Table 819

Characterization and Chemical Tests to Study Betalain Structure

Method

Spectroscopy

Hydrolysis of betacyanins

Hydrolysis of betaxanthins

Heating Alkali fusion

Betaxanthin synthesis

Formation of neoderivatives Color

Evaluated Characteristic

Red-violet betacyanins: Xmax = 540 nm

Yellow betaxanthins: Xmax = 480 nm

Acid: with dilute aqueous HCl; yields mixtures of aglycones in both isomeric forms, 15R and 15S epimers

Enzymatic: produces only the 15S isomer

With aqueous 1 N HCl or 0.6 N ammonia: produces betalamic acid and free amino acids

Betanin is broken into betalamic acid and cyclo-DOPA 5-O-glucoside

Betanidin is split into 4-methylpyridine-2,6-dicarboxylic acid and formic acid; methodology used to reveal the carbon structure: betanidin produces betanin-isobetanin in a ratio of 3:2, whereas with isobetanin the ratio is 2:3

Betanin in 0.6 N ammonia solution is mixed with an amino acid 10 M; if the amino acid is glutamic acid, then vulgaxanthin-II is the betaxanthin

Betalain is mixed with diazomethane in methanol solution to form the corresponding methyl esters

Evaluated by tristimulus colorimetry; in red beet cultivars, b values may be used as an estimation of the betaxanthin-betacyanin ratio

DOPA = 5,6-dihydroxyphenylalanine.

Source: Adapted from Delgado-Vargas et al. (2000).17

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