Cloning and characterization of an intracellular esterase from the wine-associated lactic acid bacterium Oenococcus oeni

Characterization of differences in physicochemical properties, volatile organic compounds and non-volatile metabolites of prune wine by inoculation of different lactic acid bacteria during malolactic fermentation

To investigate the effects of inoculating with three strains of lactic acid bacteria on prune wine quality during malolactic fermentation, this study determined its antioxidant activity, phenolic compounds, organic acids, and volatile/non-volatile metabolites. The results showed that inoculation with Lactobacillus paracasei SMN-LBK improved the antioxidant activity and phenolic compounds of prune wine. 73 VOCs were detected in prune wine by HS-SPME-GC-MS, and VOC content increased by 4.3% and 9.1% in MLFS and MLFB, respectively. Lactobacillus delbrueckii subsp. Bulgaricus showed better potential for winemaking, and citral and 5-nonanol, were detected in the MLF samples. 39 shared differential metabolites were screened and their metabolic pathways were investigated based on nontargeted metabolomics. Differences in amino acid and flavonoid content between strains reflected their specificity in flavonoid biosynthesis and amino acid biosynthesis. These findings will provide useful information for the biochemical study and processing of prune wine.

An overview of mammalian and microbial hormone-sensitive lipases (lipolytic family IV): biochemical properties and industrial applications

In mammals, hormone-sensitive lipase (EC 3.1.1.79) is an intracellular lipase that significantly regulates lipid metabolism. Mammalian HSL is more active towards diacylglycerol but lacks a lid covering the active site. Dyslipidemia, hepatic steatosis, cancer, and cancer-associated cachexia are symptoms of HSL pathophysiology. Certain microbial proteins show a sequence homologous to the catalytic domain of mammalian HSL, hence called microbial HSL. They possess a funnel-shaped substrate-binding pocket and restricted length of acyl chain esters, thus known as esterases. These enzymes have broad substrate specificities and are capable of stereo, regio, and enantioselective, making them attractive biocatalysts in a wide range of industrial applications in the production of flavors, pharmaceuticals, biosensors, and fine chemicals. This review will provide insight into mammalian and microbial HSLs, their sources, structural features related to substrate specificity, thermal stability, and their applications.

Oenococcus oeni Lifestyle Modulates Wine Volatilome and Malolactic Fermentation Outcome

In this study, nine Oenococcus oeni strains were tested for their ability to adhere to polystyrene using mMRS and wine as culture media. Moreover, planktonic and biofilm-detached cells were investigated for their influence on malic acid degradation kinetics and aroma compound production. Three strains were able to adhere on polystyrene plates in a strain-dependent way. In particular, MALOBACT-T1 and ISO359 strains mainly grew as planktonic cells, while the ISO360 strain was found prevalent in sessile state. The strain-dependent adhesion ability was confirmed by confocal laser scanning microscopy. Planktonic and biofilm detached cells showed a different metabolism. In fact, biofilm-detached cells had a better malic acid degradation kinetic and influenced the aroma composition of resulting wines, acting on the final concentration of esters, higher alcohols, and organic acids. Oenococcus oeni in biofilm lifestyle seems to be a suitable tool to improve malolactic fermentation outcome, and to contribute to wine aroma. The industrial-scale application of this strategy should be implemented to develop novel wine styles.

Expression, Characterisation and Homology Modelling of a Novel Hormone-Sensitive Lipase (HSL)-Like Esterase from Glaciozyma antarctica

