Effects of Various Salts Added to Sodium Chloride on the Taste and Properties of

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1 Food Sci. Technol. Res., 16 (1), 31 38, 21 Effects of Various Salts Added to Sodium Chloride on the Taste and Properties of Diluted Egg Sol/Gels and Cooked Rice Tomoko Ichikawa * and Michiko Shimomura Faculty of Home Economics, Otsuma Women s University, Chiyoda-ku, Tokyo , Japan Received March 1, 29; Accepted September 1, 29 Various salts can be substituted for sodium chloride (NaCl) to give food a salty taste. In these experiments, a small percentage of total NaCl was replaced by another salt (,, ). The effects of these various salts on the physical strength and water-retention ability of egg sol/gels were investigated. In addition, the saltiness of diluted egg gels and solid cooked rice seasoned by these salt mixtures was evaluated by a large number of individuals. Results showed that substitution of Na by Mg or Ca salt imparted the egg white gels with high breaking stress and strain, and the egg gels showed less water loss by syneresis as compared with gels to which Mg or Ca salt alone had been added. Furthermore, substitution by K or Mg salt was acceptable by taste in egg solution gel and boiled rice, but when Ca was substituted, it was acceptable by taste only in boiled rice. Keywords: salts, egg sol/gel, breaking strength, syneresis, sensory evaluation *To whom correspondence should be addressed. ichikawa@otsuma.ac.jp Introduction Table salt used as an ingredient in foods is usually pure sodium chloride (NaCl). Recently however, natural salt, which contains small quantities of calcium chloride ( ) and magnesium chloride ( ), has also appeared on the market. Although the amount of salt added to cooked foods is only 1-2% of total weight of foods, it serves as a seasoning to make the food palatable. Therefore, the effects of these salts on properties such as taste, saltiness, color, hardness, and texture of cooked foods must be determined. Previous studies by Ichikawa et al. (21; 27) on the effects of NaCl and other salts added at different concentrations to diluted whole egg and egg white solutions yielded the following results regarding the properties and saltiness of egg sols and gels. For egg white solutions with univalent NaCl or salts, the breaking strength of gels was lower than for solutions with divalent or salts, although it increased gradually with increasing salt concentration. The amount of liquid released by syneresis from gels with divalent salts was significantly greater than from that with univalent salts. Moreover, the breaking strength of gels with the same charge showed the same behavior, after adjusting the sols to the same ph value. Hatae (25) summarized the effects of various factors (e.g. coexistence of other ionic substances) on the salt intensity of NaCl. They found that salt intensity was significantly lowered when NaCl was substituted with more than 2%, or more than 1% (Shimada et al., 1989). However, no significant difference was found in the preference for 2% or 1% substituted NaCl solutions. Furthermore, addition of seasoning for taste (monosodium glutamate; MSG) to the above mixed salts made the evaluation of salty taste more difficult than for aqueous salt solutions without MSG (Matsumoto et al., 1979). This study investigates the effects of different salt components (,, and ) substituting a small part of NaCl on the physical strength and water-retention ability of egg sol/gels in which egg protein coagulates with salt. Additionally, sensory evaluation is conducted on the salty taste of diluted egg gels (a model of chawanmushi; i.e. diluted egg sols in a china soup bowl) and of solid cooked rice with these salts. Experimental Materials Special grade reagents of NaCl,, 6H 2 O, and 2H 2 O were purchased and used as salts added to the samples. Fresh eggs and rice ( Aki-

