The FTIR spectrum of pure SPI is shown in Fig. 1a. The main absorption peaks are related to C=O stretching at 1630 cm-1 (amide I), N–H bending at 1530 cm-1 (amide II) and C–N stretching(amide III) at 1230 cm -1[21,22]. The broad band observed in the 3500–3000 cm-1 range is attributable to free and bound O–H and N–H groups, which are able to form hydrogen bonding with the carbonyl group of the peptide linkage in the protein [23].