Effect of ethanol on gelation and microstructure of whey protein gels in the presence of NaCl

The heat-induced gelation of whey proteins in the presence of sodium chloride (0-300 mM) and ethanol (0-70.0% w/w) has been investigated by confocal microscopy, texture analysis and rheology. In the presence of NaCl, the alcohol-induced gels had a low porosity and formed a "particulate" network, as evidenced by confocal microscopy. Even 1% of ethanol was able to form very elastic gels, to increase their rigidity 3 times, while the presence of 10% ethanol increased the storage modulus considerably compared to the native proteins without ethanol. The substantial effect of alcohol on gel stiffness was ascribed to non-covalent interactions (mainly hydrogen bonding) as well as to intra- and intermolecular disulfide linkages. The type of forces that prevailed were dependent on the ethanol content. Generally, the synergistic effect of ethanol, heating, and NaCl on the mechanical and microstructural properties of whey protein isolate gels might have useful implications for the development of new food products with various functionalities.