J. Home Econ. Jpn. Vol. 50 No.12 1217•`1222 (1999)

Similar Preference for Natural Mineral Water between

Female College Students and Rats

Yukiko ESUMI and Ikuo OHARA*

Shimane Women's Junior College, Matsue 690-0044, Japan * Faculty of Home Economics, Kobe Women's University, Suma-ku, Kobe 654-8585, Japan

The preference for natural mineral water was studied with female college students and rats. Four

commercially available types of natural mineral water from Japan and overseas were selected for a

sensory evaluation. Tap water was used as a control. The amounts of calcium, magnesium, sodium and

potassium in each water sample were measured by atomic absorption spectrophotometry, and the hardness was measured by the chelatometric method. The subjects were female college students with

normal taste perception. Subsequently, 8-week-old female rats were subjected to two-bottle-choice

preference tests. The measured concentrations of calcium and magnesium in each water sample were lower than the values indicated on the labels, while the sodium and potassium concentrations were

higher. The measured hardness values were approximately 1.2 times those calculated from the

concentrations of calcium and magnesium. The hardness values of the test samples were 11.5, 58.3,

81.3, 332.3 and 534.0 mg/l, while tap water had a hardness of 38.3 mg/l. Preference tests showed that a

hardness of 58.3 mg/l produced the most favorable taste quality, while a value of more than 300 mg/l

resulted in aversion with both humans and rats. These results suggest that the acceptability of natural

mineral water is similar with both humans and rats, with a hardness of around 50 mg/l being best for

drinking water. The hardness of mineral water can be used as an index for the sensory evaluation of

drinking water.

(Received November 17, 1998; Accepted in revised form May 7, 1999)

Keywords: natural mineral water, sensory evaluation, female college students, female rats, preference,

hardness.

INTRODUCTION

Mineral water has become very popular as a soft drink in Japan (Hayakawa 1994; Suntory Co. 1995).

According to recent data, two hundred kinds of mineral water are on the market, and their market share of all drinks has suddenly increased in the last

few years (Hayakawa 1994; Suntory Co. 1995). One of the reasons for the increasing consumption is thought to be increased domestic use, including cooking, and not to increased commercial use (Hayakawa 1994).

Complaints about the deteriorating quality of drinking water, questions about the safety of tap water and the

increased consciousness for health problems are

possibly responsible for this (Hayakawa 1994; Hattou 1995; Suntory Co. 1995; Fujita 1996). There is also

the aspect that drinking bought mineral water, and not just drinking tap water, has become fashionable especially among young adults (Suntory Co. 1995). In consequence, the consumption of mineral water in

Japan is expected to continue its increase in the future.

The Society for the Study of Tasty Water, which is

sponsored by the Ministry of Public Welfare, proposed hardness to be one of the most important require-ments for tasty water (Fujita 1996). Many studies have been made in the fields of microbiology

(Hunter 1993; Hunter and Burge 1987; Rivilla and Gonzalez 1988; Stickler 1989; Ferreira et al. 1996), and chemistry and technology (Kfir and Prozesky

1982; Kataoka 1987; Sauvant et al. 1995). There is, however, little scientific information concerning the sensory nature of natural mineral water.

The objectives of this study are to investigate the best mineral water for drinking by using hardness as an index, and whether the response of rats to mineral

water can be extrapolated to that of humans.

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J. Home Econ. Jpn. Vol. 50 No.12 (1999)

MATERIALS AND METHODS

Materials

Natural mineral water products for which the

concentrations of Ca, Mg, Na and K are indicated on

the labels and which are readily available were

selected as test samples. Nine Japanese and five

imported brands (four from France and one from

Belgium) were evaluated. None of them were

carbonated. Tap water was used as a control. The

mineral contents of Ca, Mg, Na and K were measured

by an atomic absorption spectrophotometer (Type

AA-781, Japan Jarrell Ash, Kyoto, Japan) according to

the method of Japan Society for Analytical Chemistry,

Hokkaido Branch (1994). Hardness was measured by

the chelatometric method of Japan Society for

Analytical Chemistry, Hokkaido Branch (1994) and

was also calculated from the formula 2.5 X Ca+4.0 X

Mg, using the measured Ca and Mg contents

(Hattou 1995; Ueno 1994).