Microorganisms, especially those that survive in extremely cold places such as Antarctica, have gained research attention since they produce a unique feature of the protein, such as being able to withstand at extreme temperature, salinity, and pressure, that make them desired for biotechnological application. Here, we report the first hormone-sensitive lipase (HSL)-like esterase from a Glaciozyma species, a psychrophilic yeast designated as GlaEst12-like esterase. In this study, the putative lipolytic enzyme was cloned, expressed in E. coli, purified, and characterised for its biochemical properties. Protein sequences analysis showed that GlaEst12 shared about 30% sequence identity with chain A of the bacterial hormone-sensitive lipase of E40. It belongs to the H group since it has the conserved motifs of Histidine-Glycine-Glycine-Glycine (HGGG)and Glycine-Aspartate-Serine-Alanine-Glycine (GDSAG) at the amino acid sequences. The recombinant GlaEst12 was successfully purified via one-step Ni-Sepharose affinity chromatography. Interestingly, GlaEst12 showed unusual properties with other enzymes from psychrophilic origin since it showed an optimal temperature ranged between 50–60 °C and was stable at alkaline pH conditions. Unlike other HSL-like esterase, this esterase showed higher activity towards medium-chain ester substrates rather than shorter chain ester. The 3D structure of GlaEst12, predicted by homology modelling using Robetta software, showed a secondary structure composed of mainly α/β hydrolase fold, with the catalytic residues being found at Ser232, Glu341, and His371.

New Insights Into Cinnamoyl Esterase Activity of Oenococcus oeni

Some strains of Oenococcus oeni possess cinnamoyl esterase activity that can be relevant in the malolactic stage of wine production liberating hydroxycinnamic acids that are precursors of volatile phenols responsible for sensory faults. The objective of this study was to better understand the basis of the differential activity between strains. After initial screening, five commercial strains of O. oeni were selected, three were found to exhibit cinnamoyl esterase activity (CE+) and two not (CE-). Although the use of functional annotation of genes revealed genotypic variations between the strains, no specific genes common only to the three CE+ strains could explain the different activities. Pasteurized wine was used as a natural source of tartrate esters in growth and metabolism experiments conducted in MRS medium, whilst commercial trans-caftaric acid was used as substrate for enzyme assays. Detoxification did not seem to be the main biological mechanism involved in the activity since unlike its phenolic cleavage products and their immediate metabolites (trans-caffeic acid and 4-ethylcatechol), trans-caftaric acid was not toxic toward O. oeni. In the case of the two CE+ strains OenosTM and CiNeTM, wine-exposed samples showed a more rapid degradation of trans-caftaric acid than the unexposed ones. The CE activity was present in all cell-free extracts of both wine-exposed and unexposed strains, except in the cell-free extracts of the CE- strain CH11TM. This activity may be constitutive rather than induced by exposure to tartrate esters. Trans-caftaric acid was totally cleaved to trans-caffeic acid by cell-free extracts of the three CE+ strains, whilst cell-free extracts of the CE- strain CH16TM showed significantly lower activity, although higher for the strains in experiments with no prior wine exposure. The EstB28 esterase gene, found in the genomes of the 5 strains, did not reveal any difference on the upstream regulation and transport functionality between the strains. This study highlights the complexity of the basis of this activity in wine related O. oeni population. Variable cinnamoyl esterases or/and membrane transport activities in the O. oeni strains analyzed and a possible implication of wine molecules could explain this phenomenon.

Lactic acid bacteria isolated from dairy products as potential producers of lipolytic, proteolytic and antibacterial proteins

Regular consumption of fermented dairy products helps maintain a healthy microbiota and prevent gut dysbiosis-linked diseases. The lactic acid bacteria (LAB) present in food enhance the digestibility of proteins, moderate the release of fatty acids, and support human health through inhabiting the gastrointestinal tract. These desirable properties of LAB are attributed, in part, to their metabolic processes involving enzymes such as lipases, proteases, and antibacterial proteins. The LAB strains presenting higher enzymatic activities may offer improved functionality for applications in foods. The first aim of this work was to isolate and identify LAB from diverse dairy products and select those with enhanced enzymatic activities. Secondly, this work aimed to investigate the subcellular organization and identity of these enzymes after semi-purification. Out of the total 137 LAB strains isolated and screened, 50.3% and 61.3% of the strains exhibited lipolytic and proteolytic activities, respectively. Seven strains displaying high enzymatic activities were selected and further characterized for the cellular organization of their lipases, proteases, and antibacterial proteins. The lipolytic and proteolytic activities were exhibited predominantly in the extracellular fraction; whereas, the antibacterial activities were found in various cellular fractions and were capable of inhibiting common undesirable microorganisms in foods. In total, two lipases, seven proteases, and three antibacterial proteins were identified by LC-MS/MS. Characterization of LAB strains with high enzymatic activity has potential biotechnological significance in fermentative processes and in human health as they may improve the physicochemical characteristics of foods and displace strains with weaker enzymatic activities in the human gut microbiota.

