Production, Characterization and Appliction of Polymers from Rhizopus microsporus ST4 and Oil Plam Wastes

Abstract

This study aimed to produce, characterize and apply biopolymers from Rhizopus microsporus ST4 and oil palm wastes. The condition for production of biopolymer from R. microsporus ST4 were: 2% glucose, 0.05% yeast extract, 5% glutamic acid and 0.05% MgSO4 -7H2O with pH of 5.8 at 45 °C for 3 days. Under this condition, the maximum concentration of biopolymer was 12.33 g/L. Analysis of amino acid profile revealed that the biopolymer ST4 contained 99.3% of glutamic acid with a trace amount of lysine, aspartic acid, alanine and threonine. Therefore, the biopolymer from R. microsporus ST4 was considered to be polyglutamic acid (PGA). The molecular size of PGA (estimated by SDS-PAGE) was about 80 kDa and soluble in water. The recovery and characterization of biopolymers from oil palm wastes were investigated using palm oil mill effluent (POME) and oil palm trunk (OPT). For POME, the biopolymer from sterilizer condensate (SC) and decanter effluent (DE) were extracted with 5 folds (v/v) of 95% ethanol and obtained the precipitated hemicellulose from SC (HSC) and DE (HDE) of 2.16% and 2.47% (w/v), respectively. There were two sizes of Mw from each source; 42.19 kDa and 3.57 kDa from HSC, with 36.34 and 3.61 kDa from HDC were determined with a gel permeation chromatography (GPC). The maximum solubility of HSC and HDE in water were 96.82% and 99.05% respectively. Polymer from the selected OPT (0.6>OPT<2 mm) was extracted using alkaline peroxide (AP) pretreatment, then precipitated using the 3-fold volume of absolute ethanol. Under the optimal condition, the maximum concentration of the precipitated hemicellulose from OPT (PHCCM) was 26.25% (w/w). The PHCCM had a molecular weight (Mw) of 67.57 kDa and the maximum solubility in DMSO. The commercial xylan from beechwood (CXB) was found to have also two size of Mw 930 kDa and 21 kDa. The maximum solubility of CXB in water was 84.62%. Hemicellulose-maleic anhydride (MA)/polyvinyl alcohol (PVA) hydrogels were prepared by modifying from HSC (H1-H12), HDE (H13-H24), CXB (H25-H36) and PHCCM (H1-H12). HDE-MA was prepared by reacting HDE with MA (ratio 1.5:1) using dimethyl sulfoxide (DMSO) as a solvent. The reactions were performed and stirred at 50 °C for 2 h and precipitated with 3 folds (v/v) of isopropanol for 48 h and then dried in an oven at 50 °C. The dried HDE-MA were blended with PVA (ratio 1:0.55). This condition (H17) gave the highest degree of swelling (395.9%). Under the optimum conditions (H20;HDE-MA 1:1/PVA1:0.55), the highest compressive strength could reach to 21.12 MPa. Evaluation of the cytotoxicity of the hydrogels revealed that the cell viability of L929 cells (Mouse Fibroblast Cells) and antimicrobial tests on the selected hydrogel which was high swelling and strength including from HSC (H11), from HDE (H17), from commercial xylan (H35) and from PHCCM (H10), hydrogel suggested that the hydrogel was cytotoxic and had a potential for inhibition of cancer cell. The hydrogel from HDE (H17) and hydrogel from CXB (H35) exhibited inhibition zones of Staphylococcus aureus ATCC 6538 could be the probability in the field of biomedical application. The xylooligosacharide (XOS) production from HSC, HDE, CXB and PHCCM, was using the enzymatic method. Under the optimal conditions of CXB (4 U for 12h at 40 °C), the highest xylobiose (oligosaccharide) could reach to 0.05% following this polymer from OPT (4 U for 12h at 40 °C), the highest xylobiose (oligosaccharide) could reach to 0.03%. Moreover, XOS from PHCCM exhibited IC50 inhibition at 19,610 μg/mL of antioxidant activity test.