Investigation into the hardbean phenomenon in Phaseolus vulgaris L.
The textural deterioration of dry beans during storage was investigated. The primary symptoms of this hardbean phenomenon were found to be reduced viability, reduced water uptake and reduced cooking rate. It was found that the basic cause of the beans failing to cook - or soften - was the failure of the cotyledon cells to separate during the cooking process. From these initial observations it was hypothesised that reduced cell separation rate was due to either reduced turgor pressure due to reduced water uptake, or reduced pectin solubility, or both. Techniques used included light microscopy, transmission and scanning electron microscopy, thin-layer chromatography and spectrophotometry and it was found that reduced cell separation rate was due to a combination of both reduced water uptake and reduced pectin solubility. By inducing the hardbean symptoms artificially their relevance to textural deterioration were determined. The significant events within the beans during storage were found to be phytin breakdown, membrane deterioration, cation leakage, pectin demethylation and pectin calcification. By running a storage trial and thus allowing hardness to develop within the beans the sequence of events was elucidated.