The HPLC method has not been used in a routine analytical fashion. This method uses cacao bean tannin extract for the determination of grape seed tannin molecular weight. Cacao bean extract contains procyanidin polymers consisting solely of epicatechin subunits which results in well separated, easily identifiable molecular weight markers. Since grape based tannins contain the same class of subunit, their retention characteristics are similar to cacao bean tannins. Quantification was achieved by comparing the peak areas of the grape extracts with that of an epicatechin standard. In order to apply this method in a routine fashion, additional method validation was performed and the reproducibility was determined. Based on the cacao bean extract, this method is capable of achieving a reproducibility of between 3.4%and 10%in the molecular weight range of 300-2100. Using this method, grape seed extracts have been analyzed. This method has the ability to quantify phenolics over a large molecular weight range, from 290 molecular weight units to about 3800 molecular weight units. This translates to a vast amount of information that can be obtained from extracts. From the vineyards studied this year, several trends can be seen in the extracts. First, the overall extractibility of the seeds decreases over time in both vineyards. Second, the amount of monomeric material extracted into solution decreased over time. Finally, the proportion of the extract which is made up of polymeric material (material having >6 subunits) increases as the grapes mature. Information on sample reproducibility was obtained using data gathered on all samples. In general, it was determined that the reproducibility was very good using the sampling technique used. In the worst case, berry weight and sugar reproducibility was 8.8%and 1.4%respectively. The reproducibility of grape seed extracts was determined also, and ranged form 3.9%for monomeric material to 27%for the polymeric material. Sensory analysis of wines made this year indicated that there was a significant increase (p=0.05) in astringency in both vineyards as the maturity of the grapes increased. When these wines were analyzed by HPLC, polymer concentration increased as astringency perception increased. Bitterness also increased in the wines as the grapes matured although the differences were much less significant. These results are inconsistent with the grape seed data, where the extractability of the seeds decreased as grapes matured. One possible explanation is that the high sugar levels in the grapes result in a higher alcohol concentration which can extract more tannin material from the seeds. Additional work is needed to study this possible relationship.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF1995-11-16 13:49:302017-11-16 13:50:29New Parameters to Measure Ripeness