105

1. Introduction

In recent years, malignant neoplasm (cancer), cere-
brovascular disease and heart disease have become major 
causes of death among Japanese people, with approxi-
mately 75% of deaths in Japan caused by these diseases 
(Japanese Ministry of Health, Labour and Welfare, 2009 
a). Such diseases are generally called lifestyle diseases be-
cause they are thought to be strongly related to a lack of 
exercise and high intake of fat and salt. Therefore, empha-
sis has shifted from early diagnosis (secondary prevention) 
to lifestyle improvement (primary prevention) (Japanese 
Ministry of Health, Labour and Welfare, 2009 b). In this 
context, research on foods that have pharmacological ef-
fects or physiological functions, such as disease preven-
tion and health maintenance, has become more important 
(Namba, 1999; Tokui et al., 2003). Regarding the phar-
macological effects of food, there is a form of medicinal 
cooking called “Yakuzen” which is based on the philoso-
phy of Oriental medicine and is intended to maintain good 
health and improve physical condition. The preparation 
of Yakuzen dishes draws from the theory of “Yaku-shoku 

Dou-gen”, which means that the same principle underlies 
the daily diet and medical treatment, and on the yin-yang 
theory, the five-phase theory in Oriental medicine. As a 
result, Yakuzen has attracted considerable attention for the 
prevention of lifestyle diseases.

To prepare Yakuzen dishes, in-season materials with ap-
propriate properties and tastes are selected according to the 
health status and constitution of each person (Namba, 1995; 
Lan et al., 2002; Tokui et al., 2003). These properties and 
tastes are called “Sei-Mi” in Yakuzen theory. Sei-Mi con-
sists of four properties (making the human body hot, warm, 
cool, or cold) and five tastes (salty, bitter, sweet, pungent, 
and sour), and each is considered to have its own function 
in the human body (Namba, 1999; Tokui et al., 2003). If the 
concept of Sei-Mi can be applied to vegetables, a cultivar 
that has a strong flavor and a high content of functional con-
stituents related to the properties and taste is considered to 
have strong Sei-Mi and is suitable for Yakuzen dishes.

However, the inherent flavor of vegetable cultivars has 
been weakened by breeding because priority has been given 
to ease of consumption for consumers or ease of production 
for growers. In the case of eggplant (Solanum melongena 
L.), popular cultivars in Japan today are F

1
 (first filial gen-

eration) cultivars derived from a parental line with oval fruit, 
a deep purple pericarp, and high yield; these cultivars have 
improved fruit quality with less unpleasant or harsh taste. 

Evaluation of local eggplant cultivars in terms of the 
suitability as materials for “Yakuzen” dishes

S. Tsukagoshi* (1), K. Kuroda**, M. Hohjo*, F. Ikegami*, N. Kunisaki***, T. Hanamura***, K. 
Yamada***, T. Hagiwara***
*  Center for Environment, Health and Field Sciences, Chiba University, 6-2-1 Kashiwanoha, Kashi-

wa, Chiba 277-0882, Japan.
**  Faculty of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba 271-8510, Japan.
***  Research and Development Department, Nichirei Foods Inc., 9 Shinminato, Mihama-ku, Chiba 261-

0002, Japan.

Key words: functionality, local cultivars, property and taste, Solanum melongena.

Abstract: “Yakuzen” is a form of medicinal cooking based on the theories of Oriental medicine. To prepare Yakuzen dishes, 
in-season materials with appropriate properties and tastes, “Sei-Mi,” are selected according to the health status and consti-
tution of each person. In this study, the suitability of eggplant (Solanum melongena L.) cultivars for Yakuzen was evaluated 
by sensory tests and by analysis of the functional constituents considered to be closely related to the taste and functionality 
of Yakuzen dishes. Twenty-two eggplant cultivars including 21 Japanese and 1 Italian cultivar, and a Thai species (Solanum 
xanthocarpum Schrad & Wendl.) were evaluated. Principal component analysis (PCA) was used for comprehensive evalu-
ation among the cultivars. From the PCA, many of the cultivars with round or oval fruit were characterized as juicy and 
sweet and considered easy to eat; most of the long-fruit cultivars were characterized as having higher specific amino acid 
contents. The small and round fruit cultivar Dewako and the Thai species (Makhuea pro) were considered to contain many 
functional ingredients, such as ash, polyphenols, and specific amino acids, and to have higher suitability for Yakuzen dishes.

