Microstructure of Cotyledon Cells from Hard‐to‐Cook Common Beans

Two bean cultivars (FM‐240 and FM‐297) were seeded in the same location, harvested and cleaned. One portion was stored for 120 days under high temperature and humidity, and another was soaked in an acetate buffer (pH 4.0–4.1. 37°C) for 5 h. Hard‐to‐cook (HTC) defect developed in both conditions as assessed by the Mattson bean cooker. Slices of bean cotyledons were prepared to study microstructural changes as a result of the HTC condition using light and scanning electron microscopy. There were some remarkable differences in some of these changes generated by both hardening procedures. Uncooked samples hardened by storage showed smooth starch granules without any apparent deformation and somewhat similar to the control, whereas by the chemical procedure these granules were clearly deformed. Cotyledon cell separation was produced when fresh samples were cooked. Cells were smaller and separation was not as evident in HTC samples from the two procedures compared to previous fresh samples. The chemical hardening technique appeared to make more rigid the cotyledon cell structure.