J Nutr Sci Vitaminol, 65, S200–S205, 2019

Mini Review Differences in Bittern Components and Effects on Rice Porridge Taste

Kyoko Ishikawa, Hiroyoshi Sato, Yoshiko Takahashi, Yuka Endo and Hikari Sakurada

Department of Biotechnology, Faculty of Bioresource Sciences, Akita Prefectural University, 241–438 Kaidobata Nishi, Shimoshinjo Nakano, Akita 010–0195, Japan

Summary Salt is an important seasoning that adds a salty taste to enhance or suppress other tastes in cooking. Porridge is treated with salt, even with the addition of a small amount of salt to tighten its taste. This salty taste intensity is also influenced by the amount of bittern component contained in the salt because not only the bittern component but also the change of pH affects the degree of swelling and penetration into rice. However, excessive salt intake causes lifestyle-related diseases. For that reason, salt intake reduction is recom- mended. When salt and citric acid are added to the porridge simultaneously, the contrasting effects of acidity and saltiness enhance the salty flavor, allowing for the reduction of salt intake. Key Words bittern component, reduced salt, rice gruel, salt, salty taste

When preparing rice porridge, even a small amount of of membrane salt; D, salt dried by direct added salt can increase saltiness. Even a small amount spraying of at room temperature; E, salt pro- of added salt plays an important role in compensating duced by adding an umami component such as sodium other tastes. Salt (sodium chloride), a fundamentally glutamate; and F, imported salt (9). Imported are important seasoning for cooking, affects not only the further segmented by differences of raw materials and food taste but also its texture because of its penetration manufacturing methods (10): whether solar salt or and dehydration of foods. In recent years, it has become rock salt, whether they were used as salt, whether they possible to use salt containing bitter components effec- were dissolved in water and reproduced, and so on tively. A recent report has described that, when treat- (10). The main salt components actually include six: ing food with salt of high bitterness, the influence on contain chloride ion, sodium ion, sulfate ion, magne- taste might derive from bitterness, not from salt (1). sium ion, ion, and ion. Moreover, As presented herein, we introduce results of examina- the component composition changes because the pre- tion of the influence on taste by making rice porridge cipitation behavior of crystals differs depending on the using salts with different bitterness contents. Reduc- salt production method. Commercially available salts ing salt intake is recommended because excessive salt of 30 kinds were collected and analyzed to ascertain uptake causes disease. Research on low-salt food tech- their salt components, which were then compared and nology with excellent palatability is progressing actively examined according to the manufacturing method (9). to strengthen saltiness by adding aroma and flavors to Results show that group D salts have more , foods and creating alternative structures of foods (2–6). calcium, potassium, and sulfate ion than other salts. From this perspective, we are investigating the possibil- Group B salts also have more bittern components than ity of reducing salt intake using interaction between those produced using other methods. The bitter ingredi- salty taste and other taste ingredients (7, 8). We also ent amount affects the salt taste. Earlier reports describe report salty taste enhancement based on the contrast that it is identifiable by a taste sensor (11). Therefore, effect of acidity and saltiness with rice porridge (8). the salty taste quality was evaluated by taste sensor measurement and sensory evaluation (9). Furthermore, Commercial Salt Samples Containing Bittern principal component analysis was applied by combin- Components ing the inorganic component content, the taste sensor Currently, salts of many kinds are sold in Japan. These measurement value, and the sensory evaluation result. salts, whether deriving from local seawater or reprocess- Eventually, 30 commercially available salts were classi- ing from imported salt, etc., are produced using various fied. Consequently, results demonstrated that the salt is methods. Commercially available salts are classifiable an unrelated group produced by boiling seawater and by into six types (groups A–F) depending on the produc- direct spraying of seawater. Group E salts were also dif- tion method as follows (9): A, reprocessed imported ferent from the others. However, salts produced by other solar salt; B, salt produced by boiling seawater; C, salt methods have similar properties. The findings above made by adding a bittern component to the surface indicate that commercially available salts are classifiable into four groups because of different production meth- E-mail:[email protected] ods, ingredients, and taste, as shown in Fig. 1 (9).