Adv. Hort. Sci., 2014 28(2): 105-110

(1) Corresponding author: tsukag@faculty.chiba-u.jp

Received for publication 31 March 2014
Accepted for publication 07 July 2014



106

However, eggplant was introduced into Japan more than 
1,260 years ago, and it is mentioned in Nara-period docu-
ments (The Shõsõin documents) edited in 750 A.D. (Yoshi-
da, 2010). Therefore, many cultivars have been developed 
over the long history of cultivation, and even today there are 
many cultivars with local origins. The chemical composition, 
flavor, and texture of the edible parts of plants vary among 
cultivars. Local cultivars grown for many years may have 
retained more flavor, and some of them may be more suit-
able for Yakuzen dishes than the currently popular cultivars.

Regarding the functionality of foods, many studies 
have focused on certain ingredients and have discussed 
the relationship between the amounts of those ingredients 
and the functionality of the food. However, it is important 
to consider the functionality of foods comprehensively in 
Yakuzen theory. In previous studies, we used principal 
component analysis (PCA) to comprehensively evaluate 
the functionality of local cultivars, and we demonstrated 
that two local cultivars of Japanese radish (Raphanus sati-
vus L.), two of carrot (Daucus carota L.), and one of bitter 
melon (Momordica charantia L.) were more suitable for 
Yakuzen dishes than the widely used F

1
 cultivar (Saito et 

al., 2010; Tsukagoshi, et al., 2011 a, b).
In this study, two F

1
 cultivars and 21 local cultivars of 

eggplant were evaluated for their suitability as materials 
for Yakuzen dishes according to their taste and content of 
functional constituents. 

2. Materials and Methods

Plant materials and growing condition
Twenty-one Japanese eggplant cultivars with different 

fruit shapes were selected for this study (Table 1). Most 
of them were purebred cultivars, but two F

1
 cultivars were 

included. In addition, an Italian cultivar and a Thai species 
(Solanum xanthocarpum Schrad & Wendl.) were used. 
All cultivars were grown at the Center for Environment, 
Health and Field Sciences, Chiba University. Seeds of all 
cultivars were sown in 9-cm plastic pots filled with up-
land soil on 17 April 2012, and the seedlings were raised 
in a glasshouse. On 5 June seedlings were transplanted to 
the open field at a spacing of 50 cm between plants and 
100 cm between rows. Fruits were harvested when they 
reached the regular size for each cultivar. Harvest began on 
31 July and ended on 14 September. All other management 
was carried out according to the conventional methods in 
Japan (Chino, 2001).

Sensory test
Fruits were harvested on 7 and 9 August and the sen-

sory test was conducted the following day. The fruits were 
washed, cut to a size of 1.5×1.5×3.0 cm, and steamed at 
100°C for 5 min. The characteristics of steamed samples 
were evaluated by six panelists. The panelists passed rec-
ognition tests for five tastes (sweetness, umami, saltiness, 

Table 1 - Eggplant cultivars used for the experiment

Fruit shape (country) Cultivar Abbreviation Fruit length, weight and color Remark

Small, Round (Japan) Dewako De 3-8 cm, 10-15 g, deep purple

Minden Min 3-8 cm, 10-15 g, deep purple

Round (Japan) Aizu maru AM 8-10 cm, 200-300g, deep purple  

Kamo nasu KN 12-15 cm, 200-350 g, deep purple

Tonosama To approx. 15 cm, 300-450 g, deep purple

Yamatoyo maru YM 10-12 cm, 250-350g, deep purple

Money pouch (Japan) Nagaoka kinchaku NK 8-10 cm, 300-350g, deep purple  

(swelling toward the bottom) Saitama ao daimaru SA approx. 15 cm, 300-450 g, green