Synthesis of flavor esters by a novel lipase from Aspergillus niger in a soybean-solvent system

To find a lipase for synthesis of flavor esters in food processing, a total of 35 putative lipases from Aspergillus niger F0215 were heterologously expressed and their esterification properties in crude preparations were examined. One of them, named An-lipase with the highest esterification rate (23.1%) was selected for further study. The purified An-lipase had the maximal activity at 20 °C and pH 6.5 and the specific activity of 1293 U/mg. Sixty percent of the activity was maintained in a range of temperatures of 0-30 °C and pHs of 3.0-8.5. The highest hydrolysis activity of An-lipase was towards pNPC (C8), followed by pNPB (C4) and pNPA (C2), then pNPL (C12). K _m, V _max, k _cat, and k _cat/K _m towards pNPC were 26.7 mmol/L, 129.9 mmol/(L h), 23.2 s^-1, and 0.8/mM/s, respectively. The ethyl lactate, butyl butyrate, and ethyl caprylate flavor esters were produced by esterification of the corresponding acids with conversion efficiencies of 15.8, 37.5, and 24.7%, respectively, in a soybean-oil-based solvent system. In conclusion, An lipase identified in this study significantly mediated synthesis of predominant flavor esters (ethyl lactate, butyl butyrate, and ethyl caprylate) in a soybean-oil-lacking other toxic organic solvents, which has potential application in food industries.

Producción de esterasas por microorganismos: importancia y aplicación industrial

Las enzimas esterasas son de gran importancia en el área biotecnológica debido a las reacciones de interesterificación, transesterificación y esterificación que llevan a cabo. Las esterasas microbianas pueden ser secretadas por hongos filamentosos, levaduras o bacterias. En base a las características de cada enzima, éstas se pueden emplear en las industrias del vino y de lácteos, en la degradación de sustratos complejos, en biorremediación de sitios contaminados, entre otras aplicaciones. La enzima de interés debe ser caracterizada para que pueda ser producida a nivel industrial. El proceso de producción industrial de las enzimas se lleva a cabo principalmente en fermentación líquida. En general, este proceso consiste en una serie de pasos que inician con la inoculación del organismo, mismo que debe crecer en condiciones óptimas, posteriormente se lleva a cabo el pretratamiento de la enzima de interés, seguido del concentrado de ésta por medio de filtración para eliminar el excedente de agua y finalmente se realiza la purificación del producto.

Evidence of the genetic diversity and clonal population structure of Oenococcus oeni strains isolated from different wine-making regions of China

Studies of the genetic diversity and population structure of Oenococcus oeni (O. oeni) strains from China are lacking compared to other countries and regions. In this study, amplified fragment length polymorphism (AFLP) and multilocus sequence typing (MLST) methods were used to investigate the genetic diversity and regional evolutionary patterns of 38 O. oeni strains isolated from different wine-making regions in China. The results indicated that AFLP was markedly more efficient than MLST for typing O. oeni strains. AFLP distinguished 37 DNA patterns compared to 7 sequence types identified using MLST, corresponding to discriminatory indices of 0.999 and 0.602, respectively. The AFLP results revealed a high level of genetic diversity among the O. oeni strains from different regions of China, since two subpopulations and an intraspecific homology higher than 60% were observed. Phylogenetic analysis of the O. oeni strains using the MLST method also identified two major phylogroups, which were differentiated into two distinct clonal complexes by minimum spanning tree analysis. Neither intragenic nor intergenic recombination verified the existence of the clonal population structure of the O. oeni strains.

