Effect of harvesting periods and processing methods on carotenoid profile of yellow trifoliate yam flour

Abstract

Trifoliate yam (Dioscorea dumetorum) unlike other yam tubers are not harvested immediately after maturity but are left in the ground until needed as food due to hardening process which occurs few hours after harvesting. Yellow trifoliate yam pigment contains high carotenoids which are of benefit in human diet. Storage of trifoliate yam in the ground after maturity and processing of the tuber could have effect on the carotenoid contents of the tuber. Therefore, carotenoid profiles of yellow trifoliate yam flour as affected by periods of harvesting within four months of consecutives farming season and different processing methods was assessed. Freshly harvested yellow trifoliate yam was made into four treatments flour using four processing methods as follow: Raw Flour (oven dried at 60^oC), Soaked Flour (water deep at 29±2^oC) and dried (oven dried at 60^oC), Blanched Flour (water deep at 60^oC) and dried (oven dried at 60^oC), Parboiled Flour (water deep at 100±2^oC) and dried (oven dried at 60^oC). The treated flour samples were subjected to carotenoid profile using gas chromatography (model no HP6890 powered with HP ChemStation Rev. A 09.01 [1206] software). The major carotenoids detected in yellow trifoliate cultivar were carotene (31.61-81.03 μg/100 g) and β-cryptoxanthin (29.03-35.72 μg/100 g). Other carotenoids detected were viola-xanthin, lycopene, astaxanthin and antheraxanthin. Total carotenoids content (129.69 μg/100 g) of parboiled flour sample harvested at 7 months was higher than other samples. Harvesting of trifoliate yam tubers at 11 months provided yam with high concentration of carotenoids coupled with parboiling processing methods.

Keywords: Carotenoids, Harvesting periods, Processing methods, Yellow trifoliate yam