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Oenococcus oeni plays a key role in inducing malolactic fermentation in wine. Acid stress is often encountered under wine conditions. However, the lack of systematic studies of acid resistance mechanisms limits the downstream fermentation applications. In this study, the acid responses of O. oeni were investigated by combining transcriptome, metabolome, and genome-scale metabolic modeling approaches. Metabolite profiling highlighted the decreased abundance of nucleotides under acid stress. The gene-metabolite bipartite network showed negative correlations between nucleotides and genes involved in ribosome assembly, translation, and post-translational processes, suggesting that stringent response could be activated under acid stress. Genome-scale metabolic modeling revealed marked flux rerouting, including reallocation of pyruvate, attenuation of glycolysis, utilization of carbon sources other than glucose, and enhancement of nucleotide salvage and the arginine deiminase pathway. This study provided novel insights into the acid responses of O. oeni, which will be useful for designing strategies to address acid stress in wine malolactic fermentation.

Aroma compounds in fruits and related products are known to occur in free and glycosidically bound forms. In this study, free and bound volatiles in juices and wines of two kiwifruit cultivars, Actinidia deliciosa ‘Hayward’ and A. chinensis ‘Hort16A’, were analyzed by solid-phase microextraction-gas chromatography-mass spectrometry. Results showed that 67 free and 79 bound volatiles were found in juices and wines. Alcohols were the most abundant free volatiles, while the most representative bound volatiles were terpenoids. β-Damascenone and 4-methyl-3-penten-2-one released from aroma precursors were found in ‘Hort16A’ juice for the first time. Fruity, floral, and sweet flavors appeared to be the characteristic aroma in kiwifruit juices and wines. Principal component analysis showed that kiwifruit wines had a great aroma potential. Cluster analysis revealed that juices and wines had different profile of free volatiles, while similar bound volatile compositions were found. Moreover, abundant bound volatiles were discovered in these two kiwifruit pomace for the first time, indicating their potential applications in food and cosmetics industry.

Overuse and misuse of antibiotics have resulted in wide antibiotic resistance in bacteria. In this study, surface-enhanced Raman spectroscopy (SERS) was used to rapidly characterize the responses of lactic acid bacteria (LAB) to antibiotics targeting the bacterial cell wall. Lactobacillus delbrueckii subsp. bulgaricus (Lb. bulgaricus) ATCC 11842 was used to represent LAB strains that are widely used in the food industry. Penicillin G, ampicillin and vancomycin were used to treat Lb. bulgaricus ATCC 11842 at different toxic levels for 30, 60 and 90 min, respectively. SERS spectra of Lb. bulgaricus after each treatment were collected to characterize the responses of Lb. bulgaricus. The collected spectra were analyzed by principal component analysis (PCA) and partial least squares regression (PLSR). Results suggested that all three antibiotics induced significant peak changes in LAB, and the spectral changes induced by each antibiotic treatment were significantly different. Moreover, the antibiotic-induced spectral changes in Lb. bulgaricus had good correlation with its proliferation ability and could be potentially used as a base for rapid quantification of the antibiotic susceptibility of bacteria. The developed method could detect the reaction of LAB to antibiotic treatments within 3 h. Therefore, the developed SERS method has the potential to be used to rapidly discriminate and quantify the antibiotic susceptibility of LAB. Moreover, such a rapid and direct method could contribute to microbial antibiotic susceptibility detection research.

For the first time, thinned young kiwifruits (TYK) have been investigated as a source of deserted agriculture resource and evaluated for their phenolic characteristics along with antioxidant capacity. Two batches of TYK in different maturity stages (TYK1 and TYK2) and mature kiwifruits (MK) were sourced from three New Zealand cultivars. Comparing with MK, the TYK, especially TYK1, exhibited significantly higher contents of total phenolics (7.92 fold), total flavonoids (17.56 fold) and total flavanols (10.11 fold) as well as elevated and phenolic-correlated antioxidant capacities. A novel UPLC-QqQ-MS/MS method with low limit of detection (0.010-0.240 mg/L) and high accuracy (RSDs 6.79%) was established to quantify 15 phenolics in the kiwifruit extracts. Epicatechin was the prevailing antioxidant in both TKY and MK, with the highest level of 2989.23 μg/g FDW present in TYK1 of 'Zesy002' cultivar. These results provide good evidence for the development and utilization of TYK of these cultivars in food and nutraceuticals.