Sensory evaluation by female college students

Sixteen healthy subjects with normal taste sensitivi-

ty were selected from 35 students, and sensory tests

for four basic tastes (sweetness, saltiness, sourness,

and bitterness) by using filter-paper discs (Sanwa,

Nagoya, Japan; Okuda 1980; Esumi and Ohara 1995)

were conducted. The sensory evaluation was carried

out a few hours after lunch to avoid any effect from

the meal or from hunger and was conducted twice.

The menstrual cycle of the subjects was not

considered in this experiment, although taste sen-

sitivity can be influenced by it (Glanville and Kaplan

1965; Wright and Crow 1973).

Each subject drank approximately 30 ml of a test

sample at 20-22•Ž from a 50-ml plastic cup. The taste

was evaluated by the five-point ranking method; each

subject marked a sample from one to five in order of

decreasing tastiness. The samples were offered in

ascending order of hardness for the first tasting trial,

and in descending order for the second trial. Tasting

tap water was done last in both trials, since there is a

possibility that the unpleasant smell of chlorine in the

tap water could interfere with a subsequent evalua-

tion of natural mineral water. In addition to the

numerical ranking, the impression of water taste was

also recorded.

The ranking data from the sensory evaluation were

subjected to the Kramer analysis (Kramer 1960,

1963), differences being considered statistically sig-

nificant at p< 0.01 or p< 0.05.

Preference test with female rats

Sixteen female Sprague-Dawley rats (approximately

8 weeks old and weighing 160±3 g) from Japan SLC

(Hamamatsu, Japan) were housed individually in 20 X

24 X 20 cm stainless cages at a temperature of 23 •}2

℃ and relative humidity of 40-60% with a 12-h light

and dark cycle. Each cage contained two holders for

drinking tubes. Before beginning the experiment,

each animal was fed on a commercial stock diet (MF,

Oriental Yeast, Osaka, Japan). During the acclimatiza-

tion period, the rats were given tap water and

deionized water on the first day. The animals were

then trained to approach and sample a highly

preferred solution of 0.83 mm saccharin, a highly

aversive 0.6 mm urea solution and/or deionized water

in a two-choice situation for the next 5 days. All

animals were allowed free access to food and the

sample water. Following training, two-bottle-choice

preference tests between the natural mineral water

samples were conducted. The hardness values of the

water samples were 11.5, 58.3, 81.3 and 332.3 mg/l,

respectively.

Each result is given as the mean •} SD. The data

were analyzed by Student's t-test for the preference

tests, differences being considered statistically signifi-

cant at p< 0.01 or p< 0.05 .

RESULTS

The hardness and mineral contents of the natural

mineral water samples are shown in Table 1. Marked

variation in the hardness of the commercial natural

mineral water samples was found from 10 to 500 mg/i.

The mineral concentrations also varied as widely as

the hardness. Hardness when measured by the

chelatometric method averaged approximately 14%

higher than that by calculation (hardness =2.5 X Ca +

4.0 X Mg; Hattou 1995; Ueno 1994). The imported

mineral water samples were mostly harder than the

Japanese samples. When the measured mineral

concentrations were compared with the values

indicated on the label, the measured concentrations

of Ca and Mg were mostly lower, while those of Na

and K were higher. The variation coefficient between

the measured and indicated values for Ca was less

than that for Mg, Na or K.

The results of the sensory evaluation by the

ranking method for five water samples (mineral water

of 11.5, 58.3, 81.3 and 534.0 mg/l hardness and tap

water) is shown in Table 2. The smaller the total

value, the more tasty was the water among the five

samples; a hardness value of around 500 mg/l was the

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Similar Preference for Natural Mineral Water between Female College Students and Rats

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J. Home Econ. Jpn. Vol. 50 No.12 (1999)

most aversive for taste quality in both the first and

second tests, and a hardness value of 58 mg/l was the most acceptable in the second test .

