Potential of Inulin-Fructooligosaccharides Extract Produced from Red Onion (Allium cepa var. viviparum (Metz) Mansf.) as an Alternative Prebiotic Product.

Red onion is a popular ingredient in many Thai dishes and has recently been promoted for commercial cultivation. In this study, inulin-fructooligosaccharides (inulin-FOSs) were extracted from red onions in a simplified extraction method. The extract contained 24.00 ± 0.38 g/L free glucose, fructose and sucrose, while the level of FOSs was recorded at 74.0 ± 2.80 g/L with a degree of polymerization of 4.1. The extract was resistant to simulated gastrointestinal conditions, while selectively promoting probiotic lactobacilli. These outcomes resulted in inhibitory effects against various pathogenic bacteria. The in vitro batch culture fermentation of the extract by natural mixed culture indicated that an unknown sugar identified as neokestose was more rapidly fermented than 1-kestose and other longer-chain inulin-FOSs. Notably, neokestose selectively encouraged a bifidogenic effect, specifically in terms of the growth of Bifidobacteirum breve, which is an infant-type probiotic bacterium. This is the first report to state that neokestose could selectively enhance the bifidogenic effect. In summary, inulin-FOSs extract should be recognized as a multifunctional ingredient that can offer benefits in food and pharmaceutical applications.

Purification and characterization of hyperthermotolerant leucine aminopeptidase from Geobacillus thermoleovorans 47b.

A thermophilic bacterium, which we designated as Geobacillus thermoleovorans 47b was isolated from a hot spring in Beppu, Oita Prefecture, Japan, on the basis of its ability to grow on bitter peptides as a sole carbon and nitrogen source. The cell-free extract from G. thermoleovorans 47b contained leucine aminopeptidase (LAP; EC 3.4.11.10), which was purified 164-fold to homogeneity in seven steps, using ammonium sulfate fractionation followed by the column chromatography using DEAE-Toyopearl, hydroxyapatite, MonoQ and Superdex 200 PC gel filtration, followed again by MonoQ and hydroxyapatite. The enzyme was a single polypeptide with a molecular mass of 42,977.2 Da, as determined by matrix-assisted laser desorption ionization and time-of-flight mass spectrometry, and was found to be thermostable at 90 degrees C for up to 1 h. Its optimal pH and temperature were observed to be 7.6-7.8 and 60 degrees C, respectively, and it had high activity towards the substrates Leu-p-nitroanilide (p-NA)(100%), Arg-p-NA (56.3%) and LeuGlyGly (486%). The K(m) and V(max) values for Leu-p-NA and LeuGlyGly were 0.658 mM and 25.0 mM and 236.2 micromol min(-1) mg(-1) protein and 1,149 micromol min(-1) mg(-1) protein, respectively. The turnover rate (k(cat)) and catalytic efficiency (k(cat)/ K(m)) for Leu-p-NA and LeuGlyGly were 10,179 s(-1) and 49,543 s(-1) and 15,470 mM(-1 ) s(-1) and 1981.7 mM(-1 ) s(-1), respectively. The enzyme was strongly inhibited by EDTA, 1,10-phenanthroline, dithiothreitol, beta-mercaptoethanol, iodoacetate and bestatin; and its apoenzyme was found to be reactivated by Co(2+) .