2 32 takomachi ) were obtained from specific shops (Chiyoda Ward, Tokyo). Ovalbumin was purified from egg white as follows (salting out method: Ando et al., 197). Egg white was stirred at about 5 rpm in a low-speed blender for approximately 1 minute, and screened through a sieve (No. 35 mesh). Then, a saturated solution of ammonium sulfate was added, and the mixture was stirred at low temperature for about 3 min. After overnight storage at 5, the supernatant was obtained by centrifugation at 49 g for 15 min;.2 N sulfuric acid was then added to the supernatant to adjust ph to Saturated ammonium sulfate solution was then added until the liquid became cloudy, and after overnight storage, the precipitate was obtained by water-cooled (at 5 ) centrifugation at 49 g for 15 min. Next, deionized water was added to the precipitate, and the mixture was filtered to yield the supernatant liquid of ovalbumin (A). (A) was kept in a dialysis tube immersed in large quantities of deionized water at 5 with stirring, and soaked in fresh deionized water five times within 3 days to give a dialyzed liquid (B). (B) was treated by ultrafiltration (separating molecular weight: 2 Da) to prepare purified ovalbumin liquid (C). The ovalbumin content in (C) was calculated from the standard curve of absorbance at 28 nm for biochemical grade ovalbumin and determined to be 12-15%. Preparation of Egg White Gels with Salt Stirredhomogenized egg white sols were screened twice with a stainless steel sieve (No. 35 mesh). Following the addition of salted solution, the diluted egg white sols of 35% or 5% concentration were screened once more. The total salt concentration was.8%, and was composed of NaCl plus another salt. The secondary salt (,, or ) comprised either 1, 5, 1, or 2% of the total salt solution being tested. Sixty-gram fractions of the sol in a pudding mold with fluorinated resin coating on the inner surface were wrapped with polyvinylidene chloride film and heated to 9 ± 1 in a water bath for 2 min. After cooling in running water, the gels were stored at 5 for 24 h to be used in the experiments. Analyses The hardness of the prepared gel was measured using a rheometer (Yamaden, RE-335). The properties of breaking strength (breaking stress, breaking strain, and breaking energy) of samples 15-mm thick and 5 mm φ were analyzed under a 2 kg load and 99% compression ratio by a 3 mm φ plastic plunger. The amount of liquid released by syneresis from the salted gels was measured using two methods: 1) keeping, and 2) centrifugal separation. In the keeping method, gel was placed in a 9 cm φ funnel with a filter plate and wrapped with film. The amount of liquid that dropped within 1, 2, 4, and 6 min was measured. For centrifugal separation, a sample T. Ichikawa & M. Shimomura weighing about 3 g was put into a 1.8-cm φ, 1-cm long tube with a cap. The sample was set on a centrifugal separator at 2 g, 2 g, or 1, g for 3 min, and the volumes of supernatants were measured. The transformation process of egg white sol to gel was also monitored by FT-IR spectra measurement, and thermal analysis of the process was performed using differential scanning calorimetry (DSC). Infrared spectra patterns of purified ovalbumin stirred-mixed with 1.5% of one of the four kinds of salt were measured by transmittance (FT-IR-73, Japan Spectroscopic Co. Ltd.). This measurement was repeated after storage at 5 for 14 d to investigate the change of chemical structure in gels with the time. DSC analyses of water absorbed in the sample sols were performed using a Seiko Electric SSC 52 System DSC 22C. The DSC cell was heated from 4 to 1 at a rate of 1 /min. Sensory Evaluation At each stage, the sensory evaluation test was performed in three different ways, as follows. 1) Five properties of egg white gels were measured by score method: saltiness, hardness, texture (feeling smooth when touched with the tongue), taste, and total evaluation. Gels with substituted salts (1% of NaCl) were evaluated with scores (from highly evaluated +3 to low 3) in comparison with the gel containing.8% NaCl used as a control (score of ). 2) The saltiness of 35% egg white gel with.8% salt was evaluated by the following specific probit model. (a) Concentrations of NaCl in 7 referential solutions (1-7) used as controls of saltiness are shown in Table 1. (b) Panel members first tasted egg white gel with salt, then drank NaCl solutions in order from solution 1 to solution 7. The NaCl solution judged to have equal saltiness to the gel was chosen and summed for all panel members. (c) The concentration of NaCl judged equal by more than 5% of panel members was calculated for each gel by means of a probability function of normal distribution (Japanese Standard Association, 24). Table 1. Concentration of NaCl as controls of saltiness by probit method. Salt standard solution as control Salt concentration control 1.73 Control 2 (= control 1x1.1).8 Control 3 (= control 2x1.1).88 Control 4 (= control 3x1.1).97 Control 5 (= control 4x1.1) 1.6 Control 6 (= control 5x1.1) 1.17 Control 7 (= control 6x1.1) 1.29

