Sensors andand Materials,Materials, Vol.
Vol. 17,17, No.
No. 77 (2005)(2005) 397– 404
Sensors
MYU Tokyo

397

S & M 0617

Analysis of Pork Extracts by Taste Sensing Systemand the Relationship between
Umami Substances and Sensor Output
Keisuke Sasaki*, Fumio Tani1, Katsushi Sato2, Hidekazu Ikezaki3,
Akira Taniguchi3, Tadasu Emori4, Fumiyuki Iwaki5,
Koichi Chikuni and Mitsuru Mitsumoto
National Institute of Livestock and Grassland Science
2 Ikenodai, Tsukuba, Ibaraki 305-0901, Japan1
Tokushima Livestock Hygiene Service Center
5-94 Minamishomachi, Tokushima, Tokushima 770-0045, Japan
2
Anritsu Co., 1800 Onna, Atsugi, Kanagawa 243-0032, Japan
3
Intelligent Sensor Technology, Inc., 1800 Onna, Atsugi, Kanagawa 243-0032, Japan
4
Chiba Prefectural Livestock Experimental Station,
16-1 Yachimata-He Yachimata, Chiba 289-1113, Japan
5
Hyogo Prefectural Agricultural Institute, Befucho, Kasai, Hyogo 679-0103, Japan(Received October 2, 2004; accepted May 9, 2005)
Key words:

taste sensor, pork extract, umami-related substance

We investigated the application of a taste sensing system to the analysis and evaluationof a water extract prepared from the longissimus muscles of six breeds of pork. We
selected sensor probes that discriminate among the different pork breeds and applied theoutput data from selected sensor probes to principal component (PC) analysis. Then the PC
scores were used in a correlation analysis with the concentrations of the umami-relatedsubstances in pork extracts. We found that sensor output was related to the concentrationsof the umami-related substances.

1.

Introduction

In Japan, the evaluation and classification of pork carcasses have been carried out
mainly with regard to their yield and visual properties such as lean meat color, fineness ofmuscle fiber, fat color, and physical properties of the fat. These properties, especiallyvisual properties, are currently important for consumers’ choice of muscle foods in themarket.(1) On the other hand, analysis and improvement of pork taste have been necessary
for the satisfaction of varied consumers’ requirements. The visual properties of pork
carcasses are related to the quality of muscle. However, actual taste is not analyzed in theevaluation and classification of pork. For evaluation of the taste of the pork or other species*Corresponding author, e-mail address: ksuk@affrc.go.jp397

398Sensors and Materials, Vol. 17, No. 7 (2005)of meat, sensory evaluation has been used, but such sensory evaluation has not been
adapted for the routine evaluation of pork carcasses because it has been difficult in themarket to retain a sensory panel and to maintain objectivity and repeatability of evaluation.
In recent years, a biomimetic taste sensing system has been developed. Toko and coworkers have developed this taste sensing system using the electrical potential of a lipidcontaining membrane(2) and applied it to the analysis and evaluation of taste in various
kinds of foods.(3) We examined the lipid-membrane taste sensing system to see if it could
be used to discriminate and to evaluate the actual taste of pork with objectivity and/orrepeatability.
In this study, we applied the taste sensing system to the discrimination and evaluationof pork. First, we analyzed the water extracts of pork longissimus muscles for discrimination of the taste of pork meat. In addition, we examined the relationship between sensor
output data and umami-related substances, which are considered important for the taste of
the water-soluble fraction of pork.

2.

Materials and Methods

2.1 Sample preparation
Pork longissimus muscles were harvested from Landrace, Duroc, Large White, Meishan,
Berkshire and Three-way cross (Duroc × Landrace × Large White) pork carcasses. Duroc
carcasses were obtained from two different producers to investigate the variability in tasteby producer, and these samples were designated Duroc(A) and Duroc(B). All samples
were cut into cubes (each side was approximately 1.0 cm) and extracted by boiling them indistilled water for 1 h. These extracts were filtered with Advantec No. 131 filter paper andwere one-tenth the volume of the sample muscles. The extract solution was then used foranalysis by the taste sensing system.

