Characteristics and influencing factors of solid-state fermentation of Rhizopus delemar

To explore the regulatory role of Rhizopus in brewing, the culturable experiment was carried out with Rhizopus delemar. The effects of medium moisture and temperature on the spore proliferation, amylase activity, and volatile flavor compound production were studied. The model was constructed by orthogonal partial least squares discriminant analysis (OPLS-DA), and key volatile flavor compounds were screened based on variable importance in projection (VIP) values and analysis of variance P value. The results showed that moisture 45% was beneficial for R. delemar spore propagation and amylase production. The highest spore counts were (139.28±5.94)×10⁶ spores/g at 25 ℃. The highest amylase activity was (126.09±4.33) U/g at 30 ℃. The moisture 30% and temperature 40 ℃ were the optimal for the accumulation of volatile flavor substances. 36 volatile flavor compounds were added after wheat substrate was inoculated with R. delemar, and 11 key differential volatile flavor compounds (VIP>1, P<0.05) were screened out, including benzyl alcohol, heptyl acetate, methoxybenzoxime, ethyl myristate, ethanol, butyl acetate, ethyl hexanoate, ethyl acetate, ethyl octanoate, and 1-nonanol.