Protein
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the physical and chemical properties that govern protein functionality include
size, shape, amino acid composition and sequence, net charge and distribution of charges, hydrophobicity/hydrophilicity, structure, molecular flexibility/rigidity, ability to interact/react with other components
the water binding capacity of proteins is defined as
grams of water bound per gram of protein when a dry protein powder is equilibrated with water vapor at 90-95% relative humidity
for most proteins, saturated monolayer(bound water) coverage of water occurs at water activity of about __ and multilayers of water are formed at water activity __
0,7-0,8 and >0,8
saturated monolayer water is primarily associated with…
ionic, polar and apolar groups on the surface of the protein
water binding capacity of proteins is affected by
pH, ionic strength, temperature, type of salts, protein conformation
at low concentrations, salts increase the water binding capacity of proteins. why?
because hydrated salt ions, especially the anions, bind weakly to charged groups on proteins. the increase in water binding essentially comes frmo water associated with the bound ions
the water binding capacity of proteins generally decreases as the temperature is raised. why?
because of decreased hydrogen bonding and decreased hydration of ionic groups
how is the water binding capacity of proteins affected by denaturation?
generally about 10% greater than that of the native protein. this is due to an increase in surface-area-to-mass ratio with exposure of some previously buried polar and hydrophobic groups. however if denaturation leads to aggregation of the protein, then its water binding capacity may actually decrease because of displacement of water by enhanced protein-protein interactions.