Modification of the functional properties of hard-to-cook cowpea seed flours and cooked prepared pastes by γ-irradiation

Abstract

Cowpeas are an inexpensive source of quality protein but their utilisation is limited by long seed cooking time. This is exacerbated by development of the hard-to-cook (HTC) defect, which also adversely affects starch and protein functionality. Gamma-irradiation can eliminate cowpea seed insect infestation and affects seed functional properties, including reducing cooking time. Hence, the potential of γ-irradiation to modify the starch- and protein-related functionalities of HTC cowpeas was investigated. Gamma-irradiation at approximately 11 kGy was applied to the seeds of two cowpea varieties, differing in HTC susceptibility, where HTC had been induced by high-temperature, high-humidity (HTHH) storage. HTHH storage increased flour pasting peak viscosity by up to 40% in the less susceptible variety and by more than 100% in the more susceptible variety. Gamma-irradiation at least completely reversed this effect, due to starch depolymerisation and debranching. Gamma-irradiation also positively impacted on some protein-related properties adversely affected by HTC; partially reversing the reduction in flour and cooked paste nitrogen solubility index of the HTC-susceptible cowpea, as a result of protein depolymerisation. The multiple benefits of γ-irradiation: disinfection, cooking time reduction and reversing some adverse effects of HTC on functional properties could make it a viable process for improving HTC cowpea quality.