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ABSTRACT
Effects of protease and transglutaminase (TG) on dough and tortilla microstructures, shelf-stability, and protein profile were determined to infer the role of gluten in tortilla staling. Control and enzyme-treated tortillas were prepared using a standard bake test procedure and evaluated for three weeks. Confocal micrographs of control dough showed thin protein strands forming a continuous web-like matrix. Protease-treated dough had pieces of proteins in place of the continuous matrix, while TG-treated dough had thicker protein strands that were heterogeneously distributed. Control tortillas had a well-distributed continuous protein structure. Protease-treated tortilla had a continuous structure despite being composed of hydrolyzed proteins in the dough, while the TG-treated tortilla retained clumps of proteins. Both treatments resulted in shorter shelf-stability of tortillas. An evenly distributed and moderately stronger gluten network is necessary for longer retention of tortilla flexibility. Solubility of protein fractions differed among treatments, but molecular weight distribution did not differentiate control and treated dough or tortillas. The proportion of each protein fraction appears to affect staling.
Cereal Chem. 85(3):295-300
Flour tortillas firm when they are stored at 0-35°C, with the greatest firming at 22°C (Kelekci et al 2003). On the other hand, corn tortillas, which stale mainly through starch retrogradation, lose flexibility faster at refrigerated temperatures (3-10°C) than at higher or lower storage temperatures (Bueso et al 2006). This implies that components other than starch (e.g., protein, pentosans) may be involved in flour tortilla staling.
Flours with higher protein content produce tortillas that are more shelf-stable. Flours with 10.2% protein produced tortillas that lost flexibility faster than flours with >11.0% protein (Suhendro et al 1993), and an evaluation of 61 commercial tortilla flours also showed that those with 11.0-11.5% protein content yielded more shelf-stable tortillas (Waniska et al 2004). Addition of commercial wheat protein fractions to the tortilla formulation likewise improves tortilla shelf-stability. Vital wheat gluten, glutenin, and gliadin significantly retained tortilla flexibility longer (Pascut et al 2004). However, only gliadin had comparable diameters with the control, thus tortilla quality would benefit more from an increase in extensibility, which is a gliadin functionality.
Enzymes are used in the baking industry to improve dough and baked product quality. Thus, protein-modifying enzymes may be tools to determine the roles of protein in tortilla staling. Proteases...