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The aim of this study was to purify a malolactic enzyme (MLE) from Oenococcus oeni (O. oeni) strain and determine its properties in detail. O. oeni SD-2a was cultivated in the ATB broth supplemented with 7 g/L l-malic acid for harvesting the cells. After harvest, the cells were washed and disrupted for purification of MLE. MLE was purified from the supernatant of the disrupted cells through protamine sulfate precipitation, anion exchange chromatography and gel filtration chromatography. The purified MLE was identified using mass spectrometry. The MLE was purified by 43-fold with a yield of 0.42 % and possessed a specific activity of 419.2 U/mg. The purified enzyme with a nominal molecular mass of 59 kDa and a theoretical pI of 4.76 exhibited a maximum enzyme activity at 35 °C and pH 6.0, which retained over 50 % of its initial activity in the presence of 14 % (v/v) ethanol. Mn2+ was proven to be the most effective divalent cation to promote enzyme activity. Under the conditions of temperature 30 °C and pH 6.0, the K m and V max of MLE on l-malic acid were 12.5 × 10−3 M and 43.86 μmol/(min × mg), respectively. Moreover, the purified enzyme exhibited a higher stability with 0.1 M NaCl in addition and had a half-life of 30 days at 4 °C.

To investigate the effect of reduced glutathione (GSH) on the quality characteristics of apple wine, 10, 20 and 30 mg/L of GSH were added to apple juice before alcoholic fermentation. Meanwhile, apple wine fermented by Saccharomyces cerevisiae which had been pre-incubated with GSH (100 mg/L) was another experimental group. Mono-phenols, GSH and oxidized glutathione (GSSG) were determined by HPLC. Aroma compounds were analysed by GC–MS. Further, E-nose was applied to monitor the odor. After fermentation, GSH content was the same in all of the samples. However, for the apple wine with GSH addition, GSSG content increased significantly. Notably, GSH could reduce the color index, protect chlorogenic acid and phloretin, decrease the content of epicatechin and catechin as well as change the profile of aroma compounds (higher levels of 2-methyl-1-propanol, 3-methyl-1-butanol, ethyl benzoate, linalool, etc.). GSH may be used for flavor enhancement and quality improvement of apple wine.

Based on comprehensive studies in petrography, petrofabric analysis and geochemistry, this paper describes a unique and rare laminated micritic ferruginous primary dolostone crystallized and precipitated from the alkaline hot brine under the conditions of the Mesozoic faulted lake basin. The main rock-forming mineral of this dolostone is ferruginous dolomite with a micritic structure. This dolomite mostly exhibits laminae of 0.1–1 mm thick and is often discovered with other minerals, such as albite, analcite, barite and dickite, which have at least two types of interbedded laminae. Petrogeochemistry reveals that this dolostone contains a large number of typomorphic elements of hydrothermal sedimentation, including Sb, Ba, Sr, Mn, and V. In addition, the LREE is in relatively high concentrations and possesses the typical REE distribution pattern with negative Eu anomaly. Oxygen isotope values (δ18OPDB) range from 5.89‰ to 14.15‰ with an average of 9.69‰. The ratio of 87Sr/86Sr is between 0.711648 and 0.719546, with an average of 0.714718. These data indicate that the depositional environment is a stable, blocked, anoxic low-lying hot brine pool in the bottom of deep lake controlled by basement faults. The hydrothermal fluid is the alkaline hot brine formed by the combination of the infiltration lake water and mantle-derived magmatic water, consisting of many ions, including Ca2+, Mg2+ and Fe2+. Under the driving flow power of magmatic heat, gravity and compaction, the hydrothermal fluid overcame the overburden pressure and hydrostatic pressure of the lake water body, and boiled to explosion, and then the explosion shattered the original laminated micritic ferruginous primary dolostone near the vent and then formed a new type of dolostone called shattered “hydroexplosion breccias”. In the low-lying, unperturbed hot brine pool, far from the vent, the laminated micritic ferruginous primary dolostone was quickly crystallized and chemicals precipitated from the hydrotherm. This study of special rocks contributes to research into the causes of the formation of lacustrine carbonate rocks and dolostone. In particular, it provides new examples and research insights for future studies of the lacustrine dolomite from the similar Mesozoic and Cenozoic basins in China.