S200 Differences in Salt Bittern Components and Effects on Rice Porridge Taste S201

Table 2. Results of sensory evaluation of the salty taste of sample pairs (1).

Taste Profile Combination of pairs Intensity of salty taste

Saltiness Sample A Sample B Sample A Sample C Sample A Sample D Sample B Sample C Sample B Sample D Sample C Sample D **

Bitterness Sample A Sample B Sample A Sample C Sample A Sample D Sample B Sample C ** Sample B Sample D ** Sample C Sample D ** Palatability Sample A Sample B Sample A Sample C Fig. 1. Score plots of principal component (PCA) factor Sample A Sample D Sample B Sample C ** 1 versus factor 2 of 30 kinds of salt samples (9). Scor- Sample B Sample D ing plots were based on inorganic concentration data, Sample C Sample D ** response patterns of taste sensor data (Sensor 1–8), ** and sensory evaluation data. Arrows indicate the ori- p,0.01. entation and the amount of factor loading. **

Table 1. Composition of inorganic ions in the four salt samples (1). (%)

Ca K Mg Na Cl SO4

Sample A 39.3 60.7 Sample B 0.09 0.11 0.28 38.7 60.75 0.04 Sample C 0.36 0.11 0.31 38.2 59.40 1.58 Sample D 0.80 1.06 3.34 30.5 54.90 5.84

Taste Differences of Salts Produced Using Different Methods When Used for Cooking—Sensory Evalua- tion of Salt Water Differences in taste were compared when four kinds Fig. 2. Sensory scores of salty taste of the samples (1). of commercial salt with different properties were used for cooking (1). The four salts are the following: A, sodium chloride only; B, reprocessed imported solar salt; C, salt produced by boiling seawater; and D, salt dried (modified Haga’s method), investigated the saltiness, by direct spraying of seawater at room temperature. The bitterness, and preferences for the saltwater solutions. respective inorganic component contents of these salts Table 2 and Fig. 2 respectively portray the intensity of are shown in Table 1. These components are shown as taste in sensory evaluation and the significant difference solid contents remaining after water is extracted from for each combination of salts. The salty taste intensity the salt . To investigate the taste characteris- was found to be almost identical as the sodium chloride tics of these salts, we demonstrated taste discrimination content, as shown in Fig. 2, but a significant difference using a saline solution in the following manner. After was found between sample B and sample D, as shown each salt was dissolved to 1% sodium chloride content in Table 2. The bitterness intensity was felt strongly for in 1,500 mL of deionized water, the salt solution was Sample D, as shown in Fig. 2. No marked difference was kept at 70˚C. These solutions were used as samples for observed from other salts, as indicated at Table 2. These sensory evaluations. Saline evaluation was conducted results are interpreted as explained below. The follow- by 38 panelists. We conducted experiment procedures ing concentrations of the salts were used: Sample B has and analyses using Scheffe’s paired comparison method 0.0056% of and 0.0089% of mag- S202 Ishikawa K et al.

