Abstract
The thermo-solvent-tolerant lipase-producing actinomycete, Streptomyces sp. A3301, was utilized as a biocatalyst for poly (lactic acid) or PLA polymerization. The study aimed to optimize lipase immobilization conditions, characterize the immobilized lipase and apply it for PLA polymerization. The results showed using a sponge as the immobilizing matrix was the most effective method, achieving a maximum activity of 277 U/g of sponge. The optimal sponge size was determined to be 0.125 cm³ and pre-soaking the sponge in 0.1 M phosphate buffer at pH 7.0 for 24 h before use proved advantageous. Immobilization significantly enhanced the thermo-stability of the enzyme, with a relative activity ranging from 140 to 190 % within the temperature range of 30 to 60 °C. In contrast, the crude lipase exhibited thermo-stability only within the 30 - 50 °C range. The immobilized lipase demonstrated stability under PLA polymerization conditions, which involved a reaction mixture containing toluene and lactic acid and performed at 60 °C for 8 h. The immobilized lipase maintained its activity under this condition for 5 h, retaining a relative activity of 230 %, which was 1.2 times higher than the activity of the crude lipase. When the immobilized lipase was used in PLA polymerization, the resulting PLA product exhibited a molecular weight of 5,333 ± 0.02 Da, and the degree of polymerization was approximately 72. These findings underscore the potential of the immobilization technique to enhance lipase activity for PLA polymerization. HIGHLIGHTS PLA polymerization via a biological process is demonstrated. PLA can be polymerized by enzyme lipase produced by Streptomyces sp. A3301. Improving PLA polymerization with enzyme immobilization techniques. Sponge is the best immobilizer for PLA polymerization. PLA can be synthesized under mild conditions. GRAPHICAL ABSTRACT
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