Improvement of protein digestibility and modification of physical properties of cowpea flour by autoclaving and fermentation

Cowpea stands out as a legume with high nutritional value, being a source of protein, fiber, minerals, and bioactive compounds. It is widely consumed in tropical regions and used as an ingredient in various food products. However, its application can be limited by the presence of antinutritional factors, which form complexes with minerals and proteins and reduce nutrient bioavailability. Among the technological strategies studied to overcome this limitation are solid-state fermentation (SSF) with edible fungi, capable of degrading antinutritional compounds, and autoclaving, which promotes structural and chemical changes favorable to digestibility. Therefore, the use of biological and thermal treatments represents a promising alternative to enhance the functional value of cowpea and expand its use in enriched food formulations. In this study, cowpea flours were subjected to three different treatments: raw grains, autoclaved, and fermented with Pleurotus ostreatus, to investigate the effects of these processes on particle distribution and protein digestibility. Digestibility was assessed using the O-phthaldehyde (OPA) method, which measures the release of free amino groups during the action of proteolytic enzymes in the gastric and intestinal phases. Furthermore, a particle size analysis of the flours was performed, as reduced particle size is directly related to greater protein accessibility to digestive enzymes, favoring nutritional utilization. The results demonstrated that the autoclaved samples had the highest protein digestibility, with values ​​of 2.50 mg/L of NH₂ in the gastric phase and 169.80 mg/L in the intestinal phase. Next, samples fermented with Pleurotus ostreatus (30.03 mg/L gastric and 147.06 mg/L intestinal) and samples fermented without Pleurotus (10.75 mg/L gastric and 133.87 mg/L intestinal) were observed. The raw samples presented the lowest values ​​(11.16 mg/L gastric and 67.02 mg/L intestinal). The particle size distribution ranged from 362.71 μm (raw sample) to 140.39 μm (autoclaved sample), confirming the significant reduction after thermal and biological treatments. Fermentation contributed to a decrease in particle size and improved protein digestibility. However, autoclaving alone was more effective, resulting in more bioavailable nutrients and, therefore, more easily absorbed by the body. In conclusion, both autoclaving and fermentation with Pleurotus ostreatus were effective in improving protein digestibility and modifying particle size distribution. These effects reinforce the potential of processed cowpea flour as a functional ingredient in food formulations with higher nutritional value.