さつまいもの機能性飲料製造過程におけるいものにおいの変化

誌名誌名 日本食品保蔵科学会誌

ISSNISSN 13441213

著者著者玉城, 和彦江原, 勝夫玉城, 武

巻/号巻/号 33巻2号

掲載ページ掲載ページ p. 51-61

発行年月発行年月 2007年3月

農林水産省 農林水産技術会議事務局筑波産学連携支援センターTsukuba Business-Academia Cooperation Support Center, Agriculture, Forestry and Fisheries Research CouncilSecretariat

( 3 ) Food Preservation Science VOL. 33 NO. 2 2007 CArticleJ 51

Determination of Aroma Changes in Sweet Potato (Ipomoea batatas (L.) Lam)

during Sweet Potato Juice Production

T AMAKI Kazuhiko *1， EHARA Katsuo叫， TAMAKI Takeshi*3 and YAMAZAKI Takashi*

* 1 Department of Food Science & Technology， University of California Davis Davis

CA 95616 U.S.A

* 2 おかo1nstitute of Technology

2-12-1， Ookayama， Meguro-ku，おかo152-8550， Japan

* 3 To勾oBunka Junior College

6-38-1， Honcho， Nakano-ku，あわ10 164-8638， Japan

* 4 To勾oUniversity of Agriculture and Technology

2-24-16， Nakamachi， Koganei-shi，おかo184-8588， Japan

In this study， we report a comparative analysis of the changes in the aroma characteristics of sweet

potato， after boiling and saccharification during sweet potato juice production. using sensory and

instrumental methods. Although the raw sweet potato sample possessed a grassy-carrot aroma. the

boiled saccharified sample showed a distinct heavily boiled-sweet aroma. Furthermore. 26 and 42 flavor

compounds were identified in the raw sweet potato juice and boiled saccharified samples respectively.

by GC-MS. Although the raw sample showed higher levels of aldehydes. the boiled saccharified sample

yielded a headspace rich in terpenoids. ketones. furans and aromatic aldehydes.Here we elucidate the

mechanism of flavor compound formation and discuss the association of the identified volatiles and the

characteristic aroma attributes of the boiled saccharified sweet potato.

In the past. sweet potato was considered as an

important food and energy source due to its high

starch content. However. in recent times. our major

sources of energy have been derived from rice and

bread. Owing to the nutritionally rich characteristics

of sweet potato with starch as well as vital

pigments as its main components. it is crucial to

develop it as a functional food in the near future.

There have been severaJ studies of the functionality

of sweet potatolト 4) It has been reported that

deacyJated anthocyanins in purple-fleshed sweet

potato have an antimutagenic property. In addition.

they have been shown to act as anti-oxidantsl) and

reduce the extent of Jiver injury induced by carbon

tetrachloride in rats5) and humans6

).

Sweet potato produces a pJeasant aroma when

baked. Various studies have been conducted to

identify and quantify the voJatiJe organic compounds

in baked sweet potat07)叶) Some other aroma-related

* 1 E-mail: kaztamaki@hotmail.com * 3 E-mail: tkkrs130@ybb.ne.jp * 4 E-mail: tyamazak@cc.tuat.ac.jp

CReceived Nov. 20. 2006 ; Accepted Mar. 22. 2007)

compounds have also been identified. TIU et al. have

studied the contribution of some voJatiJe compounds

to sweet potato aroma and identified individual

sweet potato cuJtivars on the basis of 27 volatiles

using gas chromatograms of each cultivar. and

found the difference between cultivars of good or

poor flavor川 . SUN et al. found that maltol is a

critical component of characteristic aroma of baked

sweet potato. and is produced through the Maillard

reaction. caramelization. and Strecker degradation.

which are the most common mechanisms in the

thermally induced synthesis of aroma volatilesJJ).

Owing to its unique health benefit and aroma

property. sweet potato serves as a potential

functional food ingredient in various food

applications. In this study. functional juice using

“benihayato" sweet potato has been developed.

Benihayato is a sweet potato cuJtivar. that

resembles carrot in color. aroma and s-carotene

52 Food Preservation Science VOL. 33 NO.2 2007 C 4 )

contentω.β.carotene， independent of its role in the

formation of vitamin A， is anticarcinogenic as

evidenced by its effectiveness in the treatment and

management of cancer at di妊erentsites in several

different cancer model systems， using different

inducing agents131 in different animal species. During

the development of functional sweet potato juice，

roots of benihayato are steamed by stepwise

heating， mashed to homogeneity， and then

saccharified with amylase. However， after boiling

and saccharification the mashed juice developes a

heavy unappetizing aroma， unlike the fragrant

aroma of baked sweet potato. To suppress this

strong boiled aroma， mashed sweet potato juice is

then supplemented with other ingredients.

