Single versus dual inoculation with indigenous Saccharomyces cerevisiae strains in winemaking.

Indigenous Saccharomyces cerevisiae strains and their combinations may be used to diversify wines and add complexity to sensory profiles. Here, two S. cerevisiae strains that represent regional genetic and phenotypic specificities for two major winegrowing areas of Greece were used in single- and mixed-culture fermentations. The kinetics and metabolic activities of the strains were analyzed to evaluate the influence of each strain individually or in combination on wine quality. The two strains differentially affected the kinetics and the outcome of fermentation. They showed significant differences in the production of important metabolites that strongly affect the organoleptic profile of wines, such as volatile acidity, acetaldehyde, certain esters, and terpenes. Furthermore, the chemical and sensory profiles of wines produced by single cultures were different from those fermented by mixed-culture inoculum. The concentration of certain metabolites was enhanced (e.g. isoamyl acetate, 1-heptanol), while others were suppressed (e.g. hexyl acetate, octyl acetate). Results highlight the potential worth of indigenous S. cerevisiae strains to differentiate local wines. The mixed-culture S. cerevisiae inoculum was shown to generate novel wine characteristics, as compared to single cultures, thus offering alternatives to further diversify wines and increase their complexity.

Sweet Wine Production from the Side-Stream of Industrial Corinthian Currant Processing: Product Quality, Antioxidant Capacity, and Volatilome.

In the frame of efforts to add value to the Mediterranean currant cultivation and processing sectors, which is essential for their sustainability, sweet wine production is proposed from the finishing side-stream (FSS) of premium quality Corinthian currants, involving complete fermentation using an alcohol-tolerant yeast followed by (i) the addition of FSS to extract sugars or (ii) syrup made from FSS to adjust sweetness. Wine was also made by (iii) ceasing fermentation at the desired sugar level by ethanol addition. The non-fortified wines had 15.2-15.5% ethanol, 115-145 g/L residual sugar, 7.2-7.6 g/L titratable acidity, low volatile acidity (VA; <0.33 g/L), 280-330 mg/L phenolic content (TPC) (as gallic acid), and 23.8-35.6 mg/L antioxidant capacity (AC) (as ascorbic acid). In total, 160 volatiles were identified by SPME GC-MS, including compounds derived from the grapes, the raisin drying, and the fermentation process. The non-fortified wines had better characteristics (mainly VA, AC, and TPC) than the fortified wine, while sweetness adjustment by FSS is the simplest and lowest cost method since it does not involve ethanol or syrup addition. The proposed methods can lead to good quality sweet wines with a characteristic fruity (grape/raisin) flavor that could be commercialized as specialty raisin beverages or liqueurs.

Varietal and Geographical Discrimination of Greek Monovarietal Extra Virgin Olive Oils Based on Squalene, Tocopherol, and Fatty Acid Composition.

Extra virgin olive oil (EVOO) is an important component of the Mediterranean diet and a highly priced product. Despite the strict legislation to protect it from fraudulent practices, there is an increasing demand to characterize EVOOs and evaluate their authenticity. For this purpose, 68 monovarietal EVOOs, originating from three regions of Greece (Peloponnese, Crete, and Lesvos) and two local cultivars (Koroneiki and Kolovi), were obtained during the harvesting period of 2018-2019. Fatty acids, squalene, and tocopherols were determined chromatographically according to official methods in order to study the effect of cultivar and geographical origin. Squalene and γ-tocopherol differed significantly amongst the cultivars tested. Koroneiki samples exhibited higher squalene content than Kolovi samples, whereas the opposite was observed for γ-tocopherol. The tocopherol level was highly geographical dependent, with EVOOs from Peloponnese displaying the highest concentration of α-tocopherol, whereas the content of γ-tocopherol was significantly higher in samples from Lesvos. Unsupervised and supervised multivariate analysis resulted in a satisfactory grouping of EVOOs according to cultivar. γ-Tocopherol, squalene, and the majority of fatty acids were the most discriminant variables, with γ-tocopherol, linoleic, linolenic, and gadoleic acid being present at higher levels in samples from the Kolovi cultivar. Koroneiki samples were characterized with higher levels of squalene, palmitic, palmitoleic, and arachidic acid.