Oval (Japan) Heta murasaki HM approx. 5 cm, 30 g, deep purple  

Senryo 2 gou Se2 10-12 cm, 80-90 g, deep purple
F

1
, Control cultivar in this 

experiment
Se2 (Control) SK 10-11 cm, 150-180 g, deep purple

Wase shinkuro WS 10-12cm, 80-120 g, deep purple

Yamashina Ya 10-12cm, 80-120 g, deep purple

Long (Japan) Chikuyou Chi 20-25 cm, 120-150 g, deep purple F
1

Hakata naga Hak 40-45 cm, 200-300 g, deep purple

Hhogo naga Hho 17-18 cm, 85-90 g, deep purple

Himo nasu HN 25-30 cm, 150-200 g, pale purple

Kitta chunaga KC 10-12cm, 80-120 g, deep purple

Kurume oh naga KO 30-35 cm, 250-300 g, deep purple

Shikon sendai naga SS 8-10 cm, 20-30 g,  bluish purple

Shin nagasaki naga SN 35-40 cm, approx. 250 g, deep purple

Big, Oval (Italy) Zebra Ze 20-25 cm, 300-400 g, purple and white stripes

Small, Round (Thailand) Makhuea pro MP 4-5 cm, approx.10 g, green Solanum xanthocarpum



107

bitterness, and sourness) and the discrimination tests for 
four solutes (sucrose, sodium chloride, tartaric acid, and 
sodium glutamate). In addition, they had more than one 
year experience in evaluating vegetables and were clas-
sified as expert assessors (Japanese Society for Sensory 
Evaluation, 2009). The characteristics listed in Table 2 
were evaluated on a scale of -5 (weaker) to 5 (stronger) 
compared to Se2, the control cultivar in this study.

Taste sensor analysis and amino acid content
Approximately 50 g of fresh fruit was homogenized in 

100 mL of water in an ice bath, then filtered through cot-
ton cloth. Although filtrates were prepared separately from 
three or four fruit samples, the filtrates were mixed to obtain 
the quantity necessary for measurements. Bitterness, astrin-
gency, acridity, and pungency of the filtrates were measured 
using a taste sensor system (SA402B, Intelligent Sensor 
Technology, Kanagawa, Japan). Each value was expressed 
relative to the control cultivar (Se2), which was set at zero. 
A portion of each filtrate was filtered again through a 0.45-
μm filter (DISMIC-25CS, Advantec, Tokyo, Japan) and the 
amino acid content was measured using an amino acid ana-
lyzer (JLC-500/V, JEOL, Tokyo, Japan).

Soluble solids content
Fresh fruit was cut into small pieces and pressed in 

gauze to extract the juice. The soluble solids content of the 
juice was measured using a refractometer (PAL-1, ATA-
GO, Tokyo, Japan) and expressed as percent Brix.

Ash and polyphenol contents
The harvested fruit was stored at -30°C until use. 

Fresh-frozen fruit samples were freeze-dried and ground 
into a fine powder. Ash content was determined using the 
dry ashing method. Briefly, 0.3 g of the powder was put in 
a crucible and ashed at 550°C for 24-48 hr. After cooling, 
the weight of the residue was measured. Polyphenol con-
tent was determined using iron tartrate spectrophotometry. 
First, 0.2 g of the powder was mixed with 10 mL of dis-
tilled water, and shaken for 10 min at 80°C. After cooling, 
the sample was centrifuged at 3,000 rpm for 15 min. Then, 
3.2 mL of the supernatant was mixed with 1.6 mL of iron 
tartrate reagent (0.1% (w/v) ferrous sulfate and 0.5% (w/v) 
potassium sodium tartrate) and 3.2 mL of phosphate buffer 
(0.1 M, pH7.5). The absorbance at 540 nm was then mea-
sured using a spectrophotometer (U-2000, Hitachi, Tokyo, 
Japan). The polyphenol content was calculated from a 

Table 2 - Evaluation of the taste of eggplant cultivars by sensory test (z)

