Subcritical water hydrolysis of eggshell membrane and its physicochemical characteristics

The insolubility of eggshell membrane (ESM) limits it application. This study utilized a green process subcritical water (SW), to prepare soluble ESM and compared it with acid hydrolysis. The effect of SW temperature on the yields of total protein, free amino acids, and glycosaminoglycan in the hydrolysate was investigated. Hydrolysates generated at 180-210 °C exhibited the highest protein (40.57 ± 2.40 mg/g ESM concentrate), peptides (20.36 ± 0.43 mg/g), hyaluronic acid (8.19 ± 0.34 mg/g), and chondroitin sulfate (11.68 ± 0.76 mg/g) content. Acid hydrolysis exhibited significantly lower protein hydrolysis (p < 0.05) and total free amino acid content than subcritical water hydrolysis. Collagen was observed in the SW hydrolysate, and its secondary structure transformed from the stable α-helix to unstable β-aggregates as the temperature increased. Scanning electron microscopy confirmed the disruption of the ESM fiber. SDS-PAGE analysis further revealed the presence of low-molecular-weight peptides in the hydrolysate. Compared to acid hydrolysates, hydrolysates obtained from SW exhibited higher degree of hydrolysis, and therefore, demonstrated greater free radical scavenging activity. Hence, SW hydrolysates can be used to develop functional foods from ESM. These results provide promising future directions for preparing active ESM.