Table 3. Results of sensory evaluation of rice porridges was lower for Sample D than those of other salt pairs, (1). as shown in Table 2 and Fig. 2. Therefore, results dem- onstrate that the bittern component amount strongly Intensity of rice Taste Profile Combination of Pairs affects the salt taste (1). porridge Taste Differences in Salts Produced Using Different Saltiness Sample A Sample B Production Methods and Used for Cooking—Sen- Sample A Sample C Sample A Sample D sory Evaluation of Rice Porridge Sample B Sample C ** We have reported evaluation results of the taste of Sample B Sample D porridge prepared using the salt solution used for the Sample C Sample D ** experiment above (1). Rice porridge was prepared in the ** following manner: salt corresponding to about 0.56% of Other tastes Sample A Sample B sodium chloride was dissolved in 1,400 mL of distilled Sample A Sample C water. The samples contained 9.00 g, 10.02 g, 9.36 g, Sample A Sample D ** and 11.12 g, respectively, of salts of Sample A, Sample Sample B Sample C B, Sample C, and Sample D. To 1,400 mL of distilled Sample B Sample D water containing each salt, 200 g of rinse-free rice was Sample C Sample D * added and cooked (IH heat retainer RC-10 HY; Toshiba Palatability Sample A Sample B Corp.). The rice porridge was prepared as three-quarter Sample A Sample C porridge. After preparation, it was mixed thoroughly Sample A Sample D for 10 s, steamed for another 30 min, and mixed thor- Sample B Sample C * oughly for 10 s to prepare a sample for sensory evalu- Sample B Sample D ** ation. Table 3 and Fig. 3 respectively portray the taste Sample C Sample D ** intensity in sensory evaluation and the significant dif- ference in each combination of salts. Sample pairs with p,0.05, p,0.01. * ** sample A and sample D were judged respectively as hav- ing strong and weak salty tastes, as shown in Fig. 3. Significant differences were found between sample pairs with sample D and the other salts examined as shown in Table 3. Despite addition of the same amount of sodium chloride in the porridge, the salty taste intensity dif- fers, as shown in Table 3 and Fig. 3. Apparently, ingre- dients other than sodium chloride influence the taste. Significant differences were found in the combinations of sample A and sample D, sample C and sample D for the intensity of taste other than saltiness, as shown in Table 3. In addition, among responses to the question of what tastes other than a salty taste were found for Sample D, one response cited sweetness instead of bit- terness. Sample D showed a significant difference from all other salts in terms of palatability, as shown in Table 3. The deliciousness of the porridge prepared from sam- ple D is attributable to the use of a salt that is preferred Fig. 3. Sensory scores of the salty taste of rice porridges over other salts. For evaluation of the saline solution, a (1). tendency of avoiding strong bitterness was noted, but it was a different response for porridge preparation. Rice porridge has a simple cooking method: it uses only rice, water, and salt as starting materials. However, the kind nesium sulfate, the magnesium chloride concentration of salt and pH influence the rice swelling and water contained in Sample C is 0.013%, as shown in Table 1. penetration into rice (12–15). In our experiments, the However, the aqueous solution prepared using sample D concentrations of the salt added to samples A–D were containing many bittern components contained 0.12% almost equal, but the pH levels of the aqueous solution of magnesium chloride and 0.06% of magnesium sul- were, respectively, 6.07, 6.25, 6.10, and 9.95. The pH fate. The amounts thereof were more than 10 times of the porridge prepared from samples A, B, and C was those of other edible salts, as shown in Table 1. In gen- shown to be almost equal to the pH of the aqueous solu- eral, salt with a high bittern component has strong bit- tion, but the pH of the porridge prepared from sample terness. The bitterness of the sample pairs with sample D is shown as 6.89. Based on the results described D was evaluated as strong because the bitter component above, we concluded that the bittern component in the of sample D was greater than that of the other salts, as salt influences the expression of taste based on interac- shown in Table 2 and Fig. 2. Evaluation of palatability tion with other taste ingredients. It also affects cooking Differences in Salt Bittern Components and Effects on Rice Porridge Taste S203

Fig. 5. Sensory evaluation of the salt solution at Fig. 4. Sensory evaluation of the salt solution at 0.584% (W/V) with citric acids. The ordinate shows 0.234% (W/V) with citric acids. The ordinate shows the number of panelists who answered that the sample the number of panelists who answered that the sample tasted saltier (7, 8). tasted saltier (7, 8).