Volatilome of Chill-Stored European Seabass (Dicentrarchus labrax) Fillets and Atlantic Salmon (Salmo salar) Slices under Modified Atmosphere Packaging.

Fish spoilage occurs due to production of metabolites during storage, from bacterial action and chemical reactions, which leads to sensory rejection. Investigating the volatilome profile can reveal the potential spoilage markers. The evolution of volatile organic molecules during storage of European seabass (Dicentrarchus labrax) fillets and Atlantic salmon (Salmo salar) slices under modified atmosphere packaging at 2 °C was recorded by solid-phase microextraction combined with gas chromatography-mass spectrometry. Total volatile basic nitrogen (TVB-N), microbiological, and sensory changes were also monitored. The shelf life of seabass fillets and salmon slices was 10.5 days. Pseudomonas and H2S-producing bacteria were the dominant microorganisms in both fish. TVB-N increased from the middle of storage, but never reached concentrations higher than the regulatory limit of 30-35 mg N/100 g. The volatilome consisted of a number of aldehydes, ketones, alcohols and esters, common to both fish species. However, different evolution patterns were observed, indicating the effect of fish substrate on microbial growth and eventually the generation of volatiles. The compounds 3-hydroxy-2-butanone, 2,3-butanediol, 2,3-butanedione and acetic acid could be proposed as potential spoilage markers. The identification and quantification of the volatilities of specific fish species via the development of a database with the fingerprint of fish species stored under certain storage conditions can help towards rapid spoilage assessment.

Extraction of Phenolic Compounds from Palm Oil Processing Residues and Their Application as Antioxidants.

The side streams derived from the palm oil production process, namely palm kernel cake, palm pressed fibre, palm kernel shells and empty fruit bunches, were evaluated as sources of phenolic compounds. Among these streams, kernel cake had the highest total phenolic content (in mg of gallic acid equivalents (GAE) per g of dry sample) with a value of 5.19, whereas the empty fruit bunches had the lowest value (1.79). The extraction time and liquid-to-solid ratio were investigated to optimize the phenolic extraction. Kernel cake exhibited the highest total phenolic content (5.35 mg/g) with a liquid-to-solid ratio of 40:1 during 20 min of extraction. The main phenolic compounds of the extracts deriving from all byproduct streams were also identified and quantified with HPLC-DAD. Pyrogallol, 4-hydroxybenzoic acid, gallic acid and ferulic acid were the main compounds found in kernel cake extracts. Empty fruit bunch and pressed fibre extracts were also rich in 4-hydroxybenzoic acid, while pyrogallol was the predominant compound in kernel shell extracts. All extracts showed antioxidant activity as it was indicated from the results of DPPH analysis and subsequently tested in sunflower oil aiming to prolong its shelf life. The addition of 0.8% kernel cake extract increased the induction time of sunflower oil more than 50%. According to the results obtained in this study, kernel cake extracts could be considered as a value-added co-product with a potential application as antioxidants in the food industry.

Effect of osmotic dehydration of olives as pre-fermentation treatment and partial substitution of sodium chloride by monosodium glutamate in the fermentation profile of Kalamata natural black olives.

