Protein nanofibrils from mung bean: The effect of pH on morphology and the ability to form and stabilise foams

Protein nanofibrils (PNFs) have potential food uses due to their favorable mechanical and rheological properties. In order to use plant-based protein nanofibrils (PNFs) in new sustainable food applications, a better understanding is needed of the impact of pH on PNFs and their functional properties. In this study, we developed an improved method for generating PNFs from mung bean protein isolate and its globular 8S fraction. We then investigated how these PNFs are affected by increased pH and how pH affects their ability to form stable foams. PNFs were generated in acidic conditions (pH 2) by heating at 85 °C for 2–48 h. Formation of PNFs and the effect of increased pH on their stability were evaluated using thioflavin T fluorescence, electrophoretic gel separation, circular dichroism spectroscopy, atomic force microscopy and viscosity profiling. Foams were made by intense mixing with a homogeniser and evaluated for foam capacity, foam stability and bubble size distribution, using confocal imaging. The results showed that it is possible to optimise the fibrillation conditions for mung bean by generating a more pure initial protein isolate by salt extraction. The results also showed that pH alters the structure of PNFs by degradation and aggregation around the isoelectric point of the protein isolate. At neutral pH, the PNFs were slightly shorter than at the starting pH, but no longer formed aggregates. Fibrillated mung bean protein at pH 4–8 was found to have good foaming properties compared with non-fibrillated protein at the same conditions. The new knowledge generated in this study about how pH alters the structure and foaming properties of PNFs can pave the way for use of PNFs in new innovative food applications.