Investigating carotenoid loss after drying and storage of

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6. Effect of pre-treatment
degrade carotenoids (Baloch et al. 1977). A combination of sodium metabisulphite
(0.2%) plus salt (3%) was also shown to reduce carotenoids destruction in pre-treated
and dried carrots (Arya et al. 1982). Salting is an ancestral process of food preservation
that is still widely practiced in Africa and other parts of the world. Salting reduces
osmotic tension of cells increasing the stress on bacteria and enzymes that can degrade
food and its constituents such as carotenoids (Wijinker et al. 2006). In bread making,
sodium chloride (NaCl) has a positive effect on the preservation of carotenoids, because
it delays dough oxidation (King Arthur Flour Company 2009). It has been shown in the
case of carrot that soaking in 10% NaCl solution for 30 min at 20ºC and blanching for
2.25 min at 96ºC before air drying significantly improved carotenoid stability (Speck et
al. 1977). An alternative to salting is acidifying. Acidifying by addition of lemon or
tamarin juice is used as traditional preservation process in Eastern parts of Uganda
(Okwadi J, pers. comm. 2008). Acidity can help reduce enzymatic activity by lowering
pH value and in addition some acids have an antioxidant property (e.g. ascorbic acid).
Addition of ascorbic acid demonstrated a positive effect on the antioxidative activity of
dried carrots during storage (Yen et al. 2008). Therefore acidifying needed to be further
tested as a potential preservation of carotenoids.
The effect of low-cost pre-treatments on carotenoid retention during drying and storage
of sweet potato has been reported by very few authors (Singh et al. 2006) in comparison
with other roots or vegetables, such as, carrot. Therefore, there was a need to prove
whether these pre-treatments (single or combined) had a significant effect on carotenoid
stability in orange fleshed-sweet potato under conditions encountered in developing
countries. This study explored the impact of various pre-treatments to reduce losses after
drying and after storage (4-6 months) at ambient temperature in Uganda.
6.2 MATERIALS AND METHODS
6.2.1 Sweet potato root samples
Roots were collected from Wobulenzi, Luwero district, Uganda. Roots were of Ejumula
(deep-orange-fleshed) and Kakamega (light-orange-fleshed) varieties. Mature roots (80
kg per variety for two trials) were harvested after a growing season of six months.
Within a day after harvest, roots were washed and drained. All drying trials were carried