3 Effects of Various Salts on the Taste and Properties of Egg Sol/Gels and Cooked Rice 33 3) Properties of gels with salts were evaluated also by the ranking method: for example, the evaluated values of saltiness were in order of the degree of saltiness with 1 (the highest), 2 (next),. Panels were composed of 2 ~1 individuals (teachers and students) from Otsuma Women s University. Results and Discussion Gel Strength Properties Figure 1 shows the breaking stress and strain values of 35% and 5% egg white gels with.8% NaCl /other salts (ratios of other salts were, 1, 5, 1, and 2%). In 35% egg white gel, both stress and strain increased markedly with added or (the values were higher for than for ). The breaking stress values of gels with.8% NaCl / divalent magnesium or calcium salt (8/2) were nearly equal to those with.8% or alone (/1) (Ichikawa and Shimomura, 27). On the other hand, breaking stress values changed little with added. In 5% egg white gel, the stress and strain values for were higher than those in 35% egg white, and not significantly different from those for or. These results suggest that both the type of salt and the concentration of salt affect gel strength of diluted egg sols. An earlier study presumed that divalent salts, which could form ionic cross-links between egg protein molecules, promoted coagulation to stronger gels at lower egg sol concentrations (Migita, 1969). At higher concentrations, more intensive repulsion between protein molecules suppressed the cross-linking by divalent salts. However, the degree of promotion by was somewhat different from that by. A previous study (Ichikawa and Shimomura, 27) showed that ph influenced the degree of gel formation from sols with salts, due to ph-mediated ion dissociation. To clarify this effect, the ph of all sols used to prepare gels was adjusted to 7.4 by the addition of 2N HCl. The breaking strength values (stress and strain) of 35% egg white gels with NaCl /other salts (,, or, whose ratios were, 1, 5, 1, or 2%) were compared, as shown in Fig. 2. stress 1 3 (N/m 2 ) strain(%) MgCl2 CaCl2 Egg White : 35%, : 5% Fig. 1. Breaking stress (left) and strain (right) of egg white gels with.8% salts composed of various ratios of NaCl and other salts. stress 1 3 (N/m 2 ) strain(%) Fig. 2. Breaking stress (left) and strain (right) of 35% egg white gels with.8% salts composed of various ratios of NaCl and other salts at ph 7.4.

4 34 T. Ichikawa & M. Shimomura At -1% ratios of any of the salts, the breaking strength values did not change from those with.8% NaCl alone (% ratio). At 2% ratios of and, the breaking strength values were high. In contrast with the findings shown in Fig. 1 (35% egg white gel), in this experiment magnesium salt and calcium salt had the same effects on the properties of the gels. This result suggests that the intensity of anionic repulsion between egg protein molecules decreased at low ph, which promoted the formation of ionic cross-links by divalent salts, especially magnesium salt. Amount of Water Released by Syneresis in Gels The amount of water released by syneresis from 35% and 5% egg white gels with NaCl / other salts was measured following fixed storage times (keeping method: 1, 2, 4, and 6 min) (Fig. 3). Gels with NaCl / released comparatively less liquid, and the amount changed little as the proportion of added was increased. With NaCl / divalent salts, however, remarkably larger amounts of liquid were released, increasing with the ratio of divalent salts added. However, comparing these results with previous results from Ichikawa et al. (27), the amount of liquid released from gels with.8% NaCl / divalent magnesium or calcium salt (8 /2) was 15-2% less than with.8% or alone ( /1). Moreover, the amount of liquid released from 5% egg white gels with divalent salts was less than that released from 35% egg white gels, demonstrating the influence of egg white concentration on water retention. After the ph of the sols used to prepare gels with salts was adjusted to the same value, the amount of liquid released by syneresis in 35% egg white gels with NaCl/ other salts was measured using the centrifuge method to investigate the effects of mechanical force (Fig. 4). Similar to the case of breaking strength (Fig. 2), the amount of liquid released by syneresis in gels with NaCl / divalent magnesium or calcium salt was obviously higher keeping time:1min keeping time:2min keeping time:4min 4 keeping time : 6min Egg White : 35%, : 5% Fig. 3. Amounts of released liquid by syneresis from gels with.8% salts composed of various ratios of NaCl and other salts on keeping.

