Vulgaxanthine

Cohen, E. and Saguy, L, A rapid method of determination of betanin and vulgaxanthin 1 in beet powder using a general purpose tristimulus colorimeter, Ztschr. Lebensm. Unters. Forsch., 175, 31, 1982. 

FIGURE 13.7 Structures for the representative betalains vulgaxanthin I (betaxanthin) and betanidin (betacyanin). 

Betalains, the pigments of the red beet, have found increased use as food colorants. This unit describes a multiple-component system using visible spectrophotometry to determine the concentration of the pigment components (i.e., betacyanins and betaxanthins) calculated in terms of betanin and vulgaxanthin-I, respectively (see Basic Protocol 1). The total pigment content (betalain) is expressed as the sum of betacyanins and betaxanthins. 

In the first protocol (see Basic Protocol 1), the maximum light absorption of betanin, the major betacyanin, and vulgaxanthin-I, the major betaxanthin, are measured. The betanin and vulgaxanthin contents are calculated using each pigment s 1 % absorptivity value A,%. The method takes into account small amounts of interfering substances. 

Beet juice or beet extracts are known to contain other pigments (isobetanin, prebetanin, vulgaxanthin-II) besides betanin and vulgaxan-thin-I. The error that is introduced by calculating all betacyanins in terms of betanin and all be-... 

Figure F3.1.2 Calculation of betanin and vulgaxanthin-l in beet juice. Spectrum 1 vulgaxanthin-l spectrum 2 betanin spectrum 3 pure betanin plus vulgaxanthin-l and spectrum 4 beet juice.

Fig. 21 Calculation of vulgaxanthin-I and betanin s proportion of the absorption of beet root juice. Curve 1 Vulgaxanthin s proportion of the absorption. Curve 2 Betanin s proportion of the absorption. Curve 3 Betanin and vulgaxanthin without impurities. Curve 4 Fresh beet juice, including impurities. (From Ref. 216.)...

Fig. 22 HPLC separation of betalains in fermented red beet root extract, (a) Detection of betacyanins at 538 nm. Peaks 1 = betanin, 2 = isobetanin, 3 = betanidin, 4 = isobetanidin, 5 = prebetanin. (b) Detection of betaxanthins at 477 nm. Peaks 1 = vulgaxanthin I, 2 = vulgaxanthin II, 3 = betanin, 4 = isobetanin, 5 = betanidin, 6 = isobetanidin, 7 = prebetanin. (From Ref. 239.)...

Betanidin has three carboxyl groups (pka = 3.4), two phenol groups (pHa = 8.5), and asymmetric carbons at positions 2 and 15. The 15-position is easily isomerized under acid or basic conditions in the absence of oxygen to yield isobetanidin. Under alkaline conditions and in the presence of glutamine or glutamic acid, betanin can be converted to vulgaxanthin (Mabry 1970). 

On acid hydrolysis, miraxanthin II yields aspartic acid. The faet that the pigment has nearly the same electrophoretic mobility as the glutamic acid derivative vulgaxanthin II (44) indicates the presence of four carboxylic groups and excludes asparagine as part of the molecule. 

The following pigments were identified in admixture with other betaxanthins indicaxanihin (2), vulgaxanihin II (44), vulgaxanthin I (45), miraxanthin III (54), and betaxanthins derived from a-aminoadipic acid, valine, and leucine. 

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