Skin And Seed Extracts Differently Behave Towards Salivary Proteins

Background: Polyphenols extracted from skins and seeds showed different sensory attributes including astringency and bitterness. In previous studies, it has been demonstrated that extracts obtained either from skins or seeds interact differently with salivary proteins. Red grape winemaking consists of a maceration of the whole berries in which both skins and seeds are mixed together; however, no information on the mutual influence that skins and seeds could have on the reactivity towards saliva of hydroalcoholic extracts is known. In this study, five different  wine model solutions were prepared: the first one contained only skins (Sk), the second one contained only seeds (Sd) and the remaining three contained different skin/seed ratios, as detailed below: A (ratio 2:1 skin : seed), B(ratio 1:1 skin : seed) and C (ratio 1:2 skin: seed).  Methods: HPLC analyses were performed to determine the content of total native anthocyanins, acetaldehyde and polymeric pigments. Iron reactive phenolics, BSA reactive tannins (BSArT), vanillin reactive flavans (VRF) were also determined. The potential astringency of red samples was evaluated in vitro by the Saliva Precipitation index (SPI), which measures the reactivity of salivary proteins towards wine polyphenols. Results: The results obtained in this experiment highlighted important differences in the behavior of the samples as a function of the different skin:seed ratio. When skins and seeds  were simultaneously present (samples A, B and C), a significant lower content of anthocyanins with respect to Sk was observed. This was likely due to a possible adsorption of pigments on cell walls contained in pomaces. As the amount  of seeds increased in the solutions containing also skins, the content of VRF, BSArT, PP and acetaldehyde linearly increased. After 24 months of aging under controlled conditions, all the trends observed at 0 time were confirmed and appeared to be enhanced. Concerning the interactions toward salivary proteins, as expected, sample Sd showed the highest SPI. Surprisingly, when skins were added to a model solution containing seeds, a decrease of SPI occurred, although VRF and BSArT increased. This suggests that  anthocyanins and polymeric pigments in A, B and C samples determined a lower reactivity of compounds contained in the whole solution towards saliva proteins. SPI values are not correlated to the amount of VRF and BSArT in the samples. Conclusion: results of our study highlighted not only the important role of the skin:seed ratio in regulating the extraction of compounds from berries, but also that of anthocyanins extracted from skins in decreasing the reactivity of grape compounds towards saliva. 

Authors: Errichiello Francesco1, Guerriero Antonio1, Picariello Luigi1, Coppola Francesca1, Rinaldi Alessandra1,2, Forino Martino1 and Gambuti Angelita1

1Department of Agricultural Sciences, Grape and Wine Science Division, University of Naples Federico II
2Biolaffort, 126 Quai de la Souys, 33100 Bordeaux, France

*corresponding author:

Keywords: skin/seed extract; anthocyanins; polymeric pigments; astringency.

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