title: Thermal properties of milk fat, xanthine oxidase, caseins and whey proteins in pulsed electric field-treated bovine whole milk.
abstract: Thermodynamics of milk components (milk fat, xanthine oxidase, caseins and whey proteins) in pulsed electric field (PEF)-treated milk were compared with thermally treated milk (63 °C for 30 min and 73 °C for 15s). PEF treatments were applied at 20 or 26 kV cm(-1) for 34 μs with or without pre-heating of milk (55 °C for 24s), using bipolar square wave pulses in a continuous mode of operation. PEF treatments did not affect the final temperatures of fat melting (Tmelting) or xanthine oxidase denaturation (Tdenaturation), whereas thermal treatments increased both the Tmelting of milk fat and the Tdenaturation for xanthine oxidase by 2-3 °C. Xanthine oxidase denaturation was ∼13% less after PEF treatments compared with the thermal treatments. The enthalpy change (ΔH of denaturation) of whey proteins decreased in the treated-milk, and denaturation increased with the treatment intensity. New endothermic peaks in the calorimetric thermograms of treated milk revealed the formation of complexes due to interactions between MFGM (milk fat globule membrane) proteins and skim milk proteins. Evidence for the adsorption of complexes onto the MFGM surface was obtained from the increase in surface hydrophobicity of proteins, revealing the presence of unfolded hydrophobic regions.
authors.affiliation: Department of Food Science, University of Otago, Dunedin, New Zealand; Riddet Institute, Palmerston North, New Zealand. Electronic address: pankaj.sharma@otago.ac.nz.
authors.forename: Pankaj
authors.initials: P
authors.lastname: Sharma
authors.affiliation: Department of Food Science, University of Otago, Dunedin, New Zealand.
authors.forename: Indrawati
authors.initials: I
authors.lastname: Oey
authors.affiliation: Riddet Institute, Palmerston North, New Zealand.
authors.forename: David W
authors.initials: DW
authors.lastname: Everett
mesh_terms: D000818:Animals; D002152:Calorimetry, Differential Scanning / Q000379:methods*; D002364:Caseins / Q000032:analysis / Q000737:chemistry*; D002417:Cattle; D006017:Glycolipids / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry*; D066292:Lipid Droplets; D000067816:Whey Proteins / Q000737:chemistry*; D014969:Xanthine Oxidase / Q000032:analysis / Q000737:chemistry*
chemical_list: D002364:Caseins; D006017:Glycolipids; D006023:Glycoproteins; D000067816:Whey Proteins; C110367:milk fat globule; D014969:Xanthine Oxidase
keywords: Differential scanning calorimetry; Fat melting; Protein denaturation; Pulsed electric field; Surface hydrophobicity