Search

[Display omitted] • Texture-based classification allows to relate mineral location and texture changes during cooking of bean seeds. • Texture is positively correlated to cell wall-bound Ca2+ in cooked beans after storage. • Pectin DM in aged beans decreased with longer storage times. • Exogenous Ca2+ mainly crosslinked with pectin during cooking in CaCl 2 -treated beans. • Cotyledon cell wall-bound Ca2+ affected the cooking of beans soaked in acetate solutions. Hard-to-cook (HTC) is a textural defect that delays the softening of common bean seeds during cooking. While this defect is commonly associated with conventionally stored beans, soaking/cooking of beans in CaCl 2 solutions or sodium acetate buffer can also prolong the cooking time of beans due to formation of Ca2+ crosslinked pectin retarding bean softening during cooking. In this study, the role of the cell wall-bound Mg2+/Ca2+ content and the degree of pectin methyl esterification (DM) was quantified, as important factors for bean texture-related changes stipulated in the pectin-cation-phytate hypothesis, the most plausible hypothesis of HTC development. Evaluation of texture changes during cooking of conventionally aged beans (35 °C and 83% RH for up to 20 weeks), beans soaked/cooked in CaCl 2 solutions (0.01 to 0.1 M) or soaked in 0.1 M sodium acetate buffer (pH 4.4) revealed large bean-to-bean variations. Therefore a texture-based classification approach was used to better capture the relation between texture characteristics and cell wall polymer, in particular pectin, related changes. While cell wall-bound Ca2+ and pectin DM did not change/were not related to the texture variation during cooking of fresh beans, increased cell wall-bound Ca2+ and decreased pectin DM were associated with prolonged conventional storage of beans and their texture changes during subsequent cooking (due to pectin cross linking, retarding its solubilization during cooking). Exogenously added Ca2+ from pre-treating beans in CaCl 2 solutions promoted to a great extent the cell wall-bound Ca2+ during soaking but even more so during cooking, complementing the harder texture associated with these beans during cooking (compared to conventionally stored and fresh beans). Similarly, free Ca2+ endogenously generated by phytase-catalysed phytate hydrolysis (beans treated by acetate buffer) promoted crosslinking of pectin by Ca2+ (cell wall-bound Ca2+), delaying softening of beans during cooking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fresh/aged beans were classified into groups with different cooking textures. • Ageing leads to InsP 6 hydrolysis to lower inositol phosphates, particularly InsP 5. • InsP 6 content in cotyledons is an indicator for the extent of HTC during bean aging. • Soaking of beans causes some phytate interconversions inside cotyledons. • Released Ca2+ cations from phytate hydrolysis were bound instead of leaching out. During adverse postharvest storage of Red haricot beans, the inositol phosphate content, particularly InsP 6 , decreased significantly, along with a significant increase in InsP 5. Using a texture-based classification approach, the InsP 6 content in cotyledons was shown an indicator for the extent of hard-to-cook (HTC) development during bean aging. This textural defect development was predominated by storage-induced InsP 6 degradation, rather than phytate interconversions during soaking. Ca cations, released during storage, did not leach out significantly during subsequent soaking, suggesting that they were bound with the cell wall pectin in cotyledons, while Mg cations were mostly leached out into the soaking water due to their weak binding capacity to the pectin, and the cell membrane damages developed during HTC. Results obtained herein provide evidence for the pectin-cation-phytate mechanism in textural hardening (and its distribution after cooking) of common beans, and call for a more detailed Ca-relocation study during postharvest storage, soaking and cooking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Texture correlation of a single bean before and after ageing was established. • SEM-EDS showed cell wall-Ca concentration significantly correlated with bean texture. • InsP6 content is a key indicator of HTC development during bean ageing. • Ca originates from InsP6 hydrolysis and migrates to cell wall during storage. • Pectin DM decrease and pectin-Ca interactions occur during bean ageing upon storage. Utilization of common beans is greatly hampered by the hard-to-cook (HTC) defect induced by ageing of the beans under adverse storage. Large bean-to-bean variations exist in a single batch of beans. Therefore, a texture-based bean classification approach was applied in this detailed study on beans with known textures, to gain in-depth insights into the role of the pectin-cation-phytate mechanism in relation to the texture changes during subsequent cooking of Red haricot fresh and aged beans. For the first time, a correlation between the texture (exhibited after cooking) of a single bean seed before ageing (fresh) and its texture after ageing was established. Furthermore, scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) based in situ cell wall associated mineral quantification revealed that the cell wall associated Ca concentration was significantly positively correlated with the texture of both fresh and aged cooked Red haricot bean cotyledons, with ageing resulting in a significant enrichment of Ca at the cell wall. These additional Ca cations originate from intracellular phytate hydrolysis during ageing, which was shown to affect the texture distribution of aged beans during cooking significantly. The relocation of the mineral cations from the cell interior to the cell wall occurs mainly during storage rather than subsequent soaking of the cotyledons. In addition, the pectin-cation-phytate hypothesis of HTC was further confirmed by demethylesterification of the cell wall pectin and increased pectin-Ca interactions upon ageing of the cotyledons, finally leading to HTC development of the cotyledon tissue. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bean-to-bean variations were minimized by a texture-based sample selection. • Residual cell wall fractions after sequential pectin extractions were characterized. • Ageing induced substantial cell wall structural changes in cotyledons. • Phenolics interact with and/or are lignified in the cell wall during HTC. • FT-IR spectroscopy coupled with PCA discriminated cell wall changes during ageing. Cell wall material was isolated from selected non-aged and aged Red haricot bean cotyledons using a texture-based classification approach. Pectin-depleted residual cell wall fractions were obtained by sequential pectin extraction and were characterized to investigate in situ cell wall related molecular changes upon ageing during adverse storage of the beans. Particularly, involvement of phenolic compounds in cell wall strengthening during the ageing process, resulting in the hard-to-cook defect, was evaluated. Results show that ageing induces substantial changes at a cell-wall-structural level in the Aged sample compared to the Non-aged sample, with mainly vanillin, 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde covalently bound with sugar side-chains of pectin and/or involved in lignification-like mechanisms. FT-IR spectroscopy coupled with chemometric analysis reveals that lignin-like phenolic-cell wall polymers, which are known to reinforce cell wall structure, are present in the cell wall polysaccharide network of the Aged sample, and are therefore contributing factors to the hard-to-cook development during Red haricot bean ageing. [ABSTRACT FROM AUTHOR]

