Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2012
Publication Date: 5/4/2012
Citation: Bonnaillie, L., Tomasula, P.M. 2012. Fractionation of whey protein isolate with supercritical carbon dioxide to produce enriched alpha-lactalbumin and beta-lactoglobulin food ingredients. Journal of Agricultural and Food Chemistry. 60(20):5257-5266.
Interpretive Summary: A portion of the liquid whey leftover during cheesemaking is concentrated and dried to produce whey protein concentrates (WPC) and isolates (WPI), which are used commercially to enhance the nutritional profile or functionality of foods. The two main proteins of WPC and WPI, alpha-lactalbumin (alpha-LA) and beta-lactoglobulin (beta-LG), are present in a 1:3 ratio and have widely differing properties: beta-LG forms edible gels and foams, while alpha-LA participates in the ideal nutrition of infants, children, and may help prevent diseases and conditions associated with aging. A large-scale, economical process to separate the alpha-LA and beta-LG proteins of WPI to produce isolates or enriched fractions does not exist yet. In past studies, scientists have demonstrated that the acidic properties of supercritical carbon dioxide (SCO2) may be used to separate alpha-LA from beta-LG in WPC, by forming particles of alpha-LA that precipitate while beta-LG remains in solution. In this phase of the research, scientists are showing that processing a purer protein concentrate, WPI, at higher pressures and under precisely controlled and optimized operating conditions yields a high-performance process that can enrich the alpha-LA and beta-LG fractions up to seven times. In addition, the new SCO2 fractionation process can treat more concentrated streams than most other whey protein fractionation techniques, and produces ready-to-use, food-grade alpha-LA and beta-LG fractions that are uncontaminated with chemical or mineral additives, in an environmentally-friendly way, since CO2 can be recycled. This research will provide processors with new value-added whey protein ingredients with unique nutritional and functional benefits from low-value cheese-manufacturing byproducts, using a sustainable processing method.
Technical Abstract: A potentially economical and environmentally friendly whey protein fractionation process was developed using supercritical carbon dioxide (SCO2) as an acid to produce enriched fractions of alpha-lactalbumin (a-LA) and beta-lactoglobulin (b-LG) from whey protein isolate. To prepare the fractions, solutions containing from 2 to 10 wt.% commercial whey protein isolate (WPI) were saturated with SCO2 in a pilot-scale high-pressure reactor. At pressures up to 5000 PSI (37 MPa) and 60 to 65ºC, solubilized CO2 generated carbonic acid that lowered the pH of WPI solutions and induced the formation and precipitation of a-LA aggregates. The pH of WPI solutions was calibrated versus CO2 pressure, P, and protein concentration, C, and modeled to enable calculation of pH(P,C) on a wide range of operating conditions. The effects of pH, temperature, WPI concentration, and residence time on the kinetics of precipitation of the individual whey proteins and their final recovery yields, as well as on the relative enrichment and compositions of both protein fractions, were investigated. Gel electrophoresis and HPLC of the enriched fractions showed that different sets of operating conditions produced a-LA-enriched fractions containing more than 60% a-LA, and b-LG-enriched fractions containing more than 70% b-LG and as little as 5% a-LA, from a WPI initially comprising 57% b-LG and 21% a-LA. The resulting fractions are ready-to-use, new food ingredients with a pH of 6.0 and that contain no residual acid or chemical contaminant.