Predicting thickness perception of liquid food products from their non-Newtonian rheology.

The "mouthfeel" of food products is a key factor in our perception of food quality and in our appreciation of food products. Extensive research has been performed on what determines mouthfeel, and how it can be linked to laboratory measurements and eventually predicted. This was mainly done on the basis of simple models that do not accurately take the rheology of the food products into account. Here, we show that the subjectively perceived "thickness" of liquid foods, or the force needed to make the sample flow or deform in the mouth, can be directly related to their non-Newtonian rheology. Measuring the shear-thinning rheology and modeling the squeeze flow between the tongue and the palate in the oral cavity allows to predict how a panel perceives soup "thickness". This is done for various liquid bouillons with viscosities ranging from that of water to low-viscous soups and for high-viscous xanthan gum solutions. Our findings show that our tongues, just like our eyes and ears, are logarithmic measuring instruments in agreement with the Weber-Fechner law that predicts a logarithmic relation between stimulus amplitude and perceived strength. Our results pave the way for more accurate prediction of mouthfeel characteristics of liquid food products.

Calcium carbonate-hydrolyzed soy protein complexation in the presence of citric acid.

The influence of hydrolyzed soy proteins on calcium carbonate stabilization was studied in citric acid solution. Calcium-soy proteins interactions were characterized using a calcium ion selective electrode, turbidity, and Isothermal Titration Calorimetry. Once the meta-stable phase was reached or just after soy protein addition, spray-drying was performed and SEM, XRD, and XPS analysis were carried out on spray-dried powders. In citric acid solution calcite crystals were eroded giving rise to smaller amorphous particles. In the presence of soy proteins, complexation exothermic in nature occurred with the mineral phase, which prevented CaCO(3) from recrystallisation and kept the system in an amorphous state. SEM performed on spray-dried powder showed that soy proteins were swollen in presence of mineral phase and resulted in a decrease of calcium concentration at the extreme surface of the studied powders as demonstrated by XPS.

Study of calcium-soy protein interactions by isothermal titration calorimetry and pH cycle.

The aim of this work was to understand Ca-induced soy protein (nonhydrolyzed, NH; or hydrolyzed, H) aggregation and to characterize the involved interactions using ITC and pH cycle. The endothermic signals obtained upon titration of soy proteins with Ca were fitted with a one set of sites model. NH soy proteins bound more Ca than H soy proteins ( approximately 52 and approximately 2 mg of Ca/g of proteins, respectively). The binding constant K indicated the easier Ca binding onto H soy proteins than for NH soy proteins. The exothermic part involved by electrostatic interactions was completely hidden by the strong endothermic signal from the water molecule release. Ca binding onto soy proteins should be described as a H(+)/Ca(2+) exchange. Whatever the soy proteins, the positive value of heat capacity changes indicated a reduction in the number of surface-exposed polar residues. Ca-induced soy protein aggregation was irreversible for pH cycle to 3.5.