Since boiling in sweet potato juice production

results in potential 0妊-flavor，it can possibly be a

bottleneck in the development of an attractive

functional food using benihayato as an ingredient.

Although there are many available reports on

baked sweet potato， there are no published reports

on the volatile compounds of boiled sweet potato

Since steaming procedures are utilized during the

manufacture of sweet-potato-based food products，

including the preparation of the functional sweet

potato drinks， it is important to evaluate the nature

of the volatile compounds responsible for the flavor

of sweet potato and to elucidate the mechanisms

involved in the formation of these compounds as a

result of steaming.

Our main objective in this study is to clarify the

aroma characteristics and changes in sweet potato

aroma during sweet potato juice production by

comparing the aromas of raw and boiled

saccharified sweet potatoes. The effect of steaming

on the profile of the aroma characteristic is studied

by sensory evaluation. Next， the identity of the

volatile components is investigated by gas

chromatography CGC) and gas chromatography-mass

spectrometry CGC-MS). In addition to the mechanism

of the formation of the volatile compounds， the

aroma impact of each volatile component is

discussed by evaluating the influence of each

component on the total aroma characteristic of

sweet potato.

Materials and Methods

1. Sweet potato

The raw sweet potato cultivar “Benihayato" ，

cultivated in Kagoshima， ] apan， and harvested in

October of 2004， was used in this study. The raw

tubers of this cultivar contained 8rng of s-carotene

per 100 g wet weight.

2. Preparation of sweet potato juice

Raw sweet potato juice was prepared as follows :

1 kg of sweet potato was shredded without peeling

the skin and added to 1. 8 R of water. This

preparation was homogenized for 30 s using a

macerator. The resulting slurry was placed in a 3-R

flask. For the preparation of boiled sweet potato

juice， 1kg of sweet potato was steamed by stepwise

heating Cat 66-650

C for 3.5 h and at 1000

C for 1

h). To this preparation 1. 8 R of water and 5.0 g of

α引 nylaseCuniase BM-8， with a specific activity of

about 80， 000 u / g) were added， and the potato

mixture was incubated for 3 h under warm

conditions C600

C). Then 5.0 g ofβ-amylase C uniase

L， with a specific activity of about 80，000 u/ g) was

added to partially hydrolyze starch and incubated at

550

C for 1 h. After the incubation 50 g of

glucoamylase Cuniase 30， with a specific activity of

about 80，000 u/ g) was added to the preparation.

The mixture was incubated at 550

C for 1 h. Both

samples were cooled to room temperature，

separated into smaller beakers and wrapped in foil

In addition， 100 g each of the raw samples and

boiled juices was used for GC-MS and 100mR each of

the samples was used for sensory evaluation.

Sensory Evaluation

1. Descriptive analysis

To determine the di任erencesbetween the aromas

of raw and boiled saccharified sweet potato juices，

descriptive analysis was conducted. Thirteen

assessors who were ]apanese females， aged 19-25

years old， were recruited for the sensory evaluation

of the raw and heated sweet potato juices. The

panelists were selected using a di妊erence. test with

the following compounds at the indicated

concentrations. s-phenylethyl alcohol 10-40% Cw/w)，

methyl cyclopentenolone 10-4.5% C w / w)， isovaleric

acid 10-5.0% Cw/w)， r-undecalactone 10-45% Cw/w)

and skatole 10-5.0% Cw/w)， Call produced in Daiichi

Yakuhin Kogyo Co.， Ltd.， ] apan) .

Sensory training and sensory descriptor

development were carried out prior to the sensory

evaluation in a round-table discussion. Both raw and

boiled saccharified sweet potato juice were served

in a 150 mR glass wrapped in foil prior to the

sensory evaluation by the assessors. Table 1 shows

( 5 ) (ArticleJ Aroma Changes in Sweet Potato 53

Table 1 Sensory descriptors used in the descriptive analysis and the standard reference prepared for each

sensory descriptor

Grassy aroma

Sweet aroma

100mR of pressed juice of boiled spinach， without roots目

100m~ of maple juice， produced in LB Maple Treat Inc. Canada， diluted to 10% with

pure water

Sour aroma

Caramel aroma

Carrot aroma

Tomato aroma

Powdery aroma

Heavily boiled aroma

Sunkist 100% lemon， produced by Mitsukan Co. ]apan.

Sucrose heated up to about 170"(

Pressed carrot juice after blanching.

Heated juice after pressing tomatoes.

30 g of corn starch dissolved in 100m~ of pure water.

