Investigating carotenoid loss after drying and storage of

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6. Effect of pre-treatment
with our results, no difference in β-carotene content between sulphurated (by burning
element sulphur in an enclosed place) and un-treated (non-sulphurated) apricots after
drying in hot air or in sun was shown by Karabulut et al. (2007). After drying, however,
samples treated with sodium metabisulphite or ascorbic acid had better content than
samples soaked in deionised water (Table 6-5). Working on pineapple and papaya, Siahn
and Ishak (1990) also reported an improvement of total carotenoid content using sodium
metabisulphite (0.2%; 0.4%; 0.6%) after drying with deionised water as a control.
However, in another study by Yen et al. (2008) working on pre-treatment with a solution
of ascorbic acid (0.1%) + glucose (1%) showed that diced carrots treated with this
solution and then hot air or freeze dried had significantly better β-carotene content than
un-soaked ones, and disagrees with our results. These divergences in results after drying
between authors could be the result of the differences in food products composition, type
of chemical added and incorporation of the chemical in the food matrix.
After a typical storage period for dried sweet potato (4-6 months), there was no
significant effect of sodium metabisulphite (0.5%) as compared with un-treated or
deionised water-dipped samples (Table 6-6). Working with diced orange-fleshed sweet
potato pre-treated with 0.2% sodium bisulfite for 5 minutes at room temperature, Cinar
(2005) also did not show improvement in half life of metabisulphite-treated samples
after 120 days at 4ºC or 25ºC. Losses of β-carotene from dried carrots after 12 months at
room temperature (22-26ºC) with deionised water as control; 0.05% and 0.2% sulphite
treated were 60%; 56% and 59% respectively (Zhao and Chang 1995). This was in
accordance with our results that showed that there were few differences between
untreated and sodium metabisulphite treated samples after six months. In contrast,
Baloch et al. (1987) showed that soaking carrots in sodium metabisulphite before
dehydration had significant effect on carotenoid retention after drying and after storage
at 37ºC for 440 days (14 months). Carotenoid retention was further improved when in
addition to sulphiting carrots were also blanched. The differences of results with sodium
metabisulphite might be explained by the incorporation of sulphite into the product
which may further influence the degradation of sulphite in storage (Baloch et al. 1987).
Zhao and Chang (1995) described a sharp decrease in residual sulphite content in
sulphite-treated carrots over storage (92% loss in 12 month). Sulphite may be lost by
reaction with disulfide groups or thiols in proteins and low molecular weight