Screening sweet potato varieties commonly grown in Uganda for bread making

Abstract

Sweet potato (Ipomea batatas) is an important crop and alternative source of carbohydrates in Uganda. It is a good source of Vitamin C and E as well as dietary fiber, potassium and Iron, low in fat and cholesterol levels. The price of bread is high because most of the wheat is imported and the price could probably be lowered by substituting the portion of wheat with available locally produced materials like sweet potato flour or puree. The purpose of this research was to enhance the utilization options of locally produced sweet potato in the confectionary industry specifically by determining the local sweet potato varieties suitable for bread making. Five varieties (NKB 216, NASPOT 8, NASPOT 12 O, Ssemanda and NASPOT 11) were screened basing on their relatively high starch yield, high Amylose/Amylopectin ratio using proximate analysis, Megazyme method and also being commonly grown in Uganda. Out of the five varieties screened, two were processed into puree and flour which were used to substitute the wheat flour at 10%, 20%, 30%, 40% and 50% to determine the optimal substitution levels in bread. Sensory evaluation was carried out to determine the maximum market acceptable levels. Results showed that, bread acceptability increased as the substitution level of wheat with sweet potato flour or puree increased. Ssemanda and NASPOT 8 sweet potato substituted bread at 20% had the best quality. This was due to relatively high starch yield percentage (%) and high mylose/Amylopectin ratio of these varieties. Bread made from NASPOT 8 scored highly during sensory evaluation and was subjected to laboratory analysis. In addition, NASPOT 8 bread had higher β-carotene content (0.2 ± 0.06 RAE mg/100g) with high moisture content (34.4 ± 0.70%) compared to the control bread which had β-carotene content of (0.1 ± 0.01 RAE mg/100g) and moisture content of (43.6 ± 0.40%). During sensory analysis, sweet potato flour bread of Ssemanda variety of 20% substitution level scored highly (7.2 ±1.8) compared to the bread made from 20% mashed sweet potato of NASPOT 8 (5.9±1.7). Ssemanda is commonly grown in different parts of Uganda which means that it can easily be obtained by different processors of bread. It also has high amylose/ amylopectin ration (AML/AMP), it had high acceptable crumb structure and crust, qualities which physically attract the consumers before they decide of buying the bread thus making it a good variety to be used in bread.