Behavior of common beans under two conditions of water accessibility during cooking: Essential role of pectin solubilization in bean softening

Abstract

This study explores the softening behavior of beans during cooking at 95 °C under two conditions of water accessibility during the cooking process: water limited to the level attained in fully soaked beans and excess water (conventional cooking). We examined changes in texture (hardness) and pectin solubilization, where strongly bound pectin is converted to loosely bound pectin. Limited-water cooking (LWC) reduced pectin solubilization by half compared to conventional cooking, resulting in a (s)lower decline in bean hardness. A strong negative correlation (r = −0.977; p < 0.0001) between relative pectin solubilization and relative hardness emphasizes the critical role of pectin solubilization in regulating softening behavior. Despite the difference in water accessibility, both cooking methods required pectin solubilization to a similar extent to obtain comparable bean hardness. Microscopic analysis revealed LWC beans had minimal cell separation (6.84 %) and limited cell expansion (6829 µm²). In contrast, excess water in conventional cooking promoted substantial cell separation (12.43 %) and cell expansion (8716 µm²). Conventional cooking also causes swelling and disruption of starch granules, evidenced by the partial starch leaching into the cellular content. The study demonstrates that water accessibility critically influences pectin solubilization during cooking, directly impacting both the micro- and macroscopic structural properties of beans.