Monitoring changes in feta cheese during brining by magnetic resonance imaging and NMR relaxometry

Magnetic resonance imaging (MRI) and NMR relaxometry were used to monitor changes in feta cheese during 169 h of brining at 4.8%, 13.0% and 23.0% salt solutions. Image and relaxation data were acquired to study salt uptake and water loss due to dehydration of cheese during brining. Saturation recovery and Carr-Purcell-Meiboom-Gill (CPMG) sequences were used to determine the longitudinal relaxation (T-1) and the transverse relaxation (T-2) times, respectively. Signal intensities of T-2 weighted images decreased during 169 h of brining. An excellent linear correlation between the average signal intensity and the water content was obtained (R-2 = 0.984). The T-1 values of cheese brined at 4.8% were almost constant but T-1 values decreased for both 13.0% and 23.0% salt brined cheeses. Analysis of the CPMG decays gave relaxation spectra containing two components which decreased during brining. The short component T-2a was highly correlated with salt content (R-2 = 0.974). Results showed that NMR and MRI can be used to follow salt uptake and changes in water content in cheese during brining. (C) 2011 Elsevier Ltd. All rights reserved.