100 g of sweet potato， 50 g of noodles and O. 3 g of miso were dissolved in 250mR of

pure water with heating.

the descriptors used by the trained panel for the

raw and boiled sweet potato juices and the

preparation of the reference standard for each

descriptor. The following sensory evaluation was

performed on an individual basis. Two samples on a

tray were presented to each panelist. Raw and

boiled saccharified sweet potato samples were

presented in a glass and the panelist was asked to

score the attribute according to the appropriateness

of the reference using a 7 -point scale anchored on

the left by the term ‘none' and on the right by the

term ‘extreme' for nine aroma sensory descriptors:

overall intensity， grassy， sweet， sour， carrot， tomato，

powdery， caramel and boiled heavy. T-test was

performed to examine the significance of difference

(SPSS ver. 11. 0ω). The paneliおst岱swere also asked tω O

describe their aroma impression of the chemical

standard found in the volatiles of the raw and

boiled sweet potato juices by GC

2. Thermal desorption cold trap (TCT) analysis

Thevolatiles of the two juices were concentrated

and trapped in Tenax T A adsorbent tubes by

sparging with N， at a rate of 80mR/min and heating

at 500

C for 60 min. Each Tenax tube was placed in

the heating block of a TCT injector and heated to

2200

C to desorb the volatiles. The desorbed volatiles

were injected into GC mass spectrometers through

a TCT injector， and total ion chromatograms were

obtained . The TCT conditions are as follows

apparatus CHROMPACK Company， rod

temperature， 220t. desorption/ cold trap material.

silica mega bore column of o O. 53 mm， precool time，

2 min， cold trap temperature， -1300

C. desorption

oven temperature， 2000

C. desorption time， 1 min，

injection temperature， 2000

C. injection time， 1 min.

3. GC-MS conditions

The GC-MS conditions are as follows: apparatus，

GC Hewlett-Packard Model 6890， MS Hewlett-

Packard Model 5973， column temperature， 400

C for

10 min， and programmed increase from 400

C to

2000

C at 5 oC / min; column， fused-silica capillary

column (GL Science， TC-WAX) of 0.32 mm x 60 m，

and 0.25川 film thickness. carrier gas， He (50

KPa) ; ion source temperature， 2300

C， MS transfer

line， 2200

C in El mode， (70 e V). scan range m/z 35-

600.

Volatiles were detected in the headspace of the

samples. These compounds were measured in the

scan mode. The measured mass spectra were

compared with a library of commercially available

mass spectra and identified (i.e.wiley 275).

Results and Discussion

1 . Sensory experiment

Table 2 shows the descriptive profiles of all the

samples in terms of the nine descriptors. According

to the majority of the profiles. the boiled

Table 2 Significant differences in sensory descriptors

between the raw and boiled sweet potato juices

Sensory descriptor

Grassy aroma

Sweet aroma

raw heated significance

3.2:t0.7 2.l:t0.5 p<O.OOlホ・・3.l:t0.8 5.0:t0.7 p<O.OOl市吻市

Sour aroma 3. 1 :t 0.8 2. 5:t 0.5

Heavily boiled aroma 3.5:t O. 5 6.1:t 0.6 p< 0.001・..Carrot aroma 3.8:t O. 7 2.9土 0.6 p<0.05・Tomato aroma 2.9:t O. 5 2.9:t O. 8

Powdery aroma 3.5 :t O. 5 3.0:t O. 8

Caramel aroma 1. 8 :t O. 6 2. 1 :t O. 5

Odor intensity 3.6士0.7 4.8:t0.4 p<O.OOl・・・Values indicate the mean:t SD given by 13 panelists. Significant differences within rows indicated by asterisk • significant at O. 1 % level. "significant at 1 % level，

'significant at 5 % level

54 Food Preservation Science VOL. 33 NO.2 2007 ( 6 )

saccharified sweet potato juice has higher aroma

intensity than the raw sweet potato juice.

Significant di妊"erenceswere observed with respect

to five of the nine descriptors. Boiled saccharified

sweet potato generated more intensive aromas of

“heavily boiled" and “sweet" than the raw sweet

potato juice. with the exception of the “carrot" and

“grassy" aromas. There was also no difference in

terms of the. “caramel" .“ sour" .“tomato" or

“powdery " descriptor between the two j uices .

Interestingly. note that the intensity of the 0任flavor

component “heavily boiled" markedly increased for

the boiled sweet potato juice. The intensity of the

flavor component “sweet" also greatly increased.

From this resu1t. the aroma impression of the boiled

sweet potato juice can be both sweet and heavily

boiled.

