Co-production of poly(l-lactide)-degrading enzyme and raw starch-degrading enzyme by Laceyella sacchari LP175 using agricultural products as substrate, and their efficiency on biodegradation of poly(l-lactide)/thermoplastic starch blend film

• Co-production of poly (l-lactide)-degrading enzyme and raw starch-degrading enzyme was archived by Laceyella sacchari LP175.
• Cheap and abundant agricultural products was used for enzyme productions.
• Mechanisms on biodegradation of the bioplastic PLLA/TPS blend were elucidated.
• Application of crude enzyme could degrade 99.7% of poly-(l-lactide)/thermoplastic starch (TPS) blend within 4 h.

The co-production of poly-(l-lactide)-degrading enzyme and raw starch-degrading enzyme by the thermophilic filamentous bacterium Laceyella sacchari LP175 in liquid medium using low-cost agricultural crops as substrates was investigated. Statistical mixture design experiments indicated that 5 g of raw material – consisting of 2.35 g L−1 cassava chips and 2.65 g L−1 soybean meal in a suspension of 2.0 g L−1 K2HPO4 and 1.0 g L−1 KH2PO4 – gave the highest production of both enzymes when the culture was grown at 50 °C for 24 h cultivation. Addition of 1.0 g L−1 of poly-(l-lactide) powder and 1.0 g L−1 cassava starch to the medium increased poly-(l-lactide)-degrading enzyme and raw starch-degrading enzyme, respectively. Response surface methodology by central composite design found that the optimized concentration of 0.52 g L−1 poly(l-lactide) powder and 3.34 g L−1 cassava starch increased poly-(l-lactide)-degrading enzyme and raw starch-degrading enzyme activities up to 68.8 U mL−1 and 86.1 U mL−1, respectively. The 2% poly-(l-lactide)/thermoplastic starch (PLLA/TPS) blend (50:50) film was degraded up to 99.7% of weight loss by the crude enzyme at an initial pH of 9.0 for 4 h. The high efficiency on biodegradation of poly-(l-lactide)/thermoplastic starch blend polymer by the obtained mixed enzymes from cheap and abundant agricultural products could be applied to reduce global environment from non-biodegradable materials.