2.2 Analysis by taste sensing system
We used a taste sensing system SA402 (Anritsu Co. and Intelligent Sensor Technology,Inc.) equipped with eight different lipid membrane probes for the analysis. The composition of each lipid membrane is presented in Table 1. The measurement procedure waspreviously described by Ikezaki et al.(4) Briefly, zero-adjusted probes were applied to asample solution, and the sample output was collected. After that, a blank solution wasmeasured again before the probe was washed. The output was called the change ofmembrane potential caused by adsorption (CPA), which was fit for an aftertaste.(4) Then,probes were washed and zero-adjusted for measurement of the next sample.
Commercial beef extract (F-6359, Ariake Japan Co., Tokyo) was used to calibrate thesensor output. Differences in the sample output and CPA output between samples andcommercial beef extract were used as the measured output. Two sets of output data, suchas sample output and CPA output, were collected by the taste sensing system from pork
extracts. The output data were then subjected to statistical analysis.

Sensors and Materials, Vol. 17, No. 7 (2005)

399

Table 1
Lipids in sensor probes used in this study.
LipidDioctyl phenyl phosphonate / Hexadecanoic acidPotassium tetrakis 4-tert-butylphenyl borate / Bis 1-butylpentyl adipate
Dioctyl phenyl phosphonate / Phosphoric acid di-n-decyl ester
2-Nitrophenyl octyl ether / Phosphoric acid di-n-decyl ester
2-Nitrophenyl octyl ether / Tetradodecylammonium bromide
Dioctyl phenyl phosphonate / Tetradodecylammonium bromide
Tetradodecylammonium bromide
Dioctyl phenyl phosphonate / Phosphoric acid di-n-hexadecyl ester / Teteradodecylammonium
bromide2.3 Determination of umami-related substances
Inosin monophosphate (IMP), oligopeptides, glutamate, and total free amino acidswere analyzed for umami-related substances as described previously.(5)IMP, glutamate, and total free amino acids were determined by high-performanceliquid chromatography (HPLC). For IMP determination, pork extracts were treated withperchloric acid to remove proteins and neutralized to pH 6.5–6.8 with a potassiumhydroxide solution. Then the filtrate of neutralized samples was assayed using HPLC. The
assay conditions have been described previously for a JASCO Filepak SIL C18T column(4.6×250 mm; JASCO, Tokyo). IMP was measured with an ultraviolet detector (UV-1570;JASCO) set at 254 nm. The mobile phase was 40 mM potassium dihydrogenphosphate –60 mM dipotassium hydrogenphosphate (pH not adjusted), and the flow rate was 1.0 mL / min.
For the analysis of free amino acids and glutamate, the extract solution was treated witha final addition of 5.0% (w/v) trichloroacetic acid to remove proteins and applied to anamino acid auto-analyzer L-8500 (Hitachi, Co., Tokyo).
Oligopeptides were evaluated by Lowry’s method in a 2% (w/v) trichloroacetic acidsoluble fraction of pork extracts.

2.4 Statistical analysisSensor output (sample and CPA output) data were applied to the general linear model(GLM) for selection of the probes that to discriminate differences among pork breeds.
Subsequently, output data from the selected probes were analyzed by principal component (PC) analysis. Then the PC scores and the concentrations of the umami-relatedsubstances were applied to correlation analysis. The differences in umami-related substances among the samples were analyzed using the GLM and Duncan’s multiple range
test.
All statistical analyses were carried out by the SAS system ver 6.12 (SAS Institute,Cary, NC).

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3.

