ABSTRACT:
Protein co-precipitates were prepared by mixing skim milk with unsalted or salted whey in different ratios; 4:1, 3:1, 2:1, 1:1, and 1:2 (v/v). The pH of skim milk or the mixes with whey was adjusted to pH 7.5, and then heat treated at 90ºC for 15 min. The protein was precipitated at pH 4.6. Salt (NaCl) was added at different levels (2, 4, 6, and 8%) to unsalted whey before mixing with skim milk. Samples of skim milk and whey were taken as control for comparison. The resultant co-precipitates were assessed for nitrogen distribution and functional properties. Results of N distribution reveled that, the amount of pH 4.6 precipitated N at pH 7.5 after heat treatment decreased the decrease in the ratio of skim milk in the mixes while the amount of SN increased. Co-precipitate isolated from skim milk/unsalted whey mixes contained 10.78 to 27.08% whey protein corresponding to 15.28 to 25.31% in that isolated from skim milk/salted whey depending on the ratio of skim milk in the mixes. Functionality testing revealed that water solubility of co-precipitate decreased with the decrease in the ratio of skim milk in the mix. The solubility of co-precipitates isolated from skim milk/unsalted whey mixes was relatively less than of that isolated from skim milk/salted whey mixes. Foaming capacity of co-precipitate decreased with the decrease of skim milk ratio in the mix, particularly, in that prepared from skim milk/unsalted whey mixes. Addition of NaCl at different levels (2, 4, 6, and 8%) to unsalted whey before mixing with skim milk apparently improved the functionality of the co-precipitates, but the ratio of skim milk in the mixes had the potential effect.