Table 3 shows the mean percentage preference for

three of the same commercial mineral water samples by the female rats. The total intake among the water samples was not significantly different. The percent-

age preference for the water with a hardness value of 58.3 mg/l was significantly higher than that for the water samples with 81.3 mg/l hardness (p<0.01) and

332.3 mg/l hardness (p< 0.05). Therewas no signifi-

cant difference with the other samples . As shown in Table 4, the preference response for

the natural mineral water samples by the humans, within the range of approximately 10-80 mg//

hardness, was similar to that by the rats (r= 0.993).

DISCUSSION

The present study has demonstrated the large variation in hardness between commercial natural mineral water brands, with most of the imported ones

tested being harder than the Japanese brands. The measured values of hardness were higher than the calculated ones without exception. Although there were also large variations in the mineral concentra-

tions, the measured Ca and Mg contents were lower than those indicated on the labels, while the Na and K

contents were opposite, the measured values being higher than those indicated.

Most imported natural mineral water brands were

harder than the Japanese ones due to the concentra-tions of Ca and Mg (Table 1). Hardness is well known to be related to a country' s topography and stratum

(Hattou 1995; Hayakawa 1994). Japanese drinking water is mainly composed of rain water, while overseas water is mainly ground water. As a result,

Japanese mineral water is generally soft and imported water is hard. According to the National Nutrition Survey in Japan (Health Bureau, Health Promotion

and Nutrition Division 1997) Japanese people have an insufficient intake of Ca. Thus, drinking imported natural mineral water is probably useful for these Japanese who do not consume sufficient minerals to

supply Ca and Mg and to improve their nutritional status. The following formula has been conveniently used

for indicating the hardness of water: hardness = 2.5 X

Table 2. Sensory evaluation of commercial natural

mineral water samples by female students

Each value is expressed as the rank sum for order of liking X no. of subjects. Five samples were tested in order of a, g, j, n and tap water (TW) in the first trial, and n, j, g, a and TW in the second trial. The hardness values of a, g, j and n were 11.5, 58.3, 81.3 and 534.0 mg/l, respectively. * (p< 0.05) and ** (p< 0.01) denote signifi-cant difference by Kramer's test (Kramer 1960, 1963).

Table 3. Preference for commercial natural mineral

water samples by female rat

a The hardness values (mg/l) for a, g, j and m were 11.5,

58.3, 81.3 and 332.3, respectively. b Each value is the

mean±SD for 16 rats. Proportional intake of the left

bottle is the (intake from the left bottle/total intake) X

100. *(p< 0.05) and **(p< 0.01) denote significant dif-

ference among corresponding samples.

Table 4. Comparison of the acceptability of natural

mineral water samples by humans and rats

Each value is the mean SD for 31 humans and 48 rats.

Acceptability is expressed as the average total rank sum

for humans, and proportional intake of corresponding

mineral water/10 for rats. Hardness values of a, g and j

were 11.5, 58.3 and 81.3 mg/l, respectively.

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Similar Preference for Natural Mineral Water between Female College Students and Rats

Ca+4.0 •~ Mg (Hattou 1995; Ueno 1994). Calculated

values for the hardness by inserting the Ca and Mg

concentrations in the samples that were measured in

this experiment were only 86% of the values measur-

ed by the chelatometric method. When a regression

analysis between the measured hardness and mea-

sured Ca and Mg values was conducted, hardness =

2.6 •~ Ca+ 4.6•~ Mg + 4.4 was obtained. If the equation

for hardness= 2.6 •~ Ca+ 4.6 •~ Mg +4.4 is used instead

of 2.5 •~ Ca+ 4.0 •~ Mg, the calculated hardness is nearly

equal to the measured value, there being good

correlation (r= 0.999) between the measured and

calculated values. We therefore recommend using 2.6

×Ca+ 4.6 X Mg + 4.4 for calculating the hardness of

water. When comparing the indicated values with the

measured ones, the contents of Ca and Mg indicated on the labels were generally higher than the measured values, while the contents of Na and K were

labeled lower. In the recent National Nutrition Survey in Japan (Health Bureau, Health Promotion and Nutrition Division 1997) and other work (Contreras

1978; Couzy et al. 1995; Pennington 1996; Rodgers 1997), the insufficient intake of Ca and the excess intake of Na have been pointed out. It is probable that

insufficient minerals were labeled higher and excess minerals were labeled lower than the actual concen-trations .

