Relationship between protein structure changes and in vitro digestion of preserved egg white during pickling

In this paper, the relationship between protein structure changes and in vitro digestion of preserved egg white (PEW) during pickling was studied. Results showed that as the pickling time increased, moisture content of PEW exhibited a decreasing trend, pH value and hardness of PEW exhibited an increasing trend. Environmental Scanning Electron Microscopy (ESEM) revealed that alkali-treated duck egg white could form a more compact gel network structure during pickling. Transmission Electron Microscopy (TEM) showed that PEW consisted of two sorts of structures, namely fibrillar (from 7th to 21st day) and particulate (from 28th to 42nd day). Fourier Transform Infrared (FTIR) spectroscopy showed that there was an increase in the content of β-sheets and a decrease in the content of α-helices during pickling. Protein digestibility of PEW was highest at day 14 and the lowest at day 42. Moreover, the content of β-sheets was negatively correlated with protein digestibility. Peptides identification using LC-MS/MS highlighted that the number of different peptides were positively correlated with the pickling. The number of unique peptides was negatively correlated with protein digestibility at the end of gastric and intestinal digestion. This study would provide guidance for studying nutritional value and controlling quality of preserved eggs.