The response surface optimization of β-mannanase produced by Lactobacillus casei HDS-01 and its potential in juice clarification.

Lactic acid bacteria (LAB) is an ideal mannanase source due to the bio-safety guarantee. LAB can heterogeneously express β-mannanase or be directly used as β-mannanase-producing strains. This research originally optimized the fermentation condition for β-mannanase produced by Lactobacillus casei HDS-01. The applicable potential of the crude enzyme in juice clarification was investigated. Two-factorial design screened out three factors, i.e., fermentation time (p = 0.0001), glucose (p = 0.0013), and initial pH (p = 0.0167), which significantly affected L. casei HDS-01 β-mannanase activity. Under the predicted conditions resulting from the central composite design (CCD), i.e., fermentation time 18.23 hr, glucose 12.65 g L-1, initial pH 5.18, the model reached maximal β-mannanase activity of 81.40 U mL-1. This model was validated by conducting six repeated experiments and subsequent t-test (p = 0.6308). RSM optimization obtained a 1.33-fold increase in β-mannanase activity. This increase could also be qualitatively detected by larger clearance zone on konjac powder-MRS agar through Congo Red dyeing. The yield and clarity of crude β-mannanase-treated juices from orange, apple, and pear were significantly higher than controls without enzyme treatment. This study conferred a relatively high β-mannanase-producing LAB strain with a high bio-safety level and easy and economical use in juice clarification as well as other food-level fields.