Sensors and Materials, Vol. 17, No. 7 (2005)

Results and Discussion

First we analyzed the differences between normal and CPA output of each sensor probe
among the pork breeds. Table 2 indicates the probability of the differences in sensor output
were significant among the breeds of pork analyzed by the GLM procedure. Sensors No.
1 and 2 did not detect any difference between normal and CPA output. The differences innormal output of sensors No. 5, 6, 7, and 8, and CPA output of sensors No. 3, 4, and 7 were
statistically significant among the breeds (P < .05). These seven data points were applied
to the following PC analysis.
The results of PC analysis are presented in Table 3. Eigenvalues of PCs 1 and 2 wereover 1.0. The cumulative proportion of PCs 1 and 2 was .7656. Therefore, we applied thescores of PCs 1 and 2 to the following analysis.
Mean values of umami-related components in extracts prepared from each breed areshown in Table 4. Concentrations of IMP, total amino acids, and oligopeptides weresignificantly different among the breeds (P < .001). Glutamate concentration, however,
was not different among the breeds (P = .976). IMP concentration was the highest inDuroc(A), the second highest in Meishan, and the lowest in Duroc(B). Oligopeptide
concentration was the highest in Meishan, and the second highest in Landrace, and theTable 2
Probability that the differences in sensor output were significant among the breeds of pork. The
indication ‘ns’ means not significant (P > .05).
Sensor No.
12345678Probability
Sample output
CPA outout
nsns
ns
ns
ns
P < .001
ns
P < .001
P < .001
ns
P < .001
ns
P < .001
P < .001
P < .001
ns

Table 3
Principal component analysis of seven sets of output data of the taste sensing system applied to pork
extracts.
Principal component
1
2
3
4
5
6
7

Eigenvalue
4.0876
1.27140.80110.35410.27940.1326
0.0738Proportion
0.58400.1816
0.11440.05060.03990.01890.0105

Cumulative
0.58400.76560.88000.93060.97050.89851.0000401

Sensors and Materials, Vol. 17, No. 7 (2005)

Table 4
Concentrations of umami-related components in extracts prepared from each breed. Values are
expressed as means ± SD. Values with different superscripts in each measurement differ significantly(P < .05).
IMPtotal amino acids

oligopeptides

glutamate(nmol/ml)(mmol/ml)(mg/ml)(nmol/ml)

56.8±5.9 ab
47.8±4.6 c
61.9±5.5 a
49.7±5.9 c
60.1±3.7 a
51.8±3.1 bc
49.3±5.9 c

0.89±0.08 d
1.25±0.10 b
1.06±0.18 bcd
1.04±0.08 bcd
0.99±0.07 cd
1.74±0.43 a
1.21±0.20 bc

0.42±0.03 b
0.38±0.07 bc
0.35±0.03 c
0.29±0.03 d
0.47±0.03 a
0.34±0.04 c
0.29±0.02 d

65.2±14.761.2±29.774.2±44.6
70.3±26.7
63.9±11.2
77.5±64.4
74.8±26.7

NLandrace
8Duroc(A)5
Duroc(B)8
Large White
5Meishan
6Berkshire
5Three way cross 5

lowest in Large White. Total amino acid concentration was the highest in Burkshire, but
was low in Meishan and Landrace, although their IMP and oligopeptide concentrations
were relatively high.
The correlation coefficients between PC scores and concentrations of umami-related
substances are indicated in Table 5. The score of PC1 was negatively correlated with IMP
and oligopeptides at a significance level of P < .001. On the other hand, total free aminoacid concentration was positively correlated with PC1 (P < .01). IMP concentration had
positive and significant correlation with oligopeptide concentration (r = .327, P < .05) andwas negatively correlated with total amino acid concentration (r = –.26, P = .088). The
correlations between PC1 and umami-related substances were in good agreement with thecorrelations of total amino acids with IMP and oligopeptides. Sensor probes used in thisstudy include multi-taste-sensitive, umami-taste-sensitive, bitter-taste-sensitive, and saltytaste-sensitive. We did not investigate the correlations between sensor sensitivity and eachconcentration of umami-related components, but we considered the taste sensing systemuseful for evaluation of the taste of pork extracts, especially umami-related taste, from theresults presented in Table 5.
Figure 1 is an X-Y plot of the pork samples with PCs 1 (horizontal axis) and 2 (verticalaxis). Samples were separated to some degree among the breeds. According to the resultsof the correlation between PCs and concentrations of umami-related substances, weconcluded that the left side of the plot (negative values of PC1) tended to indicate ‘IMP andoligopeptide originated umami’, and the right side (positive values of PC1) tended toindicate ‘amino acids originated umami’. In Fig. 1, Meishan and Duroc(B) are located on
the left side (IMP and oligopeptide side) of the plot, and Berkshire, Duroc(A), and Large
White are mostly located on the right side (amino acid side). These results are in good
agreement with the difference in concentrations of the umami-related substances among
the breeds indicated in Table 4.
The taste of pork and other kinds of muscle foods are believed to be derived from watersoluble taste substances and lipid-soluble taste-active components. In the water-soluble
fraction, sourness, sweetness and umami all contribute to the taste, with umami considered402

