Investigating carotenoid loss after drying and storage of

2
1. Literature review
Foundation Project led by the HarvestPlus Challenge Program (Reaching End Users) to
promote the use of orange-fleshed varieties that have a high β-carotene content.
HarvestPlus is a global alliance of research institutions seeking to improve human
nutrition in developing countries by tackling micronutrient deficiencies in iron, zinc and
vitamin A. HarvestPlus focuses on biofortification of staple food crops (cassava, sweet
potato, maize, rice, bean, millet) that are consumed by the poor. Currently the
biofortified sweet potato varieties have shown to be capable of reducing vitamin A
deficiency in studies on children in sub-Saharan Africa (Jalal et al. 1998; van Jaarsveld
et al. 2005; Low et al. 2007).
The Natural Resources Institute of the University of Greenwich is leading the product
development, processing and marketing component of Reaching End Users Project of
HarvestPlus. Dried sweet potato can be used in the formulation of a variety of food
products such as composite flours, bakery products etc. The work reported in this thesis
contributed to this initiative in Uganda and Mozambique with the overall objective of
quantifying and understanding the mechanism of losses of carotenoids during the drying
and subsequent storage of sweet potato. The outcome of this research should help low-
income farmers and food processors use dried orange-fleshed sweet potato (OFSP) that
could potentially contribute to tackling vitamin A deficiency.
1.1.2 Vitamin A deficiency
Vitamin A or retinol is essential for human metabolism. Its main function is in the visual
cycle in the retina of the eye, but it also plays an important role in growth and
development and reproduction, and in the immune system (FAO/WHO 2002). Other
functions of vitamin A are not yet fully understood, for example, regarding its role in
regulation of gene expression (FAO/WHO 2002).
Vitamin A is found in the diet in two forms. In animal foods, preformed-vitamin A is
found as retinyl esters of fatty acids linked to membrane bound-cellular lipids and fat
containing storage cells. In plants, precursors of vitamin A called carotenoids are
associated with cellular lipids and implanted in cellular structures (FAO/WHO 2002).
Preformed vitamin A from meat is more bio-available than carotenoids from plants.
However, in developing countries, meat is generally not affordable for most poor people.