초록
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<SUP>-1</SUP> cassava chips and 2.65 g L<SUP>-1</SUP> soybean meal in a suspension of 2.0 g L<SUP>-1</SUP> K<SUB>2</SUB>HPO<SUB>4</SUB> and 1.0 g L<SUP>-1</SUP> KH<SUB>2</SUB>PO<SUB>4</SUB> - gave the highest production of both enzymes when the culture was grown at 50 <SUP>o</SUP>C for 24 h cultivation. Addition of 1.0 g L<SUP>-1</SUP> of poly-(l-lactide) powder and 1.0 g L<SUP>-1</SUP> 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<SUP>-1</SUP> poly(l-lactide) powder and 3.34 g L<SUP>-1</SUP> cassava starch increased poly-(l-lactide)-degrading enzyme and raw starch-degrading enzyme activities up to 68.8 U mL<SUP>-1</SUP> and 86.1 U mL<SUP>-1</SUP>, 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.