Formation of corn fiber gum–milk protein conjugates and their molecular characterization

Corn fiber arabinoxylan is hemicellulose B isolated from the fibrous portions (pericarp, tip cap, and endosperm cell wall fractions) of corn kernels and is commonly referred to as corn fiber gum (CFG). Our previous studies showed that CFG isolated from corn bran (a byproduct of corn dry milling) contains very little protein and is an inferior emulsifier for oil-in-water emulsion systems as compared to corn fiber gum isolated from corn fiber derived from the corn wet-milling process. The protein deficient CFG isolated from corn bran was covalently conjugated with byproducts of cheese processing, β-lactoglobulin (β-LG) and whey protein isolate (WPI) using an economical food-grade Maillard-type heating reaction for the purpose of increasing their commercialization potential as a food emulsifier and soluble nutritional additive in beverages. The formation of the CFG–protein conjugates has been confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). It has also been demonstrated that CFG–protein conjugates are capable of producing fine emulsions with better stability than either CFG or protein alone. The molecular characterization of CFG–protein conjugates was performed by high-performance size-exclusion chromatography (HPSEC) coupled to on-line multi-angle laser light scattering and viscometric detection. The analysis by HPSEC revealed that CFG–protein conjugates had higher weight-average molar mass (Mw, 340–359kDa) and polydispersity (Mw/Mₙ, 1.74) than the corresponding unconjugated CFG (Mw, 290kDa and Mw/Mₙ, 1.35). The z-average root-mean-square radius of gyration (Rgz) of CFG–protein conjugates was slightly higher (30.5–33.5nm) in comparison to CFG (29.5nm) but their weight-average-intrinsic viscosity (η) remained unchanged (about 1.32dLg⁻¹). The Mark–Houwink exponent “a” of conjugates (0.40) was lower than the unconjugated CFG (0.53) indicating the formation of a more compact structure after conjugation with protein. These findings should benefit the beverage industry, which can use this information to produce a high quality emulsifier from the low-value byproducts of corn dry milling and cheese processing.