# Sodium magnetic resonance imaging to map salt distribution in food depending on domestic salting practices

Raphaël Monod, J.-M. Bonny, Guilhem Pagès, Thierry Thomas-Danguin, Sylvie Clerjon

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Raphaël Monod, J.-M. Bonny, Guilhem Pagès, Thierry Thomas-Danguin, Sylvie Clerjon. Sodium magnetic resonance imaging to map salt distribution in food depending on domestic salting practices. 22nd World Congress of Food Science and Technology: The future of food is now: development, functionality & sustainability, IUFoST, AITA, Sep 2024, Rimini, Italy. pp.497-497. hal-04879952

HAL Id: hal-04879952

https://hal.inrae.fr/hal-04879952v1

Submitted on 10 Jan 2025

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# SODIUM MAGNETIC RESONANCE IMAGING TO MAP SALT DISTRIBUTION IN FOOD DEPENDING ON DOMESTIC SALTING PRACTICES

Raphaël Monod<fnref n="1" />,<fnref n="2" />,<fnref n="3" />, Jean-Marie Bonny<fnref n="1" />,<fnref n="2" />, Guilhem Pages<fnref n="1" />,<fnref n="2" />, Thierry Thomas-Danguin<fnref n="3" />, Sylvie Clerjon<fnref n="1" />,<fnref n="2" />

Currently, **sodium consumption is higher than the 5 g per day recommended by health organizations** (WHO Global Report on Sodium Intake Reduction, 2023). High sodium intake increasing blood pressure, an increased risk factor for cardiovascular diseases exists (Mozaffarian et al., 2014). Sodium in our diets comes from **three sources**: **salt naturally present in food**, **salt in manufactured food** and **discretionary salt**, i.e. salt that is added during cooking or at the table (Zandstra et al., 2016). This study deals with the **reduction of discretionary salt without decreasing saltiness**, as discretionary salt contributes significantly to salt intake (Bhat et al., 2020).

It was demonstrated that heterogeneous salt distribution leads to an increase of saltiness (Busch et al., 2019). To image this heterogeneity, we developed an original quantitative sodium Magnetic Resonance Imaging (MRI) protocol and we then compared three different domestic salting process.

## Samples cooking and salting

<figure><img src="image_2.png" /><figcaption>Boiled carrots,
25 min</figcaption></figure>

<caption>Sliced, 5 mm
thick</caption>

<figure><img src="image_3.png" /><figcaption>Salting procedure</figcaption></figure>

## MRI experiments

<figure><img src="image_4.png" /></figure>

**MRI basic conditions:**

9.4T UltraShielded widebore Bruker magnet

30 mm ¹H/²³Na excitation/reception Bruker volume RF coil

SPIRAL-based protocol (TE=0,78ms and TR=250ms)

Virtual slice 5 mm → anisotropic **voxel volume: 0.5*0.5*5 mm<fnref n="3" />**

**Acquisition duration** between 34 min and 4h48

MRI acquisition begin 16±2min after salting

**Original protocol tackling the 4 main ²³Na quantitative MRI issues:**

* short relaxation time of ²³Na nuclei by using an ultra-short TE sequence

* sodium low NMR sensitivity by making possible to acquire/accumulate signal up to 4h48

* inhomogeneities of the excitation/reception coil by correcting them with the double angle method (Stollberger et al., 1996)

* measurement during sodium diffusion by interlacing every 2 min the two angles acquisitions → appropriate temporal resolution obtainable with post-processing to be

**MRI analysis to obtain salt profiles**

MRIs were preprocessed with Matlab and then analyzed using Fiji software. On each image:

1. Detection of the highest and lowest signal pixels in the carrot.

2. Measure of salt profile between these two pixels (averaged on a width of three pixels to mitigate the noise)

WHO global report on sodium intake reduction. (2023). World Health Organization.

https://iris.who.int/bitstream/handle/10665/366393/9789240069985-eng.pdf?sequence=1

Mozaffarian, D., Fahimi, S., Singh, G. M., Micha, R., Khatibzadeh, S., Engell, R. E., Lim, S., Danaei, G., Ezzati, M., & Powles, J. (2014). Global Sodium Consumption and Death from Cardiovascular Causes. *New England Journal of Medicine*, **371**(7), 624–634. https://doi.org/10.1056/NEJMoa1304127

