Fa-yi Hao¹, Li-xin Lu^{1, 2,}, Chang-feng Ge³

Moisture sorption isotherm is a well established method to characterize water sorption properties and behavior of food materials. However, this approach doesn’t adequately reflect the molecular mobility that taking place during water sorption process. Nuclear magnetic resonance (NMR) can provide information about the water mobility and molecular interactions between water and food components. The biscuits with different fat addition were studied using water sorption isotherm and ¹H low-field NMR at and water activity ranging from 0.2 to 0.90, the changes in equilibrium moisture content, transverse relaxation time(T₂) and proton intensity of biscuits were defined. The T₂ were measured with Carr-Purcell-Meiboom-Gill (CPMG) sequences. It was demonstrated that fat content of biscuits influenced directly the equilibrium moisture content and water status. One or two water populations were observed as the water activity increased, each of which had a distinct relaxation time T₂ or molecular mobility. The relaxation time manifested that with the increase of fat addition, the water inside the samples became more mobile, and proton intensity indicated that the amount of water uptake decreased with increasing fat addition. The low-field NMR was demonstrated to provide complementary interpretation to that of water sorption isotherm.

Nuclear magnetic resonance, water sorption isotherm, transverse relaxation time, biscuit, fat content