Malolactic Fermentation Starter Research Articles

Preparation and Application of Directed Vat Set Indigenous Freeze-Drying Lentilactobacillus hilgardii Q19 Starter in Winemaking

In order to prepare a better direct vat set for malolactic fermentation (MLF) in high ethanol and low pH wines, the high-ethanol- and low-temperature-tolerant strain Lentilactobacillus hilgardii Q19, which was isolated from the eastern foothill of the Helan Mountain wine region in China, was used to prepare a direct vat set by vacuum freeze-drying. A superior freeze-dried lyoprotectant was obtained to create the starting culture by selecting, combining, and optimizing numerous lyoprotectants with higher protection for Q19 by using a single-factor experiment and response surface approach. Finally, the Lentilactobacillus hilgardii Q19 direct vat set was inoculated in Cabernet Sauvignon wine to carry out MLF on a pilot scale, with commercial starter culture Oeno1 as control. The volatile compounds, biogenic amines, and ethyl carbamate content were analyzed. The results showed that a combination of 8.5 g/100 mL skimmed milk powder, 14.5 g/100 mL yeast extract powder, and 6.0 g/100 mL sodium hydrogen glutamate offered better protection; with this lyoprotectant, there were (4.36 ± 0.34) × 1011 CFU/g cells after freeze-drying, and it showed an excellent ability to degrade L-malic acid and could successfully finish MLF. In addition, in terms of aroma and wine safety, compared with Oeno1, the quantity and complexity of volatile compounds were increased after MLF, and biogenic amines and ethyl carbamate were produced less during MLF. We conclude that the Lentilactobacillus hilgardii Q19 direct vat set could be applied as a new MLF starter culture in high-ethanol wines.

Preliminary study of novel autochthonous starter culture for red wine production with reduced biogenic amine content

AbstractMost Chilean red wine is produced by spontaneous malolactic fermentation (MLF), which generates prolonged fermentations resulting in uncertain results, increase production cost, and lead to biogenic amine (BA) formation. The objective of this work was to carry out a preliminary study of an autochthonous MLF starter culture to perform shorter and controlled MLF to elaborated red wines with low BA content. The autochthonous Oenococcus oeni strain (OoB6) isolated from spontaneous MLF was assayed in bioreactors using filtered and unfiltered wines. OoB6 strain efficiently carried out MLF samples showing a similar performance to commercial starter culture. Both accomplished malic acid concentrations (<0.12 g/L) significantly lower (p < .05) than the initial content (1.21 ± 0.11 g/L). OoB6 strain produced a 50% reduction in MLF time and showed very low BA formation (ca. 5 mg/L) without detecting the presence toxicological important BA histamine and tyramine.Novelty impact statement To the best of our knowledge, this work report for the first time a preliminary study of potential autochthonous MLF starter culture to elaborate Chilean red wines. Autochthonous MLF starter culture produced a 50% reduction in MLF time compared with traditional spontaneous MLF. Autochthonous MLF starter culture showed very low BA formation (ca. 5 mg/L) without detecting the presence toxicological important BA histamine and tyramine.

Identification and Characterization of Malolactic Bacteria Isolated from the Eastern Foothills of Helan Mountain in China

Malolactic fermentation (MLF) converts malic acid into lactic acid by lactic acid bacteria (LAB). MLF may affect potential wine quality impact as global warming intensifies, and the alcohol in the wine increases, which threatens MLF. Lactiplantibacillus plantarum is considered a new generation of MLF starter because of the ability of high ethanol tolerance and good enological characteristics. In this research, 132 LAB strains were isolated from the eastern foothills of Helan Mountain in Ningxia, China. Twenty-one higher ethanol tolerance isolates were obtained by 15% (v/v) ethanol preliminary screening. They were identified by 16S rRNA sequencing and differentiated by randomly amplified polymorphic DNA (RAPD). Stress factors include ethanol, pH, and SO2, and the combination of stresses was used to screen stress-tolerance strains. β-D-glucosidase activity, MLF performance, and biogenic amine content were tested to evaluate the enological characteristics. GC-MS detected the volatile components of the wine after MLF. The results showed that twenty strains were identified as L. plantarum, and one strain was Lentilactobacillus hilgardii. Especially, the strains of A7, A18, A23, A50, and B28 showed strong resistance to high ethanol, low pH, and high SO2. A7, A50, and B28 showed better β-D-glucosidase activity and thus were inoculated into cabernet sauvignon wines whose ethanol content was 14.75% (v/v) to proceed MLF. A7 finished MLF in 36 d, while the control strains Oenococcus oeni 31-DH and L. plantarum BV-S2 finished MLF in 24 d and 28 d, respectively. Nevertheless, A50 and B28 did not finish MLF in 36 d. The data showed that A7 brought a more volatile aroma than control. Notably, the esters and terpenes in the wine increased. These results demonstrated the potential applicability of L. plantarum A7 as a new MLF starter culture, especially for high-ethanol wines.

