| Abstract
| - The effect of the addition of individual whey proteins to skim milk onthe interaction between caseinmicelles and whey proteins was studied, during heat treatment at 75,80, and 90 °C. Not onlytemperature and time but also concentration affected the extent of theheat-induced reations of thewhey proteins with casein micelles. In general, higherconcentration of α-lactalbumin (α-la) in skimmilk caused an increase in the amount of this protein associated withthe micelles. On the otherhand, a further addition of β-lactoglobulin (β-lg) hardly affectedthe maximum incorporation of thisprotein with the casein micellar fraction. To determine the effectof a lower concentration of wheyprotein than that present in natural skim milk, purified α-la andβ-lg were added to separatedcasein micelles suspended in milk permeate from ultrafiltration, andthe reconstituted mixture washeated at 80 °C. In the absence of β-lg, very little α-lawas found associated with the micellarpellet after heating. When comparable amounts of whey proteinswere present, the interactionbehaviors of α-la and β-lg with casein micelles were very similar,resulting in an α-la/β-lg ratioclose to 1. In general, the ratios of α-la/β-lg associatedwith the heated micelles were significantlyaffected by the amount of protein present, either in skim milk or inthe presence of resuspendedmicelles. In milk, at temperatures <90 °C, α-la and β-lgmay interact together in the serum phase,with a ratio depending on the original protein concentration, beforeinteracting with casein micelles;this hypothesis could explain most of the observations made in thestudy. Keywords: Skim milk; heat treatment; α-lactalbumin; β-lactoglobulin;κ-casein; protein interactions
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