Effect of Alkaline Deamidation on the Structure, Surface Hydrophobicity, and Emulsifying Properties of the Z19 α-Zein

Abstract

Different deamidation conditions for the Z19 alpha-zein were studied in order to find the best conditions for the development of the emulsifying properties. Alkaline deamidation was chosen, and the effects on the peptide bond cleavage, secondary structure, emulsifying properties, and surface hydrophobicity were studied. The Z19 alpha-zein was deamidated by using 0.5 N NaOH containing 70% ethanol at 70 degrees C for 12 h. A deamidation degree (DD) of 60.6 +/- 0.5%, and a degree of hydrolysis (DH) of 5 +/- 0.5% were achieved. Analysis by far-UV circular dichroism showed that the denaturation was mainly promoted by the high temperature used during the incubation. The adequate balance between the DD and the DH results in an effective emulsifying property improvement for the Z19 alpha-zein. Thus, after the deamidation treatment, the surface hydrophobicity decreased from 9.5 x 104 +/- 6.8 x 103 to 46 x 104 +/- 2.1 x 103, and the emulsion stability increased from 18 +/- 0.7% to 80 +/- 4.7% since the oil globules stabilized by the modified protein were smaller (57.7 +/- 5.73 nm) and more resistant to coalescence than those present in the native protein emulsions (1488 +/- 3.92 nm).

Effect of acid and base treatments on structural, rheological, and antioxidant properties of α-zein

“…However, such phenomenon was not found in our zein samples, indicating that zein retained its primary structure upon the mild pH treatment. Although FTIR and zeta-potential results showed that zein underwent deamidation, especially at the conditions of pH 2.7 and pH 12.5, the band pattern of protein electrophoresis for monomer and dimer zein indicated that the deamidation of glutamine did not change the zein molecular weight, which agreed with the results of alkaline deamidated zein by Cabra et al (2007). Besides, no increase in molecular weight was observed as well, which indicates that no polymerisation of zein molecules occurred in mild pH solutions.…”

“…Therefore, zein finds many potential applications in food and pharmaceutical industries including but not limited to tablet coating and free-standing packaging materials (Hernandez-Izquierdo & Krochta, 2008), emulsifier (Cabra, Arreguin, Vazquez-Duhalt, & Farres, 2007;Casella & Whitaker, 1990;Yong, Yamaguchi, Gu, Mori, & Matsumura, 2004), chewing-gum base (Liu & Lee, 2004), antioxidant (Chiue, Iwami, Kusano, & Ibuki, 1994;Zhu, Chen, Tang, & Xiong, 2008), drug encapsulant (Guo & Shi, 2009;Hurtado-Lopez & Murdan, 2005;Liu, Sun, Wang, Zhang, & Wang, 2005;Zhong & Jin, 2009), and tissue scaffold (Gong, Wang, Sun, Xue, & Wang, 2006;Tu et al, 2009;Wang et al, 2007. Many of these applications (e.g., chewinggum base and antioxidant) are counting on zein's native property, which is high in aliphatic indexes and surface hydrophobicity (Argos et al, 1982;Cabra et al, 2007) and high in fatty acid-binding capacity (Chiue, Kusano, & Iwami, 1997). Whereas, for other applications (e.g.…”

“…emulsifier), modified zein structures with enhanced functional properties (e.g. water solubility, foaming and emulsifying properties) (Cabra et al, 2007;Casella & Whitaker, 1990;Yong et al, 2004) are preferred.…”

“…Zein structures were found to be influenced by many physico-chemical parameters, such as temperature, concentration, salt type, pH, and solvent type. It was reported that high temperatures (90°C) would denature zein's secondary and tertiary structures and result in zein oligomerization (Cabra et al, 2007). Different cations (i.e.…”

“…In the limited literature, Cabra et al (2007) reported that different pH treatments (0.5-2 N hydrochloric acid or sodium hydroxide, NaOH) with or without applying heat would induce zein deamidations, resulting in an improved emulsifying property. Under similar pH conditions (0.05 N hydrochloric acid with heat), Chiue et al (1994) found a decreased zein's fat-binding capacity leading to the loss of radical scavenging ability.…”