An investigation into lactic acid bacteria as a possible cause of bitterness in wine

[摘要] ENGLISH ABSTRACT: Spoilage, be it due to microbial actions, chemical reactions or both, poses a seriousthreat to the food and beverage industries. Not only can spoilage lead to greateconomic losses, but it can also cause industries to lose their competitive edge in theeconomic and consumer market. Considering all the modern technologies and therange of preservation techniques that are available, it is surprising that spoilage is stillan economic problem. Wine spoilage due to unpalatable bitterness, and the role oflactic acid bacteria (LAB) in causing this bitterness, have received much attentionover the years, but no definite understanding has yet emerged.The first objective of this study was to isolate, enumerate and identify the LABfrom three red grape varieties, viz. Pinotage, Merlot and Cabernet Sauvignon. TheLAB populations on the grapes of all three varieties ranged from 102 to 104 cfu/mlduring the 2001 and 2002 harvest seasons. The Cabernet Sauvignon grapes hadslightly higher numbers than the Pinotage and Merlot. The LAB population in theCabernet Sauvignon, Pinotage and Merlot wines after completion of the alcoholicfermentation ranged from 102 to 105 cfu/ml, while during 2002 the numbers in wineundergoing malolactic fermentation (MLF) ranged from 104 to 108 cfu/ml. Theisolated LAB were divided into the three metabolic groups, with 59% belonging to thefacultatively heterofermentative group, 26% to the obligately heterofermentativegroup and 15% to the obligately homofermentative group. The isolates wereidentified by means of species-specific primers as Leuconostoc mesenteroides (4),Oenococcus oeni (28), Lactobacillus brevis (15), Lb. hilgardii (15), Lb. plantarum(98), Lb. pentosus (12), Lb. paraplantarum (3), Lb. paracasei (28),Pediococcus acidilactici (2) and Pediococcus spp. (35). The most predominantspecies isolated was Lb. plantarum, followed by Pediococcus spp. The resultssuggest that Pinotage carries a more diverse LAB population in comparison to Merlotand Cabernet Sauvignon.The second objective of this study was to determine the presence of the glyceroldehydratase gene in the LAB strains by using the G01 and G02 primers. Twenty-sixstrains tested positive, namely Lb. plantarum (15), Lb. pentosus (1), Lb. hilgardii (5),Lb. paracasei (2), Lb. brevis (2) and a Pediococcus spp. (1). Interestingly, 62% ofthese strains were isolated from Pinotage. The strains all had the ability to degradeglycerol by more than 90%, and no significant differences were observed betweenthe species. The GO-possessing strains exhibited varying degrees of inhibitiontowards Gram-positive and Gram-negative bacteria, and the results suggest that thisinhibition activity may be similar to that of reuterin, which is produced by Lb. reuteri.This study can form the foundation for unravelling the causes of bitterness in redwines. Combining the results of this study with analytical, sensory and moleculardata may very well provide the industry with valuable tools with which to combat theoccurrence of bitterness.

[发布机构] Stellenbosch University