Mannanase from Lactic Acid Bacteria Pediococcus acidilactici: Production Optimization, Purification, and Application in Juice Clarification.

Pediococcus acidilactici, a generally regarded as safe (GRAS) lactic acid bacteria species, is a desirable microbial mannanase source due to its high bio-safety. P. acidilactici HDM2 isolated from dragon fruit culture was identified according to morphological, physiological, and biochemical characteristics as well as preserved nucleic acid (16S rDNA and rpoA) sequencing. A two-step response surface methodology (RSM) experiment subsequently screened out and then predicted the optimal levels of two factors which significantly affected P. acidilactici HDM2's mannanase production. The maximal enzyme activity reached 97.9 U/mL under the condition of glucose 17.5 g/L and initial pH 4.6. RSM optimization resulted in a 39.3% increase of mannanase yield which was verified by six repeated trials and consequent t-test (P < 0.05). The enhancement of mannanase production was also proved by congo-red dyeing on KGM (konjac glucomannan)-MRS (de Man, Rogosa, and Sharpe) agar. Diameter of clearance zone enlarged from 2.7 to 4.5 cm through RSM. The purified P. acidilactici HDM2 mannanase with a molecular weight of 30 KDa was then applied in fruit juice clarification process. The enzyme exhibited significantly higher clarifying efficiency than commercial mannanase in both yield and clarity for six out of eight fruits, i.e., orange, peach, grape, pear, kiwi, and grapefruit. These results promised the application of P. acidilactici HDM2's mannanase in various especially food-level fields.