Grape anthocyanins sensory properties: chemical and sensory approaches to investigate their contribution

Anthocyanins from grapes skins are known for their role on red wine color, whereas their involvement in-mouth sensory properties, such as astringency and bitterness, has been considered less relevant in red wine. However, previous results suggested their involvement in wine bitterness and mouth-feel sensation, as well as reactivity towards protein, such as bovine serum albumin (BSA) and salivary protein. In this study, anthocyanin grape skin extracts from cv Nebbiolo and Barbera were fractionated using Centrifugal Partition Chromatography (CPC) and preparative-HPLC in three fractions, i.e. glucoside (FG), acetylated (FA) and p-coumaroylated (FC) anthocyanins. Investigation of sensory properties was carried out for the extract and CPC fractions throughout chemical analyses as reactivity towards BSA and salivary protein, and tasting sessions, to determine perception threshold. Moreover, descriptive analysis was carried out for taste and mouth-feel attributes at wine concentration of each class of compounds. Descriptors were chosen after a preliminary tasting and following literature [4] and involved taste (bitterness), in-mouth astringency (particulate) and mouthfeel (irritation), and after expectoration astringency (texture). Tasters were also asked to quantify overall astringency and persistence of the stimuli and sensations. Together with total anthocyanins and CPC fractions, skin and seed tannin extracts were tasted for comparison. Regarding chemical analysis, the concentration of anthocyanin extract in wine-like solution showed a decrease after treatment with salivary protein, especially the glucoside and coumaroylated anthocyanins were significantly reduced, whereas no significant interaction was found towards BSA. Fractions analysis showed a decrease when treated with protein, FG and FA for salivary protein, and FC for both BSA and salivary protein. Best estimation threshold (BET) was calculated in model wine solution (12% ethanol, pH 3.5, 4 g/L tartaric acid), and confirmed by discriminative test. Anthocyanins are perceived at wine-scale range and descriptive analysis, carried out by a trained panel, showed their involvement especially for astringency sub-qualities. Significant differences were found for the attributes texture, particulates, and overall astringency. Skin tannin extract was found to be the highest in all those descriptors, significantly different from total anthocyanins and CPC fractions. In detail, texture and particulates descriptors of FC and FA were more silky and chalky (lower score), followed by total anthocyanins and FG with fine grain attributes (medium scores) and tannin extracts with higher scores in both the descriptors.