Cereal Chem. 70:193-195   |  VIEW ARTICLE

Induced Hard-to-Cook State in Cowpeas by Freeze-Thawing and Calcium Chloride Soaking.

K. Liu, R. D. Phillips, and K. H. McWatters. Copyright 1993 by the American Association of Cereal Chemists, Inc. 

Cowpeas stored at -18 C and ambient humidity (control) or 30 C and 64% rh (aged) for 12 months were hydrated before being subjected to freeze-thawing (FT) cycles, CaCl[2] soaking, or a combination of these. The cowpeas were monitored for electrolyte leakage, a possible indicator of cell membrane damage, and for hard-to-cook (HTC) state. Results showed that electrolyte leakage depended on storage conditions and the number of FT cycles. HTC state depended on storage conditions, the number of FT cycles, and the application sequence of FT and Ca[2+] soaking. For control cowpeas, FT slightly softened seed texture but greatly enhanced the hardening effect of Ca[2+] soaking applied subsequently. For aged cowpeas exhibiting a certain degree of HTC state, the greatest inducement of hardness was observed with Ca[2+] soaking alone. Other divalent cations exerted effects similar to those of Ca[2+] but to a lesser extent. With respect to the number of FT cycles, there was a parallel relationship in control cowpeas between electrolyte leakage after FT and HTC state induced by subsequent Ca[2+] soaking. This relationship was not observed in aged seeds because of initial high electrolyte leakage during hydration. Overall results suggest that one part of HTC inducement during cation soaking occurs through loss of cell membrane integrity that allows cations to bind intracellular components.