Abstract
Correlating the profiles of condensed tannins and phenolic compounds in grape and wine with the viticultural (e.g., grape variety, clone, terroir, vintage, climate) and enological (e.g., winemaking practices, fermentations, ageing) variables is a current task of the research in enological chemistry [1,2]. The complexity associated to the profile of these oligo-/poly-meric flavanols arises from the intrinsic variability of their constituents (type of monomers) and binding modes, along with a dependence on their stability and their tendency to evolve overtime (e.g., by further polymerization or depolymerization). Nonetheless, cyclic proanthocyanidins (c-PAC), minor condensed tannins with an interesting macrocyclic structure, have demonstrated better stability towards harsh conditions that would cause instead degradation of their conventional (non-macrocyclic) analogues [3,4]. These compounds could represent an example of stabler makers of varietal authenticity [5] if their stability proved to hold for the entire c-PAC profile and also in wine overtime. Consequently, the study of these compounds is being pursued in order to define their relationships with enological and viticultural variables, the only limitation being the lack of suitable chemical standards and limited concentrations in grape and wine samples in general. In this report, a direct isolation approach for this phenolic fraction, which favors them vs their conventional analogues, is presented. An exploratory Plackett-Burman design was applied to evaluate the significant variables affecting the extraction performance and selectivity (such as extraction time, temperature, etc.), while several procedures proposed by the literature have been tested for purification, involving ion-exchange resin purification and gel filtration, followed by mass spectrometric characterization. The optimized methods could be suitable for implementing a food-grade process and scaling-up, with potential application to recovery of secondary products of winemaking, such as grape pomace left over from large-scale white wine vinifications. The conditions for the extraction and purification are reported along with the related mass spectrometric characterizations.
[1] S. Giacosa, G.P. Parpinello, et al., Food Res. Int., 2021, 143, 110277.
[2] V. Merkyte, E. Longo, et al., Foods, 2020, 9(12), 1785.
[3] E. Longo, F. Rossetti et al., J. Am. Soc. Mass Spec., 2018, 29(4), 663.
[4] L. Zeng, P. Pons-Mercadé et al., Molecules, 2019, 24(10), 1915
[5] E. Longo, F. Rossetti et al., Food Chem., 2019, 299, 125125.