Extrusion of casein and whey protein isolate enhances anti-hardening and performance in high-protein nutrition bars

Model high-protein nutrition bars (HPNBs) were formulated by incorporating whey protein isolate (WPI) and casein (CN) at various extrusion temperatures (50, 75, 100, 125, and 150 °C) with a protein content of 45 g per 100 g. The free sulfhydryl groups, amino groups, hardness, and microstructures of HPNBs were analyzed periodically at 37 °C over a storage period of 45 days. Specifically, sulfhydryl group, amino group and surface hydrophobicity of extruded whey protein isolate (WPE) and extruded casein (CE) were significantly reduced (P < 0.05) compared to those of unextruded protein. HPNBs formulated with WPE (HWPE) and CE (HWCE) exhibited a slower hardening rate compared to those formulated with unmodified protein. Moreover, the color difference, hardness and sensory score of HPNBs after 45 days of storage were used as indicators, and the results of the TOPSIS multiple index analysis indicated that HPNB formulated with WPI extruded at 150 °C possessed the best quality characteristics.