Increasing saltiness of salts (NaCl) using mid‐infrared radiation to reduce the health hazards

Abstract Table salt, rock salt, and iodized salts (composed principally of NaCl) are commonly used in many areas, such as medicine, cooking, industry, or personal care. Common fried, salty, and spicy foods contain an excess of added salt, which has detrimental health effects, especially on the kidneys. Our research aims to enhance the inherent saltiness of these three salts, which would reduce intake and thereby minimize salt's health hazards. We invented a water‐based 2–6 μm of Mid‐Infrared Generating Atomizer (MIRGA), which, when applied to salts, caused changes in the salts' chemistry and enhanced saltiness, thus allowing the reduction of salt intake by 25%–30%. This easy‐to‐use technology did not show any side effects. MIRGA was found to have enhanced the saltiness, thus allowing the reduction of salt intake by 25%–30%. MIRGA is safe, portable, highly economical, unique in the mid‐IR laser technology, and possesses vast research scope in other areas of food science.


| INTRODUC TI ON
Sodium chloride (NaCl) is a primary source of sodium and chloride ions, vital to mediate sensory reflexes. Iodized salt is enriched with iodine salts and its intake is recommended to overcome/avoid iodine deficiency (McNeil, 2006;The Lancet, 2008). Out of 84 elements in the human body, 72 are essential and also present in rock (Himalayan) salt (Shukla & van der Zee, 2010). An excess of salt intake through the consumption of modern foods causes various irreparable health issues, which is a multifaceted scientific challenge as the saltiness, quantity of salt intake, and associated diseases are directly proportional. Most people consume around twice the recommended maximum salt level, and 2.5 million deaths could be prevented yearly if global salt consumption is reduced to the recommended level (WHO, 2016). Through this research, by applying 2-6 μm of mid-IR, we increased the saltiness of edible salts and advocated reducing the intake quantity of edible salt to prevent saltinduced morbidity. Available literature suggests that no study has been done on potentiation and concurrent quantity reduction of edible salts.

| Spraying method
Thirteenaliquotsof50 gweretakenfroma1000 gbatchofcommercially available table salt. The aliquots were packaged in polyethylene bags with a thickness of more than 50 μm, and sealed with tape. One packet was marked "C" (control) and the remaining were numbered from 1 to 12. Corresponding to the packet number, 1 to 12 MIRGA sprayings were applied from 0.25-to 0.50-m distance over the packets as one or two sprayings on one or both sides. The control packet received no spraying. Twelve sprayings had earlier been found to cause a complete loss of saltiness in the samples.
The 13 packets were individually subjected to evaluation by a sensory expert panel (Klarenbeek et al., 2014) consisting of six trained people, by consumer panel (cooks), by tasting the salt alone and also in cooked food. The results were recorded and compared. This procedure was also followed using rock salt and iodized salt.
TEM:ModelJEM-2100;Make:JEOL;HT-200 kV.Samplepreparation procedure: A small amount (~1 mg)ofpowderedsamplewas dispersed in the Isopropanol solvent, and the dispersion was then loaded over the TEM grid (lacey carbon-coated copper grid-300 mesh) for analysis. Sample-loaded dry grids were used for TEM analysis,andimageswerecapturedfromdifferentregionsat200 kVacceleration voltage.

| Trial details
The acceptability index used by the employed sensory expert panel was the hedonic scale with a 9-point nominal structure: 1-Dislike extremely, 2-Dislike very much, 3-Dislike moderately, 4-Dislike slightly, 5-Neither like nor dislike, 6-Like slightly, 7-Like moderately, 8-Like very much, 9-Like extremely (Everitt, 2009;Wichchukit & O'Mahony, 2014). The sprays were applied to the test sample packets as described in the previous section. The test samples were sprayed on one side and sensory tests were performed, followed by two sprayings (one on either side) and another sensory test.

| Sensory expert panel test results
Comparing the sensory scores of control sample with rest of the sprayed samples, four spraying samples of table salt, rock salt, and iodized salt have been scored '8' (like very much-in terms of the saltiness). Excessive number of sprayings beyond 4 has caused a gradual reduction in the sensory score. Also, the four sprayed samples has significantly reduced moisture than the control.
Increased sensory qualities and reduced moisture enhanced the saltiness preferably. Table 1 shows that the control sample is considered to have a normal taste and saltiness. In the trial samples, as the number of sprayings was increasing, the saltiness was also gradually found to be increased. After fourth spraying, the samples became more palatable than control. After the 12th spraying in table salt, 10th spraying in rock salt, and 12th spraying in iodized salt, saltiness was increased but samples became unpalatable, with an irritating and pungent taste.
In the case of the cooked samples, salt requirement was 25%-30% less in the salts sprayed four times. These sensory attribute changes wereperceivedin1-2 minutesafterspraying,andtheenhancedsensory characteristics of trialed samples were found to be retained for 18-24 months. The retention of sensory characters was conducted using accelerated stability conditions where products were stored under stress conditions. The stability of samples was then predicated using the relationship factor, the acceleration factor, and the degradation rate. The sensory panel experts' and nontrained experts' (cooks) opinions were almost similar except for a negligible difference.

| Instrumentation results
Raw data and detailed interpretations for each salt are available, respectively, in Supplementary Data D1 and Supplementary Text T1.

