Effect of different heat treatments on physicochemical properties and antioxidant characteristics of black beans

This study systematically evaluated the effects of four thermal processing methods-boiling, steaming, extrusion, and roasting-on the physicochemical properties and in vitro antioxidant activity of black beans. Notably, ash content decreased following boiling and steaming, reaching 45.5 mg.g-1 and 43.5 mg.g-1, respectively, corresponding to reductions of 8.5% and 13.3%. In contrast, extrusion and roasting led to moisture loss, resulting in ash content increases of 3.2% and 6.8%. Among the treatments, boiling significantly increased powder clumping (5.1%), primarily due to elevated moisture content, a value markedly higher than that observed for other methods. Both boiling and steaming diminished brightness, while extrusion deepened colour intensity and enhanced redness. Regarding chemical composition, polyphenol content declined after boiling and steaming (3.8 mg.g-1 and 2.9 mg.g-1, respectively) relative to untreated black bean powder (4.3 mg.g-1). Extrusion, however, elevated polyphenol levels, whereas all heat treatments reduced flavonoid content, with boiling exerting the greatest impact. Antioxidant activity also declined post-processing, with boiling having the most pronounced effect on 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) radical scavenging and steaming most affecting hydroxyl radical elimination. Extrusion emerged as the optimal processing method for black beans, and superior retention of bioactive compounds, enhanced antioxidant capacity, improved physicochemical properties (lower clumping, stable colour parameters). These findings could provide actionable insights for food industries to select processing methods that maximise nutritional value and functional properties of black bean products.