Impact of milk-to-vegetable fat ratio on infant formula emulsions stability

Infant formula produced from specific ingredient fractions have attracted increasing interest in recent years. However, the removal of milk fat, combined with the lower emulsifying capacity of serum protein fractions from milk fractionation (e.g., Serum Protein Concentrate vs. Whey Protein Concentrate), increases the susceptibility of these formulations to destabilization, particularly when milk fat is substituted with vegetable oils. The stability of dairy ingredients in powdered form is directly linked to the stability of the emulsion prior to drying, meaning that any weakening of the interfacial layer or increased tendency toward droplet coalescence can significantly impact the physical quality and functionality of the final powder. To assess the effects of milk fat replacement on emulsion stability, different milk/vegetable fat ratios emulsions were produced (0; 0.06; 0.31; and 0.63). It was highlighted that emulsions containing the highest ratio of milk fat showed the narrowest droplet size distribution, with a significant decrease of the droplet mean diameter (d₅₀), suggesting improved stability. In addition, emulsion destabilization was studied using Static Multiple Light Scattering, and higher milk fat content was linked to a significantly slower creaming rate. Moreover, droplet growth associated with coalescence and flocculation was also more limited for formulations presenting the highest milk fat content. These findings indicate that both milk fat substitution and the choice of milk protein fraction play a major role in emulsion stability. This study provides key insights for the design of novel milk-derived products.