GC-MS analysis

1. Overall aroma difference

The representative total ion chromatograms of

volatiles from samples in this study are shown in

Fig 1. The volatiles identified from the raw and

boiled saccharified sweet potato juices were

tabulated with the relative proportion of each

compound (Table 3). The total numbers of aroma

components detected by GC-MS were 26 in the raw

sweet potato juice. and 42 in the boiled saccharified

2.6e+07 2.4e+07 2.2e+07 2e+07

1. 8e+07 1.6e+07 1. 4e+07 1.2e+07 le+07 m∞000 ω∞o∞ 4∞∞∞ 2∞∞∞ 2.4e+07 2.2e+07 2e+07

1. 8e+07 1. 6e+07 1. 4e+07 1. 2e + 07 le+07

8ωo∞0 600∞∞ 4∞0000 20∞∞o

14

sweet potato juice. It appears that relative levels of

the majority of the compounds also increased after

the treatment. As earlier described. the sensory

evaluation showed that the intensity of the overall

aroma for the boiled saccharified sweet potato juice

was significantly higher than that for the raw sweet

potato juice. These suggest that the overall aroma

intensity for the boiled saccharified juice

significantly increased. as a result of the increase in

the levels of all the compounds after the treatment.

Also. the sensory test showed that the intensities

two sensory parameters (sweet and heavily boiled

aromas) significantly increased after the treatment.

This result suggests that the formation of some

volatiles and the loss of some compounds lead to a

sensory change in the characteristic aroma of sweet

potato.

Among the compounds detected and tentatively

identified in this study. the majority of the volatiles

that showed an increase in the boiled saccharified

sweet potato vapor and associatedwith its sensory

profile are aldehydes and ketones such as

acetaldehyde .β-damascenone and s-ionone.

terpenoids such as linalool. limonene.αーterpinene.

cymene. and s-cyclocitral. furans and pyrans. such

as 2-pentylfuran. furfural and 2-methylbenzofuran.

On the other hand. high-molecular-weight

aldehydes. such as 2. 3-butanedione. benzaldehyde.

29

28 45

Fig. 1 Total ion chromatograms of raw sweet potato (upper chart) and boiled sweet potato juice Oower chart)

obtained by GC-MS

Peak identification numbers correspond to compounds listed in Table 3. These volatile compounds were characterized by GC-MS under the analytical conditions described in the text. Volatiles fractionated using the TC-WAX coated 60m x O. 32mm fused-silica capillary are described in the text. The relative concentrations of most of the compounds markedly increased after the treatment.

(7) CArticleJ Aroma Changes in Sweet Potato 55

Table 3 Comparison of the concentrations of individual volatile components in headspace of volatiles from raw and heated sweet potato juices

Peak height Peak No Compound

Raw Heated

Pentane 52.0 <5 2 Acetaldehyde <5 33.5 3 2-Methylpropana 53.6 24.3 4 Acetone <5 72. 1 5 Ethyl acetate <5 25. 1 6 2-Butanone <5 30.0 7 2-Methylbutanal 33.2 35.1

8 3-Methylbutanal 37.0 87.8 9 Ethanol 12.6 39.6

10 2. 3-Butanedione (DiacetyJ) <5 40.9

11 Toluene <5 14.1 12 2-Butenal <5 15.0

13 2-Methyl-3-buten-2-01 <5 15.9

14 Hexanal 70.4 27.9 15 αーTerpinene 7.0 36.0 16 p-Mentha-1. 8-diene (Limonene) <5 15. 7 17 2-Pentylfuran 26.6 32. 7 18 Isopropyltoluene (Cymene) <5 14.0 19 Pentanol 21.1 16.0 20 Cyclohexanone <5 35. 7

21 1-0cten-3・one 33.9 <5

22 2. 2. 6-Trimethylcyclohexanone <5 29.0

23 2-Heptenal 42.6 <5 24 6-Methyl-5-hepten-2-one 24.5 20.0

25 Hexanol 33.8 23.0

26 Nonanal <5 37.5 27 3. 5. 5-Trimethyl-2-cyclohexen-1-one <5 21. 2 28 3-Ethyl-2-methyl-1. 3-hexadiene 80.2 <5 29 2-0ctenal 99.2 <5 30 Isopropenyltoluene <5 26.5 31 1. 2. 3. 4-Tetrahydro-1. 1. 6・trimethylnaphtalene <5 31. 0 32 1-0cten-3-01 60.4 19.6

33 2. 4-Heptadienal 42.0 <5 34 Furfural 50.5 89.6

35 2-Ethylhexanol <5 53.6

36 Decanal <5 50.0 37 Benzaldehyde 50.0 96.2

38 2-Nonenal 52.0 <5

39 3. 7 -Dimethyl-1. 6-octadien-3・01(LinalooJ) <5 22.0 40 2 -Methylbenzofuran <5 35.9 41 s-Cyclocitral 43.0 75.6