Fruit shape Cultivar Aroma   Softness Juiciness Sweetness Bitterness Astringency

    Good Grassy   Pericarp Flesh       & Acridity

Small, Round De (y) 0 (x) 0 -1 0 0 0 1 1

Min 1 1   0 -1 0 -1 2 1

Round AM 0 1 0 -1 0 0 0 1

KN 1 1 0 -1 0 0 0 0

To 0 0 -1 0 0 0 1 0

YM 0 0   0 1 1 1 -1 0

Money pouch NK 0 2 -3 -2 -1 -1 0 0

  SA 0 2   -4 0 -1 0 0 1

Oval HM 0 0 0 1 0 0 0 0

Se2 (Control) 0 0 0 0 0 0 0 0

SK 0 2 0 1 2 1 0 0

WS 0 0 -1 0 -1 -1 0 0

Ya 1 0   -1 0 0 0 0 0

Long Chi 0 0 0 1 0 -1 0 0

Hak 0 0 1 1 -1 0 -1 0

Hho 0 0 0 0 0 0 0 0

HN 0 1 -1 1 -1 -1 0 0

KC 0 0 -2 1 0 -1 0 1

KO 0 0 -2 1 -1 -1 0 0

SS 0 1 -1 0 0 -1 0 1

SN 0 2 0 1 -2 0 -1 0

Big, Oval Ze 2 2   0 -2 0 -1 0 2

Small, Round MP 0 3   0 -1 0 -1 0 1

(z) Eggplant fruit was cut to the size of 1.5 x 1.5 x 3.0 cm, then steamed at 100 degree C for 5 min before the test.
(y) Amino acid which is considered to be important for the functionality of eggplant in Yakuzen theory.
(x) Tastes were evaluated on a scale of -5 (weaker) to 5 (stronger) as compared to Senryo 2 gou (Se2).



108

standard curve of ethyl gallate.

Principal component analysis and characterization of cul-
tivars

Data were analyzed by principal component analysis 
(SPSS for Windows version 13), and the characteristics of 
cultivars were comprehensively evaluated to determine the 
suitability of the cultivars as materials for Yakuzen dishes.

3. Results and Discussion

Cultivars NK and SA (with money-pouch fruit shape) 
tended to have harder fruits, and long-fruit cultivars tended 
to be less sweet (Table 2). The aroma of the Italian cultivar, 
Ze was characterized as both “good” and “grassy”. How-
ever, most cultivars were very similar to Se2 (the control 
cultivar in this study) in the sensory test.

Taste sensor analysis showed that the local cultivars 
tended to have a less unpleasant taste than Se2 (Table 3). 

This result did not correspond to the results of the sensory 
test, and the difference may be due to the heating of sam-
ples before the sensory test but not before the taste sensor 
analysis. Nevertheless, we can conclude that the local cul-
tivars were not unpalatable compared with the commonly 
used cultivar.

Min, YM and some other cultivars tended to have 
higher soluble solids contents, but there was no significant 
difference between cultivars (Table 4). “Mi” (the taste) of 
eggplant is “Kan” (sweet). In Yakuzen theory, Mi means 
not only the taste on the tongue but also specific functions 
in the human body (Tokui et al., 2003). In this study, we 
could not discern differences of Kan characteristics from 
the results of sensory test and soluble solids contents 
among cultivars; therefore, the suitability of cultivars was 
evaluated on the basis of other characteristics.

Ash content was higher in cultivars De and Min (both 
of which have small, round fruit) and lower in cultivar 
WS, and tended to be lower in cultivars with oval fruit. 
“Sei” (the property) of eggplant is to cool the human 
body. Potassium accounts for most of the ash of eggplant 
fruit (USDA, 2013), and the function of this mineral is 
to release heat inducing diuresis. This function is closely 
related to the property of eggplant, and higher ash con-
tent may be related to greater suitability of cultivars for 
Yakuzen dishes.

Polyphenol content was also higher in De and Min. 
Eggplant contains polyphenols such as chlorogenic acid 
and nasunin, which are considered to have antioxidant ac-
tivity, and to suppress lipid peroxidation, aging, various 
lifestyle diseases, and cancer (Kimura et al., 1999; Noda 
et al., 2000; Kitsuda et al., 2005; Singh et al. 2009). Das et 
al. (2011) reported that grilled eggplant had a higher poly-
phenol content, though the cardioprotective ability was not 
different. The high polyphenol content in De and Min may 
increase the pharmacological value of these cultivars.

