Optimization of L(+) lactic acid production from solid pineapple waste (SPW) by Rhizopus oryzae NRRL 395

Abstract

Solid pineapple waste (SPW) is one of the most abundant agricultural wastes found in the tropic region. Improper management could lead to deposition of such waste in the environment causing other problems. Optimized bioconversion into value added products using potent microorganism could be an option to manage SPW. In this study, Rhizopus oryzae NRRL 395 was used to convert SPW to L(+) lactic acid through solid-state fermentation (SSF). The lactic acid production, reducing sugar utilization and by-product formation were studied using central composite design (CCD) after screening step using 2 level Factorial Design (2LFD). Studied parameters include moisture content (45 to 85% w/w), incubation time (0 to 7 days), temperature (25 to 45 °C), pH (4 to 8), and inoculum size (1 × 105 to 1 × 109 spores/g). During 2LFD, the highest lactic acid concentration obtained was 84.85 mg/g under the condition of 60% w/w of moisture content, 3 days of incubation, 35 °C, pH of 7 and 1 × 107 spores/g. Based on the condition suggested by CCD, the maximum lactic acid concentration of 103.69 mg/g was obtained with the following optimized SSF conditions: 67.53% w/w of moisture content, 3 days of incubation, temperature of 32.2 °C, pH of 5.6, and inoculum size of 1 × 107 spores/g. Graphic Abstract: [Figure not available: see fulltext.].