Alkaline polyacrylamide gel electrophoresis of whey protein fractions soluble at pH 4.6 from different categories of heat-treated milk: raw milk (125), pasteurized milk (129 and 130), low-heated (88, 96, 98, 81, and 42) and high-heated (86, 124, and 132) ESL milk, and UHT milk (41, 89, and 37) samples. Ig (immunoglobulins), BSA (bovine serum albumin), α-lactalbumin (α-La), and β-lactoglobulin (β-Lg) were separated depending on their negative charge.