5 Effects of Various Salts on the Taste and Properties of Egg Sol/Gels and Cooked Rice 35 than with NaCl /. The amount of liquid increased with centrifugal force in gels with NaCl / or, and was especially large with the ratio of 8 / 2 at 1 g. Chemical Change of Ovalbumin with Salts Added: IR Spectra and DSC Analyses The formation of ionic crosslinks between egg protein molecules in the transformation process of egg sols to gels was estimated by infrared spectra and thermal DSC analyses of ovalbumin/salt sols. Infrared spectra of ovalbumin sols with 1.5% salt showed similar patterns before and after incubation in a refrigerator at 4 for 14 days. The spectra after storage are shown in Fig. 5. The spectrum of every sol, including the reference (ovalbumin alone), shows bands at 165 cm -1 assigned to amide I C=O stretching and at cm -1 assigned to amide II N-H bending. Little difference is found in spectral patterns among sols with the four kinds of salts, indicating that the chemical bond in the ovalbumin molecule did not change remarkably with type of salt added, in spite of reports on the three-dimensional structural modification of egg protein (Doi, 1992; Lechevalier et al., 23). Moreover, preliminary examination of the change in molecular weight of egg white by viscosity measurement (rotorviscometer torque method) indicated that the addition of salts had little influence (data not shown). In a sol state, chemical change with salt addition was not remarkable, suggesting that the type of salt had a major effect on properties involved in the process of heat coagulation to gel. Figure 6 shows examples from the thermal analysis (DSC) of the heat coagulation process of purified ovalbumin sols with 1.5% salt obtained before and after storage for 14 days. Absorbance wave number control cm -1 NaCl Fig. 5. FT-IR spectra of ovalbumin sols with 1.5% salts added. Ovalbumin NaCl 6 ENDO Ovalbumin : on preparation Temperature ( ) Ovalbumin ENDO. NaCl centrifuge : 2G, : 1G Fig. 4. Amounts of released liquid from 35% egg white gels with.8% salts composed of various ratios of NaCl and other salts at ph 7.4 by centrifuge method. Ovalbumin : after 14 days Temperature ( ) 1. Fig. 6. DSC curves (examples) of ovalbumin sols with 1.5% salts added.

