Structure of whey protein emulsion gels containing capsaicinoids: Impact on in-mouth breakdown behaviour and sensory perception

This work investigated the sensory perception of whey protein emulsion gels containing capsaicinoids, in relation to their structure and in-mouth breakdown behaviour. The gel structure was modified by varying the oil droplet size and the ionic strength. Eighteen human subjects were used to investigate oral processing behaviour and sensory perception. The gels were classified into three groups according to their rheological properties: semisolid gel (10 mM NaCl with d(4,3) of similar to 0.17 mu m); soft and elastic gels (10 mM NaCl with d(4,3) of similar to 4, 1 and 0.5 mu m); hard and brittle gels (100 mM NaCl with d(4,3) of similar to 4, 1, 0.5 and 0.17 mu m). A power-law relationship between gel hardness and masticated bolus particle size was established: Y = 25.38X(-0.29), with R-2 = 0.69, indicating that greater hardness led to smaller bolus particle size. A power-law relationship between mouth burn perception and bolus particle size was also established: Y = 119.5X(-0.25), with R-2 = 0.76, indicating that mouth burn perception was positively related to the degree of fragmentation. A higher degree of fragmentation led to greater surface exposure during mastication and, therefore, a greater possibility of capsaicinoid molecules being released. Moreover, an increase in gel hardness led to a lower diffusion rate of capsaicinoid molecules through the gelled particles and, therefore, to lower mouth burn perception. The effects of oil droplet release after mastication and saltiness perception were less important than the degree of fragmentation and gel hardness.