Masters Theses
Date of Award
12-2024
Degree Type
Thesis
Degree Name
Master of Science
Major
Food Science
Major Professor
Qixin Zhong
Committee Members
Vermont Dia, Tao Wu
Abstract
Casein has many functional properties for developing food, pharmaceutical, and consumer products. However, casein precipitates around its isoelectric point of pH 4.6. Previously, increasing solutions of casein and propylene glycol alginate (PGA) to pH 11.30 followed by acidifying to pH 4.5 led to dispersions without precipitation, contributed by both covalent and non-covalent interactions. The covalent bonding is due to the transacylation reaction between ester groups of PGA and primarily amino groups of casein, and phosphate was speculated as a catalyst. The hypothesis of this thesis is that the transacylation reaction between sodium caseinate (NaCas) and PGA and therefore acid stability of dispersions is not only affected by the phosphate concentration but also cations binding electron-rich amino groups via the local ion-pairing mechanism. Solutions with 1% w/v NaCas and 1% w/v PGA were dissolved with 0, 10, 25, 50, 100 and 200 mM NaH2PO4, KH2PO4, NaCl, or KCl and were reacted at 22°C and pH 11.0 for 2 h, followed by adjusting pH to 7.0, centrifugation, and dialysis of the supernatant for analyses. A lowered degree of glycation (DOG) measured with the ortho-phthalaldehyde assay and more abundant casein bands observed in reducing gel electrophoresis at increased phosphate concentrations nullified the hypothesis of phosphate being a catalyst. The DOG was similar (p > 0.05) for all treatments with ≥25 mM salt, attributed to the charge screening effect. At 10 mM salt, KH2PO4 led to a higher DOG than KCl (p < 0.05), while the DOG of NaH2PO4 and NaCl treatments was similar (p > 0.05) and was lower (p < 0.05) than treatments with potassium. The ion-pairing mechanism was verified for the lower conductivity and thus stronger binding for NaCas solutions containing NaCl than those with KCl. The strong binding of Na+ with NaCas was further verified in 23Na-NMR. For 10 mM treatments, precipitation was absent for all dispersions at pH 4.5 and 3.0, and the KCl treatment had the highest solubility at pH 4.5, corresponding to its fibrous structures in atomic force microscopy. The present thesis may be significant to improve functional properties of casein for food and non-food applications.
Recommended Citation
Castellanos Paez, Bryan A., "Ion effects on alkaline conjugation and acid stability of casein-propylene glycol alginate dispersions. " Master's Thesis, University of Tennessee, 2024.
https://trace.tennessee.edu/utk_gradthes/12843
