Gelatin increases the coarseness of whey protein gels and impairs water exudation from the mixed gel at low temperatures

To understand the origin of water holding of mixed protein gels, a study was performed on water exudation from mixed whey protein (WP)-gelatin gels upon applied pressure. Mixed gels were prepared with varying WP and gelatin concentration and gelatin type to obtain gels with a wide range of gel properties. Gels were characterized for their water holding (maximum of exuded water, A_max, and ease with which water can be exuded, k), gel coarseness (from CLSM image analysis) and gel stiffness (Young's modulus) at 20 and 40 °C, below and above the melting temperature of gelatin. Gelatin caused an increase in gel coarseness of the WP network, as induced by phase separation between WP and gelatin. The effect of gel coarseness and gel stiffness on A_max was found to be intertwined but above all, dictated by the gelatin concentration and gelatin network. At 20 °C, a transition point in gelatin concentration was observed above which stiffness surpassed coarseness in importance for A_max. Above this concentration, gelatin dominates the mechanical response of the mixed system. At 40 °C, when gelatin is melted, coarser and less stiff networks, as set by the WP network, lead to higher A_max. Tailoring of the coarseness and stiffness and therefore A_max and k, can be achieved by selective mixing in terms of protein concentrations, and type of gelatin. By varying gelatin type from A to B, altered phase behavior leads to gels with higher coarseness and lower stiffness but similar A_max.