Antioxidant capacity of Pinotage wine as affected by viticultural and enological practices

[摘要] The aim of the study was to provide the South African wine industry with guidelines for the production ofPinotage wines with optimal total antioxidant capacity (TAC), while retaining sensory quality. The contribution ofindividual phenolic compounds to the wine TAC is important in this regard. The wine TAC was measured withthe 2,2 -azino-di(3-ethylbenzo-thiazoline-sulphonic acid radical cation) (ABTS +) scavenging assay. Thecontributions of individual phenolic compounds to the wine TAC were calculated from their content in the winesand the Trolox equivalent antioxidant capacity (TEAC) of pure phenolic standards. The effects of climate region,vine structure, enological techniques (pre-fermentation maceration, juice/skin mixing, addition of commercialtannins, extended maceration) and maturation (oak barrels, alternative oak products, oxygenation) on the phenoliccomposition, TAC and sensory quality of Pinotage wines were also investigated.The TEAC values of quercetin-3-galactoside, isorhamnetin and peonidin-3-glucoside were reported for thefirst time. TEAC values observed for most compounds were much lower than those reported previously, althoughTEAC values for gallic acid, caftaric acid, caffeic acid and kaempferol were consistent with some previousreports. Caftaric acid and malvidin-3-glucoside were the largest contributors to the wine TAC. The contents ofmonomeric phenolic compounds and procyanidin B1, however, only explained a small amount (between 11 and24%) of the wine TAC, with the remaining TAC attributed to oligomeric and polymeric phenolic compounds andother unknown compounds. Some synergy between different monomeric phenolic compounds was alsodemonstrated.All the viticultural and enological factors investigated affected the phenolic composition of Pinotage wines,while the wine TAC was only affected by some treatments. Changes in wine TAC could not always be explainedby changes in phenolic composition as the contribution of oligomeric, polymeric and unknown compounds couldnot be assessed, but could play a large role. Differences in wine colour were also difficult to explain due to thelarge number of factors involved and the dark wine colour, which made objective measurements difficult. Theconcentration of vitisin A, an orange-red pyranoanthocyanin, was increased consistently as a result of prefermentationmaceration treatments and affected the wine colour of oxygenated wines. Increased wine TAC wasobserved when cultivating Pinotage grapes on bush vines and in cooler climatic regions, compared to cultivationon trellised vines in warmer climatic regions. All the climatic regions and vine structure treatments, however,resulted in wines with good sensory quality. In terms of enological techniques, pumping-over, as opposed topunching-down and rotor treatments, is not recommended as a juice/skin mixing technique, due to reduced wineTAC, colour and sensory quality. Pre-fermentation maceration, addition of commercial tannin preparations, andoak maturation using traditional and alternative treatments, resulted in improved sensory quality, but with nochange in wine TAC. However, optimisation of the tannin addition protocol may result in increased wine TAC ifadditions are made after fermentation or higher dosages are used. Oxygenation of Pinotage wine needs furtherinvestigation to optimise the protocol, as improvements to the wine colour and fullness were observed for sometreatments, but loss of sensory quality and TAC were observed in most cases.

[发布机构] Stellenbosch University