• Texture of half-beans was established to minimize bean-to-bean variations. • Distribution patterns of pectic cross-linkages in cotyledon cell wall. • Microscopic evidence for chelated Ca2+ pectin in HTC common beans. • Microscopic evidence for ester-bound feruloylated pectin during HTC development. In this study, pectin changes during Red haricot bean storage under high temperature and high humidity conditions were investigated to understand the hard-to-cook (HTC) development from a microstructural point of view. First, to ensure repeatability of the microscopy results, a classification of the fresh and stored beans (aged at 35 °C and 83% relative humidity) into different hardening levels (the Non-aged, Aged and Very-hard aged sample) was performed based on the texture values of cooked half-cotyledons. Cell wall strength of the cotyledons was evaluated, showing that the aged samples (HTC seeds) exhibit stronger cell walls with more/stronger pectic cross-linkages than the Non-aged sample. After a sequential pectin extraction aiming at removing pectin fractions of different solubility, cell wall autofluorescence and immunolabeling of JIM7, LM9 and 2F4 epitopes in the residual materials were examined. Upon ageing, the samples exhibited an increased Ca2+-pectin and ferulic acid-pectin crosslinking, these pectic complexes being accumulated primarily at the intercellular spaces. The results suggest a contribution of both the pectin-cation-phytate hypothesis and the involvement of phenolic-pectin crosslinks in HTC development at the cotyledon during storage of common beans. [ABSTRACT FROM AUTHOR]

[Display omitted] • Texture of seven bean varieties after storage / chemical soaking was explored. • Texture changes are positively correlated with IP 6 changes in beans after storage. • Chemical soaking can be used to estimate sensitivity of beans to HTC development. • Soaking in acetate buffer is a suitable tool to estimate IP 6 hydrolysis during storage. To establish the HTC defect development, the cooking kinetics of seeds of ten bean accessions (belonging to seven common bean market classes), fresh and conventionally aged (35 °C, 83% RH, 3 months) were compared to those obtained after soaking in specific salt solutions (in 0.1 M sodium acetate buffer at pH 4.4, 41 °C for 12 h, or 0.01 M CaCl 2 at pH 6.2, 25 °C for 16 h and subsequently cooking in CaCl 2 solution, or deionised water). The extent of phytate (inositol hexaphosphate, IP 6) hydrolysis was evaluated to better understand the role of endogenous Ca2+ in the changes of the bean cooking kinetics. A significant decrease in the IP 6 content was observed after conventional ageing and after soaking in a sodium acetate solution suggesting phytate hydrolysis (release of endogenous Ca2+). These changes were accompanied by an increase in the cooking time of the beans. Smaller changes in cooking times after soaking in a sodium acetate solution (compared to conventionally aged beans) was attributed to a lower ionisation level of the COOH groups in pectin (pH 4.4, being close to pKa value of pectin) limiting pectin Ca2+ cross-linking. In beans soaked in a CaCl 2 solution, the uptake of exogenous cations increased the cooking times (with no IP 6 hydrolysis). The change in cooking time of conventionally aged beans was strongly correlated with the extent of IP 6 hydrolysis, although two groups of beans with low or high IP 6 hydrolysis were distinguished. Comparable trends were observed when soaking in CaCl 2 solution (r = 0.67, p = 0.14 or r = 0.97, p = 0.03 for two groups of beans with softer or harder texture during cooking). Therefore a test based on the Ca2+ sensitivity of the cooking times, implemented through a Ca2+ soaking experiment followed by cooking can be used as an accelerated test to predict susceptibility to HTC defect development during conventional ageing. On the other hand, a sodium acetate soaking experiment can be used to predict IP 6 hydrolysis of conventionally aged bean accessions and changes of cooking times for these bean accessions (with exception of yellow bean-KATB1). [ABSTRACT FROM AUTHOR]

