Aggregation of Lactobacillus brevis associated with decrease in pH by glucose fermentation.

Some Lactobacillus brevis strains were found to aggregate upon the addition of glucose, which resulted in glucose fermentation and pH decrease. Surface layer proteins (Slp) that represented the outermost layer of the bacteria decreased under these low pH conditions, probably because of the partial detachment of Slp from the cell surface triggered by the acidic environment. Similar observations of decreased Slp and aggregation were observed under the culture conditions, confirming that L. brevis aggregation was due to the partial Slp detachment under the acidic conditions of glucose fermentation. Such Slp detachment might affect the electrostatic nature of L. brevis cells by initiating the formation of irregular charge across the L. brevis cell surface, thereby leading to aggregation. These observations would be useful for elucidating the aggregation mechanism of lactic acid bacteria, which was considered to be involved in the probiotic effect of the bacteria.

Xylan-mediated aggregation of Lactobacillus brevis and its relationship with the surface properties and mucin-mediated aggregation of the bacteria.

Some Lactobacillus brevis strains were found to aggregate upon the addition of xylan after screening for lactic acid bacteria that interact with plant materials. The S-layer proteins of cell surface varied among the strains. The strains that displayed xylan-mediated aggregation retained its ability even after the removal of S-layer proteins. L. brevis had negative zeta potentials. A correlation between the strength of aggregation and zeta potential was not observed. However, partial removal of S-layer proteins resulted in decreases in the electric potential and aggregation ability of some strains. Therefore, xylan-mediated aggregation of L. brevis was considered to be caused by an electrostatic effect between the cells and xylan. L. brevis also aggregated in the presence of mucin, and the strengths of aggregation among the strains were similar to that induced by xylan. Thus, xylan- and mucin-mediated L. brevis aggregation was supposed to be caused by a similar mechanism.

Effect of potato ethanol residue on rat plasma cholesterol levels.

We investigated the cholesterol-lowering effect of a potato ethanol residue (PER). The plasma cholesterol levels excluding high-density lipoprotein cholesterol were lower in the rats given a PER-containing diet for 6 weeks than in the control group, whereas the fecal cholesterol levels were higher. These results suggest that PER partially reduced plasma cholesterol levels via excretion of cholesterol into the feces.

Production of Lacto-N-biose I Using Crude Extracts of Bifidobacterial Cells.

Lacto-N-biose I (LNB) is supposed to represent the bifidus factor in human milk oligosaccharides, and can be practically produced from sucrose and GlcNAc using four bifidobacterial enzymes, 1,3-ß-galactosyl-N-acetylhexosamine phosphorylase, sucrose phosphorylase, UDP-glucose-hexose 1-phosphate uridylyltransferase, and UDP-glucose 4-epimerase, recombinantly produced by Escherichia coli. Here the production of LNB by the same enzymatic method without using genetically modified enzymes to consider the use of LNB for a food ingredient was reported. All four enzymes were produced as the intracellular enzymes of Bifidobacterium strains. The mixture of the crude extracts contained all four enzymes, with other enzymes interfering with the LNB production, namely, phosphoglucomutase, fructose 6-phosphate phosphoketolase, and glycogen phosphorylase. The first two interfering enzymes were selectively inactivated by heat treatment at 47 °C for 1 h in the presence of pancreatin, and glycogen phosphorylase was disabled by hydrolyzing its possible acceptor molecules using glucoamylase. Finally, 91 % of GlcNAc was converted into LNB in the 100-mL reaction mixture containing 300 mM GlcNAc.

Identification of anthocyanins in the sprouts of buckwheat.

The anthocyanin profiles and varieties/breeding line differences of anthocyanin concentrations in common/tartary buckwheat sprouts have been studied. Four anthocyanins, cyanidin 3-O-glucoside, cyanidin 3-O-rutinoside, cyanidin 3-O-galactoside, and cyanidin 3-O-galactopyranosyl-rhamnoside, were isolated from the sprouts of common buckwheat, were separated using high-performance liquid chromatography (HPLC), and were identified using reversed-phase liquid chromatography (LC)/electrospray ionization-mass spectrometry (ESI-MS)/MS techniques. In tartary buckwheat sprouts, two anthocyanins (cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside) were identified. Among 19 common/tartary buckwheat varieties/breeding lines, Hokkai T10 contained the highest amounts of anthocyanins. Cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside concentrations in 6-10 days after seeding sprouts of Hokkai T10 ranged from 0.16 to 0.20 mg/g dry wt and from 5.55 to 6.57 mg/g dry wt, respectively. In addition, dark-grown sprouts of Hokkai T10 accumulated 0.091 and 2.77 mg/g dry wt of cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside whereas other varieties/breeding lines accumulated trace amounts of anthocyanins. Given its anthocyanin-rich red cotyledons, Hokkai T10 is a promising line for use as "Moyashi" type sprouts and is strongly recommended as a new functional food, rich in dietary anthocyanins.