Background During winemaking, malolactic fermentation (MLF) is usually induced by Oenococcus oeni owing to its high resistance to wine stress factors. To ensure a controlled and efficient MLF process, starter cultures are inoculated in wine. In previous studies, O. oeni strains with sub-lethal acid or ethanol stresses showed higher freeze-drying vitality and better MLF performance. To explore the mechanisms involved, influences of acid and ethanol stresses on O. oeni SD-2a were investigated in this study to gain a better understanding of the cross-protection responses. Results The results showed that acid and ethanol stresses both caused damage to cell membranes and decreased cellular adenosine triphosphate concentration. At the same time, acid stress increased the uptake of glutathione, while ethanol stress led to cell depolarization. The results of comparative proteomic analysis highlighted that heat shock protein was induced with almost all acid and ethanol stresses. In addition, the expression of stress-relevant genes (hsp20, clpP, trxA, ctsR, recO, usp) increased greatly with ethanol and acid stress treatments. Finally, the viability of O. oeni was improved with acid and ethanol pretreatments after freeze-drying. Conclusions This study demonstrated that acid and ethanol stresses had mixed influences on O. oeni SD-2a. Some physiological and molecular changes would contribute to a more stress-tolerant state of O. oeni, thereby improving the viability of lyophilized cells. © 2020 Society of Chemical Industry.

Persimmon tannin (PT), a primary physiological component of young persimmon, exhibits antibacterial activity against several microorganisms, but its effect on methicillin-resistant Staphylococcus aureus (MRSA) remains unclear. In this study, we found that PT from young astringent persimmon fruit had an active inhibition against several MRSA isolated from retail pork and the minimum inhibitory concentrations were 1000 μg/mL. Treatment of PT suppressed cell proliferation, caused decreases in membrane potential and intracellular ATP concentration, destroyed whole cell protein integrity, and induced S phase cell cycle arrest. Electron microscopy demonstrated that PT can change the normal morphology of MRSA and cause severe damage on cell wall and cell membrane. These results indicated that PT presented antimicrobial activity against foodborne MRSA and could be potentially developed as an alternative or supplemental agent to control the spread and infection of MRSA in foods.

Phloridzin has been an attractive target for the development of preparation methodologies due to its various applications as pharmaceutical ingredient and food additive. In this study, an enzymatic synthesis approach using engineered P. pastoris GS115 was developed to produce phloridzin. Four factors, identifying as key factors affecting the phloridzin yield, were optimized by response surface methodology as follows: induction time 121.8 h, pH 7.0, methanol 0.75%, and a rotation speed 194 rpm. The maximal yield of phloridzin reached 41.59 mg/L (95.31 μM) and the specific bioconversion rate of substrate was up to 98.50% with 1L working volume in a 5L bioreactor under the optimal conditions. Phloridzin with purity of 93.98% and recovery of 78.14% was achieved just using affinity chromatography and preparative high performance liquid chromatography ( Pre -HPLC). These results confirm the enzymatic synthesis developed provides an efficient alternative to traditional approach for the preparation of phloridzin in vitro .

Principal component analysis (PCA) and partial least squares (PLS) regression were applied to investigate the effect of glutathione-enriched inactive dry yeast (g-IDY) on the amino acids and volatile components of kiwi wine. Results indicated that the addition of g-IDY had positive effect on most amino acids of kiwi wine, especially glutamine and glycine. In case of pure juice fermentation, the concentrations of ethyl decanoate, 2-methylbutyric acid, trans-2-nonenal and hexyl butyrate had notably positive correlation with the addition of g-IDY. PLS regression indicated that the amino acids were highly interrelated to the volatile compositions, and glycine had the strongest positive impact on the concentrations of esters and total volatile components. This might explain the similar effect of g-IDY on the amino acids and volatile components of kiwi wine. Besides, PLS regression showed that E-nose was a good method to predict volatile compositions of kiwi wine, especially esters.

