Impacts of cold-extrusion whey protein isolate synergized with inulin on physicochemical characteristics of fermented milk

Abstract

Impacts of extruded whey protein isolate-inulin (EWPI-I) complexes with different inulin ratios (5%, 10%, and 15%) on the textural, sensory, and rheological characteristics of fermented milk were investigated in this work. The addition of inulin to both EWPI-I and WPI-I complexes in ratios of 0–15% resulted in a gradual increase in apparent viscosity, water holding capacity (WHC), viable counts, and consistency index K of fermented milk. However, these properties decreased during the storage period (P < 0.05). Rheology analysis revealed that the consistency index K of EWPI-I fermented milk was higher than that of WPI-I fermented milk within 14 days of storage due to the formation of high molecular WPI polymers induced by extrusion. Principal component analysis (PCA) showed that EWPI-15%I (inulin ratios of 15%) fermented milk exhibited the best characteristics among all fermented samples. Furthermore, hardness, adhesion, chewiness and WHC of EWPI-15%I fermented milk were 261.13%, 298.31%, 480.40% and 38.24% higher than those of untreated fermented milk. It was observed that on the first day of storage, the viability of S. thermophilus and L. bulgaricus in EWPI-15%I fermented milk increased by 2.99% and 3.14%, respectively, compared to untreated samples. The proliferation of S. thermophilus and L. bulgaricus was found to be more conducive with combination of EWPI and inulin. Therefore, EWPI-I complex could remarkably improve water holding capacity and rheological properties of fermented milk, which will be applied for developing fermented dairy products with high quality characteristics.