Oenococcus oeni in Chilean Red Wines: Technological and Genomic Characterization

The presence and load of species of LAB at the end of the malolactic fermentation (MLF) were investigated in 16 wineries from the different Chilean valleys (Limarí, Casablanca, Maipo, Rapel, and Maule Valleys) during 2012 and 2013, using PCR-RFLP and qPCR. Oenococcus oeni was observed in 80% of the samples collected. Dominance of O. oeni was reflected in the bacterial load (O. oeni/total bacteria) measured by qPCR, corresponding to >85% in most of the samples. A total of 178 LAB isolates were identified after sequencing molecular markers, 95 of them corresponded to O. oeni. Further genetic analyses were performed using MLST (7 genes) including 10 commercial strains; the results indicated that commercial strains were grouped together, while autochthonous strains distributed among different genetic clusters. To pre-select some autochthonous O. oeni, these isolates were also characterized based on technological tests such as ethanol tolerance (12 and 15%), SO₂ resistance (0 and 80 mg l⁻¹), and pH (3.1 and 3.6) and malic acid transformation (1.5 and 4 g l⁻¹). For comparison purposes, commercial strain VP41 was also tested. Based on their technological performance, only 3 isolates were selected for further examination (genome analysis) and they were able to reduce malic acid concentration, to grow at low pH 3.1, 15% ethanol and 80 mg l⁻¹ SO₂. The genome analyses of three selected isolates were examined and compared to PSU-1 and VP41 strains to study their potential contribution to the organoleptic properties of the final product. The presence and homology of genes potentially related to aromatic profile were compared among those strains. The results indicated high conservation of malolactic enzyme (>99%) and the absence of some genes related to odor such as phenolic acid decarboxylase, in autochthonous strains. Genomic analysis also revealed that these strains shared 470 genes with VP41 and PSU-1 and that autochthonous strains harbor an interesting number of unique genes (>21). Altogether these results reveal the presence of local strains distinguishable from commercial strains at the genetic/genomic level and also having genomic traits that enforce their potential use as starter cultures.

Biochemical characterisation and dominance of different hydrolases in different types of Daqu - a Chinese industrial fermentation starter

BACKGROUND

Daqu is a fermentative saccharification agent that is used to initiate fermentation in the production of Chinese liquor and vinegar. This study investigated the differences of amylase, protease and esterase in dominance of different types of Daqu, which can be useful for quality control and flavor improvement of Daqu production by enzyme technology.

RESULTS

Hydrolase activities in different Daqu samples were compared by principal component analysis (PCA). Based on protein electrophoresis and ¹ H NMR spectroscopy, the protein patterns and metabolites in Daqu were further analysed. The results indicated that the highest amylase activities and diversities were found in low/medium-temperature of Daqu which had light-flavour and strong-flavour. Proteases play a significant role in determining the quality of high-temperature Daqu samples which had a sauce-flavour. Furthermore, the contributions of esterase to both strong and sauce flavour development in high-temperature Daqu are similar.

CONCLUSION

Results from the present work showed that differences in amylase, protease and esterase play a leading role in different types of Daqu, which can be useful for quality control and technology development of Daqu. © 2017 Society of Chemical Industry.

