Rheological changes in nixtamalised maize starch
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In Mexico, a great deal of maize lines are growth, most of them go through the process of nixtamalisation (lye treatment at boiling temperature) to produce masa, which is used to mainly elaborate tortillas. During this process, the heat treatment brings about biochemical reactions, cross-links and molecular interactions that modify the physicochemical, structural and rheological properties of the masa as well as those of the tortillas produced. A high percentage of these changes is due to modifications in the structure of starch, the main chemical component of maize. Control starch (S) was isolated from a lot of maize and another lot of the same maize sample was subjected to lye treatment to obtain nixtamalised starch (NS). Rheological studies were carried out to determine its amylographic profile (Bravender), following a heating-cooking-cooling kinetics. Flow curves were carried out at 25 °C and 40 °C (heating-cooling, 25 °C–90C °C–40 °C), using a strain controlled rheometer (TA Instruments AR-1000) with a cone and plate system, angle of 1°. The dynamic oscillatory tests were carried out in a heating-cooling kinetics (25 °C–90 °C–25 °C) with the same geometry (angle of 1°), in dispersions with 10%(w/V) of total solids. Maximum viscosity and molecular dissociation were higher in the control starch. The flow curves show that all samples (S and NS) behave as Newtonian fluids at 25 °, which shifts to a shear-thinning behaviour at 40 °C and show a more pronounced tendency. In the dynamic tests, all starch gels obtained present weak viscoelastic gel-like behaviour predominating the elastic or storage modulus (G′) over the viscous or loss modulus (G″) during the three stages of the heating-cooling kinetics. According to tanδ values, nixtamalised starch forms amorphous gels, while control starch starch produces gels with a crystalline structure.
Key wordsnixtamalisation starch rheology zea mays
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