Abstract
This study evaluates the capacity of four hydrolytic enzymes to limit the interactions between grape cell-walls and tannins and/or to favor tannin desorption. Adsorption and desorption tests were conducted by mixing a commercial seed tannin with purified skin cell-walls from Syrah grapes, in the presence or absence of hydrolytic enzymes, in a model-wine solution. The effects of the enzymes were evaluated by measuring the tannins in solution by High Performance Liquid Chromatography (HPLC) and the changes in the cell wall polysaccharide network by Comprehensive Microarray Polymer Profiling (COMPP) while the polysaccharides liberated from cell walls were analyzed by Size Exclusion Chromatography (SEC). The results showed that the enzymes limited the interaction between tannins and cell walls, especially cellulase, pectinase and xylanase, an effect associated with the cell wall structural modifications caused by the enzymes, which reduced their capacity to bind tannins. With regards to the tannin desorption process, enzymes did not play a significant role in liberating bound tannins. Those enzymes that showed the highest effect in limiting the adsorption of tannins and in disorganizing the cell wall structure, cellulase and pectinase, did not lead to a desorption of bound tannins, although they still showed a capacity of affecting cell wall structure. The results indicate that enzymes are not able to access those polysaccharides where tannins are bound, thus, they are not a useful tool for desorbing tannins from cell walls. The practical importance implications of these findings are discussed in the manuscript.
Highlights
The concentration and composition of phenolic compounds are important parameters impacting the quality of wine, since they contribute to key wine organoleptic characteristics, like color and its stability, astringency, bitterness and aroma [1]
41.8% of the tannins become adsorbed after interaction with cell walls in the absence of enzymes
Syrah cell walls present a high capacity of binding tannins, they are lower than that reported for Monastrell cell walls, indicating that the cell wall–tannin affinity is influenced by the grape variety
Summary
The concentration and composition of phenolic compounds are important parameters impacting the quality of wine, since they contribute to key wine organoleptic characteristics, like color and its stability, astringency, bitterness and aroma [1]. Tannins and anthocyanins are the major phenolic compounds extracted from the skins and seeds of the grapes during the red wine vinification process and a high concentration of these compounds in wines has been correlated with higher projected market prices [2]. Phenolic compounds are located inside the cells. Cell-walls act like as a barrier to the extraction of the phenolic compounds present in the grape. Cell wall degradation will determine the extraction rate/speed of phenolics [5]. There are differences in the extraction rates of anthocyanins and tannins between varieties and this could be due in part to differences in the structure and/or composition of their cell walls [6]
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