Molybdenum nitride coatings were synthesized by ion-beam-assisted-deposition (IBAD). The effects of nitrogen partial pressure and bombarding ion energy on the phase formation were investigated. The coefficient of friction and wear resistance of the coatings in different environments were studied. The stoichiometric ratio of nitrogen to Mo of the molybdenum nitride phases increases with the nitrogen partial pressure, and higher bombarding ion energy was helpful to form single MoN phase. Mo 2 N, MoN or mixture of the two phases could be prepared by controlling of the ratio of nitrogen/argon and ion energy. The hardness, coefficient of friction, wear and oxidation resistance of MoN were superior to that of Mo 2 N coating. The coefficient of friction decreased with the increase of testing temperature, yet the wear resistance became lower. The change of friction in non-oxidation atmosphere was reversed to that in the open air, indicating that the low friction of MoN at elevated temperature depends on oxidation. The tribological performance of the MoO 3 phase formed by oxidation annealing showed much higher coefficient of friction than that of as-deposited MoN in all the testing conditions, and the oxygen deficient oxides were implied to be the lubricious phases.

β-D-glucosidase (βG) is one of the most interesting glycosidases for the hydrolysis of glycoconjugated precursors to release active aromatic compounds in musts and wines. Oenococcus oeni strains SD-2a and 31MBR are widely used in Chinese wines to reduce the acidity. In the present study, the βG activity of the two strains was localised and partially characterised using synthetic substrate. The activity occurred in whole cells, sonication supernatants and debris, but not in the culture supernatants for both strains. Whole cells of strain SD-2a possessed greater βG activity, while strain 31MBR showed higher enzyme activity in the sonication supernatants. Strain 31MBR exhibited higher total enzyme activity than strain SD-2a. The optimum temperatures for βG from the two strains were 40oС at pH 3.5 and 50oС at pH 5.0, respectively. Ethanol at low concentrations had a positive effect on βG activity in both strains, while a wine-like pH (3.5) decreased the enzyme activity to a great extent. Whole cells of strain SD-2a showed the highest activity among all samples tested under wine-like conditions. Thus, strain SD-2a proved to have potential for aroma improvement in winemaking.

Phloretin-2′-O-glycosyltransferase (P2′GT) catalyzes the last glycosylation step in the biosynthesis of phloridzin that contributes to the flavor, color and health benefits of apples and processed apple products. In this work, a novel P2′GT of Malus x domestica (MdP2′GT) with a specific activity of 46.82 μkat/Kg protein toward phloretin and uridine diphosphate glucose (UDPG) at an optimal temperature of 30 °C and pH 8.0 was purified from the engineered Pichia pastoris broth to homogeneity by anion exchange chromatography, His-Trap affinity chromatography and gel filtration. The purified MdP2′GT was low N-glycosylated and secreted as a stable dimer with a molecular mass of 70.7 kDa in its native form. Importantly, MdP2′GT also exhibited activity towards quercetin and adenosine diphosphate glucose (ADPG), kaempferol and UDPG, quercetin and UDP-galactose, isoliquiritigenin and UDPG, and luteolin and UDPG, producing only one isoquercitrin, astragalin, hyperoside, isoliquiritin, or cynaroside, respectively. This broad spectrum of activities make MdP2′GT a promising biocatalyst for the industrial preparation of the corresponding polyphenol glycosides, preferably for their subsequent isolation and purification. Besides, MdP2′GT displayed the lowest Km and the highest kcat/Km for phloretin and UDPG compared to all previously reported P2′GTs, making MdP2′GT favor phloridzin synthesis the most.

