Effects of different preparation methods on the physical, chemical and functional properties of protein powders from Skipjack tuna (Katsuwonus pelamis) liver

Tuna livers (TL), which are often discarded as waste, are a valuable source of protein for human consumption. However, the preparation method used affects the nutritional and functional characteristics of protein powders. This work aimed to investigate the effects of different preparation methods on the physical, chemical, and functional properties of tuna liver protein powders (TLPPs) following heat (H) treatment, heat and ultrasound-assisted (HU) extraction, alkaline pH shift (APS) process, and supercritical carbon dioxide fluid (SC-CO2 ) extraction. H at 85°C (H85), HU at 80 kHz and 100 W (HU-80-100), APS at pH 11.5 (APS 11.5), and SC-CO2 at 350 bars (SC-CO2 -350) resulted in the remarkably highest total protein content among the different preparation conditions. All TLPPs, except for APS 11.5, showed lighter color characteristics. The most abundant amino acids in all TLPPs were glutamic acid, aspartic acid and alanine. The protein solubility and foaming capacity were efficiently improved by SC-CO2-350. Nevertheless, the emulsion properties and oil holding capacity were greatly enhanced by H85 and HU-80-100, and a significant foaming stability and water holding capacity were found in APS 11.5. Therefore, the TLPPs obtained following different preparation methods are unique and could be potentially utilized as a source of protein ingredients in several food systems.