Food Science and Technology Department


Date of this Version



Alrugaibah, M. (2016). Characterization of extraction methods to recover phenolic-rich extracts from pinto beans (BaJa) that inhibit alpha-amylase and alpha-glucosidase using response surface approaches. (M.S. Thesis).


A Thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Food Science and Technology, Under the Supervision of Professor Vicki Schlegel. Lincoln, Nebraska: May, 2016

Copyright © 2016 Mohammed A. Alrugaibah


Pinto beans contain high levels of diverse phenols, known mainly for their potent antioxidative properties. However, reports have shown that phenols can inhibit the carbohydrate–hydrolysis enzymes, alpha-amylase and alpha-glucosidase, thereby retarding glucose absorption. Still, a severe gap in knowledge exists on the ability of pinto beans to inhibit these enzymes. Therefore, the objective of this project was to determine the ability of phenolic rich extracts obtained from pinto beans (BaJa) to inhibit alpha-amylase and alpha-glucosidase. The hypothesis was that pinto beans would be able to inhibit these enzymes due to the presence of high levels of chemically diverse phenols. Response surface methodology (RSM) was initially used to characterize extraction parameters that produced extracts with high total phenols (TP), total flavonoids (TF) and total condensed tannins (TCT) levels. This approach provided a starting point to identify the phenolic rich extracts and then to compare their inhibitory effects relative to one another. The project was completed by adjusting the polarity of methanol, ethanol, acetone and altering for three mixing times and solid:solvent ratios. Seventeen extracts produced by each solvent system was examined for TP, TF, TCT and their ability to inhibit alpha-amylase and alpha-glucosidase. The optimum factors as predicted by the analysis of RSM of the quadratic model for TP yields were 75:25 acetone:water, 10 percent solid:solvent and 87 minutes of mixing. For optimal TF extraction 75:25 acetone:water, 10 percent solid:solvent and 119 minutes of mixing were required. Maximum TCT values were achieved with 62:38 acetone:water, 20 percent solid:solvent and 180 minutes of mixing. Acetone extracts were also the most effective for inhibiting alpha-amylase and alpha-glucosidase (57.83, 17.59 percent /mg extract, respectively). Alpha-amylase or alpha-glucosidase inhibition did not correlate with TP, TF or TCT for the methanol extracts, but the correlation increased with the highest occurring with the acetone extracts. In summary, the significance of this project was that extracts originating from pinto beans are capable of inhibiting key carbohydrate–hydrolysis enzymes, but this property depends on the extract, most likely due to different phenol levels / types, and the presence of other nonephenolic components. Nonetheless, this food system may have potent health benefits for type 2 diabetics.

Advisor: Vicki Schlegel