Dynamic interactions of lactic acid bacteria in Korean sourdough during back-slopping process

AIMS

This study aimed to clarify the cause of quality reduction in Korean sourdough after successive back-slopping.

METHODS AND RESULTS

We investigated the dynamic changes in lactic acid bacteria during the back-slopping process using genetic fingerprinting techniques. During the initial propagation phases, the dominant lactic acid bacteria were Fructilactobacillus sanfranciscensis (<5 log CFU per g sourdough), Latilactobacillus curvatus (9·5 log CFU per g sourdough) and Levilactobacillus brevis (6·5 log CFU per g sourdough). However, after the 11th propagation, F. sanfranciscensis became more prominent (>9·0 log CFU per g sourdough), whereas L. curvatus and L. brevis rapidly decreased. Monitoring these bacteria in the co-culture system revealed that acid-tolerant F. sanfranciscensis rapidly utilized maltose (1·65 g l^-1  h^-1 ) and produced large amounts of lactic acid, whereas L. brevis and L. curvatus consumed maltose slowly and L. curvatus was poorly tolerant to lactic acid.

CONCLUSION

The results indicate that competition exists between the lactic acid bacteria in sourdough during the back-slopping process, and microbial succession by acid-tolerant species results in quality reduction of sourdough.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study uncovered the cause of microbial changes during the propagation of Korean sourdough and proposed a strategy to develop starters to produce high-quality bakery products.

Isolation and characterization of human intestinal Enterococcus avium EFEL009 converting rutin to quercetin

Quercetin is a flavonol believed to have beneficial effects on human health. Rutin, found in many plants, fruits and vegetables, is metabolized by human intestinal bacteria and converted to quercetin, where it is absorbed through the intestinal epithelium. This study aimed to isolate and characterize human intestinal bacteria capable of converting rutin to quercetin. A bacterium that can metabolize rutin was isolated from human faecal samples and identified by 16S rRNA gene sequencing. The whole-cell enzymatic activities on flavonoid glycoside and the conversion profiles of the isolate were also analysed. The bacterium was identified as Enterococcus avium EFEL009 and was shown to convert rutin to isoquercetin and then to quercetin under anaerobic conditions. Microscopic analysis revealed short chains of cocci with diameters of approx. 1 μm. β-Glucosidase was shown to be constitutively expressed in Ent. avium, while α-rhamnosidase was expressed following induction by rutin. Both enzymes were mainly localized to the cell surface. This study is the first report on the isolation of a quercetin-producing Ent. avium FEEL009, which could be a potential industrial starter bacterium.

SIGNIFICANCE AND IMPACT OF THE STUDY

Quercetin is a member of the flavonoids family reported to have better cytoprotective abilities, stronger inhibition of lipopolysaccharide-induced nitric oxide production, and better chemoprevention than rutin. This is the first report on the isolation and characterization of Enterococcus avium EFEL009 from the human intestine which is capable of converting rutin to quercetin.

No direct effects of two transgenic Bt rice lines, T1C-19 and T2A-1, on the arthropod communities

A 2-yr field trial was conducted to assess the impacts of two new transgenic Bt rice lines, T1C-19 expressing Cry1C protein and T2A-1 expressing Cry2A protein, on the arthropod community sampled via vacuum. All the arthropods were classified into five guilds, including herbivores, parasitoids, predators, detritivores, and others. The seasonal density and dominance distribution of each guild and community-level indices (species richness, Shannon-Wiener diversity index, Simpson diversity index, and evenness index) were compared among rice types. Principal response curves were used to investigate the differences of entire arthropod community of Bt rice plots relative to non-Bt rice plots. The results showed no significant difference was detected in the community-level indices and dominance distribution of guilds between Bt and non-Bt rice plots. The seasonal density of herbivores, detritivores, and others as well as density of the arthropod overall community were also not significantly affected by rice types in either year, although the density of predators and parasitoids in Bt rice plots was significantly lower than those in non-Bt rice plots. The lower abundances of Braconidae, Eulophidae, Cyrtorhinus lividipennis (Reuter) (Hemiptera: Miridae), and Theridiidae in Bt rice plots are likely attributed to the lower abundances of prey species or hosts. Principal response curves revealed that arthropod community in Bt was similar with that in non-Bt rice plots. In conclusion, our findings indicate that these two tested Bt rice lines had no marked negative effects on the arthropod community in the paddy fields.

Production of natural antimicrobial compound D-phenyllactic acid using Leuconostoc mesenteroides ATCC 8293 whole cells involving highly active D-lactate dehydrogenase