This study examined the effect of osmotic dehydration of Kalamata natural black olives as pre-fermentation treatment in combination with partial substitution of NaCl by monosodium glutamate (MSG) on the fermentation profile of olives. Osmotic dehydration was undertaken by immersing the olives in 70% (w/w) glucose syrup overnight at room temperature. Further on, three different mixtures of NaCl and MSG with/without prior osmotic dehydration of olives were investigated, namely (i) 6.65% NaCl - 0.35% MSG (5% substitution), (ii) 6.30% NaCl - 0.70% MSG (10% substitution), (iii) 5.95% NaCl - 1.05% MSG (15% substitution), and (iv) 7% NaCl without osmotic dehydration (control treatment). Changes in the microbial association (lactic acid bacteria [LAB], yeasts, Enterobacteriaceae), pH, titratable acidity, organic acids, sugars, and volatile compounds in the brine were analyzed for a period of 4 months. The final product was subjected to sensory analysis and the content of MSG in olives was determined. Results demonstrated that osmotic dehydration of olives prior to brining led to vigorous lactic acid processes as indicated by the obtained values of pH (3.7-4.1) and acidity (0.7-0.8%) regardless of the amount of MSG used. However, in non-osmotically dehydrated olives, the highest substitution level of MSG resulted in a final pH (4.5) that was beyond specification for this type of olives. MSG was degraded in the brines being almost completely converted to γ-aminobutyric acid (GABA) at the end of fermentation. Finally, the sensory assessment of fermented olives with/without osmotic dehydration and at all levels of MSG did not show any deviation compared to the control treatment.

The Use of Hanseniaspora opuntiae to Improve 'Sideritis' Wine Quality, a Late-Ripening Greek Grape Variety.

In view of climate change and the increasingly antagonistic wine market, the exploitation of native genetic resources is revisited in relation to sustainable wine production. 'Sideritis' is a late-ripening Greek grape variety, which is quite promising for counteracting wine quality issues associated with the annual temperature rise. The aim of this study was to improve the quality and to enhance the aroma of 'Sideritis' wine through the use of native yeasts. To improve vinification, Hanseniaspora opuntiae L1 was used along with Saccharomyces cerevisiae W7 in mixed fermentations (SQ). The addition of H. οpuntiae significantly altered the chemical profile of the wine compared to the single-inoculated fermentations with W7 (IS). H. opuntiae increased all the acetate esters, except for hexyl acetate and (Z)-3-hexen-1-ol acetate. The concentration of 2-phenylethyl acetate, which imparts flowery and sweet notes, exhibited a 2.6-fold increase in SQ as compared to IS wines. SQ also showed higher levels in several ethyl esters, including ethyl butyrate, ethyl heptanoate and ethyl 7-octenoate, which are associated with fruity notes compared to IS. H. opuntiae produced citronellol, a terpene associated with rose and green notes, and increased the overall acceptance of the wine. Present results are thus quite promising for improving 'Sideritis' wine quality towards a sustainable wine production in Greece in view of global warming.

Growth and Volatile Organic Compound Production of Pseudomonas Fish Spoiler Strains on Fish Juice Agar Model Substrate at Different Temperatures.

Microbial spoilage is the main cause of quality deterioration in seafood. Several strains of psychotropic Pseudomonas have been found to dominate in such products, producing a plethora of volatile organic compounds (VOC). Herein, we investigated the growth of and VOC production by seven strains of Pseudomonas associated with spoiled fish after inoculation as single and mixed cultures on model fish substrate and storage at 0, 4 and 8 °C. The results indicated a strain-dependent VOC profile that was also affected by the storage temperature. Hierarchical cluster analysis (HCA) successfully grouped the strains based on VOC profile at each studied temperature, while some potential Chemical Spoilage Indices (CSI) were revealed. The findings of the present work will contribute to the understanding of the metabolic activity of particular strains of Pseudomonas and to reveal any potential CSI for rapid evaluation of fish spoilage/freshness status.

Torulaspora delbrueckii May Help Manage Total and Volatile Acidity of Santorini-Assyrtiko Wine in View of Global Warming.

