The dynamics of starch hydrolysis and thickness perception during oral processing

While it is known that salivary amylase changes perceived thickness in starch-based foods, the dynamics of oral breakdown of starch has not been related to that of sensory perception. This work examines the associations between in-mouth oral breakdown of starch by α-amylase and thickness of a semisolid product measured instrumentally and using a sensory panel. Pureed carrots made with added waxy maize (w/w) (0% (control), 0.4% (S0.4) and 0.8% (S0.8)), were tested for dilution and hydrolysis effects with the addition of water and saliva and measuring viscosity (shear of 10 s^-1), viscoelasticity (10-0.01 Hz at 0.1% strain) and maltose release. Sensory testing was conducted using progressive profiling. Control and S0.8 pureed carrots showed similar viscosities at 10 s^-1 while S0.4 was lower. Addition of saliva had the highest impact on viscosity drop for S0.8. Viscoelastic properties of pureed carrots decreased with starch addition which decreased further with water/saliva incorporation. Starch breakdown measured in terms of maltose release did not change with starch concentration and oral processing times. Unlike instrumental viscosity results, perceived thickness of purees increased with starch concentration. During oral processing, thickness decreased at a constant rate across all samples highlighting the dilution effect of saliva. A relation was observed only between oral viscosity and starch hydrolysis and not rheological measurements. This indicates that changes in starch hydrolysis during oral processing can be used as an indicator of rate of drop in perceived viscosity in starch-based semi-solid foods such as pureed carrots.