Particle size and stability of plant-based milks - insights from various analytical techniques

The popularity of plant-based milks worldwide has driven manufacturers to develop products that closely resemble traditional cow's milk in terms of nutritional, functional, and sensory qualities. Understanding the emulsions of these milks is vital for their production. Particle size and pH control mouthfeel, texture, and stability of milks. This study aimed to establish quality control methods by examining the particle size distribution of ultra-high temperature (UHT) treated soy, almond, and oat milk, along with UHT-treated bovine milk, using various techniques such as dynamic light scattering (DLS), laser diffraction (LD), nanoparticle tracking analysis (NTA), and fluorescence confocal laser scanning microscopy (CLSM). The milks demonstrated varying particle sizes, mostly below 1 μm, but some larger particles (>1 μm) were detected, potentially comprising protein aggregates, suspended solids, or fibres. CLSM confirmed lipid aggregation in plant-based milks. Protein content, analysed by amino acid profiles, was generally lower in plant-based milks compared to bovine milk, except for soy milk. Zeta potential testing indicated colloidal instability at lower pH levels, but stability was regained with additional milk. Heating at 60 °C, however, showed no effect on the milks’ surface charge. The Zetasizer approach showed promise for quality control and product development, considering size and surface charge.