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Abstract:

The thermo-active serine peptidase aqualysin 1 (Aq1) of Thermus aquaticus was applied in bread making to study the relative contribution of thermoset gluten to bread crumb texture. Aq1 is active between 30 °C and 90 °C with an optimal activity at 65 °C. However, this peptidase is inactive during mixing, fermentation and the initial baking phase as it is inhibited by wheat endogenous serine peptidase inhibitors. Therefore, it starts hydrolyzing gluten proteins during baking above 80 °C when the enzyme is no longer inhibited. Most of the starch is then gelatinized and a thermoset gluten network is formed. As both phenomena coincide, it is difficult to evaluate the relative contribution of the physico-chemical changes in both polymers on final bread crumb texture and structure. Protein extractability with sodium dodecyl sulfate containing medium from bread crumb increased with 20% when Aq1 was added to the recipe and the molecular weight (MW) distribution of gluten proteins shifted from higher to lower MW. This suggests a less coherent gluten network structure in bread with Aq1. However, no differences in specific volume nor in crumb structure were observed between breads containing Aq1 and control bread. Texture profile analysis showed a rather small but significant impact on textural parameters such as hardness, cohesiveness, resilience, springiness and chewiness. In addition, Aq1 clearly impacted crumb coherence as the crumb was perceived to crumble more easily. The discrepancy between the impact of Aq1 on the gluten network on the one hand and the small textural differences on the other hand indicates a key role for starch in bread crumb texture, whereas thermoset gluten seems to be important for the crumb coherence.