Characterization of an acidic cold-adapted cutinase from Thielavia terrestris and its application in flavor ester synthesis

An acidic cutinase (TtcutB) from Thielavia terrestris CAU709 was purified to apparent homogeneity with 983 Um g(-1) specific activity. The molecular mass of the enzyme was estimated to be 27.3 and 27.9 kDa by SDS-PAGE and gel filtration, respectively. A peptide sequence homology search revealed no homologous cutinases from T. terrestris, except for one putative cutinase gene (XP003656017.1), indicating that TtcutB is a novel enzyme. TtcutB exhibited an acidic pH optimum of 4.0, and stability at pH 2.5-10.5. Optimal activity was at 55 °C, it was stable up to 65 °C, and retained over 30% activity at 0 °C. Km values toward p-nitrophenyl (pNP) acetate, pNP-butyrate and pNP-caproate were 8.3, 1.1 and 0.88 mM, respectively. The cutinase exhibited strong synthetic activity on flavor ester butyl butyrate under non-aqueous environment, and the highest esterification efficiency of 95% was observed under the optimized reaction conditions. The enzyme's unique biochemical properties suggest great potential in flavor esters-producing industries.

A Lactobacillus plantarum esterase active on a broad range of phenolic esters

Lactobacillus plantarum is the lactic acid bacterial species most frequently found in the fermentation of food products of plant origin on which phenolic compounds are abundant. L. plantarum strains showed great flexibility in their ability to adapt to different environments and growth substrates. Of 28 L. plantarum strains analyzed, only cultures from 7 strains were able to hydrolyze hydroxycinnamic esters, such as methyl ferulate or methyl caffeate. As revealed by PCR, only these seven strains possessed the est_1092 gene. When the est_1092 gene was introduced into L. plantarum WCFS1 or L. lactis MG1363, their cultures acquired the ability to degrade hydroxycinnamic esters. These results support the suggestion that Est_1092 is the enzyme responsible for the degradation of hydroxycinnamic esters on the L. plantarum strains analyzed. The Est_1092 protein was recombinantly produced and biochemically characterized. Surprisingly, Est_1092 was able to hydrolyze not only hydroxycinnamic esters, since all the phenolic esters assayed were hydrolyzed. Quantitative PCR experiments revealed that the expression of est_1092 was induced in the presence of methyl ferulate, an hydroxycinnamic ester, but was inhibited on methyl gallate, an hydroxybenzoic ester. As Est_1092 is an enzyme active on a broad range of phenolic esters, simultaneously possessing feruloyl esterase and tannase activities, its presence on some L. plantarum strains provides them with additional advantages to survive and grow on plant environments.

Implications of new research and technologies for malolactic fermentation in wine

The initial conversion of grape must to wine is an alcoholic fermentation (AF) largely carried out by one or more strains of yeast, typically Saccharomyces cerevisiae. After the AF, a secondary or malolactic fermentation (MLF) which is carried out by lactic acid bacteria (LAB) is often undertaken. The MLF involves the bioconversion of malic acid to lactic acid and carbon dioxide. The ability to metabolise L-malic acid is strain specific, and both individual Oenococcus oeni strains and other LAB strains vary in their ability to efficiently carry out MLF. Aside from impacts on acidity, LAB can also metabolise other precursors present in wine during fermentation and, therefore, alter the chemical composition of the wine resulting in an increased complexity of wine aroma and flavour. Recent research has focused on three main areas: enzymatic changes during MLF, safety of the final product and mechanisms of stress resistance. This review summarises the latest research and technological advances in the rapidly evolving study of MLF and investigates the directions that future research may take.

Impact of yeast strain on ester levels and fruity aroma persistence during aging of Bordeaux red wines

The impact of yeast and lactic acid bacteria strains on the fruity aroma of red wines was investigated by sensory and analytical strategies. The ester composition of four different Bordeaux red wines was quantified by HS-SPME-GC/MS. These wines, made with selected yeast and bacteria strains, were investigated at the end of alcoholic fermentation and regularly until 12 months of aging, during 2011 and 2012 vintages. Sensory analyses of wines after 3 and 12 months of aging revealed significant differences with regard to yeast strains. Bacteria seemed to have only a slight impact on changes in aromatic profile. Ester levels were strongly influenced by yeast strain and very little affected by malolactic fermentation and aging. Differences and similarities between sensory data and ester profile are discussed. This study highlights the importance of yeast strains in red winemaking. Their sensory impact remains despite the other vinification steps after alcoholic fermentation.

