Determination of vegetable tannin fractions using solid phase extraction and UV-VIS spectrophotometric technique

The correlation between low molecular mass catechins and catechin polymers in polyphenolic plant extracts was determined using the combination of solid phase extraction and UV-VIS technique. Grape seed and grape stem extracts of ten different grape cultivars were analysed during three vintages. Low molecular mass catechins were determined after solid phase extraction. Catechin polymers were calculated as the difference between catechins in raw plant extract and low molecular mass catechins. Low molecular mass catechins were present in higher amounts in the grape seed extracts (14.79 g/kg of grape seeds) than in the the grape stem extracts (4.36 g/kg of grape stems). The average relative amount of low molecular mass catechins was 56 % of total catechins in the grape seed, and 17 % in the grape stem extracts. Exceptionally high amounts of low molecular mass cate chins were estimated in the grape seed extracts of Plavac mall cv. and grape stem extracts of Okatica white cv. The average mass functions of catechin polymers, for analyzed cultivars were 11.78 g/kg of grape seeds, and 21.27 g/kg of grape stems. The ratio between low molecular masses of catechins and catechin polymers was about 1: 1 in the grape seed extracts, and 1:5 in the grape stem extracts.