Micro‐ and Macroscopic Analysis of Agglomerate‐Driven Oil Immobilization in Nut‐Based Pastes

Oil mobility is a key determinant of stability in hazelnut-based pastes, as it promotes oil separation, which in turn causes a greasy texture and increased susceptibility to oxidation. It is hypothesized that (1) grinding leads to the formation of agglomerates that immobilize oil and thus prevent oil separation and that (2) mixing disrupts these structures, resulting in destabilization and increased oil mobility. The understanding of the formation, process dependency, and functional relevance of agglomerates is limited by the lack of analytical methods for their detection. This study employed a multiscale analytical approach combining microscopic techniques (light microscopy and NMR diffusometry) for direct detection of agglomerates with macroscopic measurements (oil binding capacity, rheology, and oil separation during 4 weeks of storage) to reveal their function in nut pastes of increasing complexity: pure hazelnut pastes (100% w/w nuts), hazelnut–sugar pastes (70% w/w nuts and 30% w/w sugar), and nougat formulations. Grinding technologies (cutter, ball mill, and roller refiner) at two intensities were compared during the production of pure hazelnut and hazelnut-sugar pastes. Based on these results, nougat pastes were produced at laboratory and industrial scales using roller refining. Mixing conditions of nougat pastes were varied to evaluate the stability of agglomerates and its impact on oil mobility. Agglomerate structures were detected using microscopic techniques, depending on processing technology, intensity, and composition of hazelnut-based pastes. In macroscopic tests, their presence was associated with enhanced oil immobilization and improved product stability. These findings demonstrate that oil mobility in hazelnut-based pastes is strongly influenced by grinding and mixing conditions and highlight the relevance of a multiscale analytical approach to optimize processing for stable fat-based products.