A study of spin-lattice relaxation rates of glucose, fructose, sucrose and cherries using high-T _c SQUID-based NMR in ultralow magnetic fields

We study the concentration dependence of spin-lattice relaxation rates, T ₁ ^-1, of glucose, fructose, sucrose and cherries by using high-T _c SQUID-based NMR at magnetic fields of ∼97 μT. The detected NMR signal, S_y (T _Bp), is fitted to [1 - exp(-T _Bp/T ₁)] to derive T ₁ ^-1, where S_y (T _Bp) is the strength of the NMR signal, T _Bp is the duration of pre-polarization and T ₁ ^-1 is the spin-lattice relaxation rate. It was found that T ₁ ^-1 increases as the sugar concentrations increase. The increased T ₁ ^-1 is due to the presence of more molecules in the surroundings, which increases the spin-lattice interaction and in turn enhances T ₁ ^-1. The T ₁ ^-1versus degrees Brix curve provides a basis for determining unknown Brix values for cherries as well as other fruits.