Preparation of a PET-hydrolyzing lipase from Aspergillus oryzae by the addition of bis(2-hydroxyethyl) terephthalate to the culture medium and enzymatic modification of PET fabrics

Optimization of cultivation conditions for lipase production and the preparation of a specific lipase catalyzing the hydrolysis of polyethylene terephthalate (PET) by Aspergillus oryzae CCUG 33812 as well as modification of PET fabrics by the enzyme were investigated. The lipase activity produced by the fungus after the addition of olive oil was not efficient in changing the properties of PET samples. In order to obtain lipase activity directed toward the hydrolysis of PET, two derivatives of terephthalic acid (TPA), namely diethyl p-phthalate (DP) and bis(2-hydroxyethyl) terephthalate (BHT), and PET short fibers were used as inducers. The results showed that BHT was the best inducer. The BHT-induced extracellular lipase could catalyze the hydrolysis of the PET model substrate DP. The formation of new carboxyl groups is consistent with the increase in K/S values of dyed PET fabrics after the enzymatic treatment. Additionally, treatment with the BHT-induced lipase resulted in increased moisture regain and weight loss of PET fiber/fabric, while the water contact angle and the static half decay time decreased slightly. This indicates that hydrophilicity and anti-static ability were improved after the treatment with the BHT-induced lipase. Compounds that were solubilized by the enzymatic treatment were analyzed by spectrophotometry and high performance liquid chromatography (HPLC) with UV detection. Both analyses indicated that hydrolysis of PET occurred and that products were formed due to the catalytic action of the BHT-induced enzyme; however, no significant changes in UV absorbance and no new peaks were found in HPLC-UVD analyses of reaction mixtures with olive oil-induced lipase or PET-induced lipase. This investigation has resulted in detailed procedures for the production of PET-hydrolyzing lipase by A. oryzae and is the first report regarding the successful use of BHT as an inducer for the enzyme production.