Total utilization of Japanese pear tree prunings: extraction of arbutin and production of bioethanol

Discarded branch prunings from Japanese pear trees (Pyrus pyrifolia cv. Kousui) are promising resources containing polysaccharides and polyphenols. This study aimed at the total utilization of discarded branches. Arbutin is an inhibitor of biosynthesis of the human pigment melanin and extensively used as a human skin-whitening agent. It was found that most of the arbutin in the branches was contained in the bark (27.1 mg/g dry matter) compared with that in wood (5.2 mg/g dry matter). We evaluated the effect of the extracted solution containing arbutin (ESCA) from the bark on melanin formation in B16 melanoma cells. At a concentration of 4.0 × 10⁻³ % of ESCA, treated B16 melanoma cells showed 77.9 ± 3.9 % of the melanin production of untreated cells, with no cytotoxicity. The residue (wood) after arbutin extraction contained abundant holocellulose (69.8 %), and was accordingly hydrolyzed with cellulase and then converted into ethanol by Saccharomyces cerevisiae BA11, after microwave irradiation pretreatment. In total, 0.79 g of arbutin and 8.84 g of ethanol were produced from the 100 g of dry branches.