Investigating carotenoid loss after drying and storage of

Comparison of losses in drying processes
Artificial and natural drying
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1. Literature review
Working on drying only, there has also been a large variation of losses reported with
dryers and food commodities. Trans-"-carotene lost after sun-drying and oven cabinet-
drying of OFSP Jonathan variety was 72% and 47% respectively, and after sun-drying
and cabinet-drying of Kakamega variety, 83% and 28% respectively (Kósambo 2004).
Hence trans-"-carotene content was half in sun-exposed OFSP chips compared to
cabinet-dried chips (58°C for 4 hours). Working on other crop than sweet potato, Chavez
et al. (2007) similarly reported that losses in cassava were lower in oven drying
compared to shade and sun drying (28%, 41% and 62% respectively). It has been shown
that sun, solar and shade drying generated more β-carotene losses than oven drying on
leaves (respectively 70%, 68%, 65% and 45%) (Negi and Roy 2000). In general, in the
different food commodities studied, artificial drying (e.g. fan-operated oven cabinet) has
been reported to retain more provitamin A than natural drying (shade, solar and sun)
(Rodriguez-Amaya 1997; Van Hal 2000; Kósambo 2004).
There were however exceptions. In another study on OFSP there were no significant
differences between oven (57°C for 10 hours), solar and sun drying (6-10h) (12%, 9%
and 16% respectively) (Bengsston et al. 2008). A study on total carotenoids in various
fruits also showed that losses in an oven dryer at 50-60ºC were similar to losses in the
sun (respectively 11% compared to 13%) (Vedrina-Dragojevic et al.1997). In both
studies levels of carotenoid losses were low and this could explain the lack of
differences between artificially and naturally operated dryers.
Solar, shade and sun drying
Few publications have been found on carotenoid retention in natural drying processes
(solar, shade and sun drying). Carotenoid losses were higher in sun drying compared to
solar drying on OFSP in a study by Stollman et al. (2005) (respectively 9% and 13% on
Ejumula variety and 15% and 29% on Kakamega variety). Greater retention in solar
drying as compared to sun drying can be explained by sun light filtration. It has been
shown that exposure to light especially sun-light or UV light may induce trans-cis
photomerisation and photodegradation of carotenoids (Rodriguez-Amaya and Kimura
2004). Working on leafy vegetables (sweet potato, pumpkin, amaranth leaves etc), solar