Purification and characterization of crude fructooligosaccharides extracted from red onion (Allium cepa var. viviparum) by yeast treatment.

BACKGROUND: Yeast treatment has been used for purification of fructooligosaccharides (FOSs). However, the main drawback of this approach is that yeast can only partially remove sucrose from crude FOSs. The main objective of this research was to screen yeast strains for the capability of selectively consuming unwanted sugars, namely fructose, glucose, and sucrose, in crude FOSs extracted from red onion (Allium cepa var. viviparum) with minimal effect on FOS content. RESULTS: Among 43 yeast species isolated from Miang, ethnic fermented tea leaves, and Assam tea flowers, Candida orthopsilosis FLA44.2 and Priceomyces melissophilus FLA44.8 exhibited the greatest potential to specifically consume these unwanted sugars. In a shake flask, direct cultivation of C. orthopsilosis FLA44.2 was achieved in the original crude FOSs containing an initial FOSs concentration of 88.3 ± 1.2 g/L and 52.9 ± 1.2 g/L of the total contents of fructose, glucose, and sucrose. This was successful with 93.7% purity and 97.8% recovery after 24 h of cultivation. On the other hand, P. melissophilus FLA48 was limited by initial carbohydrate concentration of crude FOSs in terms of growth and sugar utilization. However, it could directly purify two-fold diluted crude FOSs to 95.2% purity with 92.2% recovery after 72 h of cultivation. Purification of crude FOSs in 1-L fermenter gave similar results to the samples purified in a shake flask. Extracellular ß-fructosidase was assumed to play a key role in the effective removal of sucrose. Both Candida orthopsilosis FLA44.2 and P. melissophilus FLA44.8 showed γ-hemolytic activity, while their culture broth had no cytotoxic effect on viability of small intestinal epithelial cells, preliminarily indicating their safety for food processing. The culture broth obtained from yeast treatment was passed through an activated charcoal column for decolorization and deodorization. After being freeze dried, the final purified FOSs appeared as a white granular powder similar to refined sugar and was odorless since the main sulfur-containing volatile compounds, including dimethyl disulfide and dipropyl trisulfide, were almost completely removed. CONCLUSION: The present purification process is considered simple and straight forward, and provides new and beneficial insight into utilization of alternative yeast species for purification of FOSs.

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.

X-ray-induced mutation of Bacillus sp. MR10 for manno-oligosaccharides production from copra meal.

The present study demonstrates the effectiveness of X-ray radiation in strain improvement for defective lipase production by Bacillus sp. MR10 for further application in the fermentative production of manno-oligosaccharides (MOS) from agricultural by-product, defatted copra meal (DCM). The mutants obtained were screened based on their defective lipase activity together with their ß-mannanase production performance. Among 10 selected mutants, the strain M7 was the highest promising mutant regarding the smallest lipase activity (0.05 U/ml) and the retained ß-mannanase activity similar to the parental strain (22 U/ml) were detected. The mutant M7 effectively hydrolyzed DCM to MOS with low-degree of polymerization (DP) oligomers including mannotriose (M3), mannotetraose (M4), and mannopentose (M5) as the main products. Although the pattern of DCM hydrolysis products of mutant M7 was distinctly different from wild type, the biochemical and catalytic properties of purified ß-mannanase of mutant were similar to those of wild type. Both purified ß-mannanases with apparent molecular mass of 38 kDa displayed optimal activity at pH 5-7 and 45-55°C. Co2+ and Hg2+ nearly completely inhibited activities of both enzymes, whereas Ba2+, Fe3+, and 2-mercaptoethanol obviously activated enzyme activities. Both enzymes showed high specificity for locust bean gum, konjac mannan, DCM, and guar gum. Thus, the mutant M7 has a potential for commercial production of high-quality MOS from low-cost DCM for further application in the feed industry.

Transferase Activity of Lactobacillal and Bifidobacterial ß-Galactosidases with Various Sugars as Galactosyl Acceptors.

The ß-galactosidases from Lactobacillus reuteri L103 (Lreußgal), Lactobacillus delbrueckii subsp. bulgaricus DSM 20081 (Lbulßgal), and Bifidobacterium breve DSM 20281 (Bbreßgal-I and Bbreßgal-II) were investigated in detail with respect to their propensity to transfer galactosyl moieties onto lactose, its hydrolysis products D-glucose and D-galactose, and certain sugar acceptors such as N-acetyl-D-glucosamine (GlcNAc), N-acetyl-D-galactosamine (GalNAc), and L-fucose (Fuc) under defined, initial velocity conditions. The rate constants or partitioning ratios (kNu/kwater) determined for these different acceptors (termed nucleophiles, Nu) were used as a measure for the ability of a certain substance to act as a galactosyl acceptor of these ß-galactosidases. When using Lbulßgal or Bbreßgal-II, the galactosyl transfer to GlcNAc was 6 and 10 times higher than that to lactose, respectively. With lactose and GlcNAc used in equimolar substrate concentrations, Lbulßgal and Bbreßgal-II catalyzed the formation of N-acetyl-allolactosamine with the highest yields of 41 and 24%, respectively, as calculated from the initial GlcNAc concentration.