Screening the Cordyceps militaris Strain for Reducing Glycemic Index of Rice Substrate under Solid Fermentation

In order to shorten the production cycle, reduce the cost, and obtain the fermentation product with low glycemic index (GI) and high content of active substances, the dominant strains of Cordyceps militarisfor solid fermentation of rice substrate were screened with mycelial growth rate, expected glycemic index (eGI), contents of polysaccharide and cordycepin as screening indicators. The results showed that the content of rapidly digestible starch (RDS) in all the fungal substances fermented by strains of C.militaris (Shennongda, Wanxi, Yun and Quan) decreased after fermentation, while the content of slowly digestible starch (SDS) and resistant starch (RS) increased. Further digestion kinetics in vitro showed that the eGI value in fungal substance was significantly lower than that before fermentation (P<0.05). Then combined with the results of four indexes, strain Quan was determined as the best one for solid fermentation of rice. After 25 days fermentation, the eGI value of fermentation product decreased from 80.33 (before fermentation) to 65.63, which reached the level of medium GI value. The polysaccharide content in fungal substance of Quan was 5.29%, and the content of cordycepin was 5185.98 mg/kg, which were higher than those in fruiting body. Therefore, the fermentation substance could be used to replace the fruity body in the development of nutrition and functional food, and would provide raw materials for the development of low GI products of C.militaris.