Isolation and Characterization of High-Ethanol-Tolerance Lactic Acid Bacteria from Australian Wine.

Lactic acid bacteria are very important in winemaking. In this study, 108 lactic acid bacteria isolates were obtained from high-ethanol-content (~17% (v/v)) Grenache wines during uninoculated malolactic fermentation (MLF). The 16S rRNA and species-specific PCR showed that 104 of these were Oenococcus oeni, three were Lactobacillus hilgardii, and one was Staphylococcus pasteuri. AFLP of HindIII and MseI digests of the genomic DNA of the O. oeni strains was developed for the first time to discriminate the strains. The results showed that the method was a suitable technique for discriminating the O. oeni strains. Based on the cluster analysis, nine O. oeni strains were chosen for inclusion in an ethanol tolerance assay involving monitoring of optical density (ABS600nm) and viable plating. Several O. oeni strains (G63, G46, G71, G39) survived and grew well in MRS-AJ with 17% (v/v) ethanol, while the commercial O. oeni reference strain did not. Strain G63 could also survive and grow for 168 h after inoculation in MRS-AJ medium with 19% (v/v) ethanol. These results suggest that O. oeni G63, G46, G71, and G39 could potentially be used as MLF starters for high-ethanol-content wines. All three L. hilgardii strains could survive and grow in MRS-AJ with 19% (v/v) ethanol, perhaps also indicating their suitability as next-generation MLF starter cultures.

Effect of mixed fermentation by Torulaspora delbrueckii, Saccharomyces cerevisiae, and Lactobacillus plantarum on the sensory quality of black raspberry wines

Till now, very few studies are focused on the interactive effect of wine-associated microbes including non-Saccharomyces, Saccharomyces, and lactic acid bacteria on modulating the organoleptic quality of black raspberry wines. In our study, Torulaspora delbrueckii, a widely studied non-Saccharomyces yeast, and Lactobacillus plantarum, a promising malolactic fermentation starter, were used in combination with S. cerevisiae for the production of black raspberry wine by three inoculation modes, i.e., sequential inoculation of three species (SE), co-culture of S. cerevisiae and L. plantarum (CO) and T. delbrueckii/S. cerevisiae sequential inoculation plus a spontaneous malolactic fermentation (SP), on the quality of black raspberry wine. A total of 34 aromatic compounds were identified by HS–GC–IMS technology. CO was found to boost the production of many fruity ester compounds, and scored the highest for ‘fruity’, ‘sweet’, and ‘total aroma’ attributes during sensory evaluation. SP was characterized by the lowest production of most volatile components and obtained the lowest rating. Principal component analysis showed that three samples were quite different from each other. Overall, CO had greater potential to be used in the production of black raspberry wine.

Lactobacillus plantarum, a New Biological Tool to Control Malolactic Fermentation: A Review and an Outlook

