Probing protein hydration and aging of food materials by the magnetic field dependence of proton spin-lattice relaxation times

摘要

Most cheeses can be considered as solid emulsions of milk fat in a matrix of water and proteins.Regions of each of the phases can be liquid during processing and maturation.Identifying these regions and monitoring changes in them is important as a prelude to controlling the structure of the final cheese.We concentrate n the behavior of water in the vicinity of proteins as a function of cheese aging.Our method utilizes nuclear magnetic relaxation dispersion(NMRD)associated with the frequency dependence of water spin-lattice relaxation rates using the field cycling NMR technique.This method provides insight into the dynamical behavior of water molecules on a very large time scale.Moreover,we can distinguish between molecular motion in bulk and motion in the vicinity of a source of relaxation,such as proteins.A fit of our dispersion data using a theory developed by J.-P.Korb and R.G.Bryant(J.Chem,Phys,115(2001)23)allowed us to determine the degree of hydration of proteins as a function of aging.In particular,we find that protein hydration increases with ripening,