On the reversibility of ethanol-induced whey protein denaturation

The functional properties of whey proteins after exposure to ethanol were studied. The reversibility of the ethanol-induced whey protein denaturation was investigated using different methodologies to remove ethanol, such as 10-fold dilution with water, oven-drying and freeze-drying of whey protein mixed water/ethanol solutions. The effect of ethanol on whey protein denaturation, before and after ethanol removal, was measured by analysis of difference-UV spectra, rheological measurements, confocal microscopy and differential scanning calorimetry. The results showed a retention of the denatured character of whey proteins (27-34%) after removal of ethanol. The study of the combined effect of ethanol and heat on whey protein denaturation at concentrations ranging from 10 to 70%, revealed that at an ethanol concentration of 50%, the initial extent of denaturation was maximum, while heat did not contribute any additional denaturation effect. A whey protein mixture, previously incubated in 50% ethanol and subsequently freeze-dried to completely remove ethanol, produced a gel in a cold-set gelation procedure, where gelation was promoted by addition of glucono-delta-lactone, without an initial heating step. The confocal microscope revealed significant microstructural characteristics suggesting that whey protein solutions retain a significant degree of denaturation even after ethanol removal. Differential scanning calorimetry results further showed that the presence of 50% ethanol decreased the denaturation temperature of whey proteins by more than 15 degrees C, while removal of ethanol by freeze-drying, similarly decreased the denaturation temperature by about 2 degrees C. Overall, whey proteins, exposed in ethanol, retain a significant degree of denaturation after removal of the alcohol, with possible applications as functional ingredients capable of modifying the mechanical properties of food systems.