Spectrophotometric and chromatographic studies of the principal pigments in evergreen blackberries and Alicante Bouschet grapes Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/765373860

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  • Spectrophotometric and chromatographic methods were employed to study the principal pigments in Evergreen blackberries and Alicante Bouschet grapes. Observations were made on the following items: 1. Juices expressed from the grape and blackberry 2. Principal pigments isolated from the grape and blackberry. 3. Wines made from the grape and blackberry. A Coleman Universal Spectrophotometer, Model No. 11, equipped with a single grating 35 millimicron fixed band, was used for the spectrophotometric study. Observations were made at the visible range of 400 millimicrons to 650 millimicrons at 50 millimicron intervals. Various concentrations of the juices, pigments, and wines were examined. The experiments were repeated with the samples made alkaline to pH 9 with sodium hydroxide. Blackberry wine mixed with 10, 20, 30, 40, and 50 per cent of grape wine were also examined in the sane manner. Results were shown graphically by plotting the E values against wave lengths. It was found that solutions of the higher concentrations always have the higher E values. In the spectrophotometric study, an absorption peak appeared at the 500 millimicron band in the blackberry juice which was not observed in the case of grape juice. The height of the peak was directly proportional to the concentration of the juice and it was unmeasurable when the juice was diluted to 5 per cent or lower. When the juices were made alkaline, all of them had the identical absorption curves except that the blackberry had its curves in higher positions than those of grape. Approximately twice the amount of anthocyanin pigments were isolated from the Evergreen blackberry than Alicante Bouschet grape. The principal pigments isolated from the blackberry were more intense in color than those from the grape. The isolated pigments of Evergreen blackberry and Alicante ouachet grape behaved similarly under the spectrophotometer, indicating that, qualitatively, the same pigments were obtained from blackberry and grape while using the same isolation procedure. Spectrophotometric study of the wines showed that the E values of blackberry wine were inversely proportional to the addition of grape wine. This appeared to be true in both acid and alkaline solutions. By adding 80 per cent of the alkali required to bring the wine to pH 9, more differences in E values between the various mixtures were observed. During the chromatographic atudy, using corn starch as adsorption material, a green band of approximately 1 cm deep was observed in the case of grape wine, which was absent in blackberry wine. The process of wine making changed the quality of pigments as demonstrated in the chromatographic adsorption tubes. The use of acid solution and alumina adsorption mixture as studied by Hamill and Simonds seems more promising than alkaline solution as used in the present study for the detection of in grape wine blackberry wine.
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