Fresh “Xuxiang” kiwifruit juice with or without pomace was used for fermentation with different levels of glutathione‐enriched inactive dry yeast (g‐IDY). After alcohol fermentation, the glutathione (GSH) content, color parameters, phenolic composition, and antioxidant activities of kiwi wine were determined. The results suggested that the addition of g‐IDY to kiwi juice increased GSH, glutathione disulfide, total GSH concentrations, and the total phenolic content of kiwi wine. No obvious effect on individual phenolic content was found in wine with g‐IDY. The color parameters of wines fermented with pomace were remarkably improved with addition of 100 mg/L and 300 mg/L g‐IDY. The supply of g‐IDY improved the antioxidant activities of kiwi wine fermented with pomace. Principal component analysis suggested that with the same supplies of g‐IDY, wine fermented with pomace was better than wine fermented through pure juice in all measurements. PRACTICAL APPLICATIONS: The improvements in color and antioxidant capacity of kiwi wine have always been the focus of kiwi wine brewing. Constant improvement in methods which contribute to high quality of kiwi wine provides crucial support for wine industry and even agriculture development. The aim of this study is to investigate the impacts of glutathione‐enriched inactive dry yeast (g‐IDY) on quality of kiwi wine. These results could provide feasible advices about g‐IDY application to kiwi wine for improving the sensory and nutritional properties.

The aim of this study was to evaluate probiotic properties of ten Streptococcus thermophilus strains (st1 to st10) isolated from pickles in China. These strains all had β-galactosidase activity, which laid foundation for studying their probiotic properties. In this study, the bile salt hydrolase activity, lysozyme resistance, tolerance to simulated gastric juice, bile salt tolerance, and bacterial adhesion capacity to the Caco-2 cells of these selected strains were detected in vitro conditions. The results indicated that the bile salt hydrolase activities of st2, st6, and st9 were higher than that for other strains. St10 showed the greatest lysozyme resistance (> 80% survival), followed by st9, st8, st7, st5, and st6. As for the tolerance to simulated gastric juice, st5 possessed the highest survival rate (35%), followed by st6 (30%). St6 was the best performer in both bile salt tolerance and bacterial adhesion capacity to the Caco-2 cells. The results of fluorescence microscope and electron microscope further confirmed previous studies and more intuitively demonstrated the st6 strain's tolerance to harsh environments. Overall, these strains were expected to possess beneficial properties and have the potentiality to be probiotics.

Persimmon tannin (PT) exhibits antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) isolated from retail pork. The involved molecular mechanisms were investigated for the first time using transcriptome and metabolome in this study. Results showed that subinhibitory concentration of PT (0.5 mg/ml) induced significant changes in MRSA at both transcriptional and metabolic levels, as 370 genes and 19 metabolites were differentially expressed. Bioinformatic analysis revealed that the varying genes and metabolites were mainly involved in pathways of membrane transport, amino acids, carbohydrate, and energy metabolism. The highlighted changes were those related to osmotic regulation, intracellular pH regulation, amino acid synthesis and metabolism, glycolysis, TCA cycle and iron metabolism, suggesting the multifaceted effects including cell membrane damage, amino acids limitation, energy metabolism disorder and iron deprivation induced by PT. The results provided insight into the anti-MRSA mechanism of PT, which is useful for PT’s development and application in food safety.

The β-glucosidase derived from microorganisms has attracted worldwide interest for their industrial applications, but studies on β-glucosidases from Oenococcus oeni are rare. In this paper, catalytic mechanism of a novel β-glucosidase BGL0224 of Oenococcus oeni SD-2a was explored for the first time by kinetic parameters determination, fluorescence spectroscopy and quenching mechanism analysis, molecular dynamics simulation. The results indicated that BGL0224 had universal catalytic effect on different types of glycoside substrates, but the catalytic efficiencies were different. Fluorescence quenching analysis results suggested that the quenching processes between BGL0224 and seven kinds of substrates were predominated by the static quenching mechanism. A reasonable three-dimensional model of BGL0224 was obtained using the crystal structure of E.coli BglA as a template. The analysis results of molecular simulation (RMSD, Rg, RMSF and hydrogen bonding) showed that the composite system ‘BGL0224-pNPG’ was very stable after 40 ns. The catalytic process of BGL0224 acting on ‘p-Nitrophenyl β- d -glucopyranoside’ conformed to the double displacement mechanism. Two glutamic acid residues ‘Glu178 and Glu377’ played a vital role in the whole catalytic process. Overall, this study gave specific insights on the catalytic mechanism of BGL0224, which was of great significance for developing its potential applications in food industry.

