Surface rheological properties of hydroxypropyl cellulose at air–water interface

Hydroxypropyl cellulose (HPC) is a neutral polysaccharide derived from cellulose. It is, notably, added to non-dairy whipped topping. However, if the function of HPC is well recognized, its behavior is not well known. The interaction of HPC with each component (dispersed fat droplets, emulsifiers, proteins) should be studied step by step. In order to understand better the function of HPC, air–water interfacial rheology was used to characterize the behavior of HPC at this interface, with and without emulsifier. As HPC is a flexible polymer, it shows, at room temperature, a medium value of intrinsic viscosity, which is of the same order as of galactomannan ones. Addition of HPC in the aqueous phase leads to a decrease of the air–water surface tension (down to about 45–41 mN/m) where xanthan and guar gum have smaller or negligible effect. The time to reach the equilibrium of surface tension is reached after several hours. The smaller the concentration, the longer it is to reach the equilibrium. The competition between HPC and palmitic ester (E473) was studied. Kinetics of surface tension evolution of E473/HPC systems are different from that of HPC alone: mixed systems and HPC show an evolution of surface tension in three steps that could be explained through E473/HPC competition for the air/continuous phase interface.