Characterization of a versatile arylesterase from Lactobacillus plantarum active on wine esters

The gene lp_1002 from Lactobacillus plantarum WCFS1 encoding a putative lipase/esterase was cloned and overexpressed in Escherichia coli BL21(DE3). The purified Lp_1002 protein was biochemically characterized. Lp_1002 is an arylesterase which showed high hydrolytic activity on phenyl acetate. Although to a lesser extent, Lp_1002 also hydrolyzed most of the esters assayed including relevant wine aroma compounds. Importantly, Lp_1002 exhibited hydrolytic activity at winemaking conditions, although optimal catalytic activity is observed at 40 °C and pH 5-7. The effect of wine compounds on Lp_1002 activity was assayed. From the compounds assayed (ethanol, sodium metabisulfite, and malic, tartaric, lactic and citric acids), only malic acid slightly inhibited Lp_1002 activity. Lp_1002 is the first arylesterase described in a wine lactic acid bacteria and possessed suitable biochemical properties to be used during winemaking.

Characterization of a cold-active esterase from Lactobacillus plantarum suitable for food fermentations

Lactobacillus plantarum is a lactic acid bacteria that can be found in numerous fermented foods. Esterases from L. plantarum exert a fundamental role in food aroma. In the present study, the gene lp_2631 encoding a putative esterase was cloned and expressed in Escherichia coli BL21 (DE3) and the overproduced Lp_2631 protein has been biochemically characterized. Lp_2631 exhibited optimal esterase activity at 20 °C and more than 90% of maximal activity at 5 °C, being the first cold-active esterase described in a lactic acid bacteria. Lp_2631 exhibited 40% of its maximal activity after 2 h of incubation at 65 °C. Lp_2631 also showed marked activity in the presence of compounds commonly found in food fermentations, such as NaCl, ethanol, or lactic acid. The results suggest that Lp_2631 might be a useful esterase to be used in food fermentations.

A partial proteome reference map of the wine lactic acid bacterium Oenococcus oeni ATCC BAA-1163

Oenococcus oeni is the main lactic acid bacterium that carries out the malolactic fermentation in virtually all red wines and in some white and sparkling wines. Oenococcus oeni possesses an array of metabolic activities that can modify the taste and aromatic properties of wine. There is, therefore, industrial interest in the proteins involved in these metabolic pathways and related transport systems of this bacterium. In this work, we report the characterization of the O. oeni ATCC BAA-1163 proteome. Total and membrane protein preparations from O. oeni were standardized and analysed by two-dimensional gel electrophoresis. Using tandem mass spectrometry, we identified 224 different spots corresponding to 152 unique proteins, which have been classified by their putative function and subjected to bioinformatics analysis.

Biochemical characterization of a first fungal esterase from Rhizomucor miehei showing high efficiency of ester synthesis

BACKGROUND

Esterases with excellent merits suitable for commercial use in ester production field are still insufficient. The aim of this research is to advance our understanding by seeking for more unusual esterases and revealing their characterizations for ester synthesis.

METHODOLOGY/PRINCIPAL FINDINGS

A novel esterase-encoding gene from Rhizomucor miehei (RmEstA) was cloned and expressed in Escherichia coli. Sequence analysis revealed a 975-bp ORF encoding a 324-amino-acid polypeptide belonging to the hormone-sensitive lipase (HSL) family IV and showing highest similarity (44%) to the Paenibacillus mucilaginosus esterase/lipase. Recombinant RmEstA was purified to homogeneity: it was 34 kDa by SDS-PAGE and showed optimal pH and temperature of 6.5 and 45°C, respectively. The enzyme was stable to 50°C, under a broad pH range (5.0-10.6). RmEstA exhibited broad substrate specificity toward p-nitrophenol esters and short-acyl-chain triglycerols, with highest activities (1,480 U mg(-1) and 228 U mg(-1)) for p-nitrophenyl hexanoate and tributyrin, respectively. RmEstA efficiently synthesized butyl butyrate (92% conversion yield) when immobilized on AOT-based organogel.