β-glucosidase is widely used in food industry for its glycosidic hydrolysis properties. In this paper, performance of a novel β-glucosidase BGL0224 from Oenococcus oeni for aroma enhancement of Cabernet Sauvignon wines was explored for the first time. The main projects included electronic nose, gas chromatography-mass spectrometry and sensory analysis. Principal component analysis indicated that electronic nose had the ability to discriminate different treatments by responding specifically to volatile compounds. Adding BGL0224 before alcoholic fermentation significantly increased the “aromatic index” of Cabernet Sauvignon wines. Compared with the control group, adding BGL0224 increased more than 15 volatile aroma compounds of Cabernet Sauvignon wines. Furthermore, with the addition of BGL0224 before alcoholic fermentation, the concentrations of medium-chain fatty acid ethyl esters, long-chain fatty acid ethyl esters and terpenes in wines were 3004.19 ± 36.14 μg/L, 4090.37 ± 94.07 μg/L and 210.21 ± 8.98 μg/L respectively, which were all significantly higher than other treatments. Sensory analysis showed that BGL0224 increased “tropical fruity”, “sweet fruity” and “floral notes” characteristics while inhibited “citrus” characteristics of Cabernet Sauvignon wines. Overall, this study provided support for industrial application of BGL0224 by evaluating its performance for aroma enhancement of Cabernet Sauvignon wines.

The effects of selenium (Se) addition methods on antioxidant activity and flavor properties of fermented Pleurotus eryngii (P. eryngii) using Lactobacillus plantarum (L. plantarum) inoculated and natural fermentation were investigated. After fermentation, the Se-enrichment rates in fruiting bodies of Se-added fermented P. eryngii were all more than 50%. Se addition, especially in the form of Se-enriched L. plantarum inoculation, had a significantly positive effect on total phenolic content and DPPH radical scavenging activity. Non-volatiles analysis revealed that the highest ration of lactic acid to acetic acid and the highest umami intensity were observed in P. eryngii fermented by inoculating Se-enriched L. plantarum (Lp-Se). Principal components analysis and cluster analysis of volatiles clearly separated Se-treated and plain experiments, which mainly due to dissimilarities in alcohols, aldehydes and ketones. Additionally, Lp-Se obtained the highest alcohols, especially 1-octen-3-ol with mushroom flavor. In short, Se-enriched L. plantarum inoculation could produce high-quality fermented P. eryngii.

A novel method was developed to rapidly concentrate, detect, and differentiate bacteria in skimmed milk using surface enhanced Raman scattering (SERS) mapping on 4-mercaptophenylboronic acid (4-MPBA) functionalized silver (Ag) dendrites. The 4-MPBA functionalized Ag dendritic SERS substrate was used to capture the bacterial cells and enhance the bacterial signal. Salmonella, a significantly important food pathogen, was used as the representative strain to optimize and evaluate the developed method. The capture efficiency for Salmonella enterica subsp enterica BAA1045 (SE1045) was 84.92 ± 3.25% at 106 CFU/mL and as high as 99.65 ± 3.58% at 103 CFU/mL. Four different strains, two gram-negative and two gram-positive, can be clearly distinguished by their SERS spectra using principle component analysis. A mapping technique was utilized to automatically collect 400 spectra over an area of 60 μm × 60 μm to construct a visual image for a sensitive and statistically reliable detection within 30 min. Using this method, we were able to detect as low as 103 CFU/mL bacterial cells in 50 mM NH4HCO3 solution and 102 CFU/mL cells in both 1% casein and skimmed milk. Our results demonstrate the feasibility of using SERS mapping method coupled with 4-MPBA functionalized Ag dendrites for rapid and sensitive bacteria detection in complex liquid samples.

Oenococcus oeni (O. oeni) strains are critically important for winemaking. They bring microbial stabilization, de-acidification and sensory improvement through malolactic fermentation (MLF) to almost all red wines and some white wines. In this study, 23 strains of O. oeni isolated from China were evaluated for use as MLF starter cultures. Strains were characterized and screened in wine-like media with increasing selective pressure, such as low pH and high ethanol concentration. Their abilities to conduct MLF were affected significantly by ethanol concentration and pH. Eight strains were selected and subsequently evaluated by detecting the enzyme-encoding genes involved in biogenic amines synthesis and wine aroma modification. Seven well-performing strains were further assessed in newly alcohol-fermented Cabernet Sauvignon wine. The results show that strains O. oeni CS-4b and O. oeni ME-5b exhibited better performance than the commercial starter O. oeni 31MBR in wine. Therefore, they were selected as potential MLF starters suitable for wine with high ethanol concentration and low pH.