Malolactic fermentation (MLF) in wine is an important step in the vinification of most red and some white wines, as stands for the biological conversion of l-malic acid into l-lactic acid and carbon dioxide, resulting in a decrease in wine acidity. MLF not only results in a biological deacidification, it can exert a significant impact on the organoleptic qualities of wine. This paper reviews the biodiversity of lactic acid bacteria (LAB) in wine, their origin, and the limiting conditions encountered in wine, which allow only the most adapted species and strains to survive and induce malolactic fermentation. Of all the species of wine LAB, Oenococcus oeni is probably the best adapted to overcome the harsh environmental wine conditions and therefore represents the majority of commercial MLF starter cultures. Wine pH is most challenging, but, as a result of global warming, Lactobacillus sp. is more often reported to predominate and be responsible for spontaneous malolactic fermentation. Some Lactobacillus plantarum strains can tolerate the high alcohol and SO2 levels normally encountered in wine. This paper shows the potential within this species for the application as a starter culture for induction of MLF in juice or wine. Due to its complex metabolism, a range of compositional changes can be induced, which may positively affect the quality of the final product. An example of a recent isolate has shown most interesting results, not only for its capacity to induce MLF after direct inoculation, but also for its positive contribution to the wine quality. Degrading hexose sugars by the homo-fermentative pathway, which poses no risk of acetic acid production from the sugars, is an interesting alternative to control MLF in high pH wines. Within this species, we can expect more strains with interesting enological properties.

Lactobacillus plantarum as a malolactic starter culture in winemaking: A new (old) player?

Malolactic fermentation (MLF) is a process in winemaking responsible for the conversion of L-malic acid to L-lactic acid and CO2, which reduces the total acidity, improves the biological stability, and modifies the aroma profile of wine. MLF takes place during or after alcoholic fermentation and is carried out by one or more species of lactic acid bacteria (LAB), which are either present in grapes and cellars or inoculated with malolactic starters during the winemaking process. Although the main bacterium among LAB used in commercial starter cultures for MLF has traditionally been Oenococcus oeni, in the last decade, Lactobacillus plantarum has also been reported as a malolactic starter, and many works have shown that this species can survive and even grow under harsh conditions of wine (i.e., high ethanol content and low pH values). Furthermore, it has been proved that some strains of L. plantarum are able to conduct MLF just as efficiently as O. oeni. In addition, L. plantarum exhibits a more diverse enzymatic profile than O. oeni, which could play an important role in the modification of the wine aroma profile. This enzymatic diversity allows obtaining several starter cultures composed of different L. plantarum biotypes, which could result in distinctive wines. In this context, this review focuses on showing the relevance of L. plantarum as a MLF starter culture in winemaking.

Selection and Characterisation of Oenococcus oeni and Lactobacillus plantarum South African Wine Isolates for Use as Malolactic Fermentation Starter Cultures

This study focused on characterising 23 Oenococcus oeni and 19 Lactobacillus plantarum strains isolated from the South African wine environment for the development of potential commercial malolactic fermentation (MLF) starter cultures. These strains were characterised with regards to oenological important characteristics, including the genetic screening for enzyme-encoding genes (enzymes that are involved/implicated in wine aroma modification, as well as enzymes pertaining to the wholesomeness of the final wine product), their fermentation capabilities, the ability to maintain viability during MLF, as well as the volatile acidity production. A total of three O. oeni and three L. plantarum strains were selected at the completion of this study. These six strains showed the most potential during the characterisation stages of the study and were able to successfully complete MLF in Pinotage wine. It was also found that L. plantarum strains displayed a more diverse enzyme profile than O. oeni strains, particularly with regards to the presence of the aroma-modifying enzymes β-glucosidase and phenolic acid decarboxylase (PAD), which implies the future use of this species in the modification of the wine aroma profile and use as commercial starter culture.

Protective role of glutathione addition against wine-related stress in Oenococcus oeni

Oenococcus oeni is the main species responsible for the malolactic fermentation (MLF) of wine due to its ability to survive in this environment. Some wine-related stress factors, such as ethanol and low pH, may alter the cell redox balance of O. oeni. For the first time, the ability to uptake glutathione (GSH), an almost universal tripeptide with antioxidant properties, has been associated to the improvement of stress response in O. oeni. Despite the inability of O. oeni to synthesize GSH, this bacterium can capture it from the media. The ability of 30 O. oeni strains to uptake GSH was assessed in this study. Although all of the strains tested were able to import GSH, substantial variability among them was detected. To assess the physiological function of GSH, three strains with different GSH-import capacities were selected. Significant changes in membrane fatty acids composition were observed due to GSH addition. The most relevant was the increase of cyclopropane fatty acids in cell membrane, in both the exponential and the stationary phases. Cells grown with GSH showed an improved survival against ethanol shock (14% v/v). GSH addition also increased biomass production during the adaptation to wine stress conditions (pH4, pH3.4 and 6% ethanol). The results suggest that GSH enrichment could improve the resistance to stress to O. oeni, which could be useful for the adaptation of MLF starter cultures.

