Impact of pectin characteristics on Maillard conjugate formation and their functionality in dispersed systems

There is a growing demand in the food industry for sustainable, plant-based ingredients with functional properties and clean-label potential. Plant proteins are considered promising in this context, but their application remains limited due to low solubility, restricted emulsifying capacity, and sensory shortcomings. One approach to improve these properties is the conjugation of proteins with saccharides, such as pectin. In the early stage of the Maillard reaction, covalent bonds are formed between the free amino groups of the protein and the free carbonyl groups of the pectin. The aim of this thesis was to deepen the understanding of the Maillard conjugation of plant proteins with pectin. Vacuum drying was established as an innovative method that combines conjugation and drying in a single step, enabling short reaction times, high conjugation yields, and a minimisation of undesirable side reactions. In addition, the impact of molecular characteristics of pectin, such as the degree of methoxylation and amidation, on conjugate formation, as well as on the physicochemical, techno-functional and nutritional properties of the conjugates, was investigated. Specifically, conjugation yield, molecular properties (e.g., structural changes, charge), techno-functional behaviour (e.g., emulsion stability, interfacial activity), and performance under simulated gastrointestinal conditions were comprehensively characterised. The reaction was initiated by water removal and accelerated by increasing dry matter content and temperature. Vacuum drying at 100 °C for three hours enabled high conjugation yields (45-66%) alongside complete drying and only moderate browning. Conjugation yield was both protein- and pectin-dependent: a higher lysine content, the presence of specific protein fractions, and a high degree of pectin substitution, especially through amidation, favoured covalent bond formation. Simultaneously, thermal treatment during vacuum drying led to partial pectin degradation, with the effect least pronounced in amidated pectin. In emulsification and interfacial studies, the conjugates exhibited smaller oil droplet sizes and improved emulsion stability compared to the untreated proteins. These effects were attributed to a shift in the isoelectric point (pI) and synergistic interactions between the conjugate components at the oil/water interface. Emulsion stabilisation relied on a protein-based interfacial film in combination with a pH-dependent pectin boundary layer. Depending on the pH, either steric effects (near the pI) or a combination of steric effects and electrostatic repulsion (above the pI) dominated between oil droplets. Conjugates with amidated pectin showed the highest stability across a broad pH range, due to their thermal stability and preserved polymer chain length. In contrast, unbound, thermally degraded pectin fragments promoted droplet bridging and thus destabilised the emulsion. Only interfaces stabilised by conjugates containing less-degraded pectin were resistant to mechanical stress. The in vitro digestibility of the conjugates was affected by pectin-induced structural differ-ences. In particular, conjugates with amidated pectin led to reduced protein hydrolysis due to pectin-induced gelation during the gastric phase. Limited accessibility of the protein to digestive enzymes proved to be a key factor. Depending on their digestibility, the conjugates thus showed potential for food systems designed for controlled nutrient release. In summary, this dissertation provides novel insights into the targeted and efficient production of protein-pectin conjugates via vacuum drying. Furthermore, it systematically demonstrates structure-dependent relationships between the molecular properties of the conjugates and their functional and nutritional performance. The results highlight the potential of these conjugates as natural, functional, clean-label ingredients for use in food emulsions and encapsulation systems.