Sensory and nutritional quality of orange-fleshed sweet potato crisps from roots with varying physico-chemical properties

Abstract

The sensory and nutritional quality of orange-fleshed sweet potato (OFSP) crisps can be optimized by utilizing storage roots with suitable physical and chemical properties. Three root types from the OFSP cultivars Impilo, Bophelo and 199062.1 were evaluated for physico-chemical composition in both raw and deep-fat fried state. Frying significantly lowered the L*, a*, b*, E, h and C colour values for all three root types making the crisps darker compared to raw slices. The dry matter content (%) of Impilo, Bophelo and 199062.1 roots were 19.0, 23.1 and 27.2 respectively. The low dry matter Impilo tubers had the highest glucose content while the high dry matter 199062.1 roots had the lowest, with Bophelo roots intermediate for both the dry matter and glucose content. Deep-fat frying significantly increased the oil content in the crisps. Crisps from high dry matter roots (199062.1) had significantly lower oil content (25.7 %) compared to those from medium dry matter roots (Bophelo) (32.6 %) and low dry matter roots (Impilo) (35.6 %). This reflects the influence of the physical and chemical properties of the root (e.g. dry matter content) on oil absorption. Medium to high dry matter root (Bophelo and 199062.1) crisps had higher stress and hardness values than low dry matter root (Impilo) crisps based on a compression test. High dry matter root (199062.1) crisps had significantly higher first fracture deformation values compared to low dry matter root (Impilo) crisps, with Bophelo root crisps intermediate. Crisps prepared from roots of three OFSP cultivars (Impilo, Bophelo and 199062.1) and four other commercial crisp products (butternut, pumpkin, sweet potato and carrot) were further evaluated using Flash Profile (FP) sensory methodology. The sensory profiles of crisps from Bophelo and Impilo roots were more similar and were perceived as more orange and darker, harder, sweeter and less oily compared to 199062.1 crisps. The colour, appearance and flavour of OFSP crisps was influenced by the type and content of sugar in roots, with higher glucose and fructose content in Impilo tubers resulting in darker and sweeter flavoured crisps compared to crisps from Bophelo and 199062.1 roots. The higher β-carotene content of Bophelo roots produced crisps with more intense orange colour, while crisps from 199062.1 roots had the least intense orange colour. OFSP crisps were more orange and darker in colour, and were sweeter relative to commercial samples High dry matter (199062.1) and high trans-β-carotene (Bophelo) roots can be used to produce value-added crisps with low oil, high trans-β-carotene content and with desirable textural and appearance properties for consumer acceptance. The physico-chemical variations of the OFSP storage root types affect the sensory and nutritional quality of deep-fat fried crisps and this could be exploited in crisp product diversification, in efforts to meet the varied and dynamic sensory expectations of consumers. Using roots with high dry matter (e.g. 199062.1), and high β-carotene content (e.g. Bophelo) in the production of OFSP crisps could optimize product texture, oil content, colour and β-carotene content when compared to root types of low dry matter content (e.g. Impilo). OFSP roots from 199062.1 cultivar may be an ideal choice for cost-effective low fat OFSP crisps with considerable β-carotene content. Low fat crisps would be in tandem with current nutritional thinking on the health benefits of low fat food.