CONCLUSION

RmEstA has great potential for industrial applications. RmEstA is the first reported esterase from Rhizomucor miehei.

Esterase activity of lactic acid bacteria isolated from malolactic fermentation of red wines

The goal of this study was to examine the esterase activity of 243 lactic acid bacteria (LAB) strains from wines of different red grape varieties, belonging to the genera Oenococcus, Lactobacillus, Pediococcus and Enterococcus. p-Nitrophenyl octanoate was used as substrate. All strains presented esterase activity in the first screening, but only those showing higher activity were used in subsequent studies to determine the cellular location of this activity, the influence of pH, temperature and the presence of ethanol and the substrate specificity. For the thirteen selected strains, the highest activity was observed in the intracellular fraction. Responses to pH, temperature and ethanol were strain-dependent, but for all the strains, a marked decrease in activity in presence of ethanol was observed. When the influence of pH and ethanol acting together was studied at 25 °C and 37 °C, temperature-dependent differences were not observed for any of the strains except for Oen6. In the substrate specificity assay, the majority of strains of all genera displayed a trend to more readily hydrolyse ester substrates from C8 and longer.

A low molecular mass cutinase of Thielavia terrestris efficiently hydrolyzes poly(esters)

A low molecular mass cutinase (designated TtcutA) from Thielavia terrestris was purified and biochemically characterized. The thermophilic fungus T. terrestris CAU709 secreted a highly active cutinase (90.4 U ml−1) in fermentation broth containing wheat bran as the carbon source. The cutinase was purified 19-fold with a recovery yield of 4.8 %. The molecular mass of the purified TtcutA was determined as 25.3 and 22.8 kDa using SDS-PAGE and gel filtration, respectively. TtcutA displayed optimal activity at pH 4.0 and 50 °C. It was highly stable up to 65 °C and in the broad pH range 2.5–10.5. Extreme stability in high concentrations (80 %, v/v) of solvents such as methanol, ethanol, acetone, acetonitrile, isopropanol, and dimethyl sulfoxide was observed for the enzyme. The K  m values for this enzyme towards p-nitrophenyl (pNP) acetate, pNP butyrate, and pNP caproate were 7.7, 1.0, and 0.52 mM, respectively. TtcutA was able to efficiently degrade various ester polymers, including cutin, polyethylene terephthalate (PET), polycaprolactone (PCL), and poly(butylene succinate) (PBS) at hydrolytic rates of 3 μmol h−1 mg−1 protein, 1.1 mg h−1 mg−1 protein, 203.6 mg h−1 mg−1 protein, and 56.4 mg h−1 mg−1 protein, respectively. Because of these unique biochemical properties, TtcutA of T. terrestris may be useful in various industrial applications in the future.

Synthesis of fruity ethyl esters by acyl coenzyme A: alcohol acyltransferase and reverse esterase activities in Oenococcus oeni and Lactobacillus plantarum

AIMS

To assess the abilities of commercial wine lactic acid bacteria (LAB) to synthesize potentially flavour active fatty acid ethyl esters and determine mechanisms involved in their production.

METHODS AND RESULTS

Oenococcus oeni AWRI B551 produced significant levels of ethyl hexanoate and ethyl octanoate following growth in an ethanolic test medium, and ester formation generally increased with increasing pH (4.5 > 3.5), anaerobiosis and precursor supplementation. Cell-free extracts of commercial O. oeni strains and Lactobacillus plantarum AWRI B740 were also tested for ester-synthesizing capabilities in a phosphate buffer via: (i) acyl coenzyme A: alcohol acyltransferase (AcoAAAT) activity and (ii) reverse esterase activity. For both ester-synthesizing activities, strain-dependent variation was observed, with AcoAAAT activity generally greater than reverse esterase. Reverse esterase in O. oeni AWRI B551 also esterified 1-propanol to produce propyl octanoate, and deuterated substrates ([(2)H(6)]ethanol and [(2)H(15)]octanoic acid) to produce the fully deuterated ester, [(2)H(5)]ethyl [(2)H(15)]octanoate.

