The evaluation of lysozyme under winemaking conditions

[摘要] ENGLISH ABSTRACT: The use of lysozyme in oenology is a relative new concept. It forms with bacteriocins andglucose oxidase part of biopreservation of wine. Biopreservation refers to naturalsubstances contributing to the stability of food and beverages. Lysozyme was approved in2000 by the Office International de la Vigne et du Vin (OIV) for usage in wine. Lysozyme iscommercially extracted from hen egg white and inhibits Gram-positive microorganismssuch as lactic acid bacteria (LAB). Lysozyme's mode of action is through degradation ofpeptidoglycan and cleaves the p-(1-4)-glycosidic bond between N-acetylmuramic acid(MurNAc) and N-acetyl-D-glucosamine (GlcNAc) in the polysaccharide, which formpeptidoglycan, the essential constituent of bacterial cell walls. The control of LAB duringwinemaking is especially important due to spoilage LAB that can produce biogenic amines,off-flavours, volatile acidity, ropiness, ethyl carbamate, bitterness, mannitol, geranium toneand they can also play a role in stuck alcoholic fermentation. One of the primary agentsused for the control of microorganisms is sulphur dioxide (S02) due to its anti-oxidativeand antimicrobial functions. However, the action of S02 is pH dependant and consumerdemand has increased for lowered S02 levels in wine.This study therefore focused on the evaluation of lysozyme under South Africanwinemaking conditions by investigating the influence of lysozyme on different strains ofLAB and the effect on the alcoholic fermentation tempo (AFT) during small-scalefermentations. Secondly the effect of lysozyme on acetic acid bacteria (AAB) and LABnumbers during Pinotage, Cabernet Sauvignon and Shiraz red wine vinifications wereevaluated. Other wine parameters monitored in the red wine vinifications included volatilecomponents, biogenic amine levels, colour and total phenol content.It was shown that lysozyme was effective in lowering, or completely inhibiting, LAB growthwith the exception of a few strains, thus indicating differences in sensitivity towardslysozyme between species and strains. Sensitivity to lysozyme treatments was seen forstrains 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 alcoholicfermentation (AF) included those of L. plantarum, L. fermentum, Pediococcus acidilactici,L. pentosus and Leuconostoc mesenteroides. This study showed that wine isolatedLactobacillus strains of L. brevis, L. buchneri and L. paracasei are more resistant tolysozyme concentrations during a controlled small-scale AF. No effect was observed forAFT. Furthermore, lysozyme treatment did not result in an increase in AAB growth duringAF, 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. Noconclusion could be drawn from this study on the effect on the volatile compounds andbiogenic amine and needs further investigation. Lysozyme treatment did not have anyeffect on colour or total phenol content of red wine.

[发布机构] Stellenbosch University