42 Phenylacetaldehyde (Benzeneacetaldehyde) 36.0 51. 0 43 2. 4-Nonadienal 27.9 <5

44 Naphthalene <5 19.6 45 2. 4-Decadienal 76.5 <5 46 (lR)-6. 6-Dimethylbicyclo [3. 1. 1J hept-2-ene-2-methanol (MyrtenoJ) 15.9 34.6 47 2. 4-Decadi巴nal 44.8 32.5 48 2. 6. 6-Trimethyl-1. 3・cyclohexadienyl-1-propenylketone (s-Damascenone) <5 82.6

49 Gerany lacetone <5 59.2 50 2. 6-di-tert-butyl-p-cresol (BHT) <5 43.9

51 β-Ionone <5 33.5

These volatile compounds correspond to those characterized by GC占[Sin Fig 1. The analytical conditions were described in the text. Values are expressed in peak height.

56 Food Preservation Science VOL. 33 NO.2 2007 ( 8 )

phenylacetaldehyde， 3-ethyl-2-methyl-1， 3-hexadiene， potato juice. Thus， it is possible that boiling

2， 4-decadienal. hexanal， 2-octenal， l-octene-3-o1 and

2-nonenal， were identified in higher amounts in the

raw sweet potato jUlce.

Although it is not easy to determine the

relationship between the sensory descriptor's results

of the sensory evaluation and the individual

chemical compounds identified. it may be assumed

that some of the compounds contributed to the

sensory components. The sensory impact of some

important compounds is discussed below for the

sensory parameters with a significant result.

2. Aldehydes and alcohols

Numerically， aldehydes were the main compounds

identified in both sweet potato juice samples. In this

study， the boiled saccharified sweet potato juice

showed a decrease or an increase in the levels of

aldehydes depending on their functional type.

Although the levels of low-molecular-weight

influenced the time over which the enzymes were

activated and subsequently yielded lower levels of

lipid degradation products in the boiled saccharified

sweet potato ]Ulce.

Aldehydes are important aroma impact

compounds. C6 compounds such as hexanal. (E) -2-

hexenal and (Z) -3-hexenal， contribute markedly to

the green note of the aroma 1 7ト川 • In our experiment，

the amount of hexanal decreased because of boiling.

They also showed that significant decrease in the

intensity of the aroma profile for the green note in

the boiled saccharified sweet potato juice. which

may be related to the loss of C6 aldehydes. Sensory

result also showed that the intensity of the heavily

boiled aroma greatly increased in the boiled sweet

potato juice. A reduction in the level of aroma

compounds such as C6 compounds and high-

molecular-weight compounds may result in the loss

aldehydes such as acetaldehyde showed an of the green aroma in boiled sweet potato juice and

increasing trend. those of aromatic aldehydes such

as benzaldehyde and phenylacetaldehyde， along with

C6 aldehydes. such as hexanal and 2-heptanal， and

other high-molecular-weight compounds such as 2，

4 -decadienal. 2， 4 -heptadienal. 2 -octenal and 2-

nonenal， that were present in higher proportions in

the raw sweet potato juice， showed a decreasing

trend in the boiled sweet potato juice

C6 and high-molecular-weight aldehydes are

derived from fatty acid decomposition and found at

higher levels in the homogenates of fruits. BUTTERY

et al. have shown that lipid-derived volatile

aldehydes such as cis-3-hexenal， which are present

at low levels in intact tomatoes. rapidly increase in

level after homogenization 14J• This mechanism is

proved to involve enzyme (lipoxygenase and

hydroperoxytrienoic acid lyase) -catalyzed oxidative

processes， which contribute to lipid degradation in

fatty acid substrates. Since the lipoxygenase activity

in tomato has been reported in both the

membranous and soluble portions凶 itmay lead to

enhanced lipoxidation during the homogenization of

tomato

Sweet potato contains a higher amount of lipid-

oxygenation-related enzymes附 Sincethe skin was

not discarded (during homogenization) while

preparing the boiled saccharified sweet potato juice.

it is likely that the enzymes and polyunsaturated

fatty acids present in the skin account for the

higher levels of aldehyde products in the raw sweet

contribute to the predominance 'of other aroma

compounds in the aroma profile of the boiled

saccharified sweet potato juice， which in turn may

result in a higher degree of the 0妊-flavorin boiled

saccharified sweet potato juice

Certain aldehydes such as acetaldehyde，

benzaldehyde and benzeneacetaldehyde， possess a

distinctive sweet floral aroma. Sensory evaluation

results showed that the boiled saccharified sweet

potato juice possesses a significant sweet odorCTable 2 )， and an increase in the levels of these

compounds may contribute to the sweet aroma

profile of the boiled saccharified sweet potato juice.