Rapid discrimination of strain-dependent fermentation characteristics among Lactobacillus strains by NMR-based metabolomics of fermented vegetable juice.

In this study, we investigated the applicability of NMR-based metabolomics to discriminate strain-dependent fermentation characteristics of lactic acid bacteria (LAB), which are important microorganisms for fermented food production. To evaluate the discrimination capability, six type strains of Lactobacillus species and six additional L. brevis strains were used focusing on i) the difference between homo- and hetero-lactic fermentative species and ii) strain-dependent characteristics within L. brevis. Based on the differences in the metabolite profiles of fermented vegetable juices, non-targeted principal component analysis (PCA) clearly separated the samples into those inoculated with homo- and hetero-lactic fermentative species. The separation was primarily explained by the different levels of dominant metabolites (lactic acid, acetic acid, ethanol, and mannitol). Orthogonal partial least squares discrimination analysis, based on a regions-of-interest (ROIs) approach, revealed the contribution of low-abundance metabolites: acetoin, phenyllactic acid, p-hydroxyphenyllactic acid, glycerophosphocholine, and succinic acid for homolactic fermentation; and ornithine, tyramine, and γ-aminobutyric acid (GABA) for heterolactic fermentation. Furthermore, ROIs-based PCA of seven L. brevis strains separated their strain-dependent fermentation characteristics primarily based on their ability to utilize sucrose and citric acid, and convert glutamic acid and tyrosine into GABA and tyramine, respectively. In conclusion, NMR metabolomics successfully discriminated the fermentation characteristics of the tested strains and provided further information on metabolites responsible for these characteristics, which may impact the taste, aroma, and functional properties of fermented foods.

Effect of the dates of extraction on the quality of potato pulp.

The objectives of this study were to evaluate the fundamental properties of potato pulp and to explore its potential uses. Lactic acid bacteria were the dominant microbes in potato pulp over the season (maximum being 10(8)/g). The water content in potato pulp was approximately 80% in all season. Starch and fiber were the main components of potato pulp, amounting to 80% of the dried matter regardless of the season. The fermentation of potato pulp by Rhizopus oryzae progressed only in the potato pulp extracted at the end of the season. This indicated that the fermentation of potato pulp was influenced by the dates of extraction, and it was assumed that the quality of the components, such as pectin, varied with such dates.

Direct Imaging of Carboxymethyl Cellulose-mediated Aggregation of Lactic Acid Bacteria Using Dark-field Microscopy.

The ecological functions of lactic acid bacteria (LAB) have been utilized in human life for food processing and probiotic therapy. Understanding the interaction mechanisms between LAB and food ingredients may help to clarify the fermentation process and physiological functions of LAB in the production of fermented foods made from plant materials and dairy products. However, the interaction mechanisms have yet to be fully clarified. Although laser diffraction was used for measuring the size changes of aggregates caused by the interaction between LAB and food ingredients, aggregate sizes could not be determined because of the precipitation of aggregates and its disruption from stirring. Therefore, a microscopy-based method for directly visualizing their interactions is required. We directly observed aggregation processes of LAB cells mediated by water-soluble polysaccharides, carboxymethyl cellulose (CMC), by dark-filed microscopy (DFM). DFM could visualize CMC-mediated cell aggregation with high contrast in real time, and revealed that the aggregates were formed by repeated collisions of LAB cells in a suspension. This suggests that our method can be used as a useful assay to directly visualize grain formation caused by interactions between LAB cells and various polysaccharides in food ingredients.

Molecular cloning of the gene for 2,6-beta-D-fructan 6-levanbiohydrolase from Streptomyces exfoliatus F3-2.

The gene encoding a 2,6-beta-D-fructan 6-levanbiohydrolase (LF2ase) (EC 3.2.1.64) that converts levan into levanbiose was cloned from the genomic DNA of Streptomyces exfoliatus F3-2. The gene encoded a signal peptide of 37 amino acids and a mature protein of 482 amino acids with a total length of 1560 bp and was successfully expressed in Escherichia coli. The similarities of primary structure were observed with levanases from Clostridium acetobutylicum, Bacillus subtilis, B. stearothermophilus (51.0-54.3%) and with LF2ase from Microbacterium levaniformans (53.9%). The enzyme from S. exfoliatus F3-2 shared the conserved six domains and the completely conserved five amino acid residues with family 32 glycosyl hydrolases, which include levanase, inulinase, and invertase. These observations led to the conclusion that the enzyme belongs to family 32 glycosyl hydrolases.