Non-Saccharomyces (NS) yeasts are gaining popularity in modern winemaking for improving wine quality. Climate change is one of the biggest challenges winegrowing now faces in warm regions. Here, Lachancea thermotolerans LtS1 and Torulaspora delbrueckii TdS6 combined with Saccharomyces cerevisiae ScS13 isolated from Assyrtiko grapes from Santorini island were evaluated in grape must fermentation with the aim to mitigate major consequences of temperature rise. Different inoculation protocols were evaluated, including simultaneous and sequential mixed-strain inoculations, displaying significant variation in the chemical and kinetic characteristics. Both LtS1 and TdS6 could raise the titratable acidity (TA). TdS6 also reduced the volatile acidity (VA) and was thus chosen for further evaluation in microvinifications and pilot-scale fermentations. Consistent with lab-scale trials, sequential inoculation exhibited the longest persistence of TdS6 resulting in minimum VA levels. Diethyl succinate, ethyl propanoate, and ethyl isobutyrate were significantly increased in sequential inoculations, although a decline in the net total ester content was observed. On the other hand, significantly higher levels of TA, succinic acid, and 2-methylpropanoic were associated with sequential inoculation. The overall performance of TdS6 coupled with a high compatibility with S. cerevisiae suggests its use in the fermentation of Santorini-Assyrtiko or other high sugar musts for the production of structured dry or sweet wines.

Volatile Organic Compounds and 16S Metabarcoding in Ice-Stored Red Seabream Pagrus major.

The profiles of bacterial communities and volatile organic compounds (VOCs) of farmed red seabream (Pagrus major) from two batches during ice storage were studied using 16S metabarcoding (culture independent approach) and headspace Solid Phase Micro-Extraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS) analysis, respectively. Sensory attributes and microbiological parameters were also evaluated. At Day 12 (shelf-life for both batches based on sensory evaluation), using classical microbiological analysis, Total Viable Counts (TVC) were found at the levels of 7-8 log cfu/g, and Pseudomonas and/or H2S producing bacteria dominated. On the other hand, the culture independent 16S metabarcoding analysis showed that Psychrobacter were the most abundant bacteria in fish tissue from batch 1, while Pseudomonas and Psychrobacter (at lower abundance) were the most abundant in fish from batch 2. Differences were also observed in VOC profiles between the two batches. However, combining the VOC results of the two batches, 15 compounds were found to present a similar trend during fish storage. Of them, 2-methylbutanal, 3-methylbutanal, 3-methyl-1-butanol, ethanol, 2,4 octadiene (2 isomers), ethyl lactate, acetaldehyde and (E)-2-penten-1-ol could be used as potential spoilage markers of red seabream because they increased during storage, mainly due to Psychrobacter and/or Pseudomonas activity and/or chemical activity (e.g., oxidation). Additionally, VOCs such as propanoic acid, nonanoic acid, decanoic acid, 1-propanol, 3,4-hexanediol and hexane decreased gradually with time, so they could be proposed as freshness markers of red seabream. Such information will be used to develop intelligent approaches for the rapid evaluation of spoilage course in red seabream during ice storage.

Microbiological assessment of aerobically stored horse fillets through predictive microbiology and metabolomic approach.

The aim of this work was to investigate the microbial association of horse fillets during aerobic storage at isothermal conditions (0-15 °C). Samples were analyzed microbiologically, and in parallel the metabolic profile of the samples was quantified by HS-SPME/GC-MS and HPLC-PDA-RI. Considering HPLC results, the concentration of propionic, formic, lactic and succinic acids decreased during aerobic storage of horse fillets, contrary to acetic, citric, butyric and isobutyric acids, which increased. As far as the volatilome formation during aerobic storage is concerned, pentanal, hexanal, octanal, nonanal, decanal, were correlated with fresh samples, while diacetyl, acetoin, 2-heptanone, 2-octanone, hexanoic acid, 3-methyl-butanol, 2-methy-butanol and 3-methyl-butanal detected in spoiled ones. Herein, a support vector machine regression model using data from 0, 5 and 15 °C predicted the responses of the dataset at 10 °C with a correlation coefficient 0.915 and 0.910 for training and testing, respectively.

