The ability of sodium dodecyl sulfate (SDS) to plasticize edible films from whey protein isolate (WPI) was assessed. SDS was not able to plasticize WPI films on its own, but it was an effective coplasticizer in films containing either sorbitol or glycerol as the main plasticizer. In films that contained sorbitol, a mass ratio of SDS to WPI (R S:W) of 0.2 resulted in films that were more extensible and more soluble but with almost unchanged water vapor permeability (WVP). In films that contained glycerol, the same R S:W resulted in less extensible and soluble films with slightly higher WVP values. Values of R S:W > 0.3 resulted in antiplasticization, although there was a reduction in WVP. At R S:W > 1 films were so brittle that they could not be handled without breaking. The mechanical properties of WPI films that contained SDS were comparable to published values for other proteinaceous, edible films. Keywords: Plasticizer; Young's modulus; tensile strength; protein/surfactant interactions

The use of ultrasound to determine the sugar content of fruit juices and drinks has been assessed. The velocity of ultrasound and the density were measured in solutions of D-glucose, D-fructose, and sucrose at various concentrations (0-40% w/v) and temperatures (10-30°C). The velocity of ultrasound was measured in 50 : 50 wt : wt mixed solutions of sucrose and D-glucose over the same range of concentrations and temperatures. Measurements of the velocity of ultrasound, the density and the refractive index were made on various fruit juices and drinks at 20°C. The sugar content of the juices and drinks was determined by enzymatic assay. Ultrasonic measurements are shown to predict sugar contents in pure sugar solutions to within 0.2% wlv and in mixed sugar solutions to within 0.5% w/v. The ultrasonic measurements were sensitive to sugar species. It is shown that ultrasound compares well with other techniques for sugar content determination in fruit juices and drinks, and has the advantage that the equipment can be used for on-line process control. Applications for this ultrasonic technique are proposed. KeywordsDensity measurement, refractive index measurement, enzymatic assay, pure sugar solutions, mixed sugar solutions, process control.

The role of sulfhydryl/disulfide interchange in determining the water vapor permeability (WVP) and mechanical properties of edible films from whey protein isolate (WPI) was investigated. Nearly total inhibition of sulfhydryl/disulfide interchange by the sulfhydryl blocking agent N-ethylmaleimide (NEM) reduced protein solubility by 50%, but had no effect on WVP, Young's modulus, yield stress, or breaking stress. Breaking strain was reduced significantly at high levels of added NEM. Reduction of disulfide bonds with cysteine had no effect on WVP. The effects of hydrogen bonding far outweigh those of disulfide bonding in WPI films.

No abstract

No abstract