Alcohols were also identified in both samples.

Interestingly， note that the level of alcohols with six

carbon atoms， such as hexanol， decreased in the

boiled saccharified sweet potato juice. C6 alcohol is

also responsible for the herbaceous odor of several

fruits叫 .and thus such a decrease may contribute to

the loss of the green aroma of boiled saccharified

sweet potato.

3. Ketone compounds

A distinctive increase in the levels of ketones was

observed after boiling. The relatively higher

proportions of acetone， s-ionone.β-damascenone， 2-

hydroxy-2 . 6， 6 -trimethyl-cyclohexanone in the

boiled sweet potato juice can be explained by the s

-carotene oxidative mechanism， which may

contribute to the enhanced sweet aroma of the

boiled saccharified sweet potato juice.

( 9 ) CArticleJ Aroma Changes in Sweet Potato 57

β-carotene acts as a precursor that forms β-

damacenone via enzymatic and nonenzymatic

pathways such as thermal degradation2J).22¥In other

food systems containing β-carotene， the oxidative

degradation ofβ-carotene also forms a mixture ofβ-

ionone，β-damacenone， 2-hydroxy-2， 6， 6-trimethyl-

cyclohexanone23¥β-cyclocitral24l and acetone25J.

Benihayato tubers have been found to contain 8

mg ofβ-carotene per 100 g (wet basis)， which is as

much major component as that in carrot， and it is

assumed that the s-carotene oxidative mechanism

results in the production of these compounds

Certain ketones， such as s-ionone， 2， 3-butanedione，

and geranyl acetone， possess a sweet floral aroma

and may add a sweet floral note to the total sweet

profile of boiled saccharified potato jUlce. An

increase in the level of these compounds in

considerable amounts in the boiled saccharified

sweet potato juice， may reflect the result of the

sensory evaluation of the high intensity of the

sweet aroma. Although β-damascenone possesses a

heavy floral aroma and contribute to the floral note，

owing to its strong odor intensity and low threshold

(threshold in water : 0.2昭!R-)回 ithas often been

considered to contribute to the overall off-flavor27).28).

Sensory evaluation results showed a higher intensity

of the heavily boiled aroma in the boiled

saccharified sweet potato juice， suggesting that the

higher proportion ofβ-damascenone found after

boiling may contribute to not only the sweet note，

but also the off-flavor note.

Interestingly， note that the sensory panelists

indicated the carrot-like aroma in the raw sweet

potato juice. Although it is widely known that

vegetables containing high β-carotene content emit a

distinct carrot-like aroma when bruised， the reason

behind this remains to be elucidated. Although the

association with the smell produced and s-carotene

breakdown is not yet known， it is possible that an

oxidative carotenoid is involved in the production of

aroma compounds. Because such aroma compounds

have not been identified in this study， further

studies are needed to identify these compounds.

4. Terpenoids

In this study， the levels of linalool， limonene，α-

terpinene， cymene， and β-cyclocitral increased after

boiling， (Table 3). From this result for terpenoids，

the following scheme of terpenoid synthesis is

proposed (Fig 2) : From liberated monoterpenes such

as geraniol 1 and nerol 3， the corresponding

allylic cationic species 2 and 4， respectively， are

formed by dehydration， at a boiling temperature of

about 1000

C and the presence of an acidic phenol 0. e. 2， 6-di-tert-butyl-p-cresol. Table 3)， leads to the

formation of an identical cationic species 5， whose

reaction with water furnishes linalool 6. On the

。九百人

寸ぬ什1人5

」

μ¥人2

九人

骨

骨

ん¥人

1hy3

6

人

V人1 Cyclization

2BMM

Ha岳山::円Lmumu

8 7 9

Fig.2 Proposed mechanism for formation of terpenoids via interconversion of terpenes during boiling

Geraniol 1 and nerol 3. the corresponding allylic cationic species 2 and 4. respectively. were formed by dehydration， leading to the identical cationic species 5. whose reaction with water furnished linalool 6. On the other hand， cation 4 with Z-stereochemistry underwent cyclization. which through different deprotonation pathways. is converted to limonene 8 and a-terpinene 9， the latter of which was further converted to cymene 10.

