Effect of time and storage conditions on the rheological properties of masa for corn tortillas
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The effect of storage conditions prior to handling (resting time and use of packaging) on the rheological behavior of corn masa for tortillas was evaluated. Lubricated squeezing flow methods were used at compression rates (crosshead speeds) of 0.1, 0.3 and 1.0 mm.s-1. The squeezing flow technique successfully assessed the increase in biaxial extensional viscosity, B, as a function of resting time, that is, masa becomes slightly tougher with time. The biaxial extensional viscosity of unpackaged corn masa increased significantly (P<0.05) with resting time (0 to 5 h) while changes for packaged masa were not significant. The squeezing flow method demonstrates that the biaxial extensional viscosity of corn masa, for all resting times and storage conditions, shows extensional-thinning characteristics. Hence, this property was modeled using the power-law analogy asB =KB(B)n-1, for a biaxial strain rate of 0.003 to 0.05 s-1. The relationship between biaxial extensional viscosity and biaxial strain rate, B, for packaged and unpackaged masa was described asB =22.8 -0.86BandB =[26.6 e0064t]-085B, respectively. Results encourage the use of a packaging material (such as commercially available low density polyethylene) to maintain the masa as fresh as possible prior to forming and sheeting into tortillas. 1999 Academic Press.
