Optimization and physicochemical properties of nutritional protein isolate from pork liver with ultrasound‐assisted alkaline extraction

The aim of this study was to investigate the optimal conditions of ultrasound‐assisted alkaline extraction ( UAAE ) on pork liver protein isolate ( UPLPI ) and its physico‐chemical properties. Response surface methodology was used to determine the optimal conditions for UAAE , which were at ultrasonic power 265 W, ultrasonic time 42 min, Na OH concentration 0.80%, temperature 50°C, and solvent/raw material ratio 70. The extraction yield and efficiency of UPLPI were significantly improved over the conventional alkaline extraction ( PLPI ). The results of amino acid composition showed that UAAE could increase serine (36.5 g/kg), arginine (38.1 g/kg), alanine (37.5 g/kg), proline (48.7 g/kg), phenylalanine (55.6 g/kg) and lysine (47.2 g/kg) elution amount. The changes in fourier transform infrared spectra indicated unfolding and destruction of the protein structure in UPLPI . The differential scanning calorimetry analysis presented UPLPI with a slightly lower onset and peak denaturation temperature over PLPI . Surface hydrophobicity increased and the microstructures presented larger and more pores of UPLPI , therefore, it had better in vitro digestibility than PLPI . Therefore, UPLPI might have a potential application prospect in the food field due to its changes on molecular structure as well as on the microstructure of protein by UAAE .