58 Food Preservation Science VOL. 33 NO.2 2007 (10)

other hand， cation 4 with Z-stereochemistry

undergoes cyclization， which through different

deprotonation pathways is converted to limonene 8

(by elimination of H") and a-terpinene 9 (by

elimination of H' after Hb migration， or by

elimination of Hb followed by isomerization)， the

latter of which is further converted to cymene 10

by aromatization with the loss of a H2 molecule.

In general， monoterp巴ne hydrocarbons and

oxygenated monoterpenes tend to give a sweet

aroma in the total aroma quality due to their

higher volatility and polarity.“Imo-Shochuぺatype

of distilled alcohol from fermented sweet potatoes，

has a pleasant sweet potato flavor. OHTA et al.

reported that geraniol， nerol， linalool， citronerol and

terpeneol contribute to the distinctive flavor of

sweet potato distillates with a pleasant fruity and

floral smell捌 .They found that monoterpene alcohols，

which are precursor compounds in their glycoside

forms in sweet potato， are liberated by enzymatic

hydrolysis when sweet potatoes is blended， and

geraniol and nerol are produced during fermentation.

Through distillation， these alcohols are further

converted to linalool and limonene at high

temperature under acidic condition， and contribute

to the distinctive aroma profile of sweet potato

distilled alcohol. In our sensory evaluation， a higher

intensity of the sweet note was suggested for the

boiled saccharified sweet potato juice. The

characteristics of the standard of the terpenoids

found by GC-MS are described as follows

benzaldehyde， an aroma like that of bitter almond;

linalool， lemon and rose-like; and β-cyclocitral ，

camphor and cereal-husk-like aroma. Therefore， the

high proportion of these compounds found in boiled

saccharified sweet potato vapor could be associated

with the “sweet" aroma of boiled saccharified sweet

potato ]Ulce.

5. Pyrans and furans

Only three furan and pyran compounds namely， 2-

pentylfuran， furfural and 2-methylbenzofuran， were

identified in this study. 2-pentylfuran and furfural

tended to increase in the boiled-saccharified sweet

potato ]Ulce.

It has been reported that baked sweet potato

contains various furans and pyrans71， which are

formed via the Maillard reaction or

caramelization30l.31l. The basic constituents of sweet

potato such as sugars， amino acids and fatty acids

act as the main precursors of volatiles， and are

later hydrolyzed during baking to form pyrans and

furans. Among various furan derivatives in baked

sweet potato volatiles， both maltol and furfural are

the 五nal compounds produced via amino-carbonyl

reactions. In particular， maltol has been reported to

be the potent aroma impact compound of baked

sweet potato. SUN et al. reported that a sensory

panel described the aroma of a baked sweet potato

volatile fraction with maltol as a sweet potato-like

aroma but fractions without maltol as a caramel-like

aroma22l.

In our experiment， the results of the sensory

analysis showed a higher intensity for the heavily

boiled aroma and a lower intensity for the sweet

aroma in the boiled saccharified sweet potato juice，

which indicates that 0任flavor was more

predominant after boiling and saccharification

processes. Furfural， but not maltol， was detect巴din

the boiled saccharified sweet potato juice. This may

explain why the boiled saccharified sweet potato

juice was perceived to have an unpleasant aroma

instead of a sweet potato-like aroma.

The reason furfural but not maltol was formed

during condition is linked to the temperature

di任erence between the boiled saccharified sweet

potato juice production (wherein temperature

normally does not exceed 1000

C) and the baked

sweet potato juice production (wherein temperature

normally exceeds 2000

C) (Figs. 3 and 4). Furfural is

formed according to the following scheme

Aldehyde 1， in the form of an acyclic pentose

isomer reacts with an amino acid to produce imine

2， which after isomerization forms enamine 3.

Enamine 3 after dehydration forms alkenyl imine

4. The hydrolysis of the imine part， and a second

dehydration from the resultant intermediate 5

enables the formation of dihydrofuran 6， and then

after a third dehydration， the final material， furfural

7 is formed. However， maltol under theboiled

saccharified condition is hardly synthesized due to

the low conversion feasibility of the intermediate

from 4 to 5. Although the hydrolysis of 4 in

furfural formation is considered to readily occur on

the basis of the generally low stability of imines in

under aqueous heating conditions， the C-N bond

cleavage of 4 in maltol formation may be

disfavored due to the high nucleophilicity of the

amino group that renders the C-N bond less prone

to disconnection under boiling conditions at about

1000

C (Fig. 4).

)

咽』A

唱

EA(

(ArticleJ Aroma Changes in Sweet Potato 59

付 CHO旦 Lぶ偽札R--QPR1 2 3

]ム メメJ 、RH，o昨同。

4 5

-H，o • H~CHO ゴ2叫ん6

Fig.3 Proposed mechanism of furfural formation during boiling

7

Aldehyde 1 reacts with an amino acid to produce imine 2. which upon isomerization forms enamine 3， and then after dehydration forms

alkenyl imine 4. The resultant intermediate 5， enables the formation of dihydrofuran 6 and the final product. furfural 7.