[Display omitted] • Texture of seven bean varieties after storage / chemical soaking was explored. • Texture changes are positively correlated with IP 6 changes in beans after storage. • Chemical soaking can be used to estimate sensitivity of beans to HTC development. • Soaking in acetate buffer is a suitable tool to estimate IP 6 hydrolysis during storage. To establish the HTC defect development, the cooking kinetics of seeds of ten bean accessions (belonging to seven common bean market classes), fresh and conventionally aged (35 °C, 83% RH, 3 months) were compared to those obtained after soaking in specific salt solutions (in 0.1 M sodium acetate buffer at pH 4.4, 41 °C for 12 h, or 0.01 M CaCl 2 at pH 6.2, 25 °C for 16 h and subsequently cooking in CaCl 2 solution, or deionised water). The extent of phytate (inositol hexaphosphate, IP 6) hydrolysis was evaluated to better understand the role of endogenous Ca2+ in the changes of the bean cooking kinetics. A significant decrease in the IP 6 content was observed after conventional ageing and after soaking in a sodium acetate solution suggesting phytate hydrolysis (release of endogenous Ca2+). These changes were accompanied by an increase in the cooking time of the beans. Smaller changes in cooking times after soaking in a sodium acetate solution (compared to conventionally aged beans) was attributed to a lower ionisation level of the COOH groups in pectin (pH 4.4, being close to pKa value of pectin) limiting pectin Ca2+ cross-linking. In beans soaked in a CaCl 2 solution, the uptake of exogenous cations increased the cooking times (with no IP 6 hydrolysis). The change in cooking time of conventionally aged beans was strongly correlated with the extent of IP 6 hydrolysis, although two groups of beans with low or high IP 6 hydrolysis were distinguished. Comparable trends were observed when soaking in CaCl 2 solution (r = 0.67, p = 0.14 or r = 0.97, p = 0.03 for two groups of beans with softer or harder texture during cooking). Therefore a test based on the Ca2+ sensitivity of the cooking times, implemented through a Ca2+ soaking experiment followed by cooking can be used as an accelerated test to predict susceptibility to HTC defect development during conventional ageing. On the other hand, a sodium acetate soaking experiment can be used to predict IP 6 hydrolysis of conventionally aged bean accessions and changes of cooking times for these bean accessions (with exception of yellow bean-KATB1). [ABSTRACT FROM AUTHOR]

In this study, the role of soaking beans in a sodium citrate solution (a cation chelator) at pH = 4.4 and 41 °C in directing/improving the cooking behaviour of common beans was explored. The cooking behaviour of the pre-soaked red kidney beans was determined and the corresponding changes of phytate, minerals, starch, protein and pectin were quantified. Soaking beans in citrate buffer could accelerate softening of the beans during cooking in deionised water while subsequent cooking of beans in this buffer had a limited additional effect on softening compared to cooking in deionised water. Phytate hydrolysis during soaking in citrate buffer results in a release of Mg2+ and Ca2+. Both cations were leached into the soaking medium, higher amounts being observed for Mg2+ release to the soaking media because of the lower affinity of Mg2+ for pectin. It was observed that the pectin solubilisation rate in beans treated by sodium citrate buffer was positively correlated to bean softening. All of these results point out that soaking in a citrate buffer prohibits pectin Ca2+ cross linking therefore enhancing pectin solubilisation and thus increasing the bean softening rate constants during cooking, while starch and protein were not responsible for texture evolution. • Soaking beans in sodium citrate buffer improved cookability of beans. • Mg2+/Ca2+ in cotyledons and seed coats released to the soaking/cooking medium. • Citrate buffer (pH 4.4) increased pectin solubilisation promoting bean softening. • Starch gelatinisation and protein denaturation did not play a major role in bean softening. [ABSTRACT FROM AUTHOR]