Degradation of quinolizidine alkaloids of lupin by Rhizopus oligosporus.

Rhizopus oligosporus has proven beneficial in the detoxification of lupin seeds. The fermentation process is mainly affected by the initial pH in the medium. In the range of growth of mold, there are maximum enzymatic activities in pH of 3.5 and 5.5. Metabolism change occurs at these pH levels; therefore, we studied the growth, pH changes, dry matter intake, and alkaloid degradation within 48 h of fermentation. Cultures of lupin agar (LA) with pH of 3.5 and 5.5 were made in Petri dishes with lupin flour. Results showed pH directly affects the degradation of alkaloids and fungal growth. Detoxification levels achieved were 16.58 and 63.23 % in treatments LA 3.5 and LA 5.5, respectively. Fungal growth was 0.919 mg/cm(2) in LA 3.5 and 1.081 mg/cm(2) in LA 5.5. Maximum degradation rate in LA 5.5 was given between 16 and 20 h, which coincided with maximum fungal growth. Despite having similar dry matter intake in both treatments, a pH of 3.5 did not show the same degree of detoxification. The analysis with exponential, yield of growth, yield of dry matter intake and luedeking and piret equations, confirm the relation between intake and growth with detoxification. Dry matter intake equation predicts with R (2) of 0.94 the detoxification in LA 5.5. A pH of 5.5 is directly related with detoxification and fungal development.