Investigating carotenoid loss after drying and storage of

32
1. Literature review
Isomerisation can occur in provitamin A carotenoids at temperatures above 35ºC. 9-cis is
predominantly formed above 100ºC whereas 13-cis and 15-cis are formed below 100ºC
(Doering et al. 1995).
Figure 1-18: Isomers of β-carotene. Rodriguez Amaya and Kimura (2004).
Chandler and Schwartz (1988) reported that processes that most induce cis-isomerisation
in OFSP were (in order of less to more damaging): steaming, blanching, pureeing,
microwaving, canning, baking and drum drying. Shade and sun drying did not initiate
cis-isomerisation in the examples found in literature (Kidmose et al. 2007; Mulokozi and
Svanberg 2003) on OFSP or leafy vegetables respectively. The same observation was
made by Kidmose et al. (2007) working with one variety of OFSP roots called Zappalo
and shade dried. These findings should be verified working on different varieties of
OFSP and different drying technologies.
Oxidation
Autoxidation
Because of their conjugated double bond system that absorbs free radicals, carotenoids
protect the photosynthetic apparatus from the damage of harmful oxygen species (Naik
et al. 2003). Conjugated double bounds and the electron rich system of carotenoids also
induce instability toward oxidation because of attraction for electrophilic molecules
(Siems et al. 2005). Oxidation (enzymatic or non-enzymatic (autoxidation)) is
considered to be the major cause of loss of provitamin A activity during processing and
storage. Oxidation occurs through a free radical process. Free radical reactions are