Noninvasive Analyses of Food Products Using Low-field Time-domain NMR: A Review of Relaxometry Methods

Non-Invasive Method to Predict the Composition of Requeijão Cremoso Directly in Commercial Packages Using Time Domain NMR Relaxometry and Chemometrics

“…The analysis of TD-NMR relaxometry of large samples, such as fresh fruits and oilseeds [ 18 , 19 , 20 ] and industrialized packaged food, can be performed using wide bore Halback, wide gap C and H types [ 21 , 22 ], or unilateral magnets [ 23 , 24 ]. The main advantage of Halback, C, or H types over the unilateral ones is the higher homogeneity of the magnetic field, allowing the analysis of the entire or large part of the sample.…”

“…However, unilateral relaxometry has a strong magnetic field gradient, and only a small part of the sample is analyzed. Thus, the signal-to-noise ratio (SNR) in this equipment is very low and, consequently, the measuring time is much longer when compared to the developed in homogeneous magnets [ 21 ].…”

“…Most TD-NMR applications use the T 2 measurements [ 1 , 25 ]. These analyses are performed using Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence, a single shot sequence that is very insensitive to the flip angle error and rf magnetic field inhomogeneity [ 21 ]. Applications based on the longitudinal (T 1 ) relaxation time are rarely used because the standard pulse sequences (inversion-recovery, saturation-recovery, progressive saturation, etc.)…”

“…are not single shot sequences. Therefore, the measuring time is more than one order of magnitude longer than the CPMG measurement [ 21 , 26 ].…”

“…When 90° pulses are used, CWFP signals depend on both T 1 and T 2 relaxation time. The first application of CWFP pulse sequence in low-field TD-NMR was proposed to enhance SNR to determine the hydrogen content in solvents and oil in seeds [ 21 , 25 , 27 ]. More recently, modifications in the CWFP pulse sequence were made, allowing to determine T 1 time in a fast and accurate way.…”