Lactic acid bacteria in wine: technological advances and evaluation of their functional role

Currently, the main role of Lactic Acid Bacteria (LAB) in wine is to conduct the malolactic fermentation (MLF). This process can increase wine aroma and mouthfeel, improve microbial stability and reduce the acidity of wine. A growing number of studies support the appreciation that LAB can also significantly, positively and negatively, contribute to the sensorial profile of wine through many different enzymatic pathways. This is achieved either through the synthesis of compounds such as diacetyl and esters or by liberating bound aroma compounds such as glycoside-bound primary aromas and volatile thiols which are odorless in their bound form. LAB can also liberate hydroxycinnamic acids from their tartaric esters and have the potential to break down anthocyanin glucosides, thus impacting wine color. LAB can also produce enzymes with the potential to help in the winemaking process and contribute to stabilizing the final product. For example, LAB exhibit peptidolytic and proteolytic activity that could break down the proteins causing wine haze, potentially reducing the need for bentonite addition. Other potential contributions include pectinolytic activity, which could aid juice clarification and the ability to break down acetaldehyde, even when bound to SO2, reducing the need for SO2 additions during winemaking. Considering all these findings, this review summarizes the novel enzymatic activities of LAB that positively or negatively affect the quality of wine. Inoculation strategies, LAB improvement strategies, their potential to be used as targeted additions, and technological advances involving their use in wine are highlighted along with suggestions for future research.Carla Virdis, Krista Sumby, Eveline Bartowsky and Vladimir Jirane

Comparative analysis of the Oenococcus oeni pan genome reveals genetic diversity in industrially-relevant pathways

BACKGROUND: Oenococcus oeni, a member of the lactic acid bacteria, is one of a limited number of microorganisms that not only survive, but actively proliferate in wine. It is also unusual as, unlike the majority of bacteria present in wine, it is beneficial to wine quality rather than causing spoilage. These benefits are realised primarily through catalysing malolactic fermentation, but also through imparting other positive sensory properties. However, many of these industrially-important secondary attributes have been shown to be strain-dependent and their genetic basis it yet to be determined. RESULTS: In order to investigate the scale and scope of genetic variation in O. oeni, we have performed whole-genome sequencing on eleven strains of this bacterium, bringing the total number of strains for which genome sequences are available to fourteen. While any single strain of O. oeni was shown to contain around 1800 protein-coding genes, in-depth comparative annotation based on genomic synteny and protein orthology identified over 2800 orthologous open reading frames that comprise the pan genome of this species, and less than 1200 genes that make up the conserved genomic core present in all of the strains. The expansion of the pan genome relative to the coding potential of individual strains was shown to be due to the varied presence and location of multiple distinct bacteriophage sequences and also in various metabolic functions with potential impacts on the industrial performance of this species, including cell wall exopolysaccharide biosynthesis, sugar transport and utilisation and amino acid biosynthesis. CONCLUSIONS: By providing a large cohort of sequenced strains, this study provides a broad insight into the genetic variation present within O. oeni. This data is vital to understanding and harnessing the phenotypic variation present in this economically-important species.Anthony R Borneman, Jane M McCarthy, Paul J Chambers and Eveline J Bartowsk

Acetic Acid Bacteria: Physiology and Carbon Sources Oxidation

Acetic acid bacteria (AAB) are obligately aerobic bacteria within the family Acetobacteraceae, widespread in sugary, acidic and alcoholic niches. They are known for their ability to partially oxidise a variety of carbohydrates and to release the corresponding metabolites (aldehydes, ketones and organic acids) into the media. Since a long time they are used to perform specific oxidation reactions through processes called “oxidative fermentations”, especially in vinegar production. In the last decades physiology of AAB have been widely studied because of their role in food production, where they act as beneficial or spoiling organisms, and in biotechnological industry, where their oxidation machinery is exploited to produce a number of compounds such as l-ascorbic acid, dihydroxyacetone, gluconic acid and cellulose. The present review aims to provide an overview of AAB physiology focusing carbon sources oxidation and main products of their metabolism

Malolactic Fermentation

E. J. Bartowskyhttp://nla.gov.au/anbd.bib-an4796466

Timing of malolactic fermentation inoculation in Shiraz grape must and wine: influence on chemical composition

