Separation and Characterization of Reconstituted Skim Milk Powder Treated with Mineral Chelators

Abstract

Separation and Characterization of Reconstituted Skim Milk Powder Treated with Mineral ChelatorsAmy Sue KringleThe proteins found in milk are largely important in the functionality of many dairy products and dairy processes. The casein micelle system in milk is a complex and highly studied system. The micelle is thought to be a sponge like structure containing four caseins, α s1 , α s2 , β, and κ casein, and bound together with colloidal calcium phosphate. When a chelating agent such as a citrate, phosphate, or polyphosphate are added to milk systems, the CCP is bound to the chelator and removed from the micelle. It has been shown through past research that the use of calcium chelating agents disrupts the calcium phosphate equilibrium and allows for the dissociation of the casein micelle and release of the individual caseins. Once the caseins are disrupted from micellar form and in solution, it may be possible to separate out different casein streams for functional usage in dairy products using common separation techniques.This thesis project seeks to evaluate the feasibility of separating milk treated with calcium chelators using various separation techniques to evaluate the individual casein fractions of this disrupted system. Four separation methods (ultracentrifugation, membrane filtration, heat coagulation, and coagulation based on pH) were employed to separate out the caseins based on selected properties, specifically density, molecular weight, and solubility. In ultracentrifugation, three speeds were tested, the heat coagulation study tested two temperatures, and pH based coagulation tested four different pHs to determine their impact on overall protein levels and individual casein yields. Skim v milk powder was reconstituted and chelator was added at 1, 50, or 100 mEq/L treatment level. These samples were then separated using aforementioned techniques, and the supernatant or permeate was analyzed for total protein content, individual casein composition, turbidity, and mean particle size.Analysis of centrifugal separation studies shows the interaction between chelator type, chelator level, and centrifugation speed had a significant impact on the amount of protein released from the casein micelle (p<0.001). Samples treated with 50 mEq of sodium hexametaphosphate and centrifuged at 60,000xg released significantly more protein into the supernatant than other samples. The type of chelator was not found to be statistically significant in impacting the proportion of α casein or β casein in the samples, but the interaction of chelator level and centrifugal force was found to have an impact.Larger proportions of α casein and lower proportions of β casein were seen in samples treated with low levels of chelator (1 mEq) and low levels of centrifugal force (30,000xg). Although the type of chelator used was not seen to cause significant difference in the supernatant of samples, it is important to note that when comparing the chelated samples to the control samples, drastic differences were seen in the turbid...