Changes in physical, chemical and functional properties of whey protein isolate (WPI) and sugar beet pectin (SBP) conjugates formed by controlled dry-heating

Authors: Qi, Phoebe; XIAO, YINGPING - Zhejiang University; Wickham, Edward

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2017
Publication Date: 1/27/2017
Citation: Qi, P.X., Xiao, Y., Wickham, E.D. 2017. Changes in physical, chemical and functional properties of whey protein isolate (WPI) and sugar beet pectin (SBP) conjugates formed by controlled dry-heating. Food Hydrocolloids Journal. doi: 10.1016/j.foodhyd.2017.01.032.

Interpretive Summary: An emulsifier consists of a water-loving hydrophilic head and an oil-loving hydrophobic tail. By positioning itself at the oil/water or air/water interface, it stabilizes emulsions of oil and water, which would separate without the emulsifier. Whey protein, a major milk protein, is often used as a natural emulsifier in a variety of food products such as salad dressing and frozen dessert in conjunction with polysaccharides, which act as thickeners and gelling agents. However, whey protein becomes less soluble and unstable when heated and processed. We carried out research on combining and heating whey proteins and sugar beet pectin, one of the most versatile polysaccharides, in the dry state under mild and controlled conditions to look for ways to improve the properties of whey. The results showed that by conjugating with pectin, whey protein became more soluble in water and its emulsification stability was also improved. This work established an optimal condition (3:1), e.g. protein to pectin ratio for producing conjugated biopolymers with these improved functional properties. This study will help guide us to design new whey protein formulations with improved quality and characteristics for uses in a wide range of food products.

Technical Abstract: A Maillard type reaction in the dry state was utilized to create conjugates between whey protein isolate (WPI) and sugar beet pectin (SBP) to achieve improved functional properties including solubility, colloidal stability and oil-in-water emulsion stability. To optimize the reaction conditions, mixtures of WPI and SBP at varying weight ratios, 5:1, 3:1 and 1:1, were heated at 60 degrees C, 79% RH for 72 hrs. Changes in the physical properties, i.e. solubility, and chemical compositions, i.e. free sulfhydryl and amine contents were assessed using chemical assays. Bradford assay results demonstrated that the protein solubility of WPI increased significantly, approximately 20% by reacting with lower levels of SBP (5:1 and 3:1) whereas the total powder solubility was not affected until an equal ratio of SBP was used, and the reduction was only approximately 15%. The free sulfhydryl (SH) and primary (NH2) and secondary amine (NH) contents of WPI were also mitigated by conjugating with SBP. The formation of the covalent conjugates between WPI and SBP was confirmed by SDS-PAGE gel electrophoresis through staining for both proteins and glycoproteins. The UV-VIS spectroscopy showed significant changes in the molecular electronic transition states of both WPI and the feruloyl moieties of SBP upon interaction and conjugation. Measurements of zeta-potential, particles size distribution and average particle size demonstrated that the WPI-SBP conjugates prepared at the weight ratio of 3:1 were most effective at stabilizing oil-in-water emulsions than other ratios used in this work.