Reversible and irreversible components of bean hardening

The hard-to-cook defect was partitioned into reversible and irreversible components using common beans, previously stored under a range of temperatures (15, 30, 45 degrees C) and water activities (0.59, 0.75, 0.86 a(w)), that were soaked and cooked in distilled water or a 5% (w/v) aqueous solution of Na-2 EDTA. Results of phytate analysis and fluorescence microscopy led to the conclusion that these components reflect the pectin-phytate mechanism or reversible hardening and the lignification mechanism or irreversible hardening. Modeling of the hardening process indicated that the rate of the irreversible reaction was more dependent on storage temperature while the reversible reaction was a strong function of water activity. These data help to explain the multiple mechanism aspect of bean hardening.