Abstract
In this study, the physicochemical properties of microwave-assisted cassava starch-stearic acid complex was investigated. The effects of the modification methods were assessed using a scanning electron microscope, differential scanning calorimeter and rapid visco analyser. Native cassava starch showed mostly polygonal shape with some granules irregular and round in shape. Native cassava starch with added stearic acid had slight changes in shape while microwaved cassava starch showed irregular and dented granules with pin-holes or fissures. Native cassava starch modified with stearic acid alone or microwaved cassava starch with added stearic acid showed decreased swelling power as compared to the native starch. Pasting properties of cassava starch were significantly affected by stearic acid addition or microwaving. Stearic acid addition alone reduced the peak viscosity slightly (approx. 7%), adding stearic acid to microwaved cassava starch reduced the peak viscosity by approximately 9%, while microwaving cassava starch-stearic acid mixture showed greater reduction in peak viscosity (approx. 19%). Pasting of native or microwaved cassava starch with stearic acid resulted in the formation of type I amylose-lipid complexes, with melting temperatures ranging from approx. 92 to 102oC. Microwaving can improve complexation of stearic acid with cassava starch to produce modified starch with higher thermal stability and increased final viscosity
Highlights
Cassava (Manihot esculanta Crantz) is a root widely consumed in many parts of the world including Africa
Pasting of native or microwaved cassava starch with stearic acid resulted in the formation of type I amylose-lipid complexes, with melting temperatures ranging from approx. 92 to 102oC
The average size of the native cassava starch granules ranged between 4 and 10 μm, which is in the range of values (2-20 μm) reported for cassava starch (Rolland-Sabaté et al, 2013; Rolland-Sabaté et al, 2012; Zhu, 2015)
Summary
Cassava (Manihot esculanta Crantz) is a root widely consumed in many parts of the world including Africa. It is a good source of starch, which may be explored in various industrial applications due to its remarkable characteristics such as high freeze-thaw stability, high paste viscosity and clarity which are advantageous for applications industrially (Nwokocha et al, 2009). Cassava starch represents a valuable ingredient in food and pharmaceutical industries, in the native form, the starch is unsuitable for most industrial applications This is because native starches generally they have poor resistance to processing conditions such as shear, pH and heat frequently encountered in the industry. Researchers are focusing on the use of environmentally friendly method such as the use of natural chemicals e.g. lipids (Oyeyinka et al, 2018; Oyeyinka et al, 2017a) and physical methods such as microwaving (Lewandowicz et al, 2000; Oyeyinka et al, 2019)
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