Zandstra, E. H., Lion, R., & Newson, R. S. (2016). Salt reduction: Moving from consumer awareness to action. *Food Quality and Preference*, **48**, 376–381. https://doi.org/10.1016/j.foodqual.2015.03.005

Bhat, S., Marklund, M., Henry, M. E., Appel, L. J., Croft, K. D., Neal, B., & Wu, J. H. Y. (2020). A Systematic Review of the Sources of Dietary Salt Around the World. *Advances in Nutrition*, **11**(3), 677–686. https://doi.org/10.1093/advances/nmz134

Stollberger R, Wach P. (1996) Imaging of the active B1 field in vivo. *Magn Reson Med*, **35**, 246–251. https://onlinelibrary.wiley.com/doi/10.1002/mrm.1910350217

This work was supported by the French National Research Agency (ANR-19-CE21-0009, Sal&Mieux project) and the INRAE Department TRANSFORM.

## Salt distribution (during the first 1h24 after salting)

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

**Voxel volume:** 0.5*0.5 mm<fnref n="2" /> (in plane) *5 mm (virtual slice thickness)

**Acquisition duration:** 1h08

These quantitative maps result from an **acquisition period lasting from 0h16 to 1h24 after salting**. We see the rectangular virtual slice in the carrot and the cross section of the 3 reference tubes. As expected, the sodium distribution was symmetrical for the salting in water procedure. Carrots being unsliced during cooking, sodium penetrated similarly through the carrot's external part towards the carrot's core during cooking. Contrary to salting on the plate for which salting was performed after slicing. Therefore, sodium can be everywhere on the slice edge. Obviously, for the 3 modalities, the maximum sodium intensities are located at the surface of the samples.

<figure><img src="image_8.png" /></figure>

Salt profiles are then extracted from the images between the highest and the lowest signal pixels.

* In water salt spatial variations < at the plate salt spatial variations

* At the plate : fine sea salt < Fleur de sel spatial variations

* At the plate repeatability << in water repeatability

The higher variability for the at the plate process is easily explain by the process itself: some carrots slices had probably no salt crystals in contact with the sampe, while some had one or multiple crystals.

<figure><img src="image_9.png" /></figure>

Mean salt
gradients

The spatial derivative function was calculated between 1 and 8 mm for all samples and averaged

**Mean salt gradients are significantly different:**

* In water < at the plate with Fleur de sel (.= p<0,1, *= p<0,05, **= p<0,01)

* In water < at the plate with fine sea salt (p<0,01, at 3mm only, not shown on the graph)

## Time evolution after salting

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

The same salt profiles extraction has been done on MRIs acquired for 4 periods post salting. We observe:

→ a **drastic decline of salt variations with time for at the plate process** especially with Fleur de sel.

→ on images acquired from 2h32 to 3h40 post salting and later, salting on the plate and salting in water show very similar trends.

An original quantitative sodium mapping by 23Na MRI was successfully applied to compare salting practices of boiled carrots.

Our first result is that **salting at the plate, with bigger crystals (Fleur de sel) enhances salt heterogeneities**. This result is coherent with previous sensory analysis showing that salting at the plate with Fleur de sel can compensate a 30% salt reduction.

We also observe a **drastic decline on heterogeneities with time after salting**. This observation is of high interest for catering services or canteens that usually prepares and

seasons food hours before lunch or dinner time.

To complete this study, other foodstuff, like meat or cereals, very different in terms of structure and composition, should be studied to generalize our findings and better advice on salt practices which will help lowering salt intake.

<figure><img src="image_14.png" /></figure>

Main result from sensory analysis

Adding Fleur de sel on the plate can compensate from a 30% reduction in salt content without compromising salty taste

<footnote n="1">¹ Université Clermont Auvergne, INRAE, UR QuaPA, 63122, Saint-Genès-Champanelle, France</footnote>

<footnote n="2">² INRAE, PROBE research infrastructure, AgroResonance facility, 63122, Saint-Genès-Champanelle, France</footnote>

<footnote n="3">³ Centre des Sciences du Goût et de l'Alimentation, INRAE, CNRS, Institut Agro, Université Bourgogne, F-21000 Dijon, France</footnote>