Effect Of Lactic Acid Bacteria Fermentation On The Functional Activity And Flavor Quality Of Cordyceps Militaris Pulp

Cordyceps militaris is recognized as an edible fungus with many pharmacological activities.However,it's product form is single,and the related basic research is few.Fermentation is one of the most popular method in enhancing the added value of the food.In this paper,the main active substances and antioxidant capacity of C.militaris pulp were studied after selecting the suitable lactic acid bacteria for the fermentation of C.militaris pulp,and the effect of pre-treatment sterilization on the flavor quality of the lactic acid bacteria fermented C.militaris pulp was further evaluated.The research results are as follows:(1)C.militaris pulp contains antimicrobial substances and low content of soluble solids(about 1.0%),which may be detrimental to the growth of lactic acid bacteria.The adaptability of Lactobacillus plantarum(LP)and Pediococcus pentosaceus(PP)to C.militaris pulp was significantly better than that of Lactobacillus acidophilus(LA)and Streptococcus thermophilus(ST),with good acid tolerance,sugar consumption and acid production,proliferation and metabolism ability.Compared with PP,LP had higher adaptability to low-sugar and low-protein substrates,stronger growth activity,and no adverse flavor was produced in fermented C.militaris pulp.Therefore,LP was selected for subsequent experiments.(2)LP effectively degraded 7 nucleoside compounds in C.militaris pulp and produced uracil.The LP strain used in this experiment could produce extracellular polysaccharide.During the fermentation process,the extracellular polysaccharide(crude)content continued to increase,while the crude polysaccharide content in C.militaris pulp first decreased and then increased.LP fermentation had no significant effect on the content of D-mannitol in C.militaris pulp.During fermentation,the content of carotenoids decreased significantly,corresponding to b~*value decreased significantly,while the contents of total phenols and total flavonoids increased significantly.After fermentation,the DPPH free radical scavenging rate,total antioxidant capacity of FRAP and SOD activity of C.militaris pulp were significantly increased.In the fermentation process,the main active substance group in C.militaris pulp was significantly positively correlated with the antioxidant capacity group(p<0.01).(3)LP mainly uses glucose in C.militaris pulp to produce lactic acid,and metabolizes citric acid and malic acid.Ultra-high pressure(UHP)pretreatment is more beneficial to LP's consumption of sugar to produce acid.Pasteurization pretreatment can promote the metabolism of amino acids in LP,and UHP pretreatment can promote the generation of aromatic amino acids after fermentation.After pasteurization and UHP pretreatment of C.militaris pulp by LP fermentation,the contents of five 5'-nucleotides were significantly increased,and the content of 5'-uridine was the most obvious change.(4)Both pretreatments increased the total amount of flavor substances in C.militaris pulp,but decreased the number of species.The pasteurization pretreatment significantly increased the content of aldehyde in the pulp,corresponding to the enhancement of cooking taste and pungent smell.UHP pretreatment significantly increased the content of alcohol and promoted the formation of special aroma of C.militaris.According to the sensory evaluation of flavor,compared with the pasteurized C.militaris pulp,the flavor of the UHP pretreated C.militaris pulp before fermentation was closer to that of the fresh pulp,and the aroma and umami after fermentation were more concentrated.