Physicochemical properties of liquid virgin whey protein isolate

Liquid virgin whey protein isolate (LVWPI) was produced by concentrating and fractionating virgin whey, the permeate from microfiltration of acidified (pH 6) skim milk before cheesemaking. The virgin whey was subjected to a two-stage ultrafiltration system, which consisted of spiral wound and hollow fiber polysulfone membrane (10 kDa cut-off) modules. The LVWPI contained 26.1% (w/w) total solids, about 91% of which were whey proteins (WPs). Density and viscosity at 20 °C were 1.11 g mL−1 and 11.65 mPa s, respectively. The pH was constant for 38 days at 4 °C. Apparent viscosity at 122.3 s−1 shear rate and activation energy of flow were lower than those of WP isolate (WPI) and concentrate (WPC-80) solutions at 10–50 °C and 5–25% (w/w) WP concentrations. The LVWPI apparent viscosity after heating became identical to unheated WPI solution. The results of the study indicate that LVWPI was richer in native WP than commercial products and may serve as an excellent source of easy-to-use and nutritionally superior WPs.