The effects of flour types and storage temperatures on the staling of wheat flour tortillas

Abstract

Flours from 12 wheat cultivars, grown in two locations (Uvalde and McGregor) over two years (1999 and 2000), were processed into tortillas. The environment and cultivars affected protein content and quality, which significantly affected tortilla quality. Cultivars grown in McGregor had low protein and poor mixogram characteristics (<3.0 MU and long mixing time) and produced tortillas with short shelf stabilities. Some cultivars grown in Uvalde had high mixogram resistance (>3.8 MU and short mixing time), which produced thick, small and translucent tortillas. Some of the flours within the range of 3.0-4.5 MU and 10.5-13.0% produced good tortillas. Flour with higher mixing resistance and low protein content or lower mixing resistance and higher protein content produced good quality tortillas. This suggests that some combination of flour mixing resistance and protein content may be useful to predict tortilla quality. Tortillas were stored at -60, -12, 0, 4, 22, and 35⁰C to evaluate staling. Subjective rollability and two-dimensional extensibility tests measured changes in texture of tortillas. Frozen tortillas stored for over 25 days retained their fresh attributes. However tortillas staled more when stored at 22⁰C than at 0, 4, or 35⁰C. Tortillas stored at 0, 4, 22, and 35⁰C had increasing force, work and modulus of deformation values during storage. More staling occurred at 4⁰C for first 3 days and, then at 22⁰C after 7 days. Tortillas stored at 22⁰C and 35⁰C had less than two weeks shelf stability while tortillas stored under refrigeration had more than three weeks shelf stability. Tortillas began to stale at the optimum staling temperature of bread but much of the firming of tortillas occurred at a similar temperature to the staling of cakes (22⁰C). The higher temperature of optimum staling for tortillas suggests that more firming could be due to protein changes than from starch retrogradation. Measured flour properties did not directly correspond to improved tortilla qualities of larger diameter, increased opacity and longer shelf stability. Some combination of flour protein content and mixing resistance, however, may be useful to predict tortilla quality.