The identification of antibacterial compounds in Chardonnay and their influence on secondary (malolactic) fermentation


Project Number
US MB 01 2002

Project title
The identification of antibacterial compounds in Chardonnay and their influence on secondary (malolactic) fermentation

Project leader
Dicks, L M T

Institution
University of Stellenbosch

Project description
Like all wine, Chardonnay is produced by fermenting grape must with selected strains of Saccharomyces cerevisiae, followed by a secondary (malolactic) fermentation. Of all malolactic bacteria isolated from wine Oenococcus oeni is the best adapted, principally responsible for malolactic fermentation and widely used as malolactic starter culture. Despite this, surprisingly few basic studies have been done on Oenococcus oeni and other malolactic bacteria. Little is known about the influence of intrinsic and extrinsic factors on the growth and enzymatic activity, including malolactic activity, of these bacteria.

The ecology of malolactic bacteria in wines is influenced by the composition of the wine, interactions between the lactic acid bacteria (and yeast), and the technology of vinification. Many of these so called claims are unresearched and remain hypotheses. It is well known that external factors such as pH, sulphur dioxide, alcohol and temperature have a delaying affect on the growth of malolactic bacteria. These factors may even act synergistically and have an even greater antimicrobial affect on malolactic bacteria. More intriguing is the observation that grape must inoculated with Saccharomyces. cerevisiae N96 often undergoes sluggish malolactic fermentation, whereas wines inoculated with other yeasts do not.

The production of bacteriocins (antimicrobial proteins) by lactic acid bacteria is a well-recorded phenomenon and we have published many papers in the field. However, a few of the more recent papers published described the presence of non-proteinaceous antimicrobial compounds produced by lactic acid bacteria, especially strains isolated from wine. Although described, these compounds have not been characterised. This, and the fact that the wine industry suffers huge losses annually due to sluggish or stuck malolactice fermentation, especially in Chardonnay wine, prompted us to investigate the antimicrobial compounds produced by lactic acid bacteria and study the interactions among these bacteria and other malolactic bacteria.

No antimicrobial compounds could be detected in sterile Chardonnay must or in must fermented with yeast strains VIN13 and N96, respectively. We could also not detect any antibacterial compounds produced by the strains used as the malolactic starter culture.

During our studies in Chardonnay we have detected active biofilm formation of malolactic bacteria on stainless steel surfaces. The effect of the bacteriocins pediocin PD-1, plantaricin 423 and nisin on planktonic cells and established biofilms formed by a commercial starter culture of Oenococcus oeni in Chardonnay must is currently being tested. The percentage viable and non-viable cells is determined by using the BaclightTM viability probe and an epifluorescent microscope with image analysis. Preliminary results have indicated that the three bacteriocins are capable of killing the planktonic cells in a relatively short time span (less than 5 h). Thus, should bacteriocins be produced by other lactic acid bacteria during wine fermentations, chances are good that they will destroy active growing malolactic bacteria, resulting in stuck or sluggish malolactic fermentation. We have also recorded signs of removal of an established biofilm of Oenococcus oeni from stainless steel surfaces within one hour in the presence of the bacteriocins. The destruction of metabolically active malolactic bacteria situated in biofilms may be another reason for sluggish malolactic fermentation.

Presentation(s)
Nel, H A, Bauer, R, Wolfaardt, G M and Dicks, L M T. 2001. The formation of biofilms by Oenococcus oeni under winemaking conditions. Paper presented at the 16th SAAFost International Congress. 10-12 September, Durban, South Africa.

Bauer, F F and Dicks, L M T. 2001. The effect of various parameters on the antimicrobial activity of pediocin PD-1. Paper presented at the 16th SAAFost International Congress. 10-12 September, Durban, South Africa.

Nel, H A, Bauer, F F, Wolfaardt, G M and Dicks, L M T. 2001. The effect of antimicrobial peptides on biofilm formation in wine tanks and barrels. Paper presented at the 25th National Congress of the South African Society for Enology and Viticulture. 15-16 November, Somerset West, South Africa.

Articles
Nel, H A, Moes, C J, Dicks, L M T. 2001. Sluggish or stuck malolactic fermentation in Chardonnay: Possible causes, WineLand, Mnth Jul (p. 113-115)

Nel, H A, Bauer, F F, Wolfaardt, G M, Dicks, L M T. 2002. Effect of bacteriocins pediocin PD-1, plantaricin 423, and nisin on biofilms of Oenococcus oeni on a stainless steel surface, American Journal of Enology and Viticulture, v. 53 (3) (p. 191-196)

Note
Published articles serve as the Final Report.

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