Characterization of anthocyanins and condensed tannins from grapes and their qualitative incidence on astringency and bitterness sensory properties

Abstract : In red wine, phenolic compounds are generally associated with the quality of products. Among them, anthocyanins extracted from skins are responsible for wine colour. The grapevine genomes determine the anthocyanins profiles, but several factors in the vineyard can influence their accumulation, as well as post-harvest techniques can modify their extraction during winemaking. Monomeric, oligomeric and polymeric flavanols from skins and seeds contribute to astringency and bitterness of wine and during winemaking and ageing complexes formation with anthocyanins modifies wine characteristics. Several publications are available to understand flavanols sensory characteristics, whereas anthocyanins role has not consensus in scientific literature. This PhD thesis is composed by two parts. The first part deal with the evaluation of the use of gaseous ozone as post-harvest technique in red wine grapes Nebbiolo and Barbera used on both fresh grape and during withering. Ozone treatment is an innovative technology proved to avoid mycobiota spoilage and preserving from the use of sulphur dioxide. Its influence on flavanol and anthocyanin contents and extractabilities during maceration was evaluated, considering skin cell wall modification. In fresh grape, ozone influenced skin maceration for both the varieties, leading to a higher anthocyanin extraction in Nebbiolo grapes and lower in Barbera. Ozone did not influence the final individual anthocyanin extractability, respecting the varietal anthocyanin fingerprint. During dehydration, opposite trend was found: in Nebbiolo reported no change in the content of total anthocyanins just after ozone-assisted dehydration, but their extraction yield was lower. On the contrary, although lower contents of anthocyanins were found in Barbera grapes no differences in final extractability was found. Regarding oligomeric and polymeric flavanols, their extractability was less affected by the ozone treatment. Only in Nebbiolo, both oligomeric and polymeric flavanol extraction was increased in fresh grape, whereas it is slightly decrease during dehydration. The ozone-induced modification of skin cell wall composition together with skin hardness parameters fitted well in multivariate models to predict anthocyanins, oligomeric flavanols and polymeric flavanols extraction. Therefore, the ozone treatment should be adapted depending on the variety and on the target wine. In the second part, grape anthocyanins were isolated depending on the acylation patterns, i.e. glucoside, acetyl-glucoside, and cinnamoyl-glucoside by a combination of centrifugal partition chromatography (CPC) and preparative-HPLC. Protein precipitation analyses to assess astringency and sensorial analysis were carried out. Anthocyanins reacted with both bovine serum albumine and salivary proteins, in different extent, since higher interaction between anthocyanins and salivary proteins was found with a significative reduction of total extract and fractions glucoside, acetyl-glucoside, and cinnamoyl-glucoside. The latter in particular is the more reactive to salivary proteins. Sensorial analysis was carried out as detection threshold test. Best estimated threshold (BET) of anthocyanins were resulted in wine-range scale, in particular acetyl-glucoside and cinnamoyl-glucoside BET are lower of glucoside threshold, and descriptors reported were astringency and bitterness. These results show that anthocyanins can be detected as in-mouth properties contributors, and the magnitude of their involvement is related to anthocyanins acylation.
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Maria Alessandra Paissoni. Characterization of anthocyanins and condensed tannins from grapes and their qualitative incidence on astringency and bitterness sensory properties. Vegetal Biology. Université de Bordeaux; Università degli studi (Turin, Italie), 2018. English. ⟨NNT : 2018BORD0383⟩. ⟨tel-02259877⟩

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