Effects of tea and illicium verum braise on physicochemical characteristics, microstructure, and molecular structure of heat-induced egg white protein gel

Abstract Tea and illicium verum are the main raw materials of marinated egg, and play an important role in the braising process. In this study, effects of tea and illicium verum braise on the physicochemical characteristics, microstructure, and molecular structure of the heat-induced egg white protein gel were investigated. Results indicated that, with an increased in tea and illicium verum concentration, all of the moisture content, T2 and pH of tea treated boiled egg (TTBG) and illicium verum treated boiled egg (ITBG) showed a decreased trend. The water holding capacity of TTBG showed an increased first and then remained unchanged, while that of ITBG showed a rapid increased first and then decreased continually. The free sulfhydryl group and the hardness of both TTBG and ITBG showed an increased rapidly, and especially, the hardness of ITBG reached 2161.83 g at last. The surface hydrophobicity of TTBG showed an overall increased trend, while that of ITBG showed a decreased trend with a slight red-shift. Environmental scanning electron microscopy showed that TTBG gradually formed small compact aggregates, while ITBG gradually formed hypertrophy porous aggregates. Fourier transform infrared spectrometry displayed that the intramolecular β-sheets of both TTBG and ITBG showed a decreased trend, while the intermolecular β-sheets, α-helices, β-turn and intermolecular antiparallel β-sheets showed an increased trend. In general, both tea and illicium verum could improve the gel strength of boiled egg, but in a different way, and the effect of illicium verum braise on the strength of enhancing gel was better than that of tea.