Study On The Effects Of Postharvest Treatments To The Physicochemical Characteristics And Biological Activity Of Cordyceps Militaris

Cordyceps militaris, a traditional culinary and medicinal fungus which is famous in China, has abundant nutritions and delicious favor. However,the fresh fruitbody of C. militaris is easy putrefactive due to its tender tissue during storage. So it is important to find a safe and effective storage method and dry processing technology for postharvest C. militaris fruitbody. In this article, the fresh fruitbody of C. militaris was firstly treated by allyl-isothiocyanate ?AITC? during preservation and the physiological and biochemical characteristics and antioxidant activities of C. militaris were examined. Then four different drying methods were respectively used to dehydrate the postharvest fruitbody of C. militaris by comparing the physiochemical and bioactivity character. Finally, enzyme-assisted extraction and Pb²⁺ biosorption of polysaccharide from C. militaris was studied in ordor to provide the theoretical guidance for the application and development of C. militaris in food industry. The main results are as follows:The effect of different concentrations of AITC on the quality of C.militaris during postharvest preservation was investigated. AITC treatments could effectively maintain better color, cordyceps, carotenoids and total flavonoid contents, and decreased the incidence of fruit decay, meanwhile the accumulation of MDA was reduced. Moreover, the content of total phenol and the activitives of antioxidant enzymes, incuding CAT, SOD and POD, were improved with AITC treatments, while DPPH free radical scavenging ability, ABTS cationic free radical scavenging ability and the total antioxidant activity were enhanced. Among all the treatments, 15?L·L^-1 was most effective during preservation of mushroom, but 10?L·L^-1 was selected as the appropriate treatment concentration in view of economic efficiency.Four different drying methods, including sun drying, hot air drying,microwave drying and freeze drying, were used to dehydrate C. militaris and the quality of dryied C. militaris was investigated. The results indicated that freeze drying could retain the appearance and color of the product, which was similar to fresh sample. In addition, the contents of polysaccharide and cordycepin were the highest in fruitbody dried by vacuum freeze drying compared with that dried by other drying methods. However, freeze drying was time-consuming, while microwave drying had high efficiency of drying characteristics and high-quality product. in this study, microwave drying at 700W had the highest content of carotene, flavonoids and total phenol.Moreover, this drying sample had the best antioxidant activity. The sun drying was the worst one among all tested dehydration methods used to dry fruitbody of C. militaris according to the color and other quality charateristics.The enzyme assisted extraction conditions of polysaccharide from C.militaris mycelia were firstly investigated by kinetics analysis and the optimal operating was found to be: extraction temperature, 40?;solid-solvent ratio, 1:20; extraction pH, 4.0; cellulase concentration, 2.0%.The polysaccharide extraction yield was 5.99% under these optimized conditions. Furthermore, a fundamental investigation of the biosorption of Pb²⁺ from aqueous solution by the C. militaris polysaccharide was performed under batch conditions. The suitable pH ?5.0?, polysaccharide concentration (0.20g-L^-1), initial Pb²⁺ concentration (300mg·L^-1) and contact time ?40min? were outlined to enhance Pb²⁺ biosorption from aqueous medium. The Langmuir isotherm model and pseudo first order kinetic model fitted well to the data of Pb²⁺ biosorption, suggesting the biosorption of Pb²⁺onto C. militaris polysaccharide was monolayer biosorption and physical adsorption might be the rate-limiting step that controlled the adsorption process. FTIR analysis showed that the main functional groups of C.militaris polysaccharide involved in adsorption process were carbonyl,carboxyl, and alcoholic groups.