Abstract
Oenotannins are nowadays widely used as co-adjuvant in the winemaking process. The increasing cultivation and consumption of pomegranate (Punica granatum L.) leads to high amounts of by-products, mainly peels. Aim of this study was to propose a dried tannin-rich extract from pomegranate by-products as a new oenotannin. A decoction was prepared from mesocarp of the Wonderful pomegranate variety only using hot water as extracting solvent. The dried decoction was physical-chemically characterized and compared to 7 existing commercial oenotannins from different botanical origin (grape seed, oak, gallnut), according to UV-Vis Spectroscopy, Colorimetric analysis (CIELab), gelatin index, reactivity to proteins, HPLC-DAD, DPPH, and Total Polyphenols content by both Folin-Ciocalteu and the International Organization of Vine and Wine (OIV) methods. Data showed the lowest antiradical (AR) and total polyphenolic content (TPC) for the pomegranate tannin but also the highest AR/TPC ratio suggesting a good radical scavenging potential of this new tannin. Pomegranate tannin showed high reactivity with proteins, a unique chromatographic profile, and a low color impact. The new pomegranate tannin showed an interesting potential for oenological applications in particular for reducing the use of sulfites during vinification and for the white wine stabilization.
Highlights
The International Organization of Vine and Wine (OIV) authorized the use of oenological tannins to facilitate the clarification of wines and musts as long as they do not change the olfactory properties and the color of the wine [1]
The AA/total polyphenolic content (TPC) ratio was calculated in order to evaluate the antiradical activity on the basis of the total phenolic content
An extract from pomegranate by-products obtained by a green decoction process was characterized and compared to a series of oenotannins with different botanical origins in order to explain its potential use as oenotannin
Summary
The International Organization of Vine and Wine (OIV) authorized the use of oenological tannins to facilitate the clarification of wines and musts as long as they do not change the olfactory properties and the color of the wine [1]. Several types of oenological tannins are present in the market mainly differing in chemical structure, botanical origin, and/or preparation process. These include (i) hydrolyzable tannins, as gallotannins from oak galls, tara, myrabolan fruits, and nut galls, and ellagitannins from chestnut and oak; (ii) condensed tannins from grape seeds and skins, mimosa, quebracho, and acacia [2,11,12,15]. These, according to Okuda classification, are sub-classified as follow: gallotannins, characterized by several galloyl units linked each other by depside bonds (type-I hydrolyzable tannins) [24,25]; the intra- and/or intermolecular oxidative phenolic coupling to form C-C diaryland C-O diaryl- ether bonds between different galloyl residues gives rise to the formation of more than 1000 natural ellagitannins [26]. Oligomeric ellagitannins can be formed through intermolecular C-O oxidative coupling between different groups in two monomers [22,23,29]
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