3.5.2. CD Spectrum

In this study, CD spectrum analysis was applied to measure conformational changes (secondary structure) of zein in complexation (260 nm~190 nm). As seen from (Figure 4C), two peaks at 209 and 223 nm with a zero-crossing were around 203 nm (typical secondary structure) in the zein spectrum [44]. As shown in (Table 2), the α-helix, β-sheet and β-turn content of DHF-S/Z changed from 25.3 to 24.7 and 24.5%, 25.8 to 26.1 and 26.6% and 28.3 to 29.1 and 27.9%, respectively after adding CMC and ALG. These results suggested that the addition of CMC and ALG had no apparent impact on zein's secondary structure in DHF-S/Z. The behavior of CMC and ALG could possibly be the result of sophorolipid adsorption on the zein surface. This adsorption could have possibly resulted in insufficient contact between the polysaccharides and zein, which was difficult to further change the secondary structure of zein. In general, the amide I band shifts in FTIR spectra could also reflect secondary structure changes of the protein, including the band of α-helix, β-sheet, and β-turn [45]. In the FTIR spectra of our study (Figure 4B), the band of amide I did not show significant change among DHF-S/Z, DHF-CMC/S/Z and DHF-ALG/S/Z. This lack of significant change further confirmed that CMC and ALG did not impact the secondary structure of zein.

**Table 2.** Secondary structure of zein in DHF-S/Z, DHF-CMC/S/Z and DHF-ALG/S/Z.

