CONVERSION OF BETA-METHYLBUTYRIC ACID TO BETA-HYDROXY-BETA-METHYLBUTYRIC ACID BY GALACTOMYCES-REESSII

beta-Hydroxy-beta-methylbutyric acid (HMB) has been shown to increase strength and lean mass gains in humans undergoing resistance-exercise training, HMB is currently marketed as a calcium salt of HMB, and thus , environmentally sound and inexpensive methods of manufacture are bei ng sought. This study investigates the microbial conversion of beta-me thylbutyric acid (MBA) to HMB by cultures of Galactomyces reessii, Opt imal concentrations of MBA were in the range of 5 to 20 g/liter for HM B production, Preliminary shake flask experiments indicated that HMB y ields were sensitive to dissolved oxygen levels and that cell growth d ecreased significantly as MBA concentrations increased, Degradation of HMB was faster at acidic pH, and pH 7.0 was optimal for HMB productio n, Resting cells obtained from media without MBA could efficiently con vert MBA to HMB. Thus, a two-step, fed-batch fermentation procedure in which biomass was first produced, followed by coaddition of MBA and g lucose, while dissolved oxygen was maintained at 20% of saturation, wa s designed, A maximum HMB concentration of 38 g/liter was obtained aft er 136 h, and the molar conversion yield was more than 0.50 mol of HMB /mol of MBA during the fermentation.