Browsing by Author "Wassung, Riaan Frederick"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- ItemThe evaluation of lysozyme under winemaking conditions(Stellenbosch : Stellenbosch University, 2006-12) Wassung, Riaan Frederick; Du Toit, M.; Du Toit, Wessel J.; Stellenbosch University. Faculty of AgriSciences . Dept. of Viticulture and Oenology.ENGLISH ABSTRACT: The use of lysozyme in oenology is a relative new concept. It forms with bacteriocins and glucose oxidase part of biopreservation of wine. Biopreservation refers to natural substances contributing to the stability of food and beverages. Lysozyme was approved in 2000 by the Office International de la Vigne et du Vin (OIV) for usage in wine. Lysozyme is commercially extracted from hen egg white and inhibits Gram-positive microorganisms such as lactic acid bacteria (LAB). Lysozyme's mode of action is through degradation of peptidoglycan and cleaves the p-(1-4)-glycosidic bond between N-acetylmuramic acid (MurNAc) and N-acetyl-D-glucosamine (GlcNAc) in the polysaccharide, which form peptidoglycan, the essential constituent of bacterial cell walls. The control of LAB during winemaking is especially important due to spoilage LAB that can produce biogenic amines, off-flavours, volatile acidity, ropiness, ethyl carbamate, bitterness, mannitol, geranium tone and they can also play a role in stuck alcoholic fermentation. One of the primary agents used for the control of microorganisms is sulphur dioxide (S02) due to its anti-oxidative and antimicrobial functions. However, the action of S02 is pH dependant and consumer demand has increased for lowered S02 levels in wine. This study therefore focused on the evaluation of lysozyme under South African winemaking conditions by investigating the influence of lysozyme on different strains of LAB and the effect on the alcoholic fermentation tempo (AFT) during small-scale fermentations. Secondly the effect of lysozyme on acetic acid bacteria (AAB) and LAB numbers during Pinotage, Cabernet Sauvignon and Shiraz red wine vinifications were evaluated. Other wine parameters monitored in the red wine vinifications included volatile components, biogenic amine levels, colour and total phenol content. It was shown that lysozyme was effective in lowering, or completely inhibiting, LAB growth with the exception of a few strains, thus indicating differences in sensitivity towards lysozyme between species and strains. Sensitivity to lysozyme treatments was seen for strains of L. nagelii, L. pentosus, L. vermiforme, L. paraplantaum, L. hilgradii, L. plantarum, L. paracasei and L. buchneri. Strains that did not show positive growth during the alcoholic fermentation (AF) included those of L. plantarum, L. fermentum, Pediococcus acidilactici, L. pentosus and Leuconostoc mesenteroides. This study showed that wine isolated Lactobacillus strains of L. brevis, L. buchneri and L. paracasei are more resistant to lysozyme concentrations during a controlled small-scale AF. No effect was observed for AFT. Furthermore, lysozyme treatment did not result in an increase in AAB growth during AF, however, in some cases resulted in lower AAB numbers for lysozyme treated wines. Differences in LAB and AAB numbers could be seen between the tested cultivars. No conclusion could be drawn from this study on the effect on the volatile compounds and biogenic amine and needs further investigation. Lysozyme treatment did not have any effect on colour or total phenol content of red wine.