Investigating carotenoid loss after drying and storage of

ABSTRACT
Biofortified orange-fleshed sweetpotato (OFSP) is being promoted to tackle vitamin A
deficiency, a serious public health problem affecting children and pregnant/lactating
women in sub-Saharan Africa. The aim of the study was to quantify and understand the
factors influencing carotenoid losses in dried OFSP. Losses were determined in chips
after drying and storage. A preliminary study demonstrated that carotenoid levels were
not significantly different following either solar or sun drying. Carotenoid loss after
drying was generally correlated with high initial moisture content and high carotenoid
content in fresh sweetpotato roots. Losses of pro-vitamin A were less than 35% in all
cases. Flour made from OFSP could therefore be a significant source of provitamin A.
In contrast, storage of chips at room temperature in Uganda and Mozambique for four
months resulted in high losses of pro-vitamin A (ca. 70-80% loss from the initial dried
product). Low-cost pre-treatments, such as blanching, antioxidants and salting, did not
reduce carotenoid losses during storage. Enzymatic catabolism of β-carotene in dried
OFSP was considered unlikely because of low peroxidase activities at low water
activities and the loss of peroxidase activity during storage. To understand further the
factors causing the losses, dried sweet potato chips were stored under controlled
conditions of temperature (10; 20; 30; or 40ºC), water activity (0.13; 0.30; 0.51; 0.76) or
oxygen (0 [under nitrogen]; 2.5; 10 or 21% [air]). Oxygen was the main cause of
degradation followed by temperature. An Arrhenius kinetic model was used to show that
carotenoid breakdown followed first order kinetics with an activation energy of
68.3kJ.mol -1 that was in accordance with the literature. Experimental observations fitted
well with data predicted by the kinetic model. The formation of the volatile compounds,
β-ionone; 5,6-epoxy-β-ionone; dihydroactinidiolide; β-cyclocitral that were clearly
related to the degradation of β-carotene, helped further understand breakdown patterns
of β-carotene.
IV