Type II arabinogalactan (AG-II) is a suitable carbohydrate source for Bifidobacterium longum subsp. longum, but the degradative enzymes have never been characterized. In this study, we characterized an exo-␤-1,3-galactanase, BLLJ_1840, belonging to glycoside hydrolase family 43 from B. longum subsp. longum JCM1217. The recombinant BLLJ_1840 expressed in Escherichia coli hydrolyzed ␤-1,3-linked galactooligosaccharides but not ␤-1,4-and ␤-1,6-linked galactooligosaccharides. The enzyme also hydrolyzed larch wood arabinogalactan (LWAG), which comprises a ␤-1,3-linked galactan backbone with ␤-1,6-linked galactan side chains. The k cat /K m ratio of dearabinosylated LWAG was 24-fold higher than that of ␤-1,3-galactan. BLLJ_1840 is a novel type of exo-␤-1,3-galactanase with a higher affinity for the ␤-1,6-substituted ␤-1,3-galactan than for nonsubstituted ␤-1,3-galactan. BLLJ_1840 has 27% to 28% identities with other characterized exo-␤-1,3-galactanases from bacteria and fungi. The homologous genes are conserved in several strains of B. longum subsp. longum and B. longum subsp. infantis but not in other bifidobacteria. Transcriptional analysis revealed that BLLJ_1840 is intensively induced with BLLJ_1841, an endo-␤-1,6-galactanase candidate, in the presence of LWAG. This is the first report of exo-␤-1,3-galactanase in bifidobacteria, which is an enzyme used for the acquisition of AG-II in B. longum subsp. longum.

Pomegranate-derived polyphenols are expected to prevent life-style related diseases. In this study, we evaluated the ability of 8 pomegranate-derived polyphenols, along with other polyphenols, to augment SIRT3, a mammalian SIR2 homolog localized in mitochondria. We established a system for screening foods/food ingredients that augment the SIRT3 promoter in Caco-2 cells and identified 3 SIRT3-augmenting pomegranate-derived polyphenols (eucalbanin B, pomegraniin A, and eucarpanin T1). Among them, pomegraniin A activated superoxide dismutase 2 (SOD2) through SIRT3-mediated deacetylation, thereby reducing intracellular reactive oxygen species. The other SIRT3-augmenting polyphenols tested also activated SOD2, suggesting antioxidant activity. Our findings clarify the underlying mechanisms involved in the antioxidant activity of pomegraniin A.