Produce Degradation Pathways and Prevention

Produce Color and Appearance 213

resulting in a bathochromic shift of maximum light absorption to a higher wave
length of 540 nm, causing color to be red. Betaxanthins constitute the second
subgroup of betalains. Due to the missing extended conjugation in betaxanthins the
maximum light absorption is approximately 480 nm and the resulting color is yellow.

7.5.2 CHEMICAL CHANGES DURING PROCESSING AND STORAGE

The stability of betalains is affected by pH, temperature, light, water activity, oxygen,
and interaction with other compounds. Various factors affecting betalains’ stability
were reported in a comprehensive review of carotenoids, anthocyanins, and betalains
published by Delgado-Vargas et al. (2000). The betalains are relatively stable in a
wide range of pHs from 3.5 to 7.0. The optimal pH range is 5.5 to 5.8 (Huang and
vonElbe, 1987). Mild alkaline conditions lead to the degradation of betanin and
formation of betalamic acid (BA) and cyclodopa-5-O-glucoside (CDG). These two
compounds are also formed during heating of betanine under acidic conditions. The
formation of BA and CDG is reversible, with optimal regeneration at a pH range
from 4.0 to 5.0 (Huang and vonElbe, 1985). In water solutions, heating causes a
graduated reduction of red color and brown discoloration of betanin. The degradation
rate increases after exposure to light (vonElbe et al., 1974). Ascorbic acid and
isoascorbic acid decrease the light-induced oxidative degradation of betalains, and
metal chelators such as EDTA or citric acid increase the stabilizing effect of ascorbic
acid (Bilyk et al., 1981; Attoe and vonElbe, 1984). Water activity significantly
influences the stability of betalains (vonElbe, 1987). The degradation of betanin in
beet powder follows first-order kinetics, with the lowest rate at low water activity

FIGURE 7.8Betacyanins.

N

N

H

HOOC COOH

H

H

COO

R

HO^1

2

(^43)
5
6
7
8
9
10
(^1112)
14
19 15
16
17
18
20
13