Flavour degradation in dehydrated convenience foods: changes in carbonyls in quick-cooking rice and Bengalgram dhal

The carbonyl profiles of quick-cooking rice and Bengalgram (Cicer arietinum) dhal are reported. Freshly processed rice contained formaldehyde, acetaldehyde, acetone, butanal and hexanal, while freshly processed Bengalgram dhal contained 2,4-decadienals, propanal and 2-enals in addition to the above compounds. Incorporation of vanaspati (hydrogenated vegetable oil) and refined sunflower oil enhanced the proportion of acetone in quick-cooking rice and dhal. On storage, the proportion of hexanal, 2,4-decadienal and 2-heptenal, 2-octenal and 2-none-nal increased, while the proportion of acetone decreased considerably. The concentration of total carbonyls increased considerably on storage. Most of the additional aldehydes were formed from the oxidative degradation of lino-lenic and linoleic acids which decreased on storage. The rate of autoxidation, as measured by changes in peroxide value, was highest in untreated rice and dhals followed by samples containing refined sunflower oil, while the samples containing vanaspati autoxidized the slowest.