Technological aspects of bread affecting protein structure and digestibility

As one of the main food crops commercialized and consumed in the world, the importance of wheat is mainly due to the viscoelastic properties of the gluten network, determining the quality of several bakery products. Although it has remarkable technological properties, wheat or its components can induce adverse reactions in susceptible individuals, such as wheat allergy, celiac disease and non-celiac gluten sensitivity. Wheat is rarely consumed without processing, which alters its physicochemical structure and, consequently, its physiological function in the human body. These structural changes can affect gluten digestion and trigger some immune reactions. Research on the effect of technological changes on the gluten structure and the consequent impact on the immune response is still incipient and there are no clear rules for this correlation. Several additives are used in baking to strengthen the gluten network structure. Ascorbic acid, due to its role as an oxidizing agent, contributes to the formation of cross-links between proteins through disulfide bonds (SS). On the other hand, the use of organic acids, such as acetic acid present in vinegar, to improve bread preservation, can cause hydrolysis of proteins and the weakening of the gluten network, due to changes in protein configuration. In the present work, breads were formulated with the addition of ascorbic acid and vinegar, which were compared with control samples. These incorporations were able to modify the rheological behavior of the doughs and some technological properties of the breads. Vinegar contributed to a reduction of pH and an increase in acidity, both in dough and bread. The addition of 2% and 4% vinegar to the formulation resulted in a decrease in dough development time by 35.54% and 43.87% and a reduction in stability by 16.26% and 19.77%, respectively. In the fundamental rheological evaluation, a reduction in dough viscoelasticity was observed, with a decrease in elastic modulus (G') and an increase in tan δ (G''/G'). These results were associated with the formation of a more open and less dense network, as observed in confocal microscopy. With the addition of ascorbic acid, resistance to extension was increased by 49.88% and 62.56% and extensibility was reduced by 19.19% and 24.92% for samples with 100 ppm and 200 ppm of ascorbic acid, respectively, which indicated the formation of a stronger dough. Ascorbic acid contributed to an increase in G', demonstrating that the doughs formed were more viscoelastic and resistant to flow. This result is also consistent with the analysis of free sulfhydryl content, which showed an increase in SS bonds promoted by the oxidizing agent. Samples were digested in vitro and the results can contribute to a better elucidation of the impact of the structural modifications caused by additives on digestibility and immunogenicity of gluten proteins.