As mentioned above, Mi (the taste) also encompasses 
specific functions in the human body, and Mi of eggplant 
is Kan (sweet). Kan is considered to have functions such 
as supplying nutrition and energy, promoting relaxation, 
etc. Some amino acids are considered to have Kan func-
tions. For example, glutamine is an energy source for di-
gestion and plays an important role in the maintenance 
and improvement of immunity and the repair of organs 
(Ajinomoto Co. Inc., 2003 a, b), and this may correspond 
to a Kan function. Alanine has a sweet taste and supplies 
sugars to the body, and it is also considered to have a Kan 
function. The amino acids strongly related to the Kan of 
eggplant include alanine, citrulline, glycine, glutamine, 
proline and serine. Therefore, these amino acid contents 
were summed to give specific amino acid content (Table 
4): it was highest in Se2 and SN and tended to be higher 
in the long-fruit cultivars and lower in the round-fruit cul-
tivars. Total amino acid content also tended to be higher in 
the long-fruit cultivars, especially in SN. However, no oth-
er trends in amino acid content were observed. The higher 
content of specific and total amino acids in SN would indi-
cate greater suitability of this cultivar for Yakuzen dishes.

Table 3 - Evaluation of the taste of eggplant cultivars by taste sensor (z)

Fruit shape Cultivar
Bitter-
ness

Astrin-
gency

Acridity Pungency

Small, Round De (y) -0.27 (x) 0.06 -1.74 -0.69 

Min -0.38 0.04 -2.27 -0.96 

Round AM -0.23 0.20 -1.14 -0.48 

KN -0.11 0.21 -2.11 -0.94 

To -0.11 0.13 -2.18 -1.18 

YM -0.16 -0.02 -1.33 -1.30 

Money pouch NK -0.26 0.27 -1.78 -0.64 

  SA -0.07 0.30 -2.30 -1.07 

Oval HM 0.22 0.13 -1.83 -0.99 

Se2 (Control) 0.00 0.00 0.00 0.00 

SK -0.28 0.05 -1.51 -0.76 

WS -0.06 0.23 -2.26 -1.17 

Ya -0.09 0.08 -2.57 -1.30 

Long Chi -0.33 0.12 -1.39 -0.61 

Hak -0.28 -0.09 -2.55 -1.40 

Hho -0.15 0.05 -1.61 -0.86 

HN -0.01 0.15 -2.87 -1.45 

KC -0.12 0.11 -2.24 -1.28 

KO -0.43 0.07 -0.52 -0.15 

SS -0.26 0.04 -2.03 -1.00 

SN -0.47 -0.05 -2.27 -1.09 

Big. Oval Ze -0.32 -0.02 -2.73 -1.23 

Small. Round MP -0.34 0.19 -2.15 -0.75 

(z)  Taste sensor was prepared to express the value of Se2 was 
zero.

(y)  Amino acid which is considered to be important for the func-
tionality of eggplant in Yakuzen theory.

(x)  Positive and negative value means the taste was stronger and 
weaker than Se2, respectively.



109

From the PCA, 23 principal components (PCs) were de-
rived and 14 PCs were considered to be meaningful (con-
tribution rate>1). These 14 meaningful PCs accounted for 
96.6% of the total rate (data not shown). Although the first 
two PCs accounted for only 41.3% of the total rate, a two-
dimensional scatter diagram of factor loading was con-
structed. Specific and total amino acid contents were in the 
positive direction along the x-axis, and juiciness, sweetness, 
percent Brix and some unpleasant taste were in the negative 
direction. Ash, polyphenol content, and bitterness were in 
the positive direction along the y-axis, and softness was in 
the negative direction (data not shown). A two-dimensional 
scatter diagram constructed from the PC1 and PC2 scores of 
each cultivar enabled classification of the cultivars (Fig. 1). 
Many of the common F

