Highly efficient clarification of fruit juices with new pectin lyase from Bacillus velezensis

Abstract

Pectinases are widely used in the fruit juice industry for clarification, liquefaction and stabilization of juices. Primarily, these enzymes are responsible for the breakdown of long and complex molecules in the fruit pulp (pectin). Unlike the combination of polygalacturonase (PG) and pectin esterase (PE) commonly found in commercial products, pectin lyase (PNL) is the only known pectinase capable of breaking down highly esterified pectins (such those found in fruits) into short molecules via a β-elimination mechanism without producing methanol. Methanol is toxic and can be harmful to health. Commercial preparations with PNL as the major component are preferable in juices and wine processing because it avoids the production of methanol, precipitation of pectin partially de-esterified with endogenous calcium, and damage of the volatile ester content responsible for the specific aroma of various fruits. This study reports the first cloning and characterization of a PNL gene, ppr, from Bacillus velezensis, and the deduced amino acid sequence is compared with those of other lyases. In this work, the gene encoding the pectin lyase (PNL; EC 4.2.2.10) from Bacillus velezensis was successfully expressed under optimized conditions for high soluble protein expressions as soluble PNL-6His in E. coli M15[pREP4]. After expression, purification of 6xHis-labeled PNL was performed according to QIAGEN instructions. IMAC fractions were analyzed using SDS-PAGE. After purification, 3-fold purification was observed with a yield of 82%. In this study, we report for the first time a method to express PNL in E. coli and purify it as a pure native enzyme. The cloned PLN was used to clarify and liquefy apple and orange juices and to improve the flavor of these juices. In this way, pulp waste after juice extraction is reduced. Methanol content was determined by gas-liquid chromatography and was not detectable in the clarified juices.