Bean Type Strongly Drives Specific Mechanical Energy and Distinguishes Extrudate Expansion During Extrusion Processing.

Abstract

This study examined how bean type and extrusion conditions influence process behavior and quality attributes of expanded extrudates produced from pre-cooked pinto, navy, and black bean flours. Blends were extruded at three feed moisture levels (14%, 17%, and 20%, wet basis), and three screw speeds (100, 200, and 300 rpm). Product properties were strongly dependent on processing conditions and bean type. Navy beans produced more expanded and softer extrudates with expansion ratios of 1.58-2.49 and hardness values of 1.54-8.63 kg compared with pinto bean extrudates, which showed lower expansion (1.30-1.88) and higher hardness (2.62-15.55 kg). Black bean extrudates showed intermediate behavior, with expansion ratios of 1.68-2.11 and hardness values of 2.44-11.65 kg. Color change increased with more severe processing conditions for all bean types. Water solubility index (WSI) was strongly and positively correlated with specific mechanical energy (SME) for all bean flours, with Pearson correlation coefficients of r ≥ 0.97 for navy, pinto, and black beans. Scanning electron microscopy (SEM) images supported these findings, showing condition- and bean-dependent cellular structures ranging from more uniform foams to coalesced pores and locally compact regions. K-means clustering revealed three distinct extrusion product groups driven by bean type and processing intensity, distinguishing low-energy, low-expansion black and pinto bean extrudates from high-viscosity and high-SME navy bean formulations. Overall, the results show that bean type significantly affects structure development and energy demand during extrusion processing, requiring bean-specific process optimization.