HO HO HO HO H HO HO H

H01 へ入CHO去十H01 仲 丸 一一H01 へ以RHO HO HO HO HO HO!

1 2 3

ョ;了HoJPRrs引」::干6

-H，o H041一町T - oT7

Fig.4 Proposed mechanism of maltol formation during baking

8 9

Condensation with an amino acid 1 followed by the isomerization of 2 leads to the formation of enamine 3. The dehydration of enamine 3 converts it to allylamine 4. Further removal of the amine part and the cyclization of 4 and 5 converts allylamine 4 to the six-membered

compound 6. which upon two consecutive isomerizations of 7 and 8 leads to maltol 9 formation.

Conclusion potato sample possessed enhanced grassy and carrot

aroma. Using GC-MS， changes in each aroma

In this study， we produced a sweet potato drink component were identified and the formation

by the boiling and enzymatic processes. Because

there are as yet no studies of the aroma profile and

volatile compounds of sweet potato after boiling and

saccharifying processes， the di妊erences m aroma

profile between the boiled-saccharified sweet potato

juice and the raw sweet potato juice were studied

by descriptive sensory evaluation and GC. The

sensory attributes of the boiled saccharified sweet

potato juice showed a high rating for “sweet ..

aroma but also a high rating for “heavily boiled"

aroma as an off-flavor note， whereas the raw sweet

mechanism of compounds was discussed. The

evaluation of the GC / MS and sensory data

suggested that terpenoids， ketones， furans and

aromatic aldehydes are the potent aroma

compounds contributing to the change in the flavor

profile after boiling and saccharification. No maltol，

which is an important aroma contributor in baked

sweet potato， was found in the boiled saccharifed

sweet potato. Boiling may not favor the formation of

maltol， which is formed during baking. A

mechanism is also presented for the formation of

60 Food Preservation Science VOL. 33 NO.2 2007 ( 12 )

some terpenes. ketones and aldehydes that were

found at higher levels in the boiled saccharified

sweet potato juice. Although it is not easy to

identify the aroma compound of the boiled

saccharified sweet potato. the results obtained in

this study may show some association between the

identified volatiles in the boiled saccharified sweet

potato and the characteristic aroma attributes of

sweet potato. which reflect the descriptions in the

sensory evaluation given by the panelists.

Further study is planned to elucidate the aroma

impact compound by measuring the relative

contribution of each identi五ed compound to the

sensory attributes. Also better treatment methods

for sweet potato wiU be devised in future studies.

Alternatively. the baking method instead of the

boiling method for the production of sweet potato

juice should be investigated

Acknowledgement We deeply thank Dr. Minoru

Iwamoto of T. Hasegawa Co. Ltd. and the Yaku1t

Pharmaceutical Ind. Co.. Ltd . for technical

contribution.

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さつまいもの機能性飲料製造過程における

いものにおいの変化

玉城和彦判・江原勝夫叫 ・玉城 武村・山崎孝判

* 1 カリフォルニア大学デーピス校

(カリフォルニア州デービス95616)

* 2 東京工業大学

(〒152-8550 東京都目黒区大岡山 2-12-1 )

* 3 東京文化短期大学

(〒164-8683 東京都中野区本町 6-38-1 )

*4 東京農工大学

(〒184-8588 東京都小金井市中町 2-24-16)

本研究は，さつまいもを使った機能性飲料の製造工程

中，原料であるベニハヤトいもが，蒸しおよび酵素処理

により生じるにおい変化を官能評価とGC-MSにより分

析したものである。boiled-saccharified処理で、どの よう

な変化を示すかを調べたところ，まず官能試験結果，生

のベニハヤトいもは青臭さとニンジン様臭が強いが，処

理過程で甘いにおいと重いにおいが増し，においの強さ

が増すことが明らかになった。またGC-MS分析に より，

処理後，におい成分数および濃度が高くなることが明ら

かとなった。GC-MS分析による処理前と処理後の個別

におい成分の比較変化をしたところ，処理過程により，

テルペノイド，ケトン化合物，高分子のアルデヒド，芳

香族アルデヒド化合物が増加する一方，生いもの成分で

多くみられた低分子のアルデヒド化合物の含量は減少し

た。さらに，これら化合物の変化と官能評価値との関連

性，および各化合物の生成メカニズムが論じられた。

(平成18年11月20日受付，平成19年3月22日受理)