Molecular Insights into Soy Protein–Lupin Flour Meat Analogues through FTIR Spectrochemical Analysis

Fourier transform infrared (FTIR) spectroscopy and spectrochemical imaging were used to investigate the structural and compositional changes in extruded high-moisture meat analogues (HMMAs) produced from soy protein isolate and lupin flour (LF) blends. Extrusion induced shifts in the amide I band (∼1637 cm⁻¹ in raw blends to ∼1650 cm⁻¹ in HMMAs), indicating protein denaturation and structural rearrangement associated with fibrous structure formation. Changes in carbohydrate- and lipid-associated bands further reflected extrusion-driven molecular reorganization. FTIR spectrochemical analysis revealed distinct HMMA regions, including aligned protein-rich domains and lipid-starch-rich domains appearing as polygonal grids. Increasing the LF content from 15 to 45% progressively increased lipid- and carbohydrate-associated spectral features (i.e., areas of the fatty acid ester peak at 1744 cm⁻¹ and the carbohydrate peak around 1060 cm⁻¹) relative to proteins. These insights advance the understanding of structure-function relationships in HMMAs and highlight the value of FTIR spectrochemical imaging for optimizing texture and the effective design of meat analogues.