Sample Preparation Applied to Analysis of Proteins in Cowpea Seeds (Vigna unguiculata (L.) Walp.)

In this study, 20 different protocols for protein extraction of cowpea seeds in natura were evaluated taking into account four parameters: cell disruption method, time, temperature and solvent. Factorial design experiments were executed to determine the effects on the total protein content of extracts. The total protein content was determined and the results were in the range of 8.75 ± 1.3 and 86.6 ± 6.9 mg g-1. The richest protein extracts were obtained using Tris-HCl buffer at 50 ºC for 20 min for each assessed cell disruption method. However, the results using water were similar to buffer according to t-test at the 95% confidence level. Six protocols demonstrated higher extraction efficiency. Comparative proteomic study using size exclusion chromatography coupled to diode array detector (SEC-DAD) revealed that the one protocol extracted simultaneously high and low molecular mass biomolecules. In fact, the effect of microwave radiation promoted an increased solubility of biomolecules in water. The analysis of chromatographic profiles for principal component analysis (PCA) highlights the greater efficiency of extraction with the application of this protocol. Therefore, our study showed that the optimum condition for extraction of cowpea seed protein consists of water assisted by microwave radiation at 50 ºC for 20 min.