Selection and technological potential of Lactobacillus plantarum bacteria suitable for wine malolactic fermentation and grape aroma release

Lactobacillus plantarum strains have resistance mechanisms that enable them to survive and proliferate in wine, which makes them potential malolactic fermentation (MLF) starter cultures. This work focused on the technological characterization of 11 L. plantarum strains isolated from Southern Italian wines that undergo spontaneous MLF, and proposes a selection of new L. plantarum malolactic starters. These strains were characterized according to their oenological characteristics, their ability to produce biogenic amines and bacteriocins, their response to the presence of phenolic compounds, their enzymatic activities and their ability to produce wine odorant aglycones from odourless grape glycosidic aroma precursors. Finally, the malolactic activity of one selected strain was assessed in Cabernet Sauvignon wine, using two inoculation methods. L. plantarum strains tested were not producers of biogenic amines. In particular, the M10 strain showed a good resistance to high levels of ethanol and low pH, it has a good malolactic performance and β-glucosidase activity, this last one demonstrated both directly through the measurement of this enzymatic activity and indirectly by following the release of volatile aglycones from commercial and natural grape glycosidic odourless precursors. These results demonstrated the potential applicability of M10 as a new MLF starter culture, especially for high-ethanol wines.

Selection and characterization of Oenococcus oeni strains for use as new malolactic fermentation starter cultures

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.

Effects of protectant and rehydration conditions on the survival rate and malolactic fermentation efficiency of freeze-dried Lactobacillus plantarum JH287.

In this study, Lactobacillus plantarum JH287 was used as a malolactic fermentation starter in Campbell Early wine production. L. plantarum JH287 was first lyophilized, and the malolactic fermentation potential of freeze-dried L. plantarum JH287 was investigated. Different protective media and rehydration conditions were tested to improve the survival rate of freeze-dried L. plantarum JH287. Optimal protective medium contained 10% sorbitol and 10% skim milk. The optimal rehydration condition was a 1-h rehydration time conducted in the same protective media, and the combination of these two methods produced a survival rate of 86.37%. In addition, a 77.71% survival rate was achieved using freeze-dried samples that were stored at 4°C for 2months. Freeze-dried L. plantarum JH287 and Saccharomyces cerevisiae Fermivin were used to inoculate the Campbell Early grape must to decrease its malic acid content. Using this mixed-fermentation method, wine showed a decrease in malic acid content after 9days of fermentation. GC-MS analysis detected 15 volatile ester compounds in the wine. A sensory evaluation showed that the taste and aroma of mix-fermented wine were better than those of the control that had not been inoculated with L. plantarum JH287.

Technological properties of Lactobacillus plantarum strains isolated from grape must fermentation

Malolactic fermentation (MLF) is a secondary fermentation in wine that usually takes place during or at the end of alcoholic fermentation. Lactobacillus plantarum is able to conduct MLF (particularly under high pH conditions and in co-inoculation with yeasts), and some strains are commercially used as MLF starter cultures. Recent evidences suggest a further use of selected L. plantarum strains for the pre-alcoholic acidification of grape must. In this study, we have carried out an integrated (molecular, technological, and biotechnological) characterization of L. plantarum strains isolated from Apulian wines in order to combine the two protechnological features (MLF performances and must acidification aptitudes). Several parameters such as sugar, pH and ethanol tolerance, resistance to lyophilisation and behaviour in grape must were evaluated. Moreover, the expression of stress gene markers was investigated and was linked to the ability of L. plantarum strains to grow and perform MLF. Co-inoculation of Saccharomyces cerevisiae and L. plantarum in grape must improves the bacterial adaptation to harsh conditions of wine and reduced total fermentation time. For the first time, we applied a polyphasic approach for the characterization of L. plantarum in reason of the MLF performances. The proposed procedure can be generalized as a standard method for the selection of bacterial resources for the design of MLF starter cultures tailored for high pH must.

