Whey protein solutions at pH 3.5 elicited an astringent taste sensation. The astringency of whey protein isolate (WPI), the process whey protein (PWP) that was prepared by heating WPI at pH 7.0, and the process whey protein prepared at pH 3.5 (aPWP) were adjusted to pH 3.5 and evaluated by 2 sensory analyses (the threshold method and the scalar scoring method) and an instrumental analysis (taste sensor method). The taste-stimulating effects of bovine and porcine gelatin were also evaluated. The threshold value of astringency of WPI, PWP, and aPWP was 1.5, 1.0, and 0.7 mg/mL, respectively, whereas the gelatins did not give definite astringency. It was confirmed by the scalar scoring method that the astringency of these proteins increased with the increase in protein concentration, and these proteins elicited strong astringency at 10 mg/mL under acidic conditions. On the other hand, the astringency was not elicited at pH 3.5 by 2 types of gelatin. A taste sensor gave specific values for whey proteins at pH 3.5, which corresponded well to those obtained by the sensory analysis. Elicitation of astringency induced by whey protein under acidic conditions would be caused by aggregation and precipitation of protein molecules in the mouth.

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A growing fraction of plastic resins produced today are blends of two or more polymers. 1 Polymer blending offers an extraordinary rich range of new materials with enhanced characteristics regarding mechanical, chemical, or optical performances. However, most commercial blends are immiscible because nearly all polymer pairs cannot be soluble in each other. When two immiscible polymers are blended during melt extrusion, a stable morphology is reached in which one phase is mechanically dispersed inside the other. The size and shape of the dispersed phase depend on several processing parameters, including rheological and interfacial properties and the composition of the blend. By using the conventional mixing machines, the experimental limitation of domain size has been reported to be approximately 100 and 350 nm for Newtonian systems 2-6 and polymer blend systems, 7,8 respectively. Several methods 9-17 of reducing phase size and improving interfacial adhesion for the practical application of polymer blend materials have been developed. Currently, a phase structure on the micrometer or submicrometer scale, that is, microstructured blends, is technically easy to prepare using typical processing methods, such as extrusion or injection molding. However, the preparation of nanostructured polymer blends for immiscible polymers, with a phase size of less than 100 nm, is very challenging using normal processing methods currently available. Very recently, nanostructured blends have been produced from block copolymers by using conventional melt processing, 18,19 but the method shows obvious limitation for the practical application.One of the authors has very recently studied the insitu phase behavior of polymer blends under a highshear flow field. 20 It was found that immiscible poly(pphenylene sulfide)/polyamide 46 blends show a miscible region under a flow field with a high shear rate above 1000 s -1 . Moreover, the miscible region was enlarged by a higher shear rate of 3000 s -1 . Therefore, processing under high-shear flow is considered to be a very effective technique for making the immiscible polymer blends miscible. On the basis of the obtained results, the highshear extruder HSE3000mini has been developed. The extruder can reach a maximum screw rotation speed of 3000 rpm. Furthermore, the specially designed feedbacktype screw (L/D ) 1.78) has been used to make the sample to circulate in the extruder during melt mixing. The sample feed at the top of the screw was back soon at the root of the screw through the feedback path. By using this new high-shear extruder with the capability about 5 mL, PVDF and PA11 were directly meltblended. It is found that PA11 can be dispersed in the PVDF phase with a domain size of several tens of nanometers, which is the first example of a nanostructured polymer blend obtained by a simple mechanical method.Experimental Section. Poly(vinylidene fluoride) (PVDF) and polyamide 11 (PA11) used were commercially available KF850 (Kureha Chemical, Japan) and Rilsan BMN-O (Atfina Co., Ltd.), respe...