Foaming Properties and Foam Structure of Milk Determined by Its Protein Content and Protein to Fat Ratio

Abstract Milk proteins, integral to stable foam production, exhibit seasonal and type-dependent variations. Understanding the impact of protein levels with and without fat on foaming properties is essential for selecting suitable milk types and controlling the foaming process. In this study, we employed steam injection and mechanical mixing to assess foamability, foam stability, and foam structure of (1) reconstituted skim milk powder dispersions (1.5–15% solids concentration, corresponding to 0.5–5.0% protein), (2) reconstituted whole milk powder and commercial whole milk dispersions (0.5% protein), and (3) whole milk with added skim milk powder and milk protein concentrate (3.5 and 4% protein) and butter milk powder (0.5 and 1% total solid content). Results reveal that increasing solids concentration from 1.5 to 15% significantly increased lactose content, viscosity, and surface tension. However, these changes did not impact foamability or foam stability, while slightly decreasing air bubble size. At 0.5% protein, skim milk powder dispersions demonstrated higher foam volume (16 times greater) and more stable foam compared to reconstituted whole milk powder and whole milk dispersions, despite similar foam structure and appearance. These findings emphasize the substantial influence of the protein/fat ratio on milk’s foaming properties. Additionally, the addition of skim milk powder, milk protein concentrate, or butter milk powder at the investigated content did not affect the foaming properties of whole milk.