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Temperature-induced collapse of hydrogels of interpenetrating polymer networks (IPNs) poly(Nvi nyl cap ro lac t am) / po ly( N -i sop ro pyl ac ryla mide ) (PVCL/PNIPAm) and poly(N-isopropylmethacrylamide) (PNIPMAm)/PNIPAm, where both components are thermoresponsive, was studied by combination of 1 H nuclear magnetic resonance (NMR) spectroscopy, small-angle neutron scattering (SANS), differential scanning calorimetry (DSC), and dynamic mechanical measurements. Behavior of studied hydrogels (one or two transitions) was found to depend on the ratio of both IPN components. For hydrogels of IPNs containing around 50 mol% of PNIPAm monomer units, separate transitions were revealed for both components. From SANS curves, it follows that compact three-dimensional multi-chain globules are formed in PNIPMAm/PNIPAm and PVCL/PNIPAm IPN hydrogels at temperatures above the phase transition, with a gyration radius of 14-28 nm. A certain portion of spatially restricted bound water (HDO) was established for all the studied IPNs at temperature above the volume phase transition from measurements of 1 H NMR spectra, spin-spin relaxation times (T 2 ), and diffusion coefficients (D) of HDO. Slow exchange regime between bound and free water was revealed. Spin-spin relaxation times (T 2 ) and diffusion coefficients (D) as obtained for the bound HDO are up to 2 orders of magnitude smaller in comparison with "free" HDO. Higher content of bound water as found for collapsed hydrogels of IPN PVCL/PNIPAm in comparison with PNIPMAm/PNIPAm hydrogels is in accordance with swelling experiments and lower values of the shear mechanical modulus; this shows the decisive role of bound water in this respect.

Relationships were established for five sensory methods of oral and nonoral viscosity evaluation between viscosity scores and instrumentally measured dynamic viscosity for model and real Newtonian fluid foods. These relationships were then used to predict the effective shear rates under which the sensory tests were performed. The highest shear rates were predicted for viscosity perception by compression of samples between tongue and palate, and the lowest for pouring the fluid foods from a teaspoon. Mixing with a teaspoon, slurping and swallowing exhibited nearly the same dependencies of apparent shear rates on equivalent instrumental viscosity. All relations were of the hyperbolic type. The resulting relationships between the apprent shear rates and equivalent instrumental viscosity are in good agreement with a similar relationship predicted by Shama and Sherman (1973a) (see Cutler et al. 1983) for oral perception.

Mayonnaise samples, which belong to oil-in-water emulsions, were plant-scale products, which contained either 70% oil (normal products, samples 1-12) or 30% oil (type Light, which are also considered as mayonnaises according to the Czech legislation, samples 13-17). Refined rapeseed oil was used as oil phase in all cases, and all samples contained 2.0% egg yolk (in agreement with the Czech legislation), and the same amount of modified starch. Different viscosities were obtained by changing mechanical processes in the preparation of mayonnaise. An increase in energy input and in the processing temperature yields emulsions of smaller droplet size, and thus of higher values of steady state viscosity, as was observed in the preparation of salad dressing emulsions [6]. Methods Rheological procedureSamples of mayonnaise were measured in a computercontrolled rotational rheometer Rotovisco RT 10 (Gebrüder Haake GmbH, Karlsruhe, Germany) at 10 and 25°C, equipped with a vane rotor FL 20 and a Coaxial Cylinder Sensor System (Cylinder Sensors Z 43/S and Z 38/S), which was ripped to reduce slipping. The temperature was equilibrated for 15 min. The yield value τ o [Pa] and the apparent viscosity η A [Pa × s] were determined as described in 3.2.(see Figs. 1 and 2). Rheological properties and sensory texture of mayonnaiseMayonnaises are viscoplastic oil-in-water emulsions, in which rheological properties have important influences on functional properties and the sensory quality. A set of 17 samples of both traditional and light mayonnaises were tested at 10 and 25°C, using a rheoviscometer Rotovisco RT 10. Nonlinear relations were observed between the yield value and the apparent viscosity. The yield value was correlated with several sensory characteristics rated after manipulation with a spoon, but not in oral testing. No relations were obtained between the apparent viscosity and sensory characteristics. The yield value and the texture acceptability were related significantly to the flavour acceptability. Multivariate statistical techniques were found advantageous for improving the prediction of the texture acceptance.

The intensity of sweet, bitter or astringent tastes is reduced by consumption of edible oil or oil emulsions immediately before the ingestion of test solutions. The basic taste substances were dissolved in 30% aqueous ethanol, flavoured with plant extracts. The time-intensity dependence was influenced similarly. The sensitivity of taste receptors returned to the original value within 15-20 min. Intensities of acidic or salty tastes were not affected.

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