Development and characterization of products from selected varieties of sweet potatoes (Ipomoea batatas L.) in Uganda

Abstract

This research aimed to develop and characterize sweet potato products from selected varieties from Uganda as a potential raw resource for the food processing sector. The selected local varieties included Sukali, New Kawogo, Mubalila Bbali, Njule, Nakakande, and Kasanda and the hybrid varieties included Narospot 1, Naspot 12, Naspot 8, and Naspot 13. The sweet potato varieties (both local and hybrid) were sourced from a multiplication farmer at Bombo, Luweero district and brought to the laboratory for analysis. The varieties were characterized for their vitamin A content, total polyphenols, starch, protein, fiber, ash, carbohydrate and dry matter content. The starch extracted from the sweet potatoes was also characterized. Sweet potato products, including bread, cakes, cookies, instant porridge and meal powder were developed using Naspot 13 and Kasanda. The instant porridge and meal were made by incorporating sweet potato flour with silverfish, egg, and milk powders, followed by extrusion cooking and milling. These products were evaluated for texture, rheological properties, and other nutritional attributes. The selected local and hybrid sweet potato varieties exhibited significant variation in both skin and pulp color. The dry matter content ranged between 29.5% in Nakakande and 42.8% in New Kawogo. Beta-carotene content varied between 6.48 μg/g in Sukali and 65.56 μg/g in Njule. Polyphenol content ranged between 0.178% and 0.554%, in Naspot 8 and Kasanda respectively. pH values ranged between 6.42 and 7.60 in Kasanda and Nakakande respectively. Crude ash content varied between 0.25% and 1.67%, with Nakakande and Naspot 13 having the lowest and highest values. Crude fat content ranged between 1.67% and 5.50%, with Narospot 1 and Naspot 12 having the lowest and highest values. Crude fiber content ranged between 2.22% and 4.50%, with Mubalila Bbali and Naspot 8 having the lowest and highest values. Protein content ranged between 1.79% and 4.77%, with Mubalila Bbali and Naspot 8 having the lowest and highest values. Moisture content ranged between 57.2% and 70.5%, with New Kawogo and Nakakande having the lowest and highest values. Total carbohydrate content ranged between 21.8% and 32.2%, with Njule and New Kawogo having the lowest and highest values. Regarding the physicochemical characteristics of the extracted starch, its water holding capacity ranged between 0.81 g/g and 1.20 g/g; Peak viscosity ranged between 10834 cP and 14399 cP; trough viscosity between 1081 cP and 5353 cP; breakdown between 6671 cP and 10194 cP; final viscosity between 3101 cP and 5867 cP; setback viscosity between 152 cP and 2803 cP. Peak time varied between 3.4 seconds and 4.1 seconds, and pasting temperature ranged between 73.2°C and 78.9°C. The developed products i.e. bread at 30% sweet potato flour inclusion and cakes & cookies upto 80% sweet potato flour inclusion exhibited good sensory and consumer acceptability. While increase in amount of sweet potato flour led to firmer textures and reduced sensory acceptance, moderate inclusion (up to 10-12.5%) offered a good balance between optimizing substitution and maintaining consumer preferences. The proximate composition and texture of bread, cookies, and cakes made from sweet potato flour (Naspot 13 & Kasanda) varied according to the formulation. These products exhibited good sensory and consumer acceptability comparable to those made with 100% wheat flour. The vitamin A and beta-carotene content were notably higher in products derived from Naspot 13 (orange-fleshed variety). The formulated meal and porridge, which included silverfish, egg, and milk powders, had varying protein content averaging 15%. Sensory acceptability varied based on milk powder and silverfish content. In conclusion, the selected Ugandan sweet potato varieties (both local and hybrid) demonstrated favorable functional properties and can be effectively used to produce high-quality baked products at high levels of wheat substitution, especially in cakes and cookies.