Hydrolysis of the potato glycoalkaloid alpha-chaconine by filamentous fungi.

Three strains of filamentous fungi have been isolated from potato sprouts to obtain an enzyme degrading the glycoalkaloids. All of the strains hydrolyzed alpha-chaconine and not alpha-solanine when grown on the sprouts. From strain HP341, identified as Plectosphaerella cucumerina, the enzyme hydrolyzing alpha-chaconine was purified on columns of DEAE-Toyopearl and Phenyl-Toyopearl. The partially purified enzyme hydrolyzed alpha-chaconine to beta1-chaconine but not to beta2- or gamma-chaconine, suggesting that the enzyme is a rhamnosidase specific for the hydrolysis of the rhamnose (C1-C4) glucose linkage in alpha-chaconine. Conversion of alpha-chaconine to beta1-chaconine may be the first step of detoxification for filamentous fungi to grow on potato sprouts that accumulated antifungal alpha-chaconine.

Molecular cloning of the gene encoding the di-D-Fructofuranose 1,2':2,3' dianhydride hydrolysis enzyme (DFA IIIase) from Arthrobacter sp. H65-7.

The gene encoding an intracellular enzyme hydrolyzing di-d-fructofuranose 1,2':2,3' dianhydride (DFA III) (DFA IIIase) was cloned from the genomic DNA of Arthrobacter sp. H65-7 for the first time. The single open reading frame (ORF) of the DFA IIIase gene consisted of 1368-bp encoding 455 amino acids. DFA IIIase showed a phylogenetically distinct position from other inulin-degrading enzymes and showed similarity only with inulin fructotransferases (depolymerizing) (inulase II, EC 2.4.1.93) from Arthrobacter globiformis C11-1, Arthrobacter sp. A-6, and Arthrobacter sp. H65-7 (48.7-50.3%), and inulin fructotransferase (DFA I-producing) (EC 2.4.1.200) from A. globiformis S14-3 (44.4%). An Escherichia coli transformant harboring a recombinant plasmid, pINB2, in which the DFA IIIase gene was fused with the beta-galactosidase of pUC19 and under the control of the lac promoter, expressed DFA IIIase and the cloned enzyme produced inulobiose from DFA III similarly to the DFA IIIase of the wild-type strain, Arthrobacter sp. H65-7.

Endophytes as producers of xylanase.

One hundred and sixty-nine endophytic fungi and 81 endophytic bacteria were isolated from 14 plants in total. Among them, 155 fungi (91.7%) and 52 bacteria (64%) were found to produce xylanase. The inside part of plants is a novel and good source for isolating xylanase producers in comparison with soil.

Purification of the extracellular pectinolytic enzyme from the fungus Rhizopus oryzae NBRC 4707.

The pectinolytic enzyme from the solid-state culture of Rhizopus oryzae NBRC 4707 was purified to homogeneity by column chromatography on CM-Toyopearl 650 M and hydroxylapatite. The molecular weight of the enzyme was estimated by SDS-polyacrylamide gel electrophoresis to be 31,000 and was reduced to 29,700 after treatment with endoglycosidase H. Maximal activity was observed near pH 4.5 at 45 degrees C. The enzyme was shown to be endopolygalacturonase, as judged from the formation of oligogalacturonides as its reaction products. The addition of purified enzyme, as expected, enhanced the formation of lactic acid and ethanol in potato pulp grown with R. oryzae.

Identification of a gene, FMP21, whose expression levels are involved in thermotolerance in Saccharomyces cerevisiae.

Elucidation of the mechanism of high temperature tolerance in yeasts is important for the molecular breeding of high temperature-tolerant yeasts that can be used in bioethanol production. We identified genes whose expression is correlated with the degree of thermotolerance in Saccharomyces cerevisiae by DNA microarray analysis. Gene expression profiles of three S. cerevisiae strains showing different levels of thermotolerance were compared, and we chose three of them as candidate genes. Among these genes, FMP21 was investigated as a thermotolerance-related gene in S. cerevisiae by comparing the growth at high temperature with the gene expression in eight strains. The expression ratio of FMP21 at 37°C was correlated with the doubling time ratio at a coefficient of determination of 0.787. The potential involvement of the Fmp21 in the thermotolerance of yeasts was evaluated. The FMP21 deletion variant showed a decreased respiratory growth rate and increased thermosensitivity. Furthermore, the overexpression of FMP21 improved thermotolerance in yeasts. In conclusion, the function of Fmp21 is important for thermotolerance in yeasts.

Production of lactic acid from xylose and wheat straw by Rhizopus oryzae.