Growth and consumption of L-malic acid in wine-like medium by acclimated and non-acclimated cultures of Patagonian Oenococcus oeni strains.

Five Oenococcus oeni strains, selected from spontaneous malolactic fermentation (MLF) of Patagonic Pinot noir wine, were assessed for their use as MLF starter cultures. After the individual evaluation of tolerance to some stress conditions, usually found in wine (pH, ethanol, SO2, and lysozyme), the behavior of the strains was analyzed in MLO broth with 14% ethanol and pH3.5 in order to test for the synergistic effect of high ethanol level and low pH and, finally, in a wine-like medium. Although the five strains were able to grow in MLO broth under low pH and/or high ethanol, they must be acclimated to grow in a wine-like medium. Additionally, glycosidase and tannase activities were evaluated, showing differences among the strains. The potential of the strains to ferment citrate was tested and two of the five strains showed the ability to metabolize this substrate. We did not detect the presence of genes encoding histidine, tyrosine descarboxylase, and putrescine carbamoyltransferase. All the strains tested exhibited good growth capacity and ability to consume L-malic acid in a wine-like medium after cell acclimation, and each of them showed a particular enzyme profile, which might confer different organoleptic properties to the wine.

Prevalence ofLactobacillus plantarumandOenococcus oeniduring spontaneous malolactic fermentation in Patagonian red wines revealed by polymerase chain reaction-denaturing gradient gel electrophoresis with two targeted genes

Background and Aims Information regarding the composition and dynamics of microbial communities throughout winemaking is always valuable to control the process and contributes to improving the quality of wine. The aims of this work were to analyse the diversity of lactic acid bacteria (LAB) species present during the spontaneous malolactic fermentation (MLF) of Patagonian red wines, and to isolate and identify native LAB species. Methods and Results Samples of Merlot and Pinot Noir wines were collected during three vintages at one commercial cellar. Through polymerase chain reaction (PCR)-rpoB/denaturing gradient gel electrophoresis (DGGE), it was possible to identify 15 LAB species and through PCR-16S rRNA V3 region/DGGE, 11 LAB species, during spontaneous MLF of these wines, mostly, Oenococcus oeni and Lactobacillus plantarum. These two species were also largely recovered by culture and analysed by the random amplified polymorphic DNA–PCR technique. Isolates of these two LAB species exhibited considerable genotypic heterogeneity. Conclusions The prevalence of O. oeni and Lb. plantarum in all samples suggests that both species are involved in leading the spontaneous MLF of these Patagonian wines. The analysis of the LAB microbiota in wine by PCR-DGGE using two gene regions enabled addition to the number of species that can usually be detected during MLF. Significance of the Study The study offered a more complete knowledge of the LAB community present in wines in a cellar in the Argentine Patagonia during the spontaneous MLF. Our findings are particularly relevant, because they contribute to the possibility of designing an MLF starter composed of native strains of Lb. plantarum and O. oeni.

Biodiversity of Lactobacillus plantarum from traditional Italian wines.

In this study, 23 samples of traditional wines produced in Southern Italy were subjected to microbiological analyses with the aim to identify and biotype the predominant species of lactic acid bacilli. For this purpose, a multiple approach, consisting in the application of both phenotypic (API 50CHL test) and biomolecular methods (polymerase chain reaction-denaturing gradient gel electrophoresis and 16S rRNA gene sequencing) was used. The results showed that Lactobacillus plantarum was the predominant species, whereas Lb. brevis was detected in lower amount. In detail, out of 80 isolates 58 were ascribable to Lb. plantarum and 22 to Lb. brevis. Randomly amplified polymorphic DNA-polymerase chain reaction was used to highlight intraspecific variability among Lb. plantarum strains. Interestingly, the cluster analysis evidenced a relationship between different biotypes of Lb. plantarum and their origin, in terms of wine variety. Data acquired in this work show the possibility to obtain several malolactic fermentation starter cultures, composed by different Lb. plantarum biotypes, for their proper use in winemaking processes which are distinctive for each wine.

