Influence of ohmic heating on rheological and electrical properties of reconstituted whey solutions

摘要

Reconstituted whey solutions (in the range of 8-24% w/v solute concentrations) were heated from 20 degree C to prescribed temperatures (30, 40, 50, 60, 70 or 80 degree C) ohmically by applying voltage gradients of 20, 30 or 40 V/cm, and conventionally at water bath. Electrical conductivity changes with increasing temperature were linear during ohmic heating. Whey solutions have non-Newtonian characteristics since Herschel-Bulkley model satisfactorily fitted the experimental shear stress-shear rate data. "n" values were in the range of 0.520-1.503. The whey solution having 24% concentration had a yield stress of 0.006-0.024 Pa at low temperatures. Although temperature and concentration were critical factors for the consistency and the electrical conductivity changes during heating (p < 0.01), the voltage gradient was not effective statistically. The high correlation (between -0.910 and -0.991) was obtained between changes of electrical conductivity and consistency coefficient values during ohmic heating. Since activation energies for ohmic heating (26.34-45.79 kJ/mol) depending on solute concentration were lower than conventional heating (26.70-50.04 kJ/mol), reconstituted whey solutions were less sensible to temperature changes during ohmic heating. It was recommended that ohmic heating could be applied as a faster alternative heating method in the whey processing.