Kinetics, aggregation behavior and optimization of the fractionation of whey protein isolate with hydrochloric acid

Authors: Bonnaillie, Laetitia; Tomasula, Peggy

Submitted to: Journal of Food and Bioproducts Processing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2012
Publication Date: 1/20/2012
Citation: Bonnaillie, L., Tomasula, P.M. 2012. Kinetics, aggregation behavior and optimization of the fractionation of whey protein isolate with hydrochloric acid. Journal of Food and Bioproducts Processing. DOI: 10.1016/j.fbp.2012.01.002.

Interpretive Summary: Whey protein isolate (WPI) is the most concentrated source of whey proteins obtained from the cheese-making process, and is well-recognized for its nutritional value. WPI contains more than six different types of proteins and their functional and nutritional values are improved further when the two main proteins are separated from each-other by means of a chemical or technological process. For example, one of the main proteins, beta-lactoglobulin, creates superior foams and gels similar to that of egg whites. The other protein, alpha-lactalbumin, contains amino-acids that are ideal for infant and senior nutrition, muscle-building, and other health-related needs. One way to separate the two proteins is to add an acid such as citric or hydrochloric acid, into a heated WPI solution. This causes all the proteins but beta-lactoglobulin to separate from the solution as a solid. The solid can then be removed from the liquid, and two protein ‘fractions’ are obtained. By changing the type and amount of acid used, and studying the effects of temperature and time on the separation of the proteins, information was obtained in the laboratory that will be used to design a new larger-scale process that can handle larger quantities of concentrated WPI solutions to produce larger quantities of the enriched protein fractions for commercial use in an efficient, economical and environmentally-friendly way.

Technical Abstract: Concentrated WPI solutions (10% (w/w)) containing approximately 30% alpha-lactalbumin (alpha-LA) and 60% beta-lactoglobulin (beta-LG) were fractionated with HCl at acidic pH and moderate temperatures to denature alpha-LA and recover the alpha-LA aggregates via centrifugation. Aggregation behavior and the kinetics of aggregate formation and protein denaturation were analyzed as a function of four process parameters: pH (3.0 to 5.5), temperature (50 to 70 deg C), reaction time (0 to 180 min) and protein concentration (10 to 29%). Denaturation and aggregation of alpha-LA appeared to be rate-limited, with a logarithmic dependence of time and a possibly bimodal rate of nucleation. While denaturation of alpha-LA is quick, the rate of aggregation of alpha-LA proteins varied greatly with pH and temperature. Aggregates as large as 300 Um were noted after 120 min at pH 4.0 and 60 deg C. The process parameters were optimized to obtain both a high aggregate yield and an optimal composition for the aggregate fraction. The optimally enriched fractions contained 62% alpha-LA in the aggregate fraction, and 98% beta-LG in the liquid fraction, with respective recoveries of 99% and 74%, and were obtained at pH 4.0-4.1 and 60 deg C, with a reaction time greater than 10 minutes and a 10% WPI solution. Over the range of pH studied, aggregation of beta-LG was considered negligible at 60 deg C, and all the beta-LG recovered in the aggregate was attributed to liquid holding. However, tripling the WPI concentration to 30% (w/w) did not reduce the purity of the aggregate considerably, due to an acceleration of the rate of alpha-LA aggregation, pointing to a concentration-dependent mechanism. This HCl-fractionation study is to be used as a template for the optimization of an economical, environmentally-friendly process using supercritical C02 as an acid to produce enriched fractions of alpha-LA and beta-LG with a high yield, using concentrated WPC or WPI solutions to reduce water handling and processing costs.