Rhizopus oryzae NBRC 5378 was the best among 56 strains of R. oryzae for the production of lactic acid from xylose. This strain produced lactic acid from wheat straw powder by a simultaneous saccharification and fermentation process, with a yield of 0.23 g/g from cellulose and hemicellulose in wheat straw.

Conversion of beet molasses and cheese whey into fatty acid methyl esters by the yeast Cryptococcus curvatus.

Eighty-one yeast isolates from raw milk were surveyed for the production of fatty acid methyl esters (FAME). Only one species, identified as Cryptococcus curvatus, produced FAME at a detectable level. Cr. curvatus TYC-19 produced more FAME from beet molasses and cheese whey medium than other strains of the same species. In both media, the major FAME produced were linoleic and oleic acid methyl esters. Sequence analysis of the internal transcribed spacer region of ribosomal DNA indicated that TYC-19 diverged from the same species.

Presence of glucosylceramide in yeast and its relation to alkali tolerance of yeast.

Glycosylceramide is a membrane lipid that has physiological functions in eukaryotic organisms. The presence of glucosylceramide has been confirmed in some yeast; however, the extent of the role of glucosylceramide in yeast is unknown. Thus, the extent of presence of glucosylceramide in yeast was surveyed using 90 strains of 24 genera. The strains were divided into two groups according to whether they had glucosylceramide (45 strains) or not (45 strains). The distribution of the ceramide glucosyltransferase gene (EC 2.4.1.80), which catalyzes glucosylation to a sphingoid lipid in glucosylceramide synthesis, and the phylogenetic classification of the strains were in agreement with those of glucosylceramide. Thus, the presence of glucosylceramide in yeast was caused by the presence of the gene involved in glucosylceramide synthesis and was closely associated with yeast evolution. Furthermore, the relationship between glucosylceramide presence and alkali tolerance of yeast was evaluated. The yeast with glucosylceramide tended to grow at higher pH, and a ceramide-glucosyltransferase-defective mutant from Kluyveromyces lactis did not grow at pH 8.5 even though the parent strain could grow under the same conditions. These results indicate that glucosylceramide in yeast might be a component that enables yeast to grow under alkali conditions.

Lactic acid fermentation of potato pulp by the fungus Rhizopus oryzae.

Thirty-eight strains of the fungus Rhizopus oryzae were grown on potato pulp, an agricultural by-product of the starch industry. Either lactic acid or fumaric acid and ethanol were formed, and the ratio differed among the strains tested. The highest amount of L(+)-lactic acid (10 mg/g fresh matter) was observed in the pulp fermented for six days by Rhizopus oryzae IFO 4707. The IFO 4707 strain rapidly reduced the hardness and pH of potato pulp within one day followed by the gradual synthesis of lactic acid. A composition analysis showed that the enzymes secreted from the fungal cells hydrolyzed starch efficiently with partial degradation of the cell wall. Rhizopus oryzae may be used as an inoculant for ensiling potato pulp and other agricultural by-products containing starch.

Genetic diversity in Rhizopus oryzae strains as revealed by the sequence of lactate dehydrogenase genes.

Twenty-seven strains of Rhizopus oryzae accumulating predominantly lactic acid were shown to possess two ldh genes, ldhA and ldhB, encoding NAD-dependent lactate dehydrogenases. Variation in nucleotide sequence was identified for each gene from different strains, and similar phylogenetic trees were obtained based on the nucleotide sequences of both genes. The other 21 strains of R. oryzae accumulating predominantly fumaric and malic acids contained a single ORF of ldhB. Compared to the strains accumulating predominantly lactic acid, a lower degree of sequence divergence was found in ldhB, resulting in a separate cluster in the phylogenetic tree. The high similarity (>90%) spanning the ORF and adjacent regions demonstrates that ldhA and ldhB are derived from the same ancestor gene. The strains accumulating predominantly fumaric and malic acids lack functional ldhA, which plays a role in lactic acid synthesis and may form a lineage separated from the strains accumulating predominantly lactic acid in the genus Rhizopus.

rDNA ITS sequence of Rhizopus oryzae: its application to classification and identification of lactic acid producers.

Rhizopus oryzae is an important organism for its production of organic acids such as lactic acid, fumaric acid, etc. To date, there were no easy methods to classify strains according to their acid production. The sequences of the ribosomal RNA-encoding DNA (rDNA) internal transcribed spacer (ITS) region of 64 strains of R. oryzae were analyzed and found to conserve mutations correspond to acid production. We have devised a way to use these mutations for a novel method to identify lactic-acid-producing Rhizopus oryzae, by designing specific polymerase chain reaction (PCR) primers on them. Touch down PCR using these primers amplified the ITS DNA of lactic acid producers specifically. By this method, we could isolate lactic acid producing strains from Indonesian fermented foods.