91C-35

The dairy industry would benefit from development of low-field magnetic resonance (MR) as a method of rapid and non-destructive determination of moisture content of cheese products.  A key aspect of the development of MR moisture measurement is examination of the T₂ decay behavior.  The two components primarily responsible for the MR spin-spin relaxation (T₂) signal of cheese products are fat and water.  If the moisture component of the signal can be distinguished from the fat component, it should be possible to measure moisture using an MR sensor.  Prior to MR experiments, all samples were equilibrated at 60, 70, and 80°C in a convection oven.  CPMG-T₂ tests were conducted on pure milkfat samples and process cheese products.  The T₂ decay curves of milkfats were modeled using a two-term exponential and one-term stretched exponential models.  A previous study conducted on cheese analogs demonstrated that the best models for these samples were a three-term exponential model and a two-term stretched exponential model.  Each of these models had an additional term when compared to the models used for analyzing milkfat.  These terms were used to describe the T₂ decay of the water.  In this study, the three-term exponential and two-term stretched exponential models were fit to the process cheese data and the relationship between moisture content and T₂ values of process cheese samples was determined.  The results of the relaxation decay curve analyses using these models were compared on the basis of their standard errors of fit and their sensitivity to changes in moisture content.  The two-term stretched exponential model proved to be sufficiently versatile to give good moisture content predictions for a data set consisting of four brands of process cheese products having distinctly different compositions and a relatively wide range of moistures (45.8 to 62.0%).