Study On The Mechanism And Regulation Of Quality Deterioration Of Main Edible Fungi After Harvest

There are a variety of edible fungi in China, both production and number of species in China rank at the top in the world. However, the postharvest handling of edible fungi is difficult due to their highly perishable nature. Therefore, how to distribute these "short-life" edible fungi and extend their shelf-life, has been paid much attention by researchers as well as farmers. The main problems for postharvest edible fungi are postharvest senescence, browning, cap-opening and microbial attack. In our project, button mushroom (Agaricus bisporus) and shiitake mushroom (Lentinula edodes) were chosen as the main targets to study on:(1) The mechanism of lignification in edible fungi; (2) Structure and composition changes in the cell wall in relation to texture of edible fungi; (3) Microbial infection in postharvest edible fungi; (4) Influence of integrated application of UV-C and modified atmosphere packaging on quality properties of edible fungi; and (5) Effect of integrated application of gamma irradiation and modified atmosphere packaging on physicochemical and microbiological properties of edible fungi.The main research findings were summarized as follows:1. Button mushrooms firmness showed a positive correlation with accumulation of lignin in the tissue. It suggested that increase in firmness of mushrooms during senescence may be a consequence of tissue lignification. MAP treatments could not inhibit phenylalanine ammonia lyase (PAL) activity, however, it can suppress lignification process by inhibiting the activity of peroxidase (POD) and the accumulation of lignin. Correlation between the cinnamyl alcohol dehydrogenase (CAD) activity and lignin accumulation was not obvious.2. The metabolism of cell wall composition can influence the quality of shiitake mushroom. MAP treatments helped in maintenance of mushroom texture. M2 treatment (four macroholes) can best preserve the original texture while mushrooms in Mo (no holes) became soft and deteriorated, possibly due to higher CO2 accumulation, lower cellulose, lignin and chitin content. Control mushrooms showed the highest firmness value due to significant increase of cellulose and chitin. All the three MAP treatments reduced losses of protein and polysaccharides, Transmission electron microscopy (TEM) performed on caps at harvest and after 16 days indicated that disintegration of plasmalemma had been alleviated by M2 treatment, leading to better cell wall preservation.3. The predominant spoilage microorganism in postharvest button mushrooms were Pseudomonads, psychrophilic bacteria and mesophilic bacteria, the number of which reached 9.40,7.87 and 6.61 log cfug-1, respectively after 20d of 4℃storage; The predominant spoilage microorganism in postharvest shiitake mushroom was Pseudomonads, it reached 8.81 log cfug-1 after 20d of storage; In oyster mushroom, the predominant spoilage microorganism were yeasts and molds, it reached 10.64 log cfug-1 after 12d of storage, increased by 5.33 log cfug-1 compare to initial count, significant higher than the others (p<0.05); In enoki mushroom, the predominant spoilage microorganism were yeasts and molds, psychrophilic bacteria and Pseudomonads, the number of them reached 7.65,7.10 and 6.83 log cfug-1, respectively after 12d of storage. Button mushroom and shiitake mushroom are susceptible to Pseudomonads attack, oyster mushroom and enoki mushroom are more susceptible to yeasts and molds attack.4. Shiitake mushrooms treated with UV-C (4.0 kJ/m2) maintained a high level of firmness and reduced the increase in MDA content during shelf-life storage. Treated samples showed higher total flavonoids, ascorbic acid, and delayed the increases in both O2.- production rate and H2O2 content. Furthermore, the treatment increased the antioxidant enzymes activities of CAT, SOD, APX and GR throughout storage period. These results indicate that postharvest application of UV-C radiation can enhance antioxidant capacity and extend the shelf life in shiitake mushrooms.5. All the gamma irradiation (1.0 kGy,1.5 kGy and 2.0 kGy) were effective in retarding mushroom sensory deterioration.60Coγirradiation (1.0 kGy) was most effective in maintaining proper level of shiitake mushroom firmness. Samples treated with 1.0 kGy also exhibited smaller initial declines in soluble protein, higher increases in total sugar content and lower levels of malondialdehyde accumulation. Furthermore, 1.0 kGy promoted the accumulation of phenolics compound and showed higher antioxidant ability during storage. At higher doses,2.0 kGy resulted in a higher microbial reduction, but showed negative effects on texture, chemical properties and functional components. Thus, application of gamma irradiation in combination with MAP can extend the storage life of shiitake mushroom up to 16-20 d.