Polyphenols are the predominant ingredients in apple seeds. However, few data are available on the phenolic profile or antioxidant activity in apple seeds in previous researches. In this study, low-molecular-weight phenolic compounds and antioxidant activity in seeds, peels, and flesh of seven apple cultivars grown in northwest China were measured and analyzed using HPLC and FRAP, DPPH, ABTS assays, respectively. HPLC analysis revealed phloridzin as the dominant phenolic compound in the seeds with its contents being 240.45–864.42mg/100gDW. Total phenolic content (TPC) measured by the Folin–Ciocalteu assay in apple seed extracts of seven cultivars ranged from 5.74 (Golden Delicious) to 17.44 (Honeycrisp)mgGAE/gDW. Apple seeds showed higher antioxidant activity than peels or flesh; antioxidant activity in seeds varied from 57.59 to 397.70μM Trolox equivalents (TE)/g FW for FRAP, from 37.56 to 64.31μM TE/g FW for DPPH, and from 220.52 to 708.02μM TE/g FW for ABTS. TPC in apple seeds was significantly correlated with all three assays. Principal component analysis (PCA) indicated that Honeycrisp was characterized with high contents of total polyphenols and phloridzin. Our findings suggest that phenolic extracts from apple seeds have good commercial potential as a promising antioxidant for use in food or cosmetics.

β-Glucosidases play an important role in food industry. Oenococcus oeni are typical lactic acid bacteria that initiate malolactic fermentation of wines. 35 β-glucosidases from O. oeni were selected and their conserved domains and evolutionary relationships were further explored in this study. The homology analysis results indicated that 35 β-glucosidases were basically derived from GH1 and GH3 family. A novel β-glucosidase was successfully expressed and characterized. The recombinant protein, referred to as BGL0224, consisted of a total 480 amino acids with an apparent molecular weight of 55.15 kDa and was classified as GH1 family. It achieved the highest activity at pH 5.0 and 50 °C. The activity and stability were significantly increased when 12% ethanol was supplemented to the enzyme. Using p-NPG as substrate, the Km, Vmax and Kcat of BGL0224 were 0.34 mM, 382.81 U/mg and 351.88 s−1, respectively. In all, BGL0224 has good application prospects in food industry.

Ethanol acclimations have been proven to be beneficial for enhancing the viability of lyophilized Oenococcus oeni. To explore the relevant mechanisms, cell integrity, protein patterns, morphology, exopolysaccharides (EPS) content of lyophilized O. oeni SD-2a with ethanol acclimations were investigated in this research. After freeze-drying, the improvement of cell integrity was found in all ethanol acclimated cells. Comparative proteomics combined with bioinformatics revealed the important role of central carbohydrate metabolism, polysaccharides production, cell envelope biosynthesis and stress responses related proteins with ethanol acclimations in freeze-dried O. oeni SD-2a. Extracellular polymeric substances were observed in mild ethanol (5% and 8%) adapted cells using scanning electron microscope. In addition, mild ethanol (5% and 8%) adapted cells showed higher EPS content. Transcriptional analysis showed that citrate lysis gene over-expressed in all ethanol acclimated freeze-dried cells. Therefore, citrate was added in culture medium and it is highlighted that the addition of citrate was useful for the growth of freeze-dried O. oeni SD-2a. These results provide new insights of molecular mechanisms regulated by ethanol acclimation and improve our understanding of biological characteristics involved in freeze-dried O. oeni.

Malolactic fermentation (MLF), usually induced by Oenococcus oeni (O. oeni), is an important process to improve wine quality. Acid acclimation has been proven to be useful for enhancing the viability of lyophilized O. oeni. To explain the involved mechanisms, cell integrity, morphology and protein patterns of lyophilized O. oeni SD-2a were investigated with acid acclimation. After lyophilization, improvement of cell integrity and more extracellular polymeric substances (EPS) were observed in acid acclimated cells. Combined with GO and KEGG analysis, different abundant proteins were noticeably enriched in the carbohydrate metabolism process, especially amino sugar and nucleotide sugar metabolism. The most significant result was the over-expression of proteins participating in cell wall biosynthesis, EPS production, ATP binding and the bacterial secretion system. This result indicated the important role of acid acclimation on cell envelope properties. In addition, protein response to stress and arginine deiminase pathway were also proven to be over-expressed.

