Lactic acid production from solid pineapple waste using Rhizopus Oryzae NRRL 395

Abstract

Solid pineapple waste (SPW) is one of the most abundant agricultural wastes found in tropic region. It was reported about 40-50% of the wastes generated from pineapple canning industry are from solid wastes. Their disposal poses a serious environmental pollution problem. This study looks into the potential of utilizing a mixture of solid pineapple waste including residual pulp, peels, cores, stems and leaves for the production of lactic acid by Rhizopus oryzae NRRL 395 in solid state fermentation (SSF). Characterization of SPW using Fourier transform infrared (FT-IR) and Scanning electron microscope (SEM) indicate that the structural and chemical composition of autoclaved SPW was suitable for use as SSF substrate. Screening studies through 2-level factorial (2LF) design revealed that R. oryzae NRRL 395 was best suited for lactic acid metabolism under the conditions of SSF system. The optimum SSF condition in shake flasks conducted based on central composite design was obtained at 67.53%, 3 days of incubation, at temperature of 32.2°C, pH of 5.6, and inoculum size of 1×107 spores/g, with 1.21 fold increment of lactic acid yield compared to that produced in one-factor-at-a-time experiment. This study has successfully designed a novel modified Memmert-tray bioreactor to analysed the effects of lactic acid production in larger scale (1kg) SSF of SPW. The highest concentration of lactic acid in the bioreactor was obtained at condition variables of 70 ± 2% of humidity chamber with 2 Liters per minute (LPM) aeration rate, incubation temperature of 30°C, pH 6 and 70% of initial moisture content of SPW bed, where the SSF was run for 3 days.The lactic acid yield (Yp/s), maximum and overall lactic acid productivity of R. oryzae NRRL 395 in modified Memmert-tray bioreactor were 1.03, 1.05, 1.14 fold higher than those under optimum condition performed in shake flask system. As a conclusion, a significant lactic acid production from SPW by Rhizopus oryzae NRRL 395 has proved that it could be contributed towards the sustainability of agricultural industry by creating wealth from waste and promoting economic biotechnology for future development.