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Summary Wheat starch was extrusion cooked with the addition of three commercial vegetable oils, namely; palm oil, soybean oil and sunflower oil. The effects of the addition of the oils on the degree of starch conversion as well as extrudates expansion were investigated. In order to conduct a comparison between the three added oils, the barrel temperatures, material feed rate, water content and finally the screw speed were fixed. The three selected oils were added at concentrations varied from 1% to 8% on starch dry basis and the quantities added were controlled through the whole process. The results suggested that for the three vegetable oils used, the specific mechanical energy (SME) was decreased as the oil concentration increased up to 5% and further rise in concentration did not impart significant changes. This drop in the SME values was accompanied with a decrease in the extent of starch conversion. This was assessed by rapid viscosity analyser (RVA) viscosity and water solubility and absorbance measurements. The effect of the addition of oil on extradites’ sectional expansion was complex in which a significant increase until 5% oil concentration was reached and further increase of oil quantities resulted in a drastic reduction. This effect was observed for all three oils and no significant differences between oils were noticed. All extrudates exhibited a v-type crystalline pattern which was ascribed to the amylose lipid complex formation. However, the crystallinity indices indicated no interference by the three oils to the complex formation. This suggested that the endogenous lipids naturally present in wheat starch were sufficient to complex the starch. |
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