ABSTRACT
CONTENTS 4.1 Introduction ............................................................................................................ 80 4.2 Molecular Properties of Caseins .............................................................................. 80 4.3 Molecular Properties of Whey Proteins ................................................................... 86 4.4 Functional Properties of Milk Proteins ................................................................... 88 4.5 Changes in the Structure and Properties of Milk Proteins during Processing
and Storage ............................................................................................................. 90 4.6 Characteristics of Major Bovine Milk Proteins Using HPLC Online with UV
Spectroscopy ........................................................................................................... 92 4.6.1 Derivative UV Spectroscopy-General Characteristics of the Method ....... 92 4.6.2 Prefractionation of Milk Proteins ............................................................... 92 4.6.3 High-Performance Liquid Chromatography-Application to Milk
Protein Analysis .......................................................................................... 93 4.6.4 Strategies of Protein Identi cation Based on the Derivatives of
UV Spectra ................................................................................................. 93 4.6.4.1 Identi cation Based on the Parameters Characterizing the
Shape of the UV-Spectrum Derivatives ....................................... 93 4.6.4.2 Identi cation via the Libraries of UV-Spectrum Derivatives ........ 95
4.6.5 Example of the Application of HPLC Online with UV Spectroscopy ......... 96 4.7 Electrophoretic Methods for Milk Protein Analysis ................................................ 98
4.7.1 One-Dimensional Polyacrylamide Gel Electrophoresis ................................ 98 4.7.2 Two-Dimensional Electrophoresis ............................................................... 99 4.7.3 Capillary Electrophoresis............................................................................. 99
4.8 Other Methods ..................................................................................................... 100 Acknowledgment ........................................................................................................... 100 References ...................................................................................................................... 100
4.1 Introduction In the living world, many protein systems are formed through the association of monomeric subunits. Such associated molecules have a xed structure and comprise several identical or di erent subunits. Milk possesses a protein system constituted by two major families of proteins: caseins (insoluble) and whey proteins (soluble). Whey proteins are globular molecules with a substantial content of α-helix motifs, in which acidic/basic and hydrophobic/hydrophilic amino acids are distributed in a fairly balanced way along their polypeptide chains [1]. When compared with the conventional globular proteins such as whey, caseins have a unique structure [2]. e characteristic feature of caseins is their amphiphilicity. is special trait is observed in the structure of the principal caseins that comprise fragments of protein molecules possessing both hydrophilic and hydrophobic properties. In milk, caseins occur mostly in the form of porous, spherical, and large-sized molecules referred to as casein micelles. Micellar casein di ers from many other protein systems with respect to at least two aspects. First, although micelles are large and have a xed structure, they are characterized by signi cant variability. e smallest micelles with a diameter of around 25 nm have approximately 450 monomeric subunits, while the largest micelles with a diameter greater than 150 nm may contain more than 10,000 monomeric subunits [3]. Second, even such a large number of monomeric subunits aggregate in an orderly manner, forming micelles from the four main, nonidentical monomeric subunits-αs1, αs2, β, and κ-caseins.