Near infrared spectroscopy (NIRS) combined with chemometric analysis was investigated for its potential to classify the geographical origin and predict δ(13)C and δ(15)N values of lamb meat samples (n=99) from three pastoral regions and two agricultural regions of China. Principal component analysis (PCA), discriminant partial least squares analysis (D-PLS), linear discriminant analysis (LDA) and partial least squares regression (PLSR) were used for data analysis. D-PLS and LDA correctly classified 100% of the both pastoral and agricultural region samples, and gave a total correct classification of 88.9% and 75% to the five individual region samples, respectively. The best PLSR calibration models for predicting δ(13)C and δ(15)N of lamb meat were obtained with the determination coefficient (R(2)) 0.76 and 0.87, respectively. These results show that NIRS combined with chemometrics can be used as a rapid and effective method to discriminate the geographical origin and estimate the δ(13)C and δ(15)N of lamb meat.

Dietary oat or oat products may potentially help to fight against high risk of cardiovascular diseases and β-glucan in oat was considered as a central player. The present study aimed to investigate the effects of dietary oat whole meal or β-glucan on insulin sensitivity and energy metabolism of rats. Rats were fed with control diet, oat whole meal based diet, or control diet with supplemented β-glucan for 4 weeks. Oat whole meal and β-glucan increased insulin sensitivity index. Interestingly, supplementation of oat whole meal or β-glucan induced increases in intestinal Na(+)K(+)-ATPase activity, Ca(2+)Mg(2+)-ATPase activity, and energy charge, particularly in the distal part of small intestine (ileum). Furthermore, amounts of Bifidobacterium and Lactobacillus in colon contents were elevated by oat whole meal or β-glucan. These findings provide an insight into that β-glucan increased insulin sensitivity and benefited intestinal health.

The aim of this study was to evaluate the susceptibility of 43 strains of lactic acid bacteria, isolated from Chinese yogurts made in different geographical areas, to 11 antibiotics (ampicillin, penicillin G, roxithromycin, chloramphenicol, tetracycline, chlortetracycline, lincomycin, kanamycin, streptomycin, neomycin, and gentamycin). The 43 isolates (18 Lactobacillus bulgaricus and 25 Streptococcus thermophilus) were identified at species level and were typed by random amplified polymorphic DNA analysis. Thirty-five genotypically different strains were detected and their antimicrobial resistance to 11 antibiotics was determined using the agar dilution method. Widespread resistance to ampicillin, chloramphenicol, chlortetracycline, tetracyclines, lincomycin, streptomycin, neomycin, and gentamycin was found among the 35 strains tested. All of the Strep. thermophilus strains tested were susceptible to penicillin G and roxithromycin, whereas 23.5 and 64.7% of Lb. bulgaricus strains, respectively, were resistant. All of the Strep. thermophilus and Lb. bulgaricus strains were found to be resistant to kanamycin. The presence of the corresponding resistance genes in the resistant isolates was investigated through PCR, with the following genes detected: tet(M) in 1 Lb. bulgaricus and 2 Strep. thermophilus isolates, ant(6) in 2 Lb. bulgaricus and 2 Strep. thermophilus isolates, and aph(3')-IIIa in 5 Lb. bulgaricus and 2 Strep. thermophilus isolates. The main threat associated with these bacteria is that they may transfer resistance genes to pathogenic bacteria, which has been a major cause of concern to human and animal health. To our knowledge, the aph(3')-IIIa and ant(6) genes were found in Lb. bulgaricus and Strep. thermophilus for the first time. Further investigations are required to analyze whether the genes identified in Lb. bulgaricus and Strep. thermophilus isolates might be horizontally transferred to other species.

