Het verkennen van proces–structuurrelaties langs de waardeketen van gewone bonen: een multischaalbenadering

With growing public awareness of healthy diets and climate issues, beans are increasingly gaining interest as part of the protein shift toward more plant-based diets. In the Global South, where beans are already staple foods, rapid urbanization and the resulting lifestyle changes are increasing the demand for convenient, time-saving bean-based products. This shift in eating preferences calls for a diversified range of appealing, convenient bean-based foods. Cooking is the key processing step that softens beans to a palatable texture suitable for consumption and digestion. Bean softening strongly depends on intrinsic properties and interactions with cooking conditions. In addition, bean cookability can be compromised by hard-to-cook (HTC) defects, which are particularly prevalent in the Global South due to adverse storage conditions. Consequently, understanding process-structure relations along the bean value chain is necessary. Therefore, this PhD research aimed to obtain quantitative insights into the softening behavior of beans at different structural length scales during processing. All (pre)cooking experiments were performed on fully presoaked beans (16 h, 25 °C) to ensure proper hydration of whole seeds and cooking uniformity. To begin with, quantitative multiscale changes during cooking and their interrelations were evaluated to better understand the softening behavior of bean seeds. A strong linear correlation between hardness and the extent of cell separation indicates that softening is predominantly driven by cell separation rather than cell expansion. Regarding volume changes, substantial cell expansion during the initial cooking phase was strongly associated with increased cotyledon volume, whereas the significance of cell separation increased at later stages. Importantly, swelling of the whole bean was controlled mainly by the seed coats rather than the cotyledons, and this effect became less pronounced with aging. Thermal analysis of the extent of starch gelatinization and protein denaturation indicates their limited contributions to bean softening. Both aging (altering inherent structure) and limited water access during cooking (changing extrinsic conditions) considerably reduced cell separation due to delayed and/or limited pectin solubilization, resulting in a firmer texture. Despite these differences, beans exhibited comparable relative hardness once a similar relative extent of pectin solubilization was achieved. These findings demonstrate the critical role of pectin solubilization at the middle lamella in regulating the softening behavior, which directly impacts the microstructure and texture of beans. The subsequent study investigated storage-induced subcellular changes that impair pectin solubilization of the cotyledon cell wall, in the context of the HTC defect. The study simultaneously examined two main HTC hypotheses related to modifications of cell wall polysaccharides, the pectin-cation-phytate hypothesis and the phenolics involved hypothesis, across five bean accessions. The investigated accessions varied in physical characteristics, cooking behavior, and sensitivity to HTC defect. For the first time, multiplexed staining of cotyledon cell wall tissues using the 2F4 antibody and basic fuchsin enabled concurrent visualization of Ca2+-crosslinked pectin along cellular junction linings and phenolic crosslinked compounds accumulated at junction corners, respectively. Their distinct spatial distributions suggest that multiple HTC mechanisms collectively reinforce the cell wall and delay pectin solubilization during cooking. Quantitative fluorescence analysis showed no correlation in changes of the two hypotheses across bean accessions, suggesting independent mechanisms. More importantly, phenolic crosslinking showed a greater relative increase upon aging than the calcium-pectate accumulation, which may indicate a more dominant role in HTC development. Precooked dehydrated beans are characterized as shelf-stable products that offer dual benefits: preventing HTC development during storage and reducing preparation time for consumers. The impact of precooking and rehydration strategies on the rehydration behavior of precooked dehydrated beans was investigated. Beans were precooked under varying time and water conditions to generate varying (micro)structures, then gently dehydrated at 40 °C. Bean microstructure and hardness after each processing step were evaluated and linked to rehydration performance under direct (23 °C, 90 °C) and two-step (23 °C followed by 90 °C) approaches. Extensively precooked beans with lower hardness values showed greater cell separation and substantial cell wall thinning, resulting in a more porous structure with weakened cell wall integrity after dehydration. These features enhanced rehydration capacity and the rates of water diffusion. The two-step rehydration process was recommended to avoid grainy texture and white cores, indications of insufficient hydration. Significantly, bean structure (hardness, cell separation) after rehydration reflected the state established during precooking and did not soften further, despite additional pectin solubilization. This indicates that the softening of precooked dehydrated beans is driven by water diffusion rather than by pectin solubilization. Therefore, beans must be precooked to a palatable level acceptable for consumption before dehydration to ensure desirable texture upon rehydration. Overall, this PhD provides qualitative and quantitative microstructural insights that greatly complement changes at macroscopic and molecular levels and clarifies the factors influencing bean cookability along the value chain. This study emphasizes the importance of integrating texture-based classification into sample selection to reduce bean-to-bean variation, and of investigating localized changes rather than relying on averages from overall tissue analysis when investigating HTC mechanisms.