Potential ramifications of the effects of sub-lethal ultraviolet B-radiation on the subsequent three subcultures of Lactobacillus fermentum BT 8219 during fermentation in biotin-supplemented soymilk and their probiotic properties

Abstract

The aim of our study was to evaluate the potential ramifications of sub-lethal ultraviolet B radiation (SUVBR) on Lactobacillus fermentum BT 8219 cells through to three subsequent subcultures during fermentation in biotin-supplemented soymilk (biotin-soymilk). Lactobacillus fermentum BT 8219 cultures were irradiated in Petri dishes (diameter 56 cm2) with UVB at a dosage of 60 J m−2 using a GS Gene Linker UV Chamber. Cell lethality was observed immediately after SUVBR, followed by higher growth than that shown by the control during fermentation in biotin-soymilk (P < 0.05). This enhanced growth was associated with enhanced β-glucosidase specific activity, leading to increased bioconversion of isoflavone glucosides to aglycones (P < 0.05). The first, second and third subcultures of the treated cells and the control showed similar growing characteristics, enzymes and isoflavone bioconversion activities in biotin-soymilk (P > 0.05). In comparison to the control, SUVBR affected the functional properties of parent cells by reducing their tolerability towards acid (pH 2) and bile, lowering their inhibitory activities against selected pathogens and reducing their ability for adhesion (P < 0.05). Acid tolerance and adhesion ability of the subsequent subcultures of the treated cells showed comparable traits with the control (P> 0.05), while reduced bile tolerance and antimicrobial property were observed up to the second subcultures of the treated cells (P < 0.05). Our results suggest that SUVBR could be utilised to produce putative probiotic cells and to increase the bioactivity of biotin-soymilk via fermentation with L. fermentum BT 8219 for the development of functional foods.