FTIR
Peak at 3410 cm −1 corresponds to OH groups water (in crystalohydrates) content in the sample. This peak is increased in 12 sprayed samples by 28% than control and four sprayed samples.Peakat1635 cm −1 indicates the distinct presence of scissor peak of a water molecule (-OH stretch), this peak is decreased in four sprayed samples by 3%; however, in 12 sprayed samples, an increase of this peak by 36% can be noticed, which caused an unpleasant taste. Peak at 1018 cm −1 arises from the presence of silicates (SO 3 2− ), which decreased by 1% in four sprayed samples and increased by 26% in 12 sprayed samples, which also caused an unpleasant taste (Figure 2b).

GC-MS
The rock salt sample contains many aldehyde and long-chain fatty acids. After four sprayings, the saltiness is increased and the longand short-chain fatty acids were found. More precisely, the longchain fatty acid (C18, 6-Octadecenoic acid) might have broken down to medium chain (C11, undecylenic acid) during spraying. When the rock salt sample was sprayed 10 times, there were found the major peak of pentadecen-1-ol acetate and 13-octadecenal. These both could be the by-products of long-chain fatty acid degradation and transformation ( Figure 3a).

FTIR
Peakat3410 cm −1 indicates the presence of water content (in crystalohydrates) in the control. This peak decreased for 2-fold in the four sprayed samples and 2.7-fold in the 10 sprayed samples. Peak at 2924 cm −1 indicates the presence of bicarbonates; this peak is increased by 3% in the four sprayed samples and 136% in the 10 sprayedsamples,whichcausedunpleasanttaste.Peakat1627 cm −1 originates from fluorides; this peak decreased by 46% and 48% in thefourandthe10sprayedsamples,respectively.Peakat1481 cm −1 comes from carbonates, and decreased by 35% and 33% in the 4 and the10sprayedsamples,respectively.Peakat1018 cm −1 arises from silicates, and increased five times and seven times in the 4 and the 10 sprayed samples, respectively (Figure 3b).

PXRD
The 10-time sprayed sample has the most number of visible peaks.
There are six prominent peaks observed in this sample's XRD. The peak around 46.0° has highest intensity in the four-time sprayed sample. This is followed by control and 10 sprayed samples. Peak at around 75.0° is highest at the 10 times sprayed sample, followed by control sample and the four times sprayed samples. Peak at around 28.0° is highest in the 10 times sprayed sample, followed by four times sprayed sample and the control samples. Peak at around 55.0° is highest in 10 times sprayed, followed by the four-time sprayed sample. This peak is absent in the control sample. The 10-time sprayed sample has one more peak at 20.1° which is absent in both control sample and 4-time sprayed samples. Shifting of the most prominent peak to higher 2-theta value is observed in both sprayed samples (Figure 3c).

TEM
Sprayings altered the shape of the particles. Control: Particles display a nonuniform shape with an average size of ~138 nm. Four sprayed samples: Cuboid-shaped particles are present with an average particle size of ~81 nm.Ten sprayed samples: Particles show nano-needle shape with an average diameter of ~55 nm (Figure 3d).
The average transmission signal increased in the four sprayed samples by 5.62%. In the 12 sprayed samples, the average transmission drops again, but it is still higher than the control sample by an average of 2.98%. Therefore, assuming no significant irregularities exist in the measurements, the spraying process reduces the average mid-infrared absorption in the sample. The observed changes in the fingerprint region may be interpreted as

F I G U R E 2 (Continued)
the four-time sprayed sample being more favorable than the control sample and the 12-time sprayed sample (due to higher S=O stretching vibration).  Walker et al., 2004;Wang & Reeber, 1996). The XRD pattern shows good crystalline structure with minimal amorphous phases.
However, minor peaks are fairly discernible.
Control and four-time sprayed samples have several visible minor peaks that correspond to halite with cubic crystal structure.
Twelve-time sprayed samples have only three visible minor peaks.
Shifting of peaks to lower 2-theta is observed for 4-time and 12-time sprayed samples. 12.8,13.4,14.3,14.7,15.7,16.2,16.6,17.4,17.9,18.1,19.2,19.7,20.3,and21.0 minarepresentincontrol.Someofthesepeaksaremissinginthe5and12sprayedsamples.Foursprayed sampleshaveadditionalpeaksat13.7and17.1 min.Twelvesprayedsampleshaveadditionalpeaksat7.9,9.8,and15.5 min.(b)FTIRspectra ofTableSalt:Peakat3410 cm −1 corresponding for OH groups water (in crystalohydrates) content is increased in 12 sprayed samples. Peak at1635 cm −1 indicates that the distinct presence of scissor peak of a water molecule (-OH stretch) decreased in four sprayed samples and increasedin12sprayedsamples.Peakat1018 cm −1 decreased in four sprayed samples and increased in 12 sprayed samples. (c) PXRD spectra of   Table salt: Major differences between the control and sprayed samples are noticed in the peaks around 46.0°, 75.0°, 28.0°, 55.0°. Ten sprayed samples have the most number of visible peaks and extra peak at 20.1° which is absent in the control and four sprayed samples. Shifting of the most prominent peak to higher 2-theta value is observed in both sprayed samples. (d) TEM of Rock salt: All the three samples show difference in particle size and shape. Control has nonuniform shaped particle of average size of ~138 nm.Foursprayedsampleshavecuboid-shaped particles of average size of ~81 nmand10sprayedsamplesshownano-needle-shapedparticlewithanaveragediameterof~55 nm.

