Poly(l-lactide)-Degrading Enzyme Production by Laceyella sacchari LP175 Under Solid State Fermentation Using Low Cost Agricultural Crops and Its Hydrolysis of Poly(l-lactide) Film

Abstract

The aim of this study was to investigate the enhancement of poly(l-lactide) (PLLA)-degrading enzyme production by Laceyella sacchari LP175 under solid state fermentation (SSF) using low-cost agricultural crops as substrates and its hydrolysis of poly(l-lactide) film. Cassava chip, soybean meal and corncob were used to investigate the enzyme production using a statistical mixture design method. The effect of various inducers and SSF growth conditions parameters affecting PLLA-degrading enzyme production were also investigated. The fermentation of solid substrates was up-scale in a static tray bioreactor. The crude enzyme extracted from the fermented solid substrate was used to evaluate the biological degradation of PLLA film at 50 °C for 24 h. The results of substrate combination showed that 5 g of the substrate mixture, consisting of 4.3 g cassava chips and 0.7 g soybean meal, yielded 320 U/g dry solid. The addition of 0.1 g peptone to the mixture of solid materials increased enzyme production up to 456 U/g dry solid. The production of enzyme in a static tray bioreactor with optimized physical conditions yielded the maximum enzyme production, 472 U/g dry solid. The 20 mL reaction consisting of 8600 mg/L PLLA film was degraded by the crude enzyme extracted from the fermented solid substrate. Agricultural crops and wastes contain significant amounts of nutrients for microbial growth and products. This is the first reported of PLLA degrading enzyme production under SSF using low-cost substrates showing the possibility for application in large-scale biological recycling of bio-plastic as a future sustainable process.