Phenyllactic acid (PLA) is an antimicrobial compound naturally synthesized in various fermented foods and its D-form of PLA is known to be more active than the L-isomer. In this study, Leuconostoc mesenteroides ATCC 8293 cells, elaborating D-lactate dehydrogenase (D-ldh) were used to produce D-PLA from phenylpyruvic acid (PPA). When cultured in the presence of PPA (≤50 mmol l(-1)), growing cells produced a maximum yield of 35 mmol l(-1) of D-PLA, and the yields were between 75·2 and 83·3%. Higher conversion yields were obtained at pH 6·0-7·0 when growing cells were used, while the optimum pH range was broader for resting cells. The time required for the complete conversion of PPA into PLA could be shortened to 3 h using resting cells. D-ldh, an enzyme encoded by the LEUM_1756 gene of Leuc. mesenteroides ATCC 8293, was found to be responsible for the conversion of PPA into PLA. The Km and kcat values of the enzyme for PPA were found to be 15·4 mmol l(-1) and 5645 s(-1), respectively. The conditions required for the efficient production of D-PLA were optimized for both growing and resting cells of Leuc. mesenteroides, with special emphasis on achieving high stereoselectivity and conversion yield. Significance and impact of the study: This is the first study on the production of D-phenyllactic acid, which is a natural antimicrobial compound, from phenylpyruvate using Leuconostoc mesenteroides cells. The strain, ATCC 8293, that was used in the study, possesses high stereoselectivity and delivers a high yield. Therefore, it might be a promising candidate for use in large-scale production facilities and in fermented foods.

New cold-adapted lipase from Photobacterium lipolyticum sp. nov. that is closely related to filamentous fungal lipases

A Photobacterium strain, M37, showing lipolytic activity, was previously isolated from an intertidal flat of the Yellow Sea in Korea and identified as Photobacterium lipolyticum sp. nov. In the present study, the corresponding gene was cloned using the shotgun method. The amino acid sequence deduced from the nucleotide sequence (1,023 bp) corresponded to a protein of 340 amino acid residues with a molecular weight of 38,026. No sequence similarity was found with any known bacterial lipases/esterases; instead, the most similar enzymes were several filamentous fungal lipases. Although the similarity was very low (less than 16%), there were many conserved regions over the entire sequence and N-terminal oxyanion hole (RG) region, a signature sequence of filamentous fungal lipases. The novel protein M37 was produced in both a soluble and insoluble form when the Escherichia coli cells harboring the gene were cultured at 18 degrees C. The soluble protein exhibited lipase activity in a pH-stat assay using an olive oil emulsion. The M37 lipase also displayed a maximum activity at 25 degrees C and maintained its activity at a low temperature range (5-25 degrees C) with an activation energy (E(a)) of 2.07 kcal/mol. Accordingly, these results indicate that the M37 lipase from P. lipolyticum sp. nov. is a new cold-adapted enzyme.

Transglycosylation reactions of Bacillus stearothermophilus maltogenic amylase with acarbose and various acceptors

It was observed that Bacillus stearothermophilus maltogenic amylase cleaved the first glycosidic bond of acarbose to produce glucose and a pseudotrisaccharide (PTS) that was transferred to C-6 of the glucose to give an alpha-(1-->6) glycosidic linkage and the formation of isoacarbose. The addition of a number of different carbohydrates to the digest gave transfer products in which PTS was primarily attached alpha-(1-->6) to D-glucose, D-mannose, D-galactose, and methyl alpha-D-glucopyranoside. With D-fructopyranose and D-xylopyranose, PTS was linked alpha-(1-->5) and alpha-(1-->4), respectively. PTS was primarily transferred to C-6 of the nonreducing residue of maltose, cellobiose, lactose, and gentiobiose. Lesser amounts of alpha-(1-->3) and/or alpha-(1-->4) transfer products were also observed for these carbohydrate acceptors. The major transfer product to sucrose gave PTS linked alpha-(1-->4) to the glucose residue. alpha,alpha-Trehalose gave two major products with PTS linked alpha-(1-->6) and alpha-(1-->4). Maltitol gave two major products with PTS linked alpha-(1-->6) and alpha-(1-->4) to the glucopyranose residue. Raffinose gave two major products with PTS linked alpha-(1-->6) and alpha-(1-->4) to the D-galactopyranose residue. Maltotriose gave two major products with PTS linked alpha-(1-->6) and alpha-(1-->4) to the nonreducing end glucopyranose residue. Xylitol gave PTS linked alpha-(1-->5) as the major product and D-glucitol gave PTS linked alpha-(1-->6) as the only product. The structures of the transfer products were determined using thin-layer chromatography, high-performance ion chromatography, enzyme hydrolysis, methylation analysis and 13C NMR spectroscopy. The best acceptor was gentiobiose, followed closely by maltose and cellobiose, and the weakest acceptor was D-glucitol.

[Infection status of anisakid larvae in anchovies purchased from local fishery market near southern and eastern sea in Korea]

A survey was carried out on the larval anisakis in anchovies (Engrauris japonica) which were caught from April to June in 1993 at the southern and eastern sea in Korea. Anisakids in anchovies were morphological classified into Anisakis type I and II and Contracaecum type B and C, after fixation in 70% alcohol and clearing in lactophenol. A total of 171 larval anisakids were collected from 150 anchovies (6.9%) out of 2,180 examined. The infection rates showed no relation with length of the anchovies. The numbers of anisakids by organs of anchovies were 96 (56.1%) from the muscle, 65 (38.0%) from the omentum, 7 (4.1%) from the intestine, 2 (1.7%) from the stomach and 1 (0.6%) from the testis. Infection rates of anchovies with anisakids by localities were 5.1% at Taebyon, 8.0% at Sokcho and 9.2% at Chungmu. The larval anisakids in anchovies may infect humans who often eat raw anchovies.