Quantitative 23Na MRI in food during sodium diffusion

Currently, sodium consumption is significantly higher than the 5 g per day recommended by health organizations. The main source of dietary sodium comes from the salt added to food. The Sal&Mieux project aims at finding domestic salting practices that can enhance saltiness perception while reducing or maintaining salt content. For this study, carrots boiled in water were used as the food model. Two practices were compared. On one hand, sprinkling salt on the food after cooking and on the other one, adding salt during cooking (ie in the cooking water). Two salts were compared namely fine sea salt and ‘Fleur de sel’ (which have bigger crystals). Sodium distribution, which is assumed to influence saltiness perception, can be assessed by quantitative MRI (qMRI). Given that the salt concentration in the cooked food is not in equilibrium, a quantitative mapping method with adequate temporal resolution was essential to monitor the diffusion of salt after cooking effectively. B₁ correction was performed to accurately quantify sodium distribution in cooked carrots. The selective Double Angle Method (DAM) with 90° and 30° prescribed angles was used¹. A modified sequence alternating between these two angles every minute was applied to account for sodium diffusion during acquisition. The total sequence duration can be optimized to fit the best ratio between acquisition time and SNR. To tackle the short relaxation times, a non-cartesian spiral acquisition was used. Experiments were conducted using a 9.4 T imager equipped with a 30-mm diameter ¹H/²³Na volume coil for both excitation and reception. Thanks to this methodology quantitative sodium maps were successfully obtained for the two salting practices. Then, it was possible to monitor the sodium temporal evolution in the different parts of the cooked carrots. 5 carrots were analysed per modality to improve the results’ robustness. To obtain these quantitative maps the carrots were only salted twice as much as is usually done in domestic settings. Preliminary results show that a more heterogeneous distribution of sodium is obtained when salting is performed after cooking compared to when salting is performed during cooking, especially when bigger crystals are used. This can explain differences in salt perception measured during sensory analyses. The expected results should allow us to highlight practices in terms of table salt use that can easily be adopted by consumers to increase the sensory availability of discretionary salt therefore lowering salt intake.

Reference:

1. Magn Reson Med. 2012 Nov;68(5):1472-80. doi: 10.1002/mrm.24146

Acknowledgments: ANR-19-CE21-0009 Sal&Mieux, INRAE TRANSFORM division