CONCLUSIONS

Wine LAB exhibit ethyl ester-synthesizing capability and possess two different ester-synthesizing activities, one of which is associated with an acyl coenzyme A: alcohol acyltransferase.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates that wine LAB exhibit enzyme activities that can augment the ethyl ester content of wine. This knowledge will facilitate greater control over the impacts of malolactic fermentation on the fruity sensory properties and quality of wine.

Molecular characterization of a novel arylesterase from the wine-associated acetic acid bacterium Gluconobacter oxidans 621H

An arylesterase from the wine-making acetic acid bacterium, Gluconobacter oxidans, was cloned and expressed into Escherichia coli. The soluble 76.8 kDa dimeric enzyme obtained, Est0881, was purified in only two steps with a 3.1-fold purification, 43% recovery, and a specific activity of 214 U/mg for the hydrolysis of p-nitrophenyl acetate. The optimum pH and temperature were 7.0 and 40 °C, respectively. The substrate specificity of this arylesterase was higher toward short chain p-nitrophenyl esters (C(2) to C(4)) and also toward aromatic esters, such as phenyl acetate. The deduced amino acid sequence shares high identity with esterases of the HSL family. The inhibition results obtained showed that the enzyme was a serine esterase, belonging to the A-esterases (arylesterases) and contains a catalytic triad composed of Ser163, Asp263, and His293 in the active site. Est0881 retained significant activity under conditions simulating those of wine-making (75% activity at 20% ethanol), making it a promising biocatalyst for modulating the final aroma of wine.

Identification and characterization of a novel cold-adapted esterase from a metagenomic library of mountain soil

A novel lipolytic enzyme was isolated from a metagenomic library after demonstration of lipolytic activity on an LB agar plate containing 1% (w/v) tributyrin. A novel esterase gene (estIM1), encoding a lipolytic enzyme (EstIM1), was cloned using a shotgun method from a pFosEstIM1 clone of the metagenomic library, and the enzyme was characterized. The estIM1 gene had an open reading frame (ORF) of 936 base pairs and encoded a protein of 311 amino acids with a molecular mass 34 kDa and a pI value of 4.32. The deduced amino acid sequence was 62% identical to that of an esterase from an uncultured bacterium (ABQ11271). The amino acid sequence indicated that EstIM1 was a member of the family IV of lipolytic enzymes, all of which contain a GDSAG motif shared with similar enzymes of lactic acid microorganisms. EstIM1 was active over a temperature range of 1–50°C, at alkaline pH. The activation energy for hydrolysis of p-nitrophenyl propionate was 1.04 kcal/mol, within a temperature range of 1–40°C. The activity of EstIM1 was about 60% of maximal even at 1°C, suggesting that EstIM1 is efficiently cold-adapted. Further characterization of this cold-adapted enzyme indicated that the esterase may be very valuable in industrial applications.

Investigation of the volatile composition of pinotage wines fermented with different malolactic starter cultures using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF-MS)

Headspace solid phase microextraction in combination with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (HS-SPME-GC × GC-TOF-MS) was used for the detailed investigation of the impact of malolactic fermentation (MLF) using three commercial Oenococcus oeni strains on the volatile composition of Vitis vinifera cv. Pinotage wines. GC × GC allowed the identification of 115 volatile compounds, including both major constituents and trace-level compounds, in a single analysis. A number of compounds differing in mean concentration levels between the control wines and those fermented with different starter cultures were shown for the first time to be influenced by MLF and/or the bacterial strain. Principal component analysis (PCA) provided excellent separation between the wines fermented with different MLF starter cultures and the control wine. Significantly different levels for some volatile compounds in wines fermented with one of the LAB starter cultures could be indicative of metabolic differences of this strain.