Potential Use of Selected Sweetpotato (Ipomea batatas Lam) Varieties as Defined by Chemical and Flour Pasting Characteristics

Agnes Nabubuya, Agnes Namutebi, Yusuf Byaruhanga, Judith Narvhus, Trude Wicklund

Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway.
Department of Food Technology and Nutrition, Makerere University, Kampala, Uganda.

DOI: 10.4236/fns.2012.37118                

Abstract

Chemical and functional properties of ten sweetpotato varieties were investigated. The sweetpotato were of various flesh colours which included orange, yellow, cream and white with dry matter content ranging from 30.2% - 39.2%. The sweetpotato varieties varied significantly (p < 0.05) in total amylase activity, total starch and amylose content whose value ranges were 0.256 - 0.570 mg/ml/min 68.4% - 73.6%, 16.2% - 23.4% respectively. The pH of flours from the different sweetpotato varieties ranged from 6.01 - 6.64. The pasting behaviours of the sweetpotato flours also showed significant differences (p < 0.05) in the individual parameters (peak time, pasting temperature, peak viscosity, trough viscosity, final viscosity, breakdown and setback) among the different varieties. The results revealed the influence of variety on the chemical composition of sweetpotato and their pasting properties. Correlations were also revealed among different components of the sweetpotatoes which would be a basis in selection of the varieties for processing into different products.

Keywords

Sweetpotato; Chemical Properties; Pasting Characteristics

1. Introduction

Sweetpotato (Ipomoea batatas Lam) is globally the sixth most important food crop with over 105 million metric tons produced annually [1]. Developing countries produce about 95% of the global sweetpotato. It is grown mainly in the tropics but has the ability to adapt to a wide range of climatic conditions [2]. Uganda is one of the countries with the highest annual per capita sweetpotato consumption in Africa [1]. There are several sweetpotato varieties in Uganda with different skin and flesh colours. On harvest, sweetpotato roots are stored mainly in rooms (in sacks) and in pits [3,4]. The pit is reported to be effective for at least 4 months and its use is constrained by rodents and rotting [3]. Sweetpotato can be used in various ways; boiled, steamed, baked, fried and also have the potential to be processed into various products [5]. In the developing world, they are most commonly consumed following boiling, steaming, roasting or drying [4]. Sweetpotatoes in sub-Saharan Africa are cultivated on subsistence rather than commercial scale due to lack of appropriate technologies for their utilization in food product development [6].

Sweetpotatoes have a number of physicochemical properties. They consist mainly of carbohydrates (80% to 90% of the dry weight of the roots), with starch being the most abundant component of the roots’ dry matter forming 50% - 80% [2]. The amylose/amylopectin ratio of sweetpotato starch influences the physicochemical properties of sweetpotato flour such as gelatinization, retrogradation, water absorption and pasting viscosities [7,8]. Sweetpotato contains endogenous amylolytic enzymes with the three major ones being α-amylase, β-amylase and starch phosphorylase [9]. These enzymes are important for the breakdown of starch into simpler sugars during storage and processing [10]. The presence of amylases in sweetpotato roots influences their utilization, especially in the food industry, due to the hydrolytic effect of the enzymes on sweetpotato starch which also affects the properties of the sweetpotato products. For industrial use of sweetpotatoes, there is need to have knowledge of their physicochemical properties and the effect that the different processing methods have on these properties and functionality of the different components.

Although significant varietal differences have been documented in sweetpotato physicochemical properties [6,11] there is need to assess the amylase activities of the different sweetpotato varieties and evaluate their relationship with the flour characteristics and products which can possibly be processed from them. Sweetpotatoes have great potential for utilization in the food industry for the production of a number of commercial products especially considering the fact that their starch content is high [2]. It is therefore important to get an understanding of the functional properties of the different sweetpotato varieties in order to ascertain the appropriate uses of the sweetpotatoes in food processing. The study was aimed at characterizing selected Ugandan sweetpotato varieties to determine their suitability for processing to specific products. Carbohydrate and pasting properties, and total amyloytic activities served as bench marks for the assessment.

2. Materials and Methods

2.1. Sweetpotatoes Materials

Table 1 shows the ten varieties of sweetpotato which were used in this study. The sweetpotatoes were grown in three replicates on an experimental plot in Luwero District in Central Uganda and were harvested at their physiological maturity ages (counted in months from the planting date).

Conflicts of Interest

The authors declare no conflicts of interest.

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