Physicochemical and rheological properties of skim milk with different added zinc salts

Physicochemical and rheological changes in skim milk after the addition of soluble zinc salts, zinc acetate (Zn(OAc)2), zinc sulphate (ZnSO4) and zinc gluconate (ZnGlu) at 20 °C were investigated. Addition of zinc salts resulted in a significant decrease in pH, and the solution pH from lowest to highest at the same concentration was ZnSO4 < ZnGlu < Zn(OAc)2. The colloidal phase zinc concentration increased the most when Zn(OAc)2 was added. At low concentrations of added zinc salts (<20 mmol L−1) the zinc + skim milk solutions did not gel at 20 °C for 3 h (final G′ <1 Pa). Gelation was observed when 22.5 mmol L−1 Zn(OAc)2 was added to skim milk, while it was necessary to add 30 mmol L−1 ZnSO4 and ZnGlu to achieve a final G′ >1 Pa, followed by increasing final G′ with increasing concentrations of added zinc salts. Higher colloidal phase zinc concentrations resulted in a stronger gel at 20 °C.