Inhibitory Effect of Cyclodextrins on the Discoloration Reaction of an Anthocyanidin, Pelargonidin Chloride, in Acidic Media |
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Authors: | Yoshihisa Matsui Aiko Sunouchi Tatsuyuki Yamamoto |
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Affiliation: | (1) Faculty of Life and Environmental Science, Shimane University, Nishikawatsu, Matsue, 690, Japan |
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Abstract: | An anthocyanidin, pelargonidin (PG), loses its color with time in acidic media. The rate determining step of the discoloration reaction at pH 1–4 is the nucleophilic attack of the OH- ion on PG to give a hemiacetal, which readily isomerizes to the corresponding -diketone. Native, branched, and methylated cyclodextrins (CDs) form inclusion complexes with PG to retard the discoloration. The inhibitory effect (copigmentation) of CDs on the PG discoloration is slight in -CD, significant in - and -CDs, and the largest in heptakis(2,6-dimethyl)--CD (DM--CD). The -CD and DM--CD include the phenyl moiety of PG, whereas -CD includes the benzopyrylium moiety of PG. The CD cavities protect the reaction site of included PG from the attack of the OH- ion. |
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Keywords: | cyclodextrin pelargonidin anthocyanin discoloration inclusion complex copigmentation NMR spectroscopy |
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