No abstract

Ovalbumin (OVA) is an important protein emulsifier. However, it is unstable near the isoelectric point pH, which limits its applications in the food industry. Polysaccharides may be explored to tackle this challenge by improving its pH-dependent instability. In this work, carboxymethyl cellulose (CMC) was used as a model polysaccharide to mix with OVA near its isoelectric point (pH 4.7) with subsequent mild heating at 60 °C for 30 min. The molecular interactions between OVA and CMC were comprehensively studied via a series of characterizations, including turbidity, zeta potential, intrinsic fluorescence, surface hydrophobicity, circular dichroism (CD) spectra and Fourier transform infrared spectroscopy (FTIR). The droplet sizes of the emulsions prepared by OVA-CMC were measured to analyze emulsifying property and stability. The results indicated that free OVA was easily aggregated due to loss of surface charges, while complexing with CMC significantly inhibited OVA aggregation before and after heating owing to the strong electrostatic repulsion. In addition, OVA exposed more hydrophobic clusters after heating, which resulted in the growth of surface hydrophobicity. Altogether, the heated OVA-CMC complexes presented the best emulsifying property and stability. Our study demonstrated that complexing OVA with CMC not only greatly improved its physicochemical properties but also significantly enhanced its functionality as a food-grade emulsifying agent, expanding its applications in the food industry, as development of emulsion-based acidic food products.Egg ovalbumin (OVA), the main ingredient of egg white protein, is one of the most widely used protein and a kind of important food ingredient. In addition, OVA also possesses important functionalities including emulsifying and foaming stability because it has more than 50% hydrophobic amino acids, similar to other surface-active agents 1,2 . Nevertheless, there are two major limitations for OVA to be widely used in the food industry. First, OVA is known to have poor thermal instability. It was reported that the thermal aggregation temperature of OVA was lower around its isoelectric point than that in other pH conditions, and the optimal thermal stability was in the pH range from 6 to 10 3,4 . In addition, the emulsifying property of OVA was poor near the isoelectric point as shown in our previous work 2 . Meanwhile, as a protein molecule, when the pH is reduced to around its isoelectric point (pH 4.7), OVA carries zero net surface charge and loses its emulsifying capability when used in the emulsion-based acidic food products, such as yogurt and lactic acid beverages 5 .Carboxymethyl cellulose (CMC), one of the derivatives of cellulose, has been widely used as a stabilizing agent in foods 6 . In addition, CMC is stable with strong negative charges at pH values from 2 to 10, which makes it suitable for various applications in most food products across a wide range of pH conditions. CMC is a commonly used additive to improve the processing properties of products in cos...