apples caused by different concentrations of 4 kinds of Penicillium were studied. The results showed that:infection caused by Penicillium decreasing in soluble protein content in fresh cut apples, increasing in the activity of PPO and MDA, higher the concentration, stronger the inducing capacity. But the POD activity was significantly lower than the control, holding stable and remained at a low level in the late. Also, the PG activity was decreased by infection, and higher the concentration, the deeper the level of infection.5.Study on the mechanism of antagonistic with different concentrations of two kinds of yeast on fresh-cut apples. The results showed that:the higher the concentration of yeast, lower the soluble protein content, and soluble protein content decreased faster. The total sugar content showed the same trend of relatively lower compared to control, indicating that yeast may involve the nutrition and spatial competition. The results also show that:the yeast increased PPO, POD activity in fresh-cut apples and reduced the MDA content, which inhibited the membrane peroxidation effectively. Show that the yeast induced systematic resistance activity of fresh-cut apple, playing an important role on delaying shelf life.