The Mechanism Underlying the Increase in Bread Hardness in Association with Alterations in Protein and Starch Characteristics During Room-Temperature Storage

Hardness constitutes one of the primary performance indices of bread. However, there is scarce literature regarding the study of the mechanisms of increased hardness in different breads. In this paper, the hardness and retrogradation rates of five popular brands of bread (DaliGarden, Mankattan, MianLunSi, TOLY, and ZhengMao) in China during storage at room temperature were determined, and the mechanism of increased hardness was revealed by the results in terms of Fourier transform infrared spectroscopy (FTIR), disulfide bonds, ¹³C solid-state nuclear magnetic resonance (NMR), X-ray diffraction, and differential scanning calorimetry (DSC). The results showed that the sequence for the degree of hardness increase among the five bread brands was DaliGarden > TOLY >Mankattan > MianLunSi > ZhengMao. The bread hardness was likely associated with the gliadin content; the more gliadin, the higher the hardness of the bread. All bread hardness values underwent a rapid increase during storage at room temperature. The hardness level of the bread preferred by Chinese individuals was approximately 105 g, and the hardness of the TOLY bread underwent relatively minor changes during storage at room temperature. The disulfide bond content of all breads apart from Mankattan decreased during storage at room temperature. The increase in the hardness of the bread was attributed to the ordered configuration of the amylopectin structures resulting from water evaporation. The results given in this paper offer a practical hardness index to control the quality of bread. This study is expected to contribute to better quality control and optimization in bread production, enhancing consumers' satisfaction and extending products' shelf lives.