Structural investigation of edible zein films/coatings and directly determining their thickness by FT-Raman spectroscopy

摘要

Near-infrared Fourier transform Raman (FT-Raman) spectroscopy was employed to study the molecular structure of edible zein films/coatings, which were fabricated directly from zein protein. The secondary structure of zein protein was mainly in (x-helix and remained unaltered during film formation as evidenced by the vibrational modes of amide I at 1656 cm(-1) and amide III at 1274 cm-1. Raman results indicated that hydrophobic interaction played an important role in the formation of zein film and disulfide bonding might be responsible for the structural stability of zein protein during film formation. To enhance its antimicrobial property, an antimicrobial zein film was manufactured by incorporating zein protein with benzoic acid whose structure was then characterized by FT-Raman. It showed that physical entrapment or hydrophobic interaction was crucial to the incorporation of benzoic acid with zein protein, and the secondary structure of the antimicrobial film was still maintained in (x-helical form. In addition, IFT-Raman exhibits its preference in directly determining the thickness of zein films/coatings. By correlating the Raman intensity ratio Of v(1003) to v(84) (I-1003/84) versus the thickness of zein film, a linear relationship with high coefficient (R-2 = 0.9927) was obtained, which was then used pragmatically to determine the thickness of zein coatings on apple. It showed that the IFT-Raman result (thickness = 0.27 +/- 0.01 mm) was consistent with that of classical micrometric measurement (thickness = 0.28 +/- 0.02 mm). Consequently, FT-Raman provides a direct, simple, and reagent-free method to characterize the structure and the thickness of zein films/coatings.