Developments and applications of time domain NMR methods in food science

Developments and applications of TD-NMR Method in food science

 

Luiz Alberto Colnago^1*,Tiago Bueno de Moraes²

¹ Embrapa Instrumentation, 1452 Rua XV de Novembro, São Carlos, SP, 13560-970, Brazil

² Department of Biosystems Engineering, Luiz de Queiroz College of Agriculture, University of São Paulo (USP), Av. Pádua Dias 11, Zip Code 13418-900, Piracicaba, SP, Brazil

*luiz.colnago@embrapa.br

 

Time domain NMR (TD-NMR) based on low field and low-resolution relaxometers have been used in quality control of fresh and industrialized food product for more than 50 years. They are based on cryogenic free permanent magnets, and therefore they are low cost and compact (bench top) instruments when compared to expensive and bulk high-filed NMR (HF-NMR). In TD-NMR instruments any sample, in liquid state, shows only a single broad line, up to hundred of ppm, due to the very low magnet homogeneity. Consequently, the signal does not contain information about chemical shift, spin-spin coupling and others spectral parameters usually used in HF-NMR. Therefore, the analyses are based mainly on FID or echo intensity and longitudinal (T₁) and transverse (T₂) relaxation times. These instruments were initially developed for quality control in several industries (food, agricultural, petrochemical etc) to replaced laborious and time consuming classical methods. Most of the initial quantitative applications were based on FID and/or echo amplitude and several of these methods were certified by national and international organization like ASTM, ISO and IUPAC. However, in the last 30 years these instruments have also been used in academia for basic and applied science and a large variety of new methods and applications have been developed. Most of the new applications have been based on relaxation measurements using mainly the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence for measuring T₂ and several pulse sequences to measure T₁, including some single shot ones. In this presentation, I will be showing some new NMR methods based on steady state free precession sequences, T₁ in rotating frame, new solid echo sequence as well application in food matrices. I will also show some new procedure to process relaxation data using Krylov Basis Diagonalization Method (KBDM) algorithm as a multiexponential inversion method. These pulse sequences and processing methods were applied to diverse food products like fresh meat, oilseeds, fruits and vegetables as well as industrialized food product direct in the packages.

Acknowledgments: CAPES, CNPq and FAPESP for financial support.

References

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2. Moraes, T.B.; et al. J. Magn. Reson 243, 74-78, 2014
3. Moraes, T.B.; at al, J. Magn. Reson. Open 14-15, 100090, 2023
4. Moraes, T.B.; Colnago L.A., Braz. J. Phys. 52, 43, 2022.