Volatile Composition of Industrially Fermented Table Olives from Greece.

Table olives represent one of the most important fermented products in Greece. Their highly appreciated flavor is directly associated with the volatile composition. However, extensive data on the volatile profile of table olives from Greek cultivars are scarce in the literature. For this reason, the volatile components of industrially fermented table olives from Kalamata, Conservolea and Halkidiki cultivars grown in different geographical areas within Greece were determined using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry. More than 100 volatile compounds were identified and distributed over different chemical classes. All samples were rich in esters, alcohols and acids, whereas the samples of cv. Halkidiki were also characterized by increased levels of volatile phenols. Both qualitative and quantitative differences were observed, which resulted in the discrimination of the table olives according to olive cultivar and growing location. To the best of our knowledge, this is the first systematic study on the volatile profiles of table olives from Greek cultivars that also highlights the pronounced effect of olives' growing location.

Spoilage Investigation of Chill Stored Meagre (Argyrosomus regius) Using Modern Microbiological and Analytical Techniques.

Spoilage status of whole and filleted chill-stored meagre caught in January and July was evaluated using sensory, microbiological, 16S metabarcoding and Volatile Organic Compounds (VOCs) analysis. Based on the sensory analysis, shelf-life was 15 and 12 days for the whole fish taken in January and July, respectively, while 7 days for fish fillets of both months. For the whole fish, Total Viable Counts (TVC) at the beginning of storage was 2.90 and 4.73 log cfu/g for fish caught in January and July respectively, while it was found about 3 log cfu/g in fish fillets of both months. The 16S metabarcoding analysis showed different profiles between the two seasons throughout the storage. Pseudomonas (47%) and Psychrobacter (42.5%) dominated in whole meagre of January, while Pseudomonas (66.6%) and Shewanella (10.5%) dominated in fish of July, at the end of shelf-life. Regarding the fillets, Pseudomonas clearly dominated at the end of shelf-life for both months. The volatile profile of meagre was predominated by alcohols and carbonyl compounds. After univariate and multivariate testing, we observed one group of compounds (trimethylamine, 3-methylbutanoic acid, 3-methyl-1-butanol) positively correlating with time of storage and another group with a declining trend (such as heptanal and octanal). Furthermore, the volatile profile seemed to be affected by the fish culturing season. Our findings provide insights into the spoilage mechanism and give information that helps stakeholders to supply meagre products of a high-quality level in national and international commerce.

Vinegar Production from Corinthian Currants Finishing Side-Stream: Development and Comparison of Methods Based on Immobilized Acetic Acid Bacteria.

Fruit wastes and side-streams can be used for vinegar production to create added value for the agri-food sector and enhance farmer incomes and local economies. In this study, methods for vinegar production by wild and selected acetic acid bacteria (the quick starter Acetobacter aceti and the acid-resistant Komagataeibacter europaeus), free (FC) and immobilized (IC) on a natural cellulosic carrier, are proposed using sweet wine made from the industrial finishing side-stream (FSS) of Corinthian currants as raw material. The results showed all cultures can produce vinegar with 46.65 ± 5.43 g/L acidity, from sweet FSS wine containing 5.08 ± 1.19% alcohol. The effect of immobilization was more obvious in the case of the selected culture, presenting better acetification efficiency, both fresh and after cold storage for 2 months. The vinegars had an antioxidant capacity of 263.5 ± 8.4 and 277.1 ± 6.7 mg/L (as ascorbic acid) and phenolic content 333.1 ± 12.0 and 222.2 ± 2.9 mg/L (as gallic acid) (for FC and IC, respectively). They also had a rich volatilome (140 compounds identified by SPME GC-MS), with higher percentages of esters identified in vinegars made by IC. The results are encouraging for vinegar production with IC of a mixed A. aceti and K. europaeus culture.

