Carbohydrate composition and amylase activity of sweetpotato (Ipomoea Batatas) root

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AUGUST, 2016
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Selection of sweetpotato clone(s) for production and utilisation depends on its quality attributes especially sugars, dry matter, starch content and amylase activity. The levels of these attributes are however influenced by factors such as the diversified production environments, cooking treatments, and genotypic compositions. The aim of the study is to determine the range of variation and factors of significant influence on concentrations of these attributes during growth and processing of sweetpotatoes. Development of an efficient and accurate technique for rapid assessment of these quality attributes was also relevant to the study. In order to achieve the overall aim, two main approaches were adopted; varying the levels of identified factors that alter the concentration of the attributes, and using near-infrared reflectance spectroscopy technique to develop a prediction model for their assessment. Sugars (sucrose, glucose, fructose and maltose), starch, dry matter content, amylase activity and sweetness were evaluated at harvest, during heating and after cooking. Adaptive Main Effects and Multiplicative Interaction (AMMI) model was employed to ascertain the magnitude of interactions between the factors tested. It was established that concentrations of the quality attributes were significantly affected by all the factors examined. Genotype contributed the highest variability during the growth stage while cooking treatment produced the highest effect during processing. Effect of interaction was more pronounced on amylase activity compared to sugars, dry matter and starch content. Sucrose was the predominant sugar in the raw form while levels of maltose increased substantially during cooking. High precision calibration was also developed for evaluating sugars and starch content in cooked sweetpotato roots. Sweetpotato varieties in Ghana have a wide range of quality attributes, making it a versatile crop for many food applications. Nonetheless recommendation for specific application should consider choice of production environment and processing conditions, which have significant impact on the final quality of the processed product.
A thesis submitted to The Department of Food Science and Technology, College of Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Ph.D.).