The underlying mechanism of alkali-induced ovalbumin gel transforms to sol: Physicochemical properties, structure and quantitative protein degradation analysis

Different alkalinity could impart certain desirable properties to ovalbumin (OVA), such as improving gel texture or solidification time. In this study, the physicochemical properties, structural changes, and peptide-based quantitative analysis during degradation of OVA treated with 1.25%, 1.5% and 1.75% NaOH solutions at different time were investigated. With the extension of time, the hardness, water holding capacity, particle size, surface hydrophobicity of OVA gel and the number of peptides increased dramatically, and then decreased gradually regardless of alkalinity. By contrast, the pH and springiness of OVA gel exhibited a steady downward trend. Rheological behavior revealed that the OVA gel network degraded from a high viscosity semi-fluid to an aqueous sol. The ordered gel structure was mainly contributed by beta-sheets, accompanied by constantly conversion of alpha-helices, while the liquefaction was caused by the destruction of those regular secondary structures. LC-MS/MS showed that only a small number of common peptides were obtained at different time of protein degradation, and more similar sequences were observed in peptides generated in one day. In summary, it was concluded that although alkali-induced OVA showed a definite gel-sol transformation, the underlying mechanism could not be precisely expressed by degradation into peptides of specific sequences.