The relationships between consumer liking, sensory and chemical attributes of Vitis vinifera L. cv. Pinotage wines elaborated with different Oenococcus oeni starter cultures

Malolactic fermentation (MLF) mediated by lactic acid bacteria (LAB) has been shown to modulate chemical and sensory attributes of wine. This study investigated the relation between consumer liking, chemical and sensory attributes of Vitis vinifera L. cv. Pinotage wines that were made over two vintages by four different lactic acid Oenococcus oeni starter cultures as well as a control treatment where MLF was prevented. Descriptive analysis showed that the sensory attributes buttery, caramel, vegetative flavour, fruity and nutty aroma differed significantly between the wines. These effects on the wines were not the same for the two vintages tested. Preference mapping results showed that the sensory attributes influenced the average consumer liking. The main chemical and sensory correlations found for MLF-treated wines were related to 2,3-butanedione (diacetyl) with the buttery character and various esters with fruity aromas. Although the direct effect of the bacterial starter cultures on wine sensory attributes is difficult to establish, and subject to variation over vintage, the present work suggests that the contribution of LAB starter cultures to wine sensory attributes can influence consumer liking. Selection of an MLF starter culture can thus potentially be used to develop specific wine styles.

Patagonian red wines: selection of Lactobacillus plantarum isolates as potential starter cultures for malolactic fermentation

The aim of this study was to evaluate fifty-three Lactobacillus plantarum isolates obtained from a Patagonian red wine, molecularly identified and typified using RAPD analysis, in order to select starter cultures for malolactic fermentation (MLF). The results obtained suggest a considerable genetic diversity, taking into account that all L. plantarum isolates were obtained from one cellar and one vintage. Based on the capacity to tolerate a concentration of 14% ethanol in MRS broth for 2days, eight isolates were selected for the subsequent analysis. The incidence of various wine stress factors (ethanol, acid pH, lysozyme and sulfur dioxide) on isolates growth was studied. Besides, glucosidase and tannase activities were evaluated, and the presence of genes involved in the synthesis of biogenic amines was examined by PCR. A previously characterized indigenous Oenococcus oeni strain was included with comparative purposes. Differences in technologically relevant characteristics were observed among the eight L. plantarum selected isolates, revealing an isolate-dependent behavior. Detectable glucosidase and tannase activities were found in all isolates. The presence of genes encoding histidine and tyrosine descarboxylases and putrescine carbamoyltransferase was not detected. The ability of L. plantarum isolates to grow and consume L-malic acid in simulated laboratory-scale vinifications revealed that two of them could be considered as possible MLF starter cultures for Patagonian red wines. These isolates will be subjected to further analysis, for a final winery technological characterization.

Comparative metabolic profiling to investigate the contribution ofO. oeniMLF starter cultures to red wine composition

In this research work we investigated changes in volatile aroma composition associated with four commercial Oenococcus oeni malolactic fermentation (MLF) starter cultures in South African Shiraz and Pinotage red wines. A control wine in which MLF was suppressed was included. The MLF progress was monitored by use of infrared spectroscopy. Gas chromatographic analysis and capillary electrophoresis were used to evaluate the volatile aroma composition and organic acid profiles, respectively. Significant strain-specific variations were observed in the degradation of citric acid and production of lactic acid during MLF. Subsequently, compounds directly and indirectly resulting from citric acid metabolism, namely diacetyl, acetic acid, acetoin, and ethyl lactate, were also affected depending on the bacterial strain used for MLF. Bacterial metabolic activity increased concentrations of the higher alcohols, fatty acids, and total esters, with a larger increase in ethyl esters than in acetate esters. Ethyl lactate, diethyl succinate, ethyl octanoate, ethyl 2-methylpropanoate, and ethyl propionate concentrations were increased by MLF. In contrast, levels of hexyl acetate, isoamyl acetate, 2-phenylethyl acetate, and ethyl acetate were reduced or remained unchanged, depending on the strain and cultivar evaluated. Formation of ethyl butyrate, ethyl propionate, ethyl 2-methylbutryate, and ethyl isovalerate was related to specific bacterial strains used, indicating possible differences in esterase activity. A strain-specific tendency to reduce total aldehyde concentrations was found at the completion of MLF, although further investigation is needed in this regard. This study provided insight into metabolism in O. oeni starter cultures during MLF in red wine.

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.