Extraction Optimization of Phenolic Extracts from Carioca Bean (Phaseolus vulgaris L.) Using Response Surface Methodology

There is a large consumption of beans in developing countries for their nutritional quality: high contents of complex carbohydrates, such as starch and fiber together with considerable amounts of protein. Recently, beans have also been reported as good sources of phenolic compounds. Studies upon phenolic compounds in Carioca beans are relevant because these pulses are consumed every day by millions of people, and can be associated with health-promoting activities. In this study, phenolic compounds of beans have been extracted using different extraction methods. As the results can be affected by several factors and there is no standardized methodology to extract phenolic from Carioca beans, this paper proposes the use of response surface methodology to optimize a phenolic compound extraction method. Three experiments were performed using acetone, methanol, or methanol–HCl (99:1) as solvents. For each solvent, a three-level Box–Behnken design was employed, using the sample-to-solvent ratio, temperature, and solvent concentration as factors. The response variables were total phenolic compounds (TPC); flavonoid contents (FC); and antioxidant capacity, determined by ABTS, DPPH, and FRAP assays. The optimized conditions for each solvent were compared to seven other extraction methods proposed in the literature. RP-HPLC-DAD was used to quantify the phenolics of each extract. The results were submitted to principal component analysis (PCA), which showed that the best extraction conditions for Carioca beans, among the ten methods compared, was 70% acetone at 25 °C and a 1:15 sample-to-solvent ratio. Kaempferol and chlorogenic acid were the main flavonoids and phenolic acids, respectively, found in Carioca beans.