6 36 T. Ichikawa & M. Shimomura Table 2 shows calculated mean values (number of measurement n = 3 ~ 4 for each sample) of each peak top temperature assigned to ovalbumin (Shiotsubo, 1991), as indicated in the Figure. With addition of univalent salts, the peak top shifted to a higher temperature, but with addition of divalent salts, the peak patterns changed little. After storage for 14 d with univalent salts, the peak top also shifted to a higher temperature, similar to the situation of ovalbumin peak in egg white sols (Ichikawa and Shimomura, 27). These results suggest that endothermic change, followed by heat-coagulation of ovalbumin, was delayed with univalent salts due to protein molecule ionic dissociation, especially after storage. Saltiness Sensory Evaluation Preliminary experiments using 35% egg white gel with.8% added salt showed little change in sensory score when 5% of the NaCl was replaced by another salt. As shown in Table 3, a 1% substitution of NaCl by resulted in a significantly smoother feeling of texture. However, a 1% substitution of NaCl by or reduced saltiness, increased hardness, and therefore obtained low scores in total evaluation. Consequently, as salt ingredients (.8%) were added to 35% egg white gels, substitutions by were acceptable up to 1%, and substitutions by or were acceptable up to 5%. The saltiness of egg white gel with added salt was compared to that of NaCl aqueous solution. When.8% NaCl was added to 35% egg white (which contains.35% NaCl) sol/gel, the salt content of the gel was about.92% NaCl. Table 4 shows the ratios of panel members, which judged each concentration of NaCl by the probit method mentioned above. Saltiness of gels with.8% NaCl or NaCl/other salts (95/5) was judged to be equal to that of.96% (for NaCl/ none),.853% (for / ),.83% (for / ) and.799% (for / ) NaCl aqueous solution, respectively. Therefore, a 5% substitution of NaCl by other salts resulted in a value of salty taste efficiency (to the above.92% NaCl content) equal to.98 (none),.93 (),.87 ( ), and.87 ( ), respectively. The differences of these values are in accordance with the results for saltiness shown in Table 3. To verify the practical use of the substituted salts mentioned above, saltiness sensory evaluations were carried out for chawanmushi, in which the egg protein ingredient coagulates from the heat of cooking, and for boiled rice, in which starch absorbs water, swells, and becomes gelatinized upon Table 2. DSC Peak Temperature in Ovalbumin Sols with Salts. Salt Ovalbumin On Preparation After 14 days Peak temp. Peak temp. None NaCl Table 3. Effect of different salts at 1% substitution to NaCl on the sensory evaluations of 35% egg white gels ( score method : mean value). item saltiness.15.9 **.65 * hardness ** texture.7 **.5.15 taste total evaluation *.5 * * : significant difference at 5% risk (P <.5) ** : significant difference at 1% risk (P <.1) Table 4. Salty taste efficiency of 35% egg white gels with.8% NaCl / other salts (95/5 ) [NaCl conc.=.92%]. Control NaCl conc. (%) NaCl (1) / / / panel (%) sum panel (%) sum panel (%) sum panel (%) sum total % of panel NaCl (1) / / /.96%.853%.83%.799%

7 Effects of Various Salts on the Taste and Properties of Egg Sol/Gels and Cooked Rice 37 cooking. The ratios of substitution for NaCl were 1% by, and 5% by or. The results for diluted egg solution gel serving as a model of chawanmushi are shown in Table 5. The degree of saltiness was significantly lower with salt that contained 1% than with NaCl alone serving as a control. On the other hand, salty taste preference of gels was similar between those with only NaCl and those with various salts. Gels with 5% substitution were significantly harder than gels with other salts. Furthermore, gels with 5% substitution were less preferred than those with only with NaCl with respect to hardness and total evaluation. This suggests a slight influence of on the salty taste of soft gel foods even when physical properties were not affected by salt substitution. For boiled rice (Akitakomachi) with.65% various salts, Table 6 shows the evaluation results on gloss, saltiness, hardness, and total