Reducing skim milk powder dispersion turbidity by dissociation of casein micelles at acidic and neutral pH: Physicochemical properties and possible mechanisms
Date of Award
Master of Science
Vermont P. Dia, Tao Wu
Casein micelles comprise 80% of dairy proteins. However, casein micelles as the source for protein fortification in beverages are limited due to its contribution to dispersion turbidity. On the other hand, protein beverages are experiencing substantial market growth and what follows is the demand for new protein ingredients. At acidic conditions, like those commonly found in lots of beverages, dispersions of skim milk powder (SMP) have high turbidity and readily precipitate. In order to circumvent these problems, the dissociation of casein micelles is required to reduce turbidity and improve dispersion stability during storage. Additionally, beverages with neutral pH are preferred to consumers suffering dental problems such as tooth erosion. The objectives of the present study were 1) to reduce turbidity of SMP dispersions and 2) characterize their physicochemical properties after treatment at acidic and neutral pH. To acidify SMP dispersions to pH 2.4-3.0, citric acid or glucono delta-lactone was added, followed by subsequent heating at 60, 70, 80, or 90 °C for 2, 5, 10, 30, or 60 min. A lower pH (i.e., pH 2.4) was more effective than pH 3.0 to reduce the dispersion turbidity (e.g., 223 vs 861 NTU) and the hydrodynamic diameter (e.g., 115 vs 265 nm) after heating at 90 °C for 10 min. At neutral pH, translucent dispersions were obtained with the addition of calcium chelators; sodium tripolyphosphate, trisodium citrate, or sodium hexametaphosphate. Higher concentrations of calcium chelators in SMP dispersions resulted in significant reduction in turbidity values compared to the control (e.g., 230 NTU vs >4000). The amount of dissolved calcium in the SMP serum phase apart from the casein micelles increased from ~150 to more than 500 mg/L after treatments at both acidic and neutral pH, indicating the dissociation of casein micelles due to the disruption of colloidal calcium phosphate. The SMP dispersions with modified casein structures can be utilized to produce novel types of beverages.
Choi, Inseob, "Reducing skim milk powder dispersion turbidity by dissociation of casein micelles at acidic and neutral pH: Physicochemical properties and possible mechanisms. " Master's Thesis, University of Tennessee, 2019.