TEM
Sprayings altered the shape and crystallinity of the samples. Control: it displays spherical-shaped particles with an average particle size of ~435 nmandpoorcrystallinity.Four sprayed samples: It shows irregular spherical-shaped particles with an average particle size of ~300 nm,notwellarranged,andsomeparticleshapechangedtoa leaf-like structure and poor crystallinity. Twelve sprayed samples: it displays cuboid shaped with an average particle size of ~480 nmand well arranged, patterned structure, pure material, and higher degree of crystallinity (Figure 4d).

| Salt quantity intake/use result
The MIRGA sprayed table, rock, and iodized salts were brand/batchwise used individually in cooking, dietary consumption, admixturing with other edible ingredients, in which the requirement was found to be 25%-30% lower compared to the nonsprayed control.
To summarize, all the instrumentations illustrated the effect of 2-6 mid-IR in the salts' chemistry: chemical bond alteration, compound transformation, structure, and configuration changes that lead to the enhanced or decreased inherent characters to our desire depending on the number of MIRGA sprayings applied.
The particle size of salt crystals significantly impacts the saltiness perceived and the saltiness onset time. The researcher has shown that a smaller crystal size fraction can achieve a greater maximum saltiness per unit of sodium consumed. They have been explained by differential dissolution kinetics and enhanced mass transfer of sodium across the saliva (Rama et al., 2013). Additionally, Hurst et al. (2021) have shown that the maximum perceived saltiness can be achieved by redesigning the salt particles which include small particle size, low density, and hydrophobicity. They used a range of model salt particles to explore the impact of particle design on adhesion to product, loss in-pack, rate of dissolution, and saltiness perception and ultimately generated a series of design rules to optimize saltiness perception.

F I G U R E 3 (Continued)
F I G U R E 4 (a) 13.3,14.7,16,17.4,17.8,19.7,20,20.2,and 20.9 min.Foursprayedsamplesshowadditionalpeaksataround10.4,10.6,and11.8 min,and12sprayedsamplesshowadditionalpeaksat 15.5and16.2 min.(b)FTIRspectraofIodizedsalt:Allthreesampleshavebroadsignalsintherangeof1050-1200 cm −1 associated with the S=Ostretchingvibrationofsulfateiniodizedsaltandanothersignalintherangeof3200-3600 cm −1 associated with the stretching vibration of O-H. Compared to control, the former peak is increased in both the 4 and 10 sprayed samples, whereas the latter peak shows no change in the four sprayed samples but is reduced in the 10 sprayed samples. While spraying MIRGA, most of the mid-IR energy scatters throughtheairandgetsabsorbedbythesaltmolecules.Virtuallyall organic compounds absorb mid-IR radiation which causes a change in molecule's vibrational state to move from the lower ground state to excited higher energy state (Girard, 2014). This leads to changes in chemical bonds (Mohan, 2004;Shankar, 2017) and these bond parameter changes lead to consequent changes in target's physical and chemical characters, configuration, and compound transformation depending on the dose of energy (Atkins & Paula, 2011;Datta et al., 2014;Yi,2012) applied.

| CON CLUDING REMARK S
MIRGA increased saltiness, leading to 25%-30% reduction in the quantity intake, thereby possibility of minimizing health hazards.
Through future research by altering the MIRGA's present specifications, it would be possible to continue to reduce salt usage by furtherenhancingthesalts'inherentcharacteristics(saltiness).For patients with high blood urea nitrogen, high creatinine, and renal diseases, MIRGA-sprayed salt with various degrees of saltiness can be manufactured and suitably advocated.

FU N D I N G I N FO R M ATI O N
This study received no specific funding.

CO N FLI C T O F I NTE R E S T S TATE M E NT
In accordance with the journal's policy and our ethical obligation as researchers, we, the authors, are reporting that we together are the inventors and patentee of Indian patent for MIRGA (under-patent no.: 401387) which is a major material employed in this study.

DATA AVA I L A B I L I T Y S TAT E M E N T
All data are available in the manuscript and supplementary materials.