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Purified preparations of leucoanthocyanins from several sources were heated in butanol-hydrochloric acid solutions from 50 degrees to 90 degrees C and the rate of production of cyanidin was measured. From the temperature dependence of this rate, the calculated energy of activation was of the order of magnitude of 20,000 calories. The rate-limiting step in this reaction was similar for two preparations tested, and of lower energy for a third, presumably of lower degree of polymerization.
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Joslyn et al. (1964) studied this question.
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