A novel acidic and low-temperature-active endo-polygalacturonase from Penicillium sp. CGMCC 1669 with potential for application in apple juice clarification

An endo-polygalacturonase gene (pg I) was cloned from Penicillium sp. CGMCC 1669 and expressed in Pichia pastoris. The full-length cDNA consists of 1140 bp and encodes a glycoside hydrolase family 28 protein with a calculated molecular mass of 37.5 kDa. The optimal pH and temperature of purified recombinant endo-PG I were 3.5 and 40 °C, respectively. At 0 °C, endo-PG I still retained 7.3% of the maximal activity. The enzyme had a high affinity and specificity towards polygalacturonic acid. The Kmapp and Vmaxapp values were 19.5 mg/ml and 909.1 U/min/mg, respectively. Addition of endo-PG I (3.4 U/ml) reduced the intrinsic viscosity of apple juice by 4.5%, and increased the light transmittance by 71.8%. Combination of a commercial pectin lyase and endo-PG I showed higher efficiency in juice clarification than the pectin lyase alone or the commercial pectinase widely used. These properties make endo-PG I an interesting biocatalyst for juice clarification.