Volatile Profiling of Pleurotus eryngii and Pleurotus ostreatus Mushrooms Cultivated on Agricultural and Agro-Industrial By-Products.

The influence of genetic (species, strain) and environmental (substrate) factors on the volatile profiles of eight strains of Pleurotus eryngii and P. ostreatus mushrooms cultivated on wheat straw or substrates enriched with winery or olive oil by products was investigated by headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). Selected samples were additionally roasted. More than 50 compounds were determined in fresh mushroom samples, with P. ostreatus presenting higher concentrations but a lower number of volatile compounds compared to P. eryngii. Roasting resulted in partial elimination of volatiles and the formation of pyrazines, Strecker aldehydes and sulfur compounds. Principal component analysis on the data obtained succeeded to discriminate among raw and cooked mushrooms as well as among Pleurotus species and strains, but not among different cultivation substrates. Ketones, alcohols and toluene were mainly responsible for discriminating among P. ostreatus strains while aldehydes and fatty acid methyl esters contributed more at separating P. eryngii strains.

Microbiological and Chemical Properties of Chokeberry Juice Fermented by Novel Lactic Acid Bacteria with Potential Probiotic Properties during Fermentation at 4 °C for 4 Weeks.

On the frame of this research survey, a novel potentially probiotic strain (Lactobacillus paracasei SP5) recently isolated from kefir grains was evaluated for chokeberry juice fermentation. Chokeberry juice was retrieved from the variety Aronia melanocarpa, a plant known to provide small, dark berries and to be one of the richest sources of antioxidants. The juice was subsequently fermented inoculating L. paracasei SP5 for 48 h at 30 °C. The fermented juices were left at 4 °C and tested regarding microbiological and physicochemical characteristics for 4 weeks. The potentially probiotic strain was proved capable of performing lactic acid fermentation at 30 °C. Cell viability of L. paracasei was detected in high levels during fermentation and the whole storage period, while the fermented juice showed higher levels of viability in juice with 40.3 g/L of initial sugar concentration. No ethanol was detected in the final fermented juice. Fermented chokeberry juice was characterized by aromatic desirable volatiles, which were retained in adequate levels for the whole storage period. Specifically, the occurrence of organic esters detected in fermented juices is considered as positive evidence of the provision of fruity and floral notes to the final product. During storage, total phenolics content and antioxidant activity were observed in higher levels in fermented chokeberry juice compared with non-fermented juice. Subsequently, fermentation of chokeberry juice by potentially probiotic lactic acid bacteria could provide high industrialization potential, providing the market with a nutritional beverage of good volatile quality with an enhanced shelf-life compared with an unfermented fresh juice.

Corinthian currants finishing side-stream: Chemical characterization, volatilome, and valorisation through wine and baker's yeast production-technoeconomic evaluation.

The industrial currants finishing generates a considerable amount of side-stream (FSS) with great potential for biotechnological exploitation. The chemical composition of FSS generated from the premium quality Vostitsa currants was studied. Its use for wine making (at low temperatures, using both free and immobilized yeast) combined with baker's yeast production (with minor nutrient supplementation), is also proposed. Analysis showed that FSS has a rich volatilome (including Maillard reaction/lipid degradation products), increased antioxidant capacity, and total lipid and phenolic contents, compared to the marketable product (currants). However, acidity levels and the presence of specific volatiles (such as acetate esters and higher alcohols) may be indicative of microbial spoilage. The wines made from FSS were methanol free and contained higher levels of terpenes (indicating hydrolysis of bound forms) and fermentation-derived volatiles, compared to FSS. A preliminary technoeconomic analysis for integrated wine/baker's yeast industrial production, showed that the investment is realistic and worthwhile.

Valorization of low-cost, carbon-rich substrates by edible ascomycetes and basidiomycetes grown on liquid cultures.

