Fourier Transform Infrared (FTIR) Spectroscopy
FTIR spectra of samples were scanned at room temperature by a Bruker Vertex 70 FTIR spectrometer (Bruker Daltonics, Bremen, Germany) as reported previously [9]. Different testing samples were acquired in KBr tablets. The spectra were collected with a scanning range of 4000-500 cm-1 at a resolution 4 cm-1and 32 scans. The secondary structure of protein in untreated, moist-heated, and dry-heated walnut kernel was estimated by a second derivative in the amide I region (1700–1600 cm-1). Deconvolution of the second derivative of FTIR was obtained by Savitsky–Golay algorithm from Origin Pro 2021 software (Hearne Scientific Software).