Malolactic fermentation (MLF) is an integral step in red winemaking, which in addition to deacidifying wine can also influence the composition of volatile fermentation-derived compounds with concomitant affects on wine sensory properties. Long-established winemaking protocols for MLF induction generally involve inoculation of bacteria starter cultures post alcoholic fermentation, however, more recently there has been a trend to introduce bacteria earlier in the fermentation process. For the first time, this study shows the impact of bacterial inoculation on wine quality parameters that define red wine, including wine colour and phenolics, and volatile fermentation-derived compounds. This study investigates the effects of inoculating Shiraz grape must with malolactic bacteria at various stages of alcoholic fermentation [beginning of alcoholic fermentation (co-inoculation, with yeast), mid-alcoholic fermentation, at pressing and post alcoholic fermentation] on the kinetics of MLF and wine chemical composition. Co-inoculation greatly reduced the overall fermentation time by up to 6 weeks, the rate of alcoholic fermentation was not affected by the presence of bacteria and the fermentation-derived wine volatiles profile was distinct from wines produced where bacteria were inoculated late or post alcoholic fermentation. An overall slight decrease in wine colour density observed following MLF was not influenced by the MLF inoculation regime. However, there were differences in anthocyanin and pigmented polymer composition, with co-inoculation exhibiting the most distinct profile. Differences in yeast and bacteria metabolism at various stages in fermentation are proposed as the drivers for differences in volatile chemical composition. This study demonstrates, with an in-depth analysis, that co-inoculation of yeast and bacteria in wine fermentation results in shorter total vinification time and produces sound wines, thus providing the opportunity to stabilise wines more rapidly than traditional inoculation regimes permit and thereby reducing potential for microbial spoilage.Caroline E. Abrahamse, Eveline J. Bartowsk

Microbial formation adn modification of flavour and off-flavour compounds in wine

While the colour of wine is important to consumers, it is the aroma and flavour of wine that have the greatest impact and potential for enjoyment. This sensory experience is usually pleasurable; however, it can at times be a less-than-pleasant surprise with off-aromas and off-flavours. Like any tantalizing recipe, the aromas and flavours of red and white wine originate from a blend of ingredients: the grape; yeast and bacterial metabolism during fermentation; wood (when used); and chemical reactions during wine maturation. This chapter covers the pivotal role that yeast and bacterial metabolism have in enhancing wine through their conversion to aroma and flavour active compounds. Considerable recent research has focused on developing microbial starter strains that can enhance desirable characters and reduce or eliminate off-flavours.Eveline J. Bartowsky and Isak S. Pretoriu

Acetic acid bacteria spoilage of bottled red wine-a review

Abstract not availableEveline J. Bartowsky, Paul A. Henschk

Variations in the effect of malolactic fermentation on the chemical and sensory properties of cabernet sauvignon wine: Interactive influences of oenococcus oeni strain and wine matrix composition

Background and Aims:  This study investigated the interactive effects of malolactic bacterial strain, pre-malolactic fermentation (MLF) pH value and wine matrix/style on modulating chemical and sensory impacts of MLF in Cabernet Sauvignon wine. Methods and Results:  Malolactic fermentation was conducted in two styles of Cabernet Sauvignon wine, a lighter, fruity style and a more complex style. Each wine was divided into two equal volumes, one was adjusted to pH 3.3 the other to pH 3.7. Each of these wines was further divided into four equal volumes, three of which were inoculated with three different commercial Oenococcus oeni strains and the fourth used as a non-MLF control. Following MLF, all wines were standardised to approximately pH 3.5. The MLF treatments exhibited significant strain- and wine matrix-dependent effects on a diversity of chemical components, including esters, volatile acids and higher alcohols, and on colour. Descriptive sensory analysis also demonstrated significant effects on several sensory properties. Partial least squares analysis revealed a strong correlation between important chemical components and sensory attributes, including overall fruit flavour and dark fruit aroma. Conclusions:  The extent and diversity of the impacts of MLF on wine chemical and sensory properties were directly influenced by choice of bacterial strain, pre-MLF pH and wine matrix composition. Relatively harsh conditions (pH 3.3, 14.8% alcohol) protracted the time of MLF and supported greater differences between Oenococcus oeni strains in their modulation of important wine chemical components. Significance of the Study:  This study increases knowledge of the significant impacts of MLF on wine chemical composition and associated sensory properties. Specifically, variations in the effect of MLF on wine sensory and chemical properties has been found to arise from the choice of bacterial strain and wine matrix composition/style.P.J. Costello, I.L. Francis and E.J. Bartowsk