Investigation of the molecular interactions between beta-lactoglobulin and low methoxyl pectin by multi-detection high performance size exclusion chromatography

Authors: Qi, Phoebe; Chau, Hoa - Rose; Fishman, Marshall; Wickham, Edward; Hotchkiss, Arland

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2016
Publication Date: 9/15/2016
Citation: Qi, P.X., Chau, H.K., Fishman, M., Wickham, E.D., Hotchkiss, A.T. 2016. Investigation of the molecular interactions between beta-lactoglobulin and low methoxyl pectin by multi-detection high performance size exclusion chromatography. Food Hydrocolloids Journal. doi: 10.1016/j.foodhyd.2016.09.016.

Interpretive Summary: Milk proteins are often used as emulsifiers (agents that can help prevent oil and water from separating) whereas polysaccharides (long chains of carbohydrates), are used as thickeners and gelling agents in a variety of food products ranging from mayonnaise to salad dressing. Combining milk proteins and polysaccharides may result in new food ingredients with enhanced properties, compared to the single protein or polysaccharide such as pectin, that are especially useful for improving the nutritional value, textural properties and stability of foods. However, formulations of these ingredients need to be carefully controlled on a molecular level in order to achieve the desired properties. Research in this work focused on the interactions between beta-lactoglobulin (betaLG), the most abundant whey protein of cow milk, and low methoxyl pectin, extracted from apple pomace or citrus peels, also one of the most versatile polysaccharides. Results demonstrated that a brief pre-heating treatment of the protein before combining with pectin significantly increased the amount of protein bound to pectin. Additionally, the presence of sucrose, a common table sugar, can help facilitate the interactions between betaLG and LMP at molecular level. This study helped to advance our understanding of the interactions between milk proteins and pectin. The knowledge gained in this work should also be useful in designing new formulations of food products containing dairy proteins and pectin.

Technical Abstract: Combining milk proteins and polysaccharides may result in new food ingredients with enhanced properties, compared to the single protein or polysaccharide, that are especially useful for improving the nutritional value, textural properties and stability of foods. However, formulations of these ingredients need to be carefully controlled on a molecular level in order to achieve the desired properties. To achieve controlled physiochemical, structural, and consequently, functional properties of interacting systems containing beta-lactoglobulin (beta LG) and low methoxyl pectin (LMP, DE 36.8%), solution conditions were established and studied at the weight ratio of 3:1 (w/w), pH approximately 6.50. Online multi-detection High Performance Size Exclusion Chromatography (HPSEC) was used to characterize the hydrodynamic properties of interacting biopolymer fractions in detail. Results showed that upon direct mixing, approximately 6.1% (w/w) of native dimeric betaLG molecules formed complexes with LMP molecules of two sizes, namely [Mw] approximately 250 and 55 kDa. The interactions produced complexes of altered shapes and hydrodynamic properties compared to those of betaLG and LMP controls. Heat denaturation (80 deg C, 10 min) of betaLG greatly increased its participation in the complexes as aggregates, to approximately 10.4%, which appear to favor the LMP molecules of higher [Mw]. Pre-heating LMP, however, impeded its binding ability to betaLG and increased the amount of unbound betaLG as a result. The effect of sucrose on the interactions between betaLG and LMP was also investigated using a set of similarly treated samples but consisted of sucrose removed LMP (LMP(NS)) instead of LMP. These studies demonstrated that sucrose greatly facilitated the complex formation, notably between the pre-heated betaLG and LMP. The structures of the complexes were found to be less flexible and less open in the presence of sucrose than its absence. It is suggested that sucrose contributed greatly to the stabilization of the heat-induced betaLG aggregates as they interact with LMP.