Investigating carotenoid loss after drying and storage of

31
1. Literature review
Figure 1-17: Possible scheme for carotenoid degradation. Rodriguez-Amaya and
Kimura (2004).
Isomerisation
Carotenoids are found in nature as trans-carotenoids. Under stressful conditions such as
heating and UV-light exposure, trans-carotenoids are isomerised into cis-carotenoids (9-
cis; 13-cis and 15-cis for β-carotene). Isomerisation could be considered as a negative
effect of processing since cis-isomers have less provitamin A activity (about half) than
trans-"-carotene. In addition, Deming et al. (2002) showed, in gerbils, that cis-β-
carotene is less bioavailable than trans-β-carotene. This has been subsequently
confirmed in humans (Rodriguez-Amaya and Kimura 2004).
Several researchers have reported that the preferentially formed cis-isomers from all
trans-β-carotene are 13-cis and 9-cis (Chandler and Schwartz 1988). In the OFSP variety
Jewel (raw: 90µg.g -1 on a fresh weight basis), 13-cis was found to be predominant
following various processes (blanching, canning, lye peeling, pureeing, dehydrating,
microwaving, baking). A small amount of 9-cis and 15-cis were found in canned sweet
potato (Chandler and Schwartz 1988; Lessin et al. 1997) (Figure 1-18). Raw roots may
contain small amount of the 13-cis isomer if they are stored too long (Chandler and
Schwartz 1988). The quantity of isomer formed in processed products is related to the
heat and length of treatment (Chandler and Schwartz 1988; Doering et al. 1995).