Aging indicators for stored carioca beans

High temperature, moisture content and radiation conditions, common in the tropics, accelerate the physiological post-harvest disorders in beans, affect integument color and bean hardness. This study explored the darkening and hardening mechanisms in carioca type beans during storage. The contrasting genotypes for bean darkening and hardening (BRS Estilo and BRS Pontal: rapid darkening and hardening; BRSMG Madrepérola and CNFC 10467: slow darkening and partially resistant to hardening; and a Canadian genotype of the Pinto Bean type resistant to darkening (negative control)) were evaluated right after harvest and after six months storage at 20.3 ± 0.2 °C and 78.9 ± 6.0% RH, with respect to their physicochemical, biochemical and morphological attributes. All the samples hardened with time, but the velocity of darkening did not always parallel the degree of hardening of the beans (that increase linearly with time), which indicates that the color of the bean integument was not a safe indicator to predict the culinary quality of carioca beans. During storage, the SOD (superoxide dismutase) activity and LP (lipid peroxidation) in the cotyledon increased, and the increase was more significant in the integument of the rapid-darkening genotypes. The oxidative stress detected in the beans apparently started in the green bean formation phase, continuing during post-harvest, especially for the rapid-darkening beans. Quantification of the bivalent ions in the bean fractions, together with the degree of membrane damage was positively associated with bean darkening, independent of the group. Thus, aging of the carioca beans could be triggered by a complex mechanism involving diverse intrinsic factors in different degrees according to the genotype and the post-harvest period, but some parameters could serve as indicators, as cooking time, hardness and color, to differentiate between rapid and slow darkening beans.