Fig. 6. Salty taste intensity by sensory evaluation of rice porridge with sodium chloride (quantity) and citric acid (8).

processes such as penetration and elution, eventually ing salty taste using citric acid in a saline solution (7, affecting the food taste (1). 8). For the experiments, several aqueous solutions were prepared by adding 0.013%, 0.0018%, and 0.0025% of Using a Contrastive Effect for Salt Taste Enhance- citric acid to 0.234% and 0.584% saline solution. Those ment—Sensory Evaluation of a Salt Water Solution concentrations of solutions can be discriminated from Salt can fundamentally determine the taste of pre- water. In fact, 0.0018% citric acid is a concentration at pared foods. Salt not only adds saltiness: it also interacts which one can recognize a slight sourness; 0.0025% with other taste ingredients during cooking, enhanc- citric acid is a concentration at which one can recog- ing or suppressing other tastes. Salt reduction not only nize sourness clearly. Salty taste intensities of a citric weakens the salty taste, it also alters the balance of tastes acid containing salt water solution and a citric-acid- in dishes, eventually decreasing taste overall. Therefore, free salt water solution were evaluated using pair tests. some means of reducing salt contents while maintain- evaluation was done by 23 panelists. Figure 4 ing the taste of prepared foods must be considered. In shows sensory evaluation results when adding citric contrast to suppression or enhancement of other tastes acid to 0.234% saline. Although the salty taste tended of salt, we assessed the functions of various taste com- to be suppressed with 0.0013% citric acid added saline, ponents to enhance salty taste. A mixed solution with the salty taste intensity was enhanced significantly at acidity and saltiness is known to suppress salty taste higher citric acid concentrations. The 0.234% saline with a large amount of acidity or increase of salty taste has salty taste with some sweetness, but when 0.0018% by the addition of a small amount of acidity. Reportedly, and 0.0025% citric acid was added, a clear salty taste salty taste enhancement has been done using acetic acid was discerned. Apparently, the citric acid decreases the (16) and vinegar (17–20). We sought means of enhanc- detection threshold of a salty taste. Figure 5 shows the S204 Ishikawa K et al. sensory evaluation results obtained with addition of cit- use it for cooking according to the salt characteristics. ric acid to 0.584% saline. Results show that salty taste Excessive salt intake causes lifestyle diseases. Therefore, suppression was recognized even at 0.0013% citric acid salt uptake reduction is an important issue that must addition to 0.284% saline. The results described above be addressed. Reportedly, salty taste enhancement by demonstrate that interaction between sour and salty contrastive effects of other taste ingredients such as tastes when using citric acid exhibits both a contrastive umami and acidity is effective for compensating taste effect and a suppressive effect depending on the target insufficiency because of reduced salt. In conclusion, we salt concentration, which are similar results to those presented an example using the contrastive effects of obtained from studies examining acetic acid (16). sourness and salty taste in porridge. The results might also be applicable to various dishes such as soup and Using Contrastive Effects to Reduce Salt Taste—Sen- simmered foods, with great effectiveness for reducing sory Evaluation of Rice Porridge salt contents without reducing saltiness. Mixed components of citric acid powder and salt (cit- ric acid concentrations: 0.3, 0.5, 1, 2, 3, 5, 10%) were Disclosure of State of COI prepared and mixed with salt of 0.5% corresponding No conflicts of interest to be declared. to the weight of porridge (8). Figure 6 shows that the salty taste intensities of salt porridge with and without Acknowledgments citric acid were evaluated by pair testing (8). Because This work was supported in part by a research grant of the addition of citric acid, the salty taste of porridge from The Salt Research Foundation (No.0540, 1141, tends to be felt strongly. Significant differences were also 1239) of Japan. observed in porridge with 0.5%, 1%, and 5% added cit- REFERENCES ric acid. The salty taste of porridge tends to be sensed strongly because of the addition of citric acid to the 1) Ishikawa K, Sato H, Usami R, Kumagai M, Matsunaga R. salt. Significant differences were also found among por- 2008. 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