The effects of stress shocks on the freeze-drying viability, malolactic activity and membrane fatty acid composition of the Oenococcus oeni SD-2a cells were studied. O. oeni SD-2a cells after 2 h of stress exposure exhibited better freeze-drying viability and malolactic fermentation ability. A decrease in unsaturated fatty acids/saturated fatty acids (UFA/SFA) ratio and in the C18:1 relative concentration, and an increase in cyclopropane fatty acids (CFA) content mainly due to the increase in C19cyc11 relative concentration were observed in all stress shocked cells. There was a significant negative correlation between C19cyc11 and C18:lcis11, C16:0 in all stress shocks. The freeze-drying viability exhibited a significant positive correlation with the levels of C19cyc11 in cold and acid shocks. The only significant positive correlation between the ability of O. oeni SD-2a to conduct malic acid degradation and membrane composition existed with C14:0 in ethanol shocks. In general, freeze-drying viabilities were maximum for cells with low UFA/SFA ratio and high CFA levels, and, consequently, with low membrane fluidity. Moreover, CFA formation played a major role in protecting stress shocked cells from lyophilization. However, changes observed in membrane fatty acid composition are not enough to explain the greater freeze-drying viability of cells shocked at 8% ethanol. Thus, other mechanisms could be responsible for this increase in the bacterial resistance to lyophilization.

An effective biotin–streptavidin amplified enzyme-linked immunosorbent assay (BA-ELISA) was optimized and characterized for the rapid detection of Ractopamine (RAC) residue in muscular tissue. Purification of the RAC antiserum by protein A-Sepharose 4B followed with bovine serum albumin (BSA)-Sepharose 4B affinity chromatography enhanced the sensitivity and reduce the background adsorption. Blocking with 0.5% skimmed milk power and diluting streptavidin–HRP conjugates with 0.5% BSA/phosphate-buffered saline (PBS) effectively remove the nonspecific adsorption in biotin–streptavidin amplified ELISA system. The established method allowed RAC determination with an IC50 value of 0.3 ± 0.02 ng ml−1 and a limit of detection of 0.02 ± 0.003 ng ml−1, more sensitive than the other reported methods. The variation coefficients of intra-assay and inter-assay were all below 7%. RAC residue in pig muscular tissue could be quantified without matrix effects after a 5-fold extraction and 2-fold dilution with PBS. Recoveries of RAC in pig muscular tissue ranged from 75% to 82.75%. The results were also compared with those from HPLC and a good correlation was obtained (r 2 = 0.9822). The characters show that the established biotin–streptavidin amplified ELISA could be potentially useful in rapid detection of RAC in animal-derived foods.

Elemental fingerprints were investigated for their potential to classify mutton samples according to their geographical origin. The concentration of 25 element contents in 99 mutton samples from three pastoral regions and two agricultural regions of China were analysed by ICP-MS. Multivariate statistical analysis including principal component analysis (PCA) and linear discriminate analysis (LDA) were used for this purpose. Twenty-one elements (Be, Na, Al, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Ag, Sb, Ba, Tl, Pb, Th and U) in de-fatted mutton showed significant differences (p < 0.05). LDA gave an overall correct classification rate of 93.9% and cross-validation rate of 88.9%. Furthermore, mutton samples from agricultural regions and pastoral regions were differentiated with 100% accuracy. These results demonstrate the usefulness of multi-element fingerprints as indicators for authenticating the geographical origin of mutton in China.

Decades of antibiotic use or misuse has resulted in antibiotic resistance in lactic acid bacteria, a group of common culture starters and probiotic microorganisms. This has urged researchers to study how lactic acid bacteria respond to antibiotics, so as to have a better strategy to identify and predict the antibiotic-resistant bacteria. This study aimed to characterize the biochemical profiles of Lactococcus lactis responding to antibiotics using surface-enhanced Raman spectroscopy (SERS). Lactococcus lactis exposed to antibiotics was mixed with 50-nm gold nanoparticles for subsequent SERS measurements. The SERS spectra analyzed by principal component analysis showed no significant change after 30 min of antibiotic treatment, whereas distinct changes were clearly observed after 60 and 90 min of antibiotic treatment. Different antibiotics induced different spectral changes, and these changes revealed the detailed biochemical information of cellular responses. This study demonstrates that the SERS method developed not only senses the changes in the bacterial cell wall, but also reveals details of the biochemical profiles, which help us to understand how lactic acid bacteria respond to antibiotics, as well as to set a base for the detection of antibiotic susceptibility of bacteria by SERS.

