A cooperative research by a Portuguese and a Chinese team evaluated the effect of adding tannins from seeds to the wine.
They analyzed two factors: the chromatic and the antioxidant characteristics.
They tested two commercial products: GSE100 and GSE300, both highly pure.
Two, finally, were the grapes considered: Castelao and Tinta Miuda.
The winemaking took place with fermentation on the skins and two different times of maceration, corresponding to wines rich or poor in polyphenols, respectively.
The products with natural tannins were added immediately before and after the alcoholic fermentation.
The phenolic composition, the chromatic characteristics and the antioxidant activity were evaluated by HPLC-DAD, CIElab 76 convention and DPPH test, respectively.
The results show that the adding of tannins derived from the seeds increases the color and the antioxidant activity, but only for wines poor in polyphenols.
Besides GSE300 contained higher quantities of di-procianidines and trimers of procianidines, and a lower quantity of polymeric proantocianidines, the effects on the increment of color and antioxidant activity were similar to the one registered by using GSE100.
Moreover, GSE100 released more gallic acid in wines than GSE300, besides it was not possible to reveal gallic acid in the GSE100 alone.
Finally, the research team discovered that the best results on the phenolic composition of wine were obtained by adding the products after the alcoholic fermentation.
Ana C. Neves, Maria I. Spranger, Yuqing Zhao, Maria C. Leandro, Baoshan Sun; Effect of Addition of Commercial Grape Seed Tannins on Phenolic Composition, Chromatic Characteristics, and Antioxidant Activity of Red Wine; Journal of Agricultural and Food Chemistry 2010 58 (22), 11775-11782.