Three ascomycetes (Morchella vulgaris AMRL 36, M. elata AMRL 63, Tuber aestivum AMRL 364) and four basidiomycetes strains (Lentinula edodes AMRL 124 and 126, Agaricus bisporus AMRL 208 and 209) were screened for their ability to grow on liquid static flask cultures of glucose, glycerol, molasses and waste flour-rich hydrolysates with C/N ratio of 20 and produce biomass, exopolysaccharides and lipids. The profile of lipid fatty acids was also assessed. Selected strains were furthermore cultivated in C/N = 50. Results showed that substrate consumption, biomass formation and secondary metabolites production were strain, substrate and C/N ratio dependent. The maximum biomass (X), lipid (L) and exopolysaccharides (EPS) values noted were Xmax = 25.2 g/L (C/N = 20; molasses) and Lmax = 6.51 g/L (C/N = 50; rice cereal hydrolysates) by T. aestivum strain AMRL 364 and EPSmax = 2.41 g/L by M. elata strain AMRL 63 (C/N = 50; molasses), respectively. When C/N ratio of 50 was applied, biomass, lipid production and substrate consumption seem to be negatively affected in most of the trials. The adaptation and capability of the mushroom strains to be cultivated on substrates based on agro-industrial waste streams and infant food of expired shelf date offers the opportunity to set a circular oriented bioprocess.

Gas Chromatography-Mass Spectrometry-Based Metabolite Profiling for the Assessment of Freshness in Gilthead Sea Bream (Sparus aurata).

Gilthead sea bream (Sparus aurata) is one of the most important farmed Mediterranean fish species, and there is considerable interest for the development of suitable methods to assess its freshness. In the present work, gas chromatography-mass spectrometry-based metabolomics was employed to monitor the hydrophilic metabolites of sea bream during storage on ice for 19 days. Additionally, the quality changes were evaluated using two conventional methods: sensory evaluation according to European Union's grading scheme and K-value, the most widely used chemical index of fish spoilage. With the application of chemometrics, the fish samples were successfully classified in the freshness categories, and a partial least squares regression model was built to predict K-value. A list of differential metabolites were found, which were distinguished according to their evolution profile as potential biomarkers of freshness and spoilage. Therefore, the results support the suitability of the proposed methodology to gain information on seafood quality.

Molecular Characterization and Enological Potential of A High Lactic Acid-Producing Lachancea thermotolerans Vineyard Strain.

Lactic acid production is an important feature of the yeast Lachancea thermotolerans that has gained increasing interest in winemaking. In particular, in light of climate change, the biological acidification and ethanol reduction by the use of selected yeast strains may counteract the effect of global warming in wines. Here, the enological potential of a high lactate-producing L. thermotolerans strain (P-HO1) in mixed fermentations with S. cerevisiae was examined. Among the different inoculation schemes evaluated, the most successful implantation of L. thermotolerans was accomplished by sequential inoculation of S. cerevisiae, i.e., at 1% vol. ethanol. P-HO1produced the highest levels of lactic acid ever recorded in mixed fermentations (10.4 g/L), increasing thereby the acidity and reducing ethanol by 1.6% vol. L. thermotolerans was also associated with increases in ethyl isobutyrate (strawberry aroma), free SO2, organoleptically perceived citric nuances and aftertaste. To start uncovering the molecular mechanisms of lactate biosynthesis in L. thermotolerans, the relative expressions of the three lactate dehydrogenase (LDH) paralogous genes, which encode the key enzyme for lactate biosynthesis, along with the alcohol dehydrogenase paralogs (ADHs) were determined. Present results point to the possible implication of LDH2, but not of other LDH or ADH genes, in the high production of lactic acid in certain strains at the expense of ethanol. Taken together, the important enological features of P-HO1 highlighted here, and potentially of other L. thermotolerans strains, indicate its great importance in modern winemaking, particularly in the light of the upcoming climate change and its consequences in the grape/wine system.