1
 cultivars of eggplant used for com-

mercial production in recent years have been developed to 
improve ease of consumption and cultivation. Se2 is one of 
the common cultivars in Japan. It was characterized as juicy 
and sweet by the PCA and is considered easy to eat. The oth-
er cultivars with round or oval fruit were also characterized 
as juicy and sweet. On the other hand, most of the long-fruit 
cultivars were distinct from the round-fruit and oval-fruit 

Table 4 - Soluble solid, ash, polyphenol and amino acid content of eggplant cultivars

Fruit shape Cultivar
Soluble solids

(% Brix)
Ash

(g 100 g-1 FW)
Polyphenol (z)

(mg 100 g-1 FW)
Specific amino acid (y)

(mg 100 g-1 FW)
Total amino acid
(mg 100 g-1 FW)

Small. Round De (x) 5.1 a (w) 0.60 a (w) 673.4 a (w) 120.6 284.9

Min 5.2 a 0.60 a 434.0 a 71.1 186.0

Round AM 4.8 a 0.45 ab 169.0 b 37.2 151.2

KN 5.4v 0.53 (v) 150.0v 48.8 203.1

To 4.8 a 0.39 b 253.7 ab 52.5 196.6

YM 5.3 a 0.50 ab 255.0 ab 36.3 144.3

Money pouch NK 5.0 a 0.45 ab 172.9 b 63.1 197.8

SA 4.6 a 0.50 ab 247.3 ab 39.5 167.3

Oval HM 4.7 a 0.50 ab 300.6 ab 64.5 203.1

Se2 (Control) 4.6 a 0.44 ab 129.1 b 145.6 302.0

SK 4.3 a 0.39 b 158.4 b 48.0 170.6

WS 5.1 a 0.37 b 181.9 b 52.8 199.1

Ya 4.3 a 0.40 b 248.5 ab 58.1 185.4

Long Chi 4.5 a 0.42 ab 188.1 b 34.1 161.2

Hak 4.3 a 0.38 b 127.9 b 116.3 286.5

Hho 4.8 a 0.52 ab 166.2 b 76.8 253.3

HN 4.5 a 0.52 ab 144.1 b 83.6 288.6

KC 4.4 a 0.48 ab 236.6 ab 50.8 211.0

KO 5.1 a 0.45 ab 135.1 b 93.6 314.2

SS 4.1 a 0.38 b 250.6 ab 106.1 281.8

SN 4.5 a 0.41 ab 119.2 b 139.2 342.0

Big. Oval Ze 3.8 a 0.46 ab 124.0 b 95.1 308.9

Small. Round MP 5.1 a 0.56 ab 245.9 ab 63.9 196.7

(z) Polyphenol content was expressed as ethyl gallate equivalent.
(y) Amino acid strongly related to Kan of eggplant.
(x) Abbreviations as in Table 1.
(w) Different letter within the row indicates significant difference by Tukey’s multiple range test at 5% level (n=5).
(v) Number of harvested fruit was not enough for statistical analysis.

Fig. 1  Two dimensional scatter diagram of the principal component 
score of eggplant cultivars
■: small, round ◆: round ●: monry pouch ▲: oval : long : Italy 

: Thailand. Abbreviations as in Table 1.



110

cultivars. They were characterized as having higher specific 
amino acid contents and little unpleasant taste or sweetness. 
The small and round fruit cultivar De and the Thai species 
(MP) were considered to contain many functional ingredi-
ents, such as ash, polyphenols, and specific amino acids, and 
to have greater suitability for Yakuzen dishes.

4. Conclusions

Among the local Japanese cultivars used in this study, 
cv. De is highly suitable for Yakuzen dishes because it con-
tains many ingredients associated with the properties and 
taste (Sei-Mi) of eggplant in Yakuzen theory. In addition, 
the Italian cultivar (Ze) and the Thai species were highly 
distinct. Different results may have been obtained had we 
grown the cultivars in another area or under different con-
ditions. Nevertheless, we have demonstrated that some lo-
cal eggplant cultivars have stronger Sei-Mi than current F

1
 

cultivars. These characteristics could add value to the local 
cultivars and lead to regional development.

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