Effect of bio-chemical changes due to conventional ageing or chemical soaking on the texture changes of common beans...

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 CaCl₂ at pH 6.2, 25 °C for 16 h and subsequently cooking in CaCl₂ solution, or deionised water). The extent of phytate (inositol hexaphosphate, IP₆) hydrolysis was evaluated to better understand the role of endogenous Ca²⁺ in the changes of the bean cooking kinetics. A significant decrease in the IP₆ 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 CaCl₂ solution, the uptake of exogenous cations increased the cooking times (with no IP₆ hydrolysis). The change in cooking time of conventionally aged beans was strongly correlated with the extent of IP₆ hydrolysis, although two groups of beans with low or high IP₆ hydrolysis were distinguished. Comparable trends were observed when soaking in CaCl₂ 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 IP₆ hydrolysis of conventionally aged bean accessions and changes of cooking times for these bean accessions (with exception of yellow bean-KATB1).