Maillard-Induced Glycation of Whey Protein Using Maltodextrin and Effect on Solubility, Thermal Stability, and Emulsification Properties

Abstract

With high nutritional value, and excellent physiological and functional properties, whey protein has a unique position in the protein market. Whey protein beverages, specifically, have high popularity among people looking for additional protein in their diet in an easy to consume and readily available form. Formulating beverages with whey protein, however, is not free of challenges. Despite the excellent solubility of whey protein over a wide range of pH, when whey protein beverages undergo thermal processing and prolonged storage, aggregation and a resulting loss of solubility can occur. Loss of solubility upon processing and during storage is especially prevalent near the whey protein isoelectric point (pI) (4.5). This hurdle makes production of acidic whey protein beverages (pH 3.8-4.5) with high protein content (>4.2%, to make a high protein claim) difficult. Current whey protein acidic beverages available on the market contain at most 4% protein and are formulated at pH ≤ 3.4, which makes them sour and astringent. In order to expand the market value, it would be ideal to develop shelf stable whey protein acidic beverages that can make the high protein label claim, and are produced at a slightly higher pH (3.8-4.5). Previous research attempted to achieve this goal through Maillard-induced glycation. But more work was needed to optimize this approach. It was hypothesized that the solubility and thermal stability of membrane filtered whey protein isolate will be enhanced upon glycation with food grade maltodextrin. Additionally, improvements in functionality will be recreated with a higher protein to carbohydrate ratio, with the assumption that this will eliminate the need for separation of unreacted carbohydrate, and generates a product with higher protein content. Thus, the objectives of this study were twofold: (1) Optimize Maillard-induced glycation of membrane-filtered whey protein with food grade maltodextrin following an industry feasible approach. (2) Determine the effect of Maillard-induced glycation on solubility, thermal stability, and emulsification properties of whey protein. Maillard glycation of whey protein was induced by incubating whey protein isolate with maltodextrin at 60°C, water activity (aw) of 0.49, 0.63, or 0.74, and a 1:4 and 2:1 ratio of protein to maltodextrin over a period of 48-144 h. The extent of glycation was monitored via estimation of Amadori compound formation and browning, quantification of free amino group and free lysine loss, and visualization of protein molecular weight distribution. Optimum conditions for the desired objectives were determined to be 96 h of incubation at 0.49 aw, in a 2:1 ratio of whey protein to maltodextrin, due to a plateau in Amadori compound formation, limited browning, and minimal loss of free amino groups (11%) and lysine (0.45%). Unreacted maltodextrin was removed using hydrophobic interaction chromatography to produce a purified partially glycated whey protein (PGWP) constituting ~ 94% protein and ~4% carbohydrate. The onset of denaturation of PGWP was monitored using differential scanning calorimetry (DSC), and solubility of PGWP were assessed at 5% protein concentration prior and post heat treatment at 80°C for 30 min. SDS-PAGE was used to visualize polymerization induced by heat treatment that would contribute to changes in solubility. Emulsification properties of PGWP were assessed as well, through emulsification capacity and stability measurements. Partial glycation of whey protein resulted in enhanced solubility and thermal stability of whey protein near the pI of WPI (pH 4.5) and under neutral conditions (pH 7). Around the pI of whey proteins, WPI lost ~60% of solubility, whereas PGWP remained almost entirely soluble (~8% loss). Under neutral conditions, the decrease in solubility of PGWP (~15% loss) upon heating was half as much as that of WPI (~32% loss). The enhanced solubility and thermal stability of PGWP was attributed to resistance to denaturation and reduced protein-protein interactions upon glycation. The emulsification capacity of WPI, on the other hand, was improved upon glycation by ~12%, while emulsification stability was reduced. The improvement in emulsification capacity was attributed to the conformational changes that whey protein underwent upon glycation. Overall, this work showed for the first time that limited Maillard glycation can be induced using food grade maltodextrin to produce a partially glycated protein product with a protein content greater than 90%. Compared to WPI, this high protein product had enhanced solubility and thermal stability, even at the pI of whey protein, allowing for its application in both acidic and neutral beverages with an anticipated longer shelf life at protein concentration > 4.2%. Successful formulation at protein levels that allow a high protein claim, while maintaining longer shelf-life and overall quality, provides economic gain to producers and physiological benefits to consumers.