Influence of Roasting Conditions on the Colorimetry of Cowpea Cotyledons (Vigna unguiculata (L.) Walp.)

Abstract

The cowpea (Vigna unguiculata (L.) Walp.) is a legume of great socioeconomic and nutritional importance, especially in the North and Northeast regions of Brazil, standing out for its high protein content and adaptability to semi-arid conditions. Considering its nutritional relevance and processing potential, the present study evaluated the colorimetric changes in cowpea cotyledons subjected to different roasting conditions, with variations in temperature and time. The experiment was conducted following a Central Composite Rotational Design (CCRD), comprising 12 treatments, with temperatures ranging from 150.5 °C to 249.5 °C and times from 5.9 to 34.1 minutes. Roasting was performed in an adapted coffee roaster with digital temperature control, and color measurements (L, a, and b* parameters) were obtained using a colorimeter in the CIE Lab* system. Data were subjected to analysis of variance (ANOVA), Scott-Knott test (5%), and second-order polynomial regression. The results revealed a highly significant effect (p < 0.001) of roasting conditions on all colorimetric parameters. The L* value showed a progressive reduction with increasing temperature and time, indicating marked darkening of the cotyledons. The highest L* values were observed in treatments 7 (35.49a) and 2 (35.12a), while the lowest occurred in treatments 4 (10.17f) and 8 (7.07g). The a* parameter ranged from 17.88e to 23.07a, with an increasing trend at intermediate temperatures and a decline under more severe conditions. The b* parameter varied from 6.68f to 34.46a, showing an initial rise and subsequent decrease at extreme roasting levels. The adjusted regression models presented determination coefficients above 0.93, indicating a strong fit between the independent variables and color parameters.