Effect of Storage and Heat Treatments on the Sugar

(73) Nippon Shokuhin Kogyo Gakkaishi Vol. 33, No. 6, 441～449 (1986) [Article] 441

Effect of Storage and Heat Treatments on the Sugar

Constituents in Cassava and Yambean Roots

Akiko KAWABATA*, Shigeru SAWAYAMA*, Ricardo R. Del ROSARIO**

and Marissa G. NOEL**

* Department of Nutrition, Faculty of Agriculture, Tokyo University of

Agriculture, 1-1-1, Sakuragaoka, Setagaya-ku, Tokyo 156** Institute of Food Science and Technology (IFST)

, College ofAgriculture, University of the Philippines at Los Banos

(UPLB) College, Laguna 3720, Philippines

The effect of storage and heat treatments on the sugar constituents of cassava and yambean roots

were investigated using a high performance liquid chromatography (HPLC). Essentially, the total

sugar content increased during the first one or two weeks of any 18～28 days storage period. Also,

the ratios of fructose and glucose to total sugar content increased, while the ratios of sucrose and

inositol decreased. The linamarin content increased markedly in the first 7 days, and continued to

increase for several additional days; then it gradually declined and almost disappeared before decay.

In yambean root, the three sugars of glucose, fructose and sucrose were found. Although heat trea-

tments by boiling, roasting, and drying all tended to increase the total sugar content of these roots,

the linamarin content of cassava roots and of finely-chopped cassava leaves significantly showed a

tendency to decrease by such treatments. Investigated at the same time were changes in the con-

stituent pectic substances of these roots. Finally, the changes in appearance occurring in cassave root

tissue during storage and heat treatment were observed by a scanning electron microscope (SEM).

There are various root crops grown in tropicalareas, such as the Philippines, where cassavaand yambean are among the most important, andtheir roots are usually consumed directly asfood. The changes that occur to these starchyroots during storage are important concerningtheir subsequent use. During storage, thereis known to occur a rapid accumulation oftotal sugars accompanied by a small decline instarch content.BOOTH et al.1) and RICHARD and COURSEY2)

have reported that early in cassava root storagethere appears an increase in reducing sugarcontent, which is later followed by a decreaseas storage is prolonged. Sucrose, on the otherhand, constantly increases. The effect on cy-anogenic glycoside (linamarin), remains un-clear, and there are several reports, such asby WOOD3), COOK et al.4), and FUKUBA et al.5)using the enzymatic method, and CONN6) usingpaper chromatography for determining lina-marin content.

The main aim of this study has been toelucidate in more detail the changes that occurin the sugar constituents of cassava and yam-

bean roots during storage, and as the result ofheat treatments. At the same time, the pectic

substances in these roots were determined, andthe tissue structure of these roots was observedby a scanning electron microscope (SEM).

Materials and Methods

Materials

Cassava (Manihot esculenta Crantz): Threecultivars of cassava, grown at the Institute of

Plant Breeding, University of the Philippinesat Los Banos, were used. These included cv.'Lakan' and cv. 'Vassourinha' as sweet types,and cv. 'Datu' as a bitter type.Yambean (Pachyrhizus erosus Urban): One

cultivar of yambean was used in the study.It was obtained from a market at Los Banos ,Laguna.The roots were stored under ambient con-

442 日本食品工業学会誌第33巻第6号 1986年6月 (74)

Fig. 1 Preparation of sample for HPLC

* Membrane filter

ditions (temperature ranging from 28 to 32℃,

relative humidity from 66 to 88%) from 18 to 28

days.

Methods

Determination of sugar content using a high

performance liquid chromatography (HPLC):

The determination of sugar content was done

by use of an HPLC with a TSK-GEL, LS-450

NH2 (4mm i.d. ×300mm) column made by

Toyo Soda Co,, Ltd.7) It was eluted at a flow

rate of 0.8ml/min with 75% acetonitrile in

water. The sugar contents of the cassava were

determined from the proximal, middle, and

distal parts of the parenchymal tissues of each

sample. Samples of yambean used in the study

were taken from the middle parts of the roots.

