Thermal properties of cowpea flour: a study by differential scanning calorimetry

The thermal properties of 12 varieties of cowpea flour were studied by differential scanning calorimetry (DSC). Flour samples were prepared to a paste of 60% moisture content and sealed in standard DSC pans. Samples were scanned at a heating rate of 5 degrees C/min over a scan range of 40- 130 degrees C. Samples exhibited single major endotherms, which occurred over varied temperatures. The transition enthalpy (deltaH) ranged between 1.4 J/g and 4.7 J/g. Transition onset (T(o)) and transition peak (T(p)) temperatures ranged between 75-78 degrees C and 78-82 degrees C,respectively. All the DSC parameters measured varied significantly among the varieties. The transition enthalpy (deltaH) was the most discriminating parameter and accounted for 80% of the total variance. The major chemical components of cowpea flour, starch amylose and protein are significant predictors of deltaH. Protein denaturation appears to be a significant modification which occurs during processing of cowpea seeds to flour. The transition enthalpy deltaH could become an important functional index of cowpea flour when related to some quality parameters in products that contain the flour.