Effects of gamma‐irradiation on cotyledon cell separation and pectin solubilisation in hard‐to‐cook cowpeas

Abstract

BACKGROUND : Cowpeas stored under high temperature and humidity develop the hard‐to‐cook defect (HTC). This defect greatly increases cooking times and energy costs. To better understand the mechanisms involved in the HTC defect development, the effects of gamma‐irradiation on cotyledon cellular structure and pectin solubility in two cowpea cultivars with different susceptibility to HTC defect were investigated. RESULTS : Gamma‐irradiation decreased cotyledon cell wall thickness, increased cell size, and intercellular spaces in both cowpea cultivars and reduced cooking time of the less HTC susceptible cultivar. However, it did not reverse the HTC defect in the susceptible cultivar. Gamma‐irradiation also increased the levels of cold water‐ and hot water‐soluble pectin. The irradiation effects were thus mainly due to hydrolysis of pectin fractions in the cell walls. However, chelator‐soluble pectin (CSP) solubility was not affected. CONCLUSION : As the cell wall changes brought about by gamma‐irradiation were associated with pectin solubilisation, this supports the phytate–phytase–pectin theory as a major cause of the HTC defect. However, the non‐reversal of the defect in HTC susceptible cowpeas and the absence of an effect on CSP indicate that other mechanisms are involved in HTC defect development in cowpeas, possibly the formation of alkali‐soluble, ester bonded pectins.