Effects of ultrasound assisted extraction on the physiochemical, structural and functional characteristics of duck liver protein isolate

This work investigated the impact of ultrasound assisted extraction on the physicochemical, structural and functional properties of duck liver protein isolate (UDLPI). Degreased liver powders were extracted by ultrasound working at a single frequency of 24 kHz and a fixed power of 266W by a pulsed on-time of 2 s and off-time of 3 s for 42 min in pH11.2 solution. The results revealed that UDLPI yield and the protein content increased by 67.7% and 4.6% respectively compared to that of the conventional alkaline extraction (DLPI). Ultrasound treatment could cause partial protein hydrolysis and unfolding as suggested by differential scanning calorimetry, circular dichroism and fluorescence spectroscopy analysis, leading to increased surface hydrophobicity, surface net charge and gelling property. The particle size reduced from 177.8 nm of DLPI to 156.0 nm of UDLPI. Ultrasound also promoted the storage modulus (G') and solubility of the isolate. Moreover, the foaming expansion was especially strong, compared to DLPI. However, the results of the foam stability, reactive-/total-sulfhydryl groups and sodium-dodecyl sulfate-polyacrylamide gel electrophoresis showed no significant change between UDLPI and DLPI (P>0.05). Therefore, UDLPI with better functional property could be utilized as new materials in the food industry. (C) 2016 Elsevier Ltd. All rights reserved.