Sensors and Materials, Vol. 17, No. 7 (2005)

Table 5
Correlation coefficients between principal component scores and the concentrations of the umamirelated substances. The indication ‘ns’ means not significant (P > .05).
Principal component
1
2
3
4
5
6
7

IMP
–0.606
P < .001–0.180ns0.078
ns–0.193
ns–0.220
ns0.069
ns–0.106ns

Umami relevant substances
total amino acids
oligopeptides
0.439–0.652
P < .01
P < .001
0.277–0.057
nsns0.034
0.059
ns
ns
–0.134–0.160ns
ns
0.163–0.289ns
ns
0.104–0.119
ns
ns
0.044
0.161
ns
ns

glutamate0.085
ns0.115
ns–0.114
ns0.057
ns0.071
ns–0.211
ns–0.051
ns

Fig. 1. Plot of the pork samples with scores of principal component 1 (horizontal axis) and 2(vertical axis). L, D, d, W, M, B and T in the plot indicate Landrace, Duroc(A), Duroc(B), Large
White, Meishan, Berkshire, and Three-way cross (Duroc × Landrace × Large White), respectively.

to be especially important to the taste of muscle foods. For example, it was reported that
IMP and glutamate addition increased the brothy taste intensity of beef and pork extract.(6)Postmortem conditioning of pork and chicken meat increases intramusclar amounts of IMP
and free amino acids, and the intensity of brothy umami.(7) Oligopeptides are also
considered to relate to the taste of pork.(8) In addition, glutamate and IMP are characterizedSensors and Materials, Vol. 17, No. 7 (2005)

403

as important contributors to the meat-like taste intensity of chicken extract.(9,10) Therefore,
the evaluation of umami in the water-soluble fraction is important for the evaluation ofpork taste. We were not able to evaluate the characteristics of the taste in the water-soluble
fraction by only chemical determination of taste-active substances, because there is asynergistic effect of monosodium glutamate and IMP that affects pork taste.(11)In this study, we tried to apply the taste sensing system in the evaluation of pork taste,
and we examined the relationship between sensor output and umami-related substances.
We indicated the taste characteristics of pork extracts as ‘IMP and oligopeptide originatedumami’ and ‘amino acid originated umami.’ Our findings indicate that the taste sensing
system may be useful for the evaluation and characterization of the taste of pork extract.
However, we could not indicate the characteristics of PCs except for PC1. The species oflipid membrane probes, use of the taste sensing system, and statistical analysis should beinvestigated to improve the application of the taste sensing system for analysis andcharacterization of the taste of pork and other kinds of muscle foods.
On the other hand, the differences in concentrations of umami-related substances andsensor output among the breeds were not caused by genetic differences. The samples wereobtained from different producers; therefore, the feeding, slaughter and storage conditions
were different among the pork samples in this study. We considered that the differences inumami characteristics indicated in this study did not show a common tendency. The effects
of pre- and post-harvest conditions on the output of the taste sensing system and the umami
characteristics of pork should also be investigated.
In addition, peptides and other water-soluble substances were discovered as tasteenhancers in conditioned and cooked beef, pork and chicken.(12,13) We expect that the taste
sensing system can be used to analyze the characteristics of meat taste including umamirelated substances and the effect of such taste-enhancing molecules, resulting in animproved evaluation and classification system for muscle foods.
In conclusion, we indicated that taste sensing system is useful for discrimination ofpork extracts, and that principal component scores obtained from sensor output correlatedwith umami-relevant substances. Further investigation is needed about the relationshipbetween sensory evaluation using human panels and on the output of a taste sensing system
to characterize sensor output.

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