Functional and thermal properties of nanofibrillated whey protein isolate as functions of denaturation temperature and solution pH

Nanofibrillated whey protein was obtained through heating native whey protein isolate (WPI) at 80 and 90 degrees C under acidic conditions. Then, structural, functional and thermal properties of nanofibrillated WPI at different pH levels of 2, 4 and 6 were measured and compared with the non-treated protein as a control. The results obtained by atomic force microscopy showed that the rate of fibril formation increased by increasing fibril formation temperature while the stability of nanofibrillar structures decreased at higher pH values. The extent of intermolecular beta-sheets significantly increased at a higher temperature and lower pH levels as monitored by Thioflavin T fluorescence spectrophotometry and Fourier transform infrared spectroscopy (FTIR). Nanofibrillated protein showed higher oil and water absorption capacities and better foaming properties compared to the control. Therefore, increasing the extent of fibrillar structure enhanced the functional properties of nanofibrillar whey protein. By increasing pH levels, the heat resistance of fibrillar structure decreased and the melting temperature of the fibrillated samples shifted to lower temperatures when stabilized at higher pH levels. Overall, nanofibrillar proteins at different pH showed significantly better functional properties and higher heat resistance compared to the native protein. Therefore, protein nanofibril can be commercially suggested as an additive to improve functional properties of food products.