This study was approved by the ethical committee of the Posadas Hospital (ref: 318 EUPeSe/19). Participants in this study received oral and written explanations of the protocol and signed an informed consent form for participation and use of data.

For this study, we selected three calcium salts suitable for human consumption, commonly used by the food industry and with a reported solubility allowing solutions of at least 500 mg of calcium per liter at room temperature (20°C). The solubility of these three salts theoretically allows solutions to be obtained that widely exceed this value. Calcium chloride dehydrate has solubility in water of 740 g/L at 20°C (up to 200,000 mg Ca/L), calcium gluconate monohydrate has a solubility in water of 32,7 g/L at 20°C (up to 2900 mg Ca/L), and calcium lactate pentahydrate has a solubility in water of 58 g/L at 20°C (7500 mg Ca/L) ^{25– 27} . Calcium chloride dihydrate was purchased from Sigma-Aldrich Corporation, whereas calcium lactate pentahydrate and calcium gluconate Monohydrate were purchased from Surfactan.

The concentrations used to determine the sensory detection threshold of each calcium salt were defined taking into account the solubility of different calcium salts and previous studies performed in different countries showing that 500 mg of Ca/L increases the percentage of people reaching adequate intake without exceeding the recommended upper limit for calcium intake ¹² . With this information a panel of six assessors, selected and trained following the guidelines of ISO 8586-1 ²⁸ , and with a minimum of 100 hours experience in discrimination and descriptive tests, determined the range of calcium concentrations that was used to define the seven samples for the sensory threshold test.

This expert panel using the triangle test set the lower range in 100 mg of Ca/L as below this concentration the panel did not detect any sensory difference and the upper range in 800 mg of Ca/L as above this concentration the panel detected sensory differences.

Samples were prepared with artificial mineral bottled water that complies with the standards of the water cooperative in Argentina (Instituto verificador de elaboración de soda en sifones, IVESS) ²⁹ . According to the information provided by the cooperative, this water is filtered, dechlorinated, ozone purified tap water and contains calcium 27 mg/L, sodium 32 mg/L, nitrates 10mg/L, chlorides 38 mg/L, alkalinity (CaC0 ₃) 80 mg/L, hardness (CaCO ₃) 104 mg/L and total dissolved solids 270 mg/L.

Solutions were prepared registering the weight of the salt added. The calcium concentration was measured in a sample of the final solution by atomic absorption spectroscopy at 422.7 nm (Varian AA 240FS) in an acetylene-air flame, the technique used was based on the Standard methods for the examination of water and wastewater ³⁰ . Table 1 shows the calcium concentrations tested for each salt.

The panel was selected from a consumer´s database hold by the Departamento de Evaluación Sensorial de Alimentos- Instituto Superior Experimental de Tecnología Alimentaria (DESA-ISETA) from the city of 9 de Julio (Buenos Aires, Argentina). Individuals registered in the database have previously participated in consumer panel tests and agreed to be contacted by the institute for similar tests. Those who were aged 18 or older and reported drinking water every day were invited to participate.

The number of consumers was based on the requirements of the ISO 4120:2004 ²³ , for similarity tests. The parameters considered for this work were: β:5%; α :10%; Pd:30%; leading to a total of 54 consumers. The tests were conducted in the facilities of DESA-ISETA.

We perform a triangle test to detect the threshold taste for each salt following the ISO/FDIS- 4120:2004 (E) ²³ . The consumer panel received a short training session on the triangle test methodology and the procedures required to taste water samples. As part of the training, participants were asked to detect the odd sample of three 10 ml samples, two containing water and one water supplemented with 10 grams of sugar per liter.

After the training, threshold tests were carried out. Consumers received seven batches of three solutions of 30 ml each. Each batch contained two samples of the same concentration and one of a different concentration. Samples were presented at room temperature (18–23°C) in similar polystyrene 70 mL cups coded with three-digit random to allow blinding. Consumers were asked to taste each sample in the row (left to right) and to select the odd sample. Between batches, participants were asked to neutralize taste with mineral water and white bread.

The tests were performed on different days to avoid tiredness or flavor carryover. For each salt, consumer tested three batches one session and the remaining four batches on a second session.

The statistical model developed by Hough et al. (2013) was applied to the data obtained in the triangle test ²⁴ . A random variable C is the salt concentration at which an assessor correctly discriminates a sample. The discrimination function D(c) can be defined as the probability of an assessor discriminating a sample before concentration c, i.e., D(c) = P(C ≤ c). For example, the log-normal distribution is expressed by:

and the Weibull distribution is expressed by:

Where, in Equation (1), Φ (.) is the cumulative normal distribution function and µ and σ are the model’s parameters.

In Equation (2), exp [ -exp, is the distribution function of the smallest extreme value distribution and µ and σ are the model´s parameters.

Threshold estimations were calculated for 50% discrimination ³¹ .

To estimate percent discrimination probability versus concentration distribution, data were performed in R version 4.0.0 Statistical package (The R Foundation for Statistical Computing). The survreg function of the survival package was used.

When applying the survival analysis methodology to the calcium gluconate threshold data, the best fitting distribution was the Weibull ( Equation 2). The resulting parameters ± 95% confidence intervals were μ = 6.9 ± 0.2 and σ = 0.44 ± 0.15 ³² . Percent discrimination versus concentration for this Weibull distribution is plotted in Figure 1.

The threshold value estimation corresponding to 25% discrimination ± 95% confidence intervals was 587 ± 131 mg of Ca/L, corresponding to a water sample with a calcium gluconate concentration of 6.6 ± 1.4 g/L.

We were not able to estimate the threshold value estimation corresponding to 50% discrimination as the maximum number of successful answers obtained from the consumer panel reached 44%.

For the calcium lactate threshold, the Weibull was the best fitting distribution ( Equation 2). The resulting parameters ± 95% confidence intervals were μ = 6.8 ± 0.3 and σ = 0.76 ± 0.25. Percent discrimination versus concentration for this Weibull distribution is plotted in Figure 2. The threshold value estimation corresponding to 50% discrimination ± 95% confidence intervals was 676 ± 186 mg of Ca/L, corresponding to a water sample with a calcium lactate concentration of 5.2 ± 1.4 g/L.

When the survival analysis methodology was applied to the calcium chloride threshold data, the best fitting distribution was the log-normal ( Equation 1). The resulting parameters ± 95% confidence intervals were μ = 5.7 ± 0.3 and σ = 0.83 ± 0.20. Percent discrimination versus concentration for this log-normal distribution is plotted in Figure 3.

The threshold value estimation corresponding to 50% discrimination ± 95% confidence intervals was 291 ± 73 mg of Ca/L, corresponding to a water sample with a calcium chloride concentration of 1.1 ± 0.3 g/L.

Mendeley Data: Water with added calcium. https://doi.org/10.17632/9fj6fs7kf2.1 ³²

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).