Mechanochemical-assisted extraction of protein from watermelon seeds with surfactant

Abstract Mechanochemical-assisted extraction (MCAE) was first applied to extract total protein from watermelon seeds with grinding medium of surfactant instead of alkaline. The optimal conditions of MCAE, that is, sodium bis(2-ethylhexyl)sulfosuccinate (AOT) concentration of 0.10 mol/L, water content of 20, ionic strength of 0.05 mol/L, aqueous phase pH of 7, solid to liquid ratio of 0.2 g/mL, ball milling speed of 523 rpm and ball milling time of 10.5 min were obtained by response surface methodology. The highest yield (489.967 ± 1.214 mg/g) of watermelon seeds protein (WSP) was obtained under the optimal conditions, which corresponds to an increase of 19.7% in comparison with that extracted by conventional alkaline extraction. When considering the secondary structure of protein by FTIR and SEM analysis, the random coil structure of watermelon seeds protein was obviously increased and protein aggregations were apparent by conventional alkaline extraction, suggesting the denaturation of WSP under relatively alkaline environment and no loss of protein activities with surfactant interactions, thus MCAE with surfactant retained the better quality of WSP. The results indicated that MCAE with surfactant could be a protective and effective method for the extraction of natural oil-seeds protein.