Study of black bean (Phaseolus vulgaris) and quinoa (Chenopodium quinoa) flours as a source of peptides and their effect on DPP-IV inhibition

Abstract

Plant-based proteins can be beneficial for the environment and health purposes. Nowadays, diet and a sedentary lifestyle are the cause of several health problems, such as obesity, cardiovascular diseases, cancer, and diabetes. Black beans and quinoa are important sources of plant-based proteins due to their high protein content and well-balanced amino acid presence. Black beans and quinoa are considered nutritious and rich in bioactive peptides (BP), characterized by their positive impact on healthy body functions. BP's antidiabetic, antimicrobial, antioxidant, and antihypertensive properties are some health benefits. This work aimed to evaluate black bean flour with two types of process (extruded and non-extruded) and two varieties of quinoa (white and black) as a source of bioactive peptides with potential DPP-IV inhibitory activity. All flours were evaluated at two levels of milling. The study of the raw materials encompassed a particle size analysis, a morphological analysis using a scanning electron microscope (SEM) and a proximate characterization. Black bean with level 1 milling had 98% of particles with a smaller diameter than 813.25±8.35 m, while for black bean flour with level 2 milling, this diameter was 566.54±43.82 m, showing that the second milling yielded flour with finer particles. On the other side, white quinoa with level 1 milling had 98% of particles with a maximum diameter of 697.21±110.40 m, while white quinoa with level 2 milling had 98% of particles with a maximum diameter of 546.28±26.33 m. The morphological and proximate analysis showed that samples were rich in starch and protein. The quinoa flour varieties had 15.13±1.55 and 15.51±0.70% of protein (white and black quinoa flour, respectively), the black bean flour had 18.93±1.63%, and the extruded black bean flour had 22.75±0.44% of protein. All flour samples had between 62.26±1.46% to 63.45±1.55% of total carbohydrates. Afterward, the protein fraction was extracted by alkaline procedure at pH 12, resulting in high extraction yield and purity. Black bean with finer milling had the highest protein extraction yield with 82.87±3.97%, and fine-milled white quinoa had the highest protein purity with 61.33±2.83%. Protein hydrolysis was then carried out using 1% alcalase (% w/w of protein) for 0,1, 2, 4 and 6 hours at 60 °C. The degree of hydrolysis (DH) was determined, with extruded black bean showing the highest DH (354.8%). The electrophoretic profile showed the different protein fractions (globulin, albumin and phaseolin). It is also noticeable that the bands are much broader below 10 kDa, showing that the molecular weight is lower, which could mean that the hydrolysis process successfully reduced the protein length. DPP-IV inhibitory activity was determined, and the results showed that white quinoa and black bean hydrolysates have the highest relative inhibition, with 50.00%. The inhibitory activity of DPP-IV contributes to the potential use of hydrolysates obtained from quinoa and black bean as an ingredient with nutraceutical functions. DPP-IV inhibition is a preventive and therapeutic mechanism of action for type 2 diabetes.