Soymilk bio-enrichment by indigenously isolated riboflavin-producing strains of Lactobacillus plantarum

Abstract

Lactobacilli (n = 68) isolated from human feces and fermented milk products were screened for the production of riboflavin (vitamin B2) by culturing into riboflavin assay medium (RAM). Cell-free culture supernatants from positive isolates (BBC32A, BBC32B, BBC33 and BIF43) were transferred onto RAM agar pre-seeded with Enterococcus faecalis MTCC2729 (a riboflavin auxotroph). The enhanced growth of B2-auxotroph confirmed the bioavailability of produced vitamin. Isolate BBC32B produced the highest riboflavin (319 ± 36 μg/l), followed by BBC33 (304 ± 91 μg/l), BBC32A (276 ± 8 μg/l) and BIF43 (257 ± 91 μg/l). All four isolates contained riboflavin genes ribG, ribB, ribA and ribH. Sequencing of DNA fragments amplified from the 16S–23S rRNA intergenic spacer region and areas flanking the 23S rRNA gene grouped these isolates within the species Lactobacillus plantarum. Identifications were confirmed by sequencing 1300-bp of amplified 16S rDNA fragments. Fermentation of soymilk by single cultures of L. plantarum BBC32B, BBC33 and BIF43 yielded 49.05%, 38.97% and 35.94% riboflavin enrichment respectively, which is more than 18.75% recorded in literature for Lactobacillus fermentum MTCC8711. Maximum levels of riboflavin were obtained within 12 h of fermentation in soymilk. Lactobacillus plantarum BBC32B may be used as starter culture for developing of riboflavin-enriched soymilk.