Influence of Protein Concentration on Heat-Induced Fouling of Oat Drink

Oat-based beverages are increasingly popular milk alternatives. However, the heat treatment required to ensure shelf stability is limited by rapid fouling formation on heated surfaces, reducing processing efficiency. Oat proteins, considered an important quality attribute of oat drinks, are suspected to play a key role in fouling initiation, but their specific contribution remains poorly understood. This study investigates the role of oat proteins in fouling formation during heat treatment on technical scale. Membrane filtration was applied and validated as sample preparation method for increasing the protein content. Fouling experiments were conducted using a previously validated fouling system with feed solutions containing different protein concentrations. Protein content was increased by filtration using 0.1, 0.8 and 1.4 µm ceramic membranes, yielding retentates with 10-21 g·100 g^-1 on a dry matter basis, and further enriched to >40 g·100 g^-1 through diafiltration. Fouling experiments (140 °C, 60 min) revealed a dependence of fouling formation on protein content in the feed solution. Fouling deposits were negligible at low protein concentrations (<2.5 g·100 g^-1), increased markedly between 8 and 14 g·100 g^-1, and reached a plateau at higher protein levels. Using oat supernatant or retentates, the protein content in the fouling correlated linearly with the protein content in the feed solution (R² = 0.98) but did not exceed ~25 g·100 g^-1, resulting in predominantly carbohydrate-based deposits. In contrast, diafiltered protein-enriched feed solutions produced larger, protein-dominated deposits. A conceptual model describing feed-dependent fouling mechanisms is proposed.