We studied pectin’s effect on the analysis of tannins in our precipitation assay, and found that the order in which the assay components were added determined whether or not precipitation was inhibited. If pectin was mixed with tannin before tannin was exposed to protein, then there was a marked inhibition of the amount of tannin precipitated. However, if the tannin was mixed with the protein prior to the addition of pectin, then there was no effect on the amount of tannin precipitated. We used citrus pectin and carboxymethylcellulose (CMC) and determined that the amount of citrus pectin required to inhibit the tannin assay by 50%was approximately 500 ng/ml whereas CMC showed 50%inhibition at about 70 ug/ml. We extracted water-soluble and EDTA soluble pectin from grape berries and found that water-soluble pectin does not inhibit tannin precipitation, but EDTA soluble fraction can. However, EDTA soluble grape pectin has a much higher 150 (1400 ug/ml) in the assay than either citrus pectin or the CMC. Thus, since the water-soluble grape pectin was ineffective at all levels tested, and the EDTA soluble pectin was only marginally effective, this result indicates that it is highly unlikely that grape pectin will interfere with the tannin solution assay. We studied tannin development in Cabernet Sauvignon, Pinot noir, Syrah and Zinfandel. Zinfandel looked very similar to Cabernet Sauvignon but compared to Cabernet Sauvignon, Syrah had more tannin in the seeds than the skins at harvest. Even though the Syrah seeds contained more than twice as much tannin as Cabernet seeds, the wine made from the Cabernet fruit had 2.4 times as much tannin (1414 mg/1) as the wine from the Syrah fruit (585 mg/1). This points to tannin extraction as being more important for the amount in the resulting wine than the amount in the fruit at harvest. In the course of experiments to determine if the “background” absorbance in our tannin assay represented polymeric pigments, we found that protein precipitation separated the polymeric pigments into two classes that we have designated LPP for large polymeric pigments, and SPP for small polymeric pigments. We devised a combined procedure based on protein precipitation and traditional SO2 bleaching methods to allow measurements of SPP and LPP in wines along with the determination of total tannin. Thus, we have extended the scope of the solution assay and we are able to use the assay to provide a direct measure of the polymeric pigments in wines.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF1999-10-18 10:34:342017-10-18 10:35:13Development of a New Assay to Measure Tannins in Grapes and Wines