evaluation by ranking test. Boiled rice with 5% substitution was significantly (p <.5) glossier than with the NaCl control. However, the other three properties evaluated were similar, and salt substitution had little effect. As mentioned above, the taste of samples with 5% substitution was not preferred for diluted egg solution gel, but was acceptable for boiled rice. These results suggest that the effects of various salts on taste evaluation were different for soft gel food formed by heating and for originally solid food, which absorbs water to gelatinize on cooking. These results correspond with those reported by Hatae (25), in that the sensibility to salty taste was lowered in solid food. Conclusion From our results, we conclude that the substitution of a small portion of NaCl with Mg or Ca salt caused egg white gels to have a high breaking stress and strain, and less water loss by syneresis as compared with Mg or Ca salt added alone. Furthermore, substitution with K or Mg salts was acceptable by taste in egg solution gel and boiled rice, but Ca Table 5. Sensory evaluation of 33% egg gels with NaCl and other salts. Rank sum 1) Significance level 2) NaCl(A) /1%(B) /5% (C) /5% (D) Saltiness Degree 212 a 286 b 249 ab 253 ab A-B** Preference 255 a 236 a 262 a 247 a Hardness Softness 242 a 217 a 294 b 247 a A-C*, B-C**, C-D* Preference 224 a 252 ab 252 ab 272 b A-D* Total Evaluation 226 a 237 ab 259 ab 278 b A-D* 1) Rank sums within the same row bearing different superscripts are significantly different. 2) Significance level (Newell and MacFarlane, 1987) : **, P <.1 (difference of value 57) ; *, P <.5 difference of value 47) (ranking method, 1 panelists) Table 6. Sensory evaluation of boiled rice preference with NaCl and other salts. Rank sum 1) Significance level 2) NaCl (A) / 1% (B) / 5% (C) / 5% (D) Color (Whiteness) 227 a a a 232 a Gloss 267 a 258 ab 257 ab 218 b A-D* Saltiness a 223 a 254 a 26.5 a Hardness 258 a 245 a 23.5 a a Total Preference 259 a 234 a 263 a 244 a (ranking method, 1 panelists) 1) Rank sums within the same row bearing different superscripts are significantly different. 2) Significance level (Newell and MacFarlane, 1987) : **, P <.1 (difference of value 57) ; *, P <.5 difference of value 47)

8 38 salt was acceptable only in boiled rice. This work was carried out as part of Studies on the Taste of Salt from the Viewpoint of Cookery Sciences supported by The Salt Science Research Foundation. References Ando, T., Yamakawa, T., Terayama, H. and Nishizawa, K. (197). Method in Biochemical Study II, Asakura Books: Tokyo, pp Doi, E. (1992). Studies on Functional Properties of Food Proteins. J. of the Japanese Society for Food Science and Technology, 39, Hatae, K. (25). Salt and Taste Sensation in Foods. Bulletin of the Society of Sea Water Science, Japan, Ichikawa, T., Watanabe, Y., Kanbe, M., Hirae, Y., Kawashima, K. and Shimomura, M. (21). Effect of Salts to the taste and Properties of egg Gels. J. of Cookery Science of Japan, 34, Ichikawa, T. and Shimomura, M. (27). Effect of Sodium Chloride and Other Salts on the Properties of Diluted Egg White Sols and T. Ichikawa & M. Shimomura Gels. Food Science and Technology Research, 13, Japanese standard association. (24). Japanese Industrial Standard. JIS Z 98. Lechevalier, V., Groguennec, T., Peznnec, S., Guérin-Dubiard, C., Pasco, M. and Nau, F. (23). Ovalubumin, Ovotransferrin, Lysozyme: Three Model Proteins for Structural Modifications at the Air-Water Interface. J. Agricultural Food Chem., 51, Matsumoto, N., Miyoshi, K. and Sugita, M. (1979). Effect of salt on cooking. J. of Cookery Science of Japan, 12, Migita, M. (1969). Protein and Cookery Science (Ⅵ). J. of Cookery Science of Japan, 2, Newell, G. J. and MacFarlane, J. D. (1987) Expanded Tables for Multiple Comparison Procedures in the Analysis of Ranked Data. J. of Food Science, 52, Shimada, A., Sato, T., Hamada, Y. and Hatae, K. (1989). Effect of salt substitutions on the taste and texture of food. Bulletin of the Society of Sea Water Science, Japan, Shiotsubo, F. (1991) Application of Food with Thermal Analysis. J. of Cookery Science of Japan, 24, No.1, 54-6, No.2,