Oat β-glucan was purified from oat bran and its effects on running performance and related biochemical parameters were investigated. Four-week-old male Sparsgue-Dawley rats, fed with/without oat β-glucan (312.5 mg kg(-1) d(-1)) for 7 weeks, were subjected to run on a treadmill system to make them exhausted. All rats were immediately sacrificed after prolonged exercise, and the major metabolic substrates were measured in serum and liver. The results showed feeding dietary oat β-glucan to rats could significantly reduce the body weight and increase the maximum running time compared with normal control (P

Detection of small molecules (hapten molecules), such as food contaminants, environmental pollutants, disease factors, drugs and so on, is an area with great significance. Immunoassay, as a simple, rapid and cost-effective detection system, is widely used for the detection of low molecular weight analytes in varied matrix. However, the number of commercial available immunoassay kits for hapten molecules is still limited, this might be partly due to the poor performance such as sensitivity of these immunoassays which can not fulfill the actual requirement. Traditionally, detection of small molecules in solution must employ competitive immunoassay formats, either with immobilized antibody or with immobilized coating conjugate. However, theoretical study has demonstrated that competitive immunoassays are inferior to noncompetitive immunoassays in terms of sensitivity, precision, kinetics and working range of analyte (Jackson and Ekins, 1986). Hence, there is a trend now to develop noncompetitive immunoassay systems for hapten molecules assay.

As an alternative to antibodies, aptamers have a great potential as analytical tools for pesticide detection. In this work, aptamers targeting acetamiprid were selected by a specific systematic evolution of ligands by exponential enrichment (SELEX) strategy, where a single-stranded DNA (ssDNA) library was immobilized and target modification was eliminated. After 18 rounds of repeated selection, the ssDNA pool was enriched and then 14 sequences were selected and carefully identified. At last, an acetamiprid-specific aptamer with the apparent dissociation constant (K(d)) estimated to be 4.98 μM was successfully obtained. Further work is ongoing to develop an aptamer-based detection method for field determination of this pesticides in agricultural products and environmental samples.

The environmental behavior of 40% profenofos EC under paddy field conditions was studied. After application of 40% profenofos EC at 900 g a.i./ha level, the initial deposits of profenofos on rice plant, soil and water were found to be 32.700, 0.224 and 3.854 mg/kg respectively. Half-lives (t(1/2)) of profenofos on those substrates were observed to be 5.47, 3.75 and 3.42 days respectively. The residue levels of profenofos on rice straw, soil and rice grain were significantly affected by the dosage and frequency applied. The obtained results might help to recommend the suitable dose and calculate the safety period of profenofos application.

Osmoregulated periplasmic glucans (OPGs) of food- and water-borne enteropathogen Shigella flexneri were characterized. OPGs were composed of 100% glucose with 2-linked glucose as the most abundant residue with terminal glucose, 2-linked and 2,6-linked glucose also present in high quantities. Most dominant backbone polymer chain length was seven glucose residues. Individual genes from the opg gene family comprising of a bicistronic operon opgGH, opgB, opgC and opgD were mutagenized to study their effect on OPGs synthesis, growth in hypo-osmotic media and ability to invade HeLa cells. Mutation in opgG and opgH abolished OPGs biosynthesis, and mutants experienced longer lag time to initiate growth in hypo-osmotic media. Longer lag times to initiate growth in hypo-osmotic media were also observed for opgC and opgD mutants but not for opgB mutant. All opg mutants were able to infect HeLa cells, and abolition of OPGs synthesis did not affect actin polymerization or plaque formation. Ability to synthesize OPGs was beneficial to bacteria in order to initiate growth under low osmolarity conditions, in vitro mammalian cell invasion assays, however, could not discriminate whether OPGs were required for basic aspect of Shigella virulence.The online version of this article (doi:10.1007/s00203-009-0538-z) contains supplementary material, which is available to authorized users.