The sensory evaluation test by female college

students demonstrates that the most tasty natural mineral water had a hardness of 58.3 mg/l in the second trial, and the sample with the least-liked taste

had a hardness of 534.0 mg/l in both the first and second trials (Table 2). As a result, the preference order for the taste of the five water samples can be

estimated as 58.3 >11.5 >81.3 or tap water >534.0 mg/1in hardness. The sample with a hardness of 58.3 mg/l

was judged to be easy to drink and pleasant to the

taste, while the 534.0 mgll sample had a complex taste involving saltiness and bitterness and left a bad aftertaste in the mouth. The test results in order from hard to soft water in the second trial show a clearer

preference for the samples than those in the first trial. This fact suggests a learning effect (Naim and Kare 1977) for the bad taste which possibly made the

tongue more sensitive. The overall responses for the acceptability of the natural mineral water samples, however, show similar results in both the first and

second trials. The preference for the commercial natural mineral

water samples by the female rats was significantly

higher for the water with 58.3 mg/l of hardness than the samples with 81.3 and 332.3 mg/l of hardness. No

significant difference was found in the other samples

(Table 3). These results imply that appropriate levels of minerals are needed for tasty drinking water, too little being as bad as too much, with around 58.3 mg/l of hardness being most favorable for the rats.

The present study has demonstrated that the

preference for different types of natural mineral water by female college students was similar to that

by rats (Table 4). Rats can therefore be used as experimental animals to discriminate the flavor of natural mineral water samples.

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387-391

ミネ ラ ル ウ ォ ー タ ー に 対 す る女 子 短 大 生 とラ ッ トの 嗜 好 性 の 類 似

江角 由希 子,小 原郁 夫*

(島根 県立 島根女 子短 期大 学,*神 戸 女子 大学 家政 学部)

原稿受付平成10年11月12日;原 稿受理平成11年5月2日

市 販 ミネ ラル ウォー ター に対す る嗜好 性 を女子 短大 生 と雌 ラ ッ トで調 べ た.ミ ネ ラル ウ ォー

ター 中のCa,Mg,Naお よびKの 含有 量 は原 子吸 光 分析 法,硬 度 はキ レー ト滴 定法 で 測定 し

た.次 に,正 常 な味覚 感 受性 であ る女子 短大 生 を被験 者 とし,ミ ネ ラル ウ ォー ター4種 と水 道

水 を試 料 として官能 評価 を行 った.一 方,ラ ッ おは,8週 齢雌 を用 い て二瓶 選択 法 によ り嗜 好

試験 を行 った.ミ ネ ラル ウ ォー ター 中のCaお よびMgの 含有 量 は ラベ ル表示値 よ りも低 く,

Naお よびKは 高 か っ た.ま た,硬 度 はCaお よびMgの 含有 量 か ら算 出 され る値 の約1.2倍

を示 した.官 能 評価 に用 い た ミネ ラル ウ ォー ターの 硬 度 は11.5,58.3, 81.3, 332.3, 534.0

mg/1で あ り,水 道 水 は38.3mg/1で あ った.女 子 短大 生,雌 ラ ッ トと も硬度58.3mg/1の ミ

ネラ ル ウ ォー ター にお い て嗜好 性 が最 も高 く,硬 度300mg/1以 上 で は嗜 好性 が 低 下 した.こ

れ らの結 果 は,女 子短 大生 と雌 ラ ッ トにお け る ミネラル ウ ォー ターの嗜好 性 は類似 してお り,

硬度 約50mg/1が 飲み 水 と して最 もお い しい とい う こ とを示唆 した.ま た,ミ ネラ ル ウォー ター におい て もおい しさの指標 と して硬 度が使 用 で きる こ とが確 認 され た.

キ ーワ ー ド:ミ ネラル ウ ォー ター,官 能評価,女 子短 大生,雌 ラ ッ ト,嗜 好性,硬 度.

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