The phenolics profile of two new kiwifruit cultivars, Zespri® SunGold and Zespri® Sweet Green, were characterized and quantified for the first time using cyclic voltammetry, an electrochemical method, combined with HPLC. Results from the cyclic voltammetry revealed high correlations with those obtained from the spectrophotometry and HPLC methods, providing evidence to support the application of cyclic voltammetry as a rapid method in determining the phenolic profile and reducing power of kiwifruit extracts. Catechol-containing phenolics were identified as the major phenolic sub-class in the skins while flavonoids and phenolic acids were abundant in flesh of the tested cultivars. Epicatechin was the predominant phenolic compound and contributor to antioxidant capacity in all samples. Results also showed that SunGold and Sweet Green (both flesh and skin) exhibited significantly higher phenolic contents and antioxidant activities comparing with the well-established commercial ‘Hayward’ cultivar, indicating their commercial value and potential applications in food and nutraceuticals.

This study explored the feasibility of degrading aflatoxin B1 (AFB1) in contaminated peanut meal by extrusion cooking. Peanut meal contaminated with AFB1 (35.8 ± 1.5 μg/kg) was extrusion-cooked in a twin-screw extruder and AFB1 was quantified by ELISA. The effects of barrel temperature, material moisture content, feed rate, and screw speed as well as their interactions on the reduction rate of AFB1 in peanuts meal were evaluated by Response surface methodology (RSM) to optimize the extrusion conditions. Under the optimal conditions (barrel temperature of 150 °C, material moisture content of 40 g/100 g, feed rate of 17 g/min, and screw speed of 152 rpm), 77.6 ± 2.2% of AFB1 was degraded. The barrel temperature and material moisture have significant influences (P

Oenococcus oeni (O. oeni) induces malolactic fermentation to improve wine quality. However, the molecular basis of mechanisms involved in its freeze-drying resistance remains unclear. In this work, O. oeni SD-2a without freeze-drying (No-FD), with freeze-drying (FD) and freeze-drying with monosodium glutamate (MSG) (FD-MSG) were investigated. Flow cytometry results showed severe cell damage in FD cells and less membrane transmissibility in FD-MSG cells. Meanwhile, extracellular polymeric substances (EPS) were detected in FD and FD-MSG cells by scanning electron microscopy. Bioinformatic analysis revealed that varying proteins were involved in carbon, lipid and nucleic acids metabolism, stress response, oxidoreductase activity and signal sensing. Among the identified proteins, the highlighted proteins were those involved in polysaccharides production and signal sensing for freeze-drying resistance and cyclopropane fatty acid metabolism for MSG addition.

The accumulation of selenium (Se) by Lactobacillus delbrueckii ssp. bulgaricus (Lb) and Streptococcus thermophilus (St) at the different cultivation conditions, including initial pH, inoculum dose (%), and temperature (°C), was investigated in this work. Se enrichment efficiency was optimized using the Design-Expert software for response surface methodology on a basis of single-factor experiment. The antioxidant activities of Se-enriched Lactic acid bacteria (LAB) were also investigated. The qualitative analysis of Se-enriched LAB was performed by FT-IR spectra. The cell morphology and chemical element components were measured by a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy. The results indicated that the optimum initial pH, inoculum doses, and temperatures of Lb and St were 5.96, 6.73%, 33.24 °C, and 6.37, 6%, 40 °C, respectively. Under the optimal conditions, the ratios of Se enrichment reached 94.34% for Lb and 97.05% for St. Furthermore, Se-enriched LAB enhanced scavenging rates on DPPH, ABTS free radical, and also heightened reducing activity. The FT-IR results showed that the two Se-enriched strains had similar characteristic absorption peaks, which were further demonstrated that both Se biomasses had the same carbonyl, carboxyl, and hydroxyl groups. Elemental selenium nanoparticles were verified around cell surfaces of Se-enriched LAB, which implied that both strains had detoxification ability when grown in liquid media containing selenite.

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.

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.

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 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.

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.