Two-stage processing for xylooligosaccharide recovery from rice by-products and evaluation of products: Promotion of lactic acid-producing bacterial growth and food application in a high-pressure process

In this study, we attempted to maximize arabinoxylan conversion into xylooligosaccharide (XOS) from rice husk and rice straw using two saccharification processes and evaluate the promotion of lactic acid-producing bacterial growth, including an investigation of the role of prebiotics in protecting probiotic bacteria in rice drink products in a high-pressure process (HPP). Hydrothermal treatment followed by enzymatic hydrolysis was designed for XOS recovery from rice husk arabinoxylan (RH-AX) and rice straw arabinoxylan (RS-AX). The hydrothermal treatment performed at 170 °C for 20 min and 180 °C for 10 min was the optimal condition to produce XOS liquor from rice husk and rice straw, respectively. Pentopan mono BG successfully recovered XOS from rice husk and rice straw residues at 50 °C, pH 5.5, an enzyme concentration of 50 U and 100 U/g substrate for 24 h. This design converted 92.17 and 88.34% (w/w) of initial RH-AX and RS-AX into saccharides, which comprised 64.01 and 59.52% of the XOS content, respectively. Rice husk xylooligosaccharide (RH-XOS) and rice straw xylooligosaccharide (RS-XOS) had degrees of polymerization ranging from 2 to 6 with some arabino-xylooligosaccharides. RH-XOS and RS-XOS were used to examine the promotion of the growth of lactic acid-producing bacteria strains in the presence of other prebiotics. RH-XOS and RS-XOS strongly promoted the growth of Lactobacillus sakei and Lactobacillus brevis, while other species showed weak to moderate growth. This study represents the first report of the powerful effect of Lactococcus lactis KA-FF1-4 on altering the utilization of XOS but not xylose. Furthermore, for the first time, we reported the capability of XOS to protect probiotics in rice drinks under high-pressure conditions. RH-XOS and RS-XOS resulted in the highest viability of approximately 11 log cfu/mL and exhibited no significant difference compared with the non-HPP treatment. Hence, rice husk and rice straw can be utilized as alternative prebiotic sources that provide biological activity and food applications in the HPP industry.