LAUSR

The prospect of utilizing yam peel hydrolysate (YPH) as a carbon source for lactic acid (LA) production using Rhizopus orysae was investigated in batch surface and submerged fermentation processes. The kinetics of biomass growth, substrate utilization and LA production were studied using models of modified Luedeking–Piret, logistic and simple Luedeking–Piret equations, respectively, for the surface and submerged processes. The YPH containing 80 g L−1 of reducing sugars (glucose, xylose, ribose and others) was obtained by acid hydrolysis (H2SO4) of 100 g L−1 of yam peel and used for fermentation. The LA yield from the YPH was 80.03% and 75.63% for the surface and submerged fermentation, respectively. These values were higher than those of synthetic glucose syrup (SGS), which were 77.36% and 38.96% for surface and submerged fermentation, respectively. The models were satisfactory for the fermentation processes with high accuracy of R2 ((0.89 to 0.96), (0.95 to 0.99) and (0.86 to 0.99)) for biomass growth, substrate (SGS/YPH) utilization and LA production, respectively. The models also elucidated that the fermentation process was growth associated (α) instead of non‐growth associated (β) because the value of α/β was greater than 1. This justified the other kinetic parameters obtained for the growth phase. Therefore, Rhizopus oryzae effectively converted YPH to LA with a high yield and purity. © 2021 Society of Industrial Chemistry and John Wiley & Sons Ltd