These roots were stored for a period of 18 to

28 days and samples were taken for analysis

every second or third day.

Samples for heat treatment were taken from

the middle parts of the roots and cut into

slices 5cm thick. They were heat-treated by

boiling at 100℃ for 18min., roasting at 200℃

for 1h., and drying at 60℃ for 19h. The

method of sample preparation for HPLC is

shown in Fig. 1.

Determination of pectic substances: Test

samples were taken from the same parts of the

cassava roots used for determining the sugar

constituents. About 25g of each sample wasgrated into ethyl alcohol, then heated repeat-edly in warm 70% ethyl alcohol solution untilno sugar could be detected by the Molischreaction. The residues were treated with ab-solute ethyl alcohol and then with ethyl ether,dried at room temperature, and pulverized topass through a 10 to 20 mesh screen. Theseprocessed residues, referred to as alcohol in-soluble solids (AIS), were used to determine

pectic substances. The pectic substances werefractionally extracted by the method of SAWAYAMAet al.8) into four fractions: the water solublefraction (W-S); the hexametaphosphate solublefraction (P-S); the hydrochlolic acid solublefraction (H-S); and the potassium hydroxidesoluble fraction (K-S). By using the meta-hydroxydiphenyl method9), the pectic sub-stances in these four fractions were determinedas anhydrogalacturonic acid.

Observation of cassava root tissue using ascanning electron microscpe (SEM): Observationand photography of the cassava root tissue wascarried out with a Nippon Denshi JSM-35 SEMafter fixation of the tissue by glutaraldehydeand osmic acid; the tissue had been dried bythe critical point drying method.

(75) KAWABATA. et al.: Sugar Constituents of Tropical Root Crops 443

Table 1 Effect of storage on the sugar constituents of cassava root (cv. 'Lakan')

Results and discussion

Effect of storage on the sugar constituents

of rootsThe results concerning changes in the sugar

constituents of cv. 'Lakan' cassava roots duringstorage are shown in Table 1. The daily samp-ling results reflect the averaging of six meas-urements, each taken individually from thethree parts (proximal, middle, and distal) oftwo roots. The six samples had remainedhealthy during the first two days of storage,but after 4 days some parts showed a minimaldeterioration due to vascular streaking10), i.e.

physiological deterioration.Moisture content in the roots decreased from

66.6% to about 60.0%, and total sugar contentincreased from about 500 to 3900mg per 100gfresh weight; the increase was essentially dur-ing the first two weeks of storage. This rapidincrease of sugar content was considered to

be a reflection of the metabolic change from

starch to sugar that occurs during storage1)2).

The ratio of fructose and glucose to total sugar

content also began increasing from the 7th

day of storage; this was similar to results from

the study by BOOTH et al.1) which showed an

increase in reducing sugar during a 2～4 week

storage period. The total amount of inositol

was not large but there was a slight tendency

for inositol to increase during storage. No

literaure concerning the amount of inositol in

cassava root was found, but the existence of

inositol in sweet potato roots is reported by

YOSHIMURA11) and NAGAHARA12).

The existence of linamarin (cyanogenic glu-

coside) found in cassava presents a serious

problem13),14) concerning the use of cassava as

a foodstuff; it has been customary to use a

sweet type cassava which contains less lina-

marin. The bitter type cassava, those which

contain large amounts of limamarin, are usually

used as raw materials to produce starch.

Though cv. 'Lakan' is of the sweet type cas-

sava, it did initially contain 17mg of limamarin

per 100g fresh weight. After 7 days storage

this increased to 35mg; yet by the 14th day

the linamarin content had reversed itself and

decreased to nearly one third its former (17mg)

value. This trend continued and at the end


Table 2 Effect of storage on the sugar constituents of cassava root (cv. 'Vassourinha')

Table 3 Effect of storage on the sugar constituents of yambean root

of three weeks, the limamarin content haddiminished to but a trace. At the same time,decay had increased to affect, at least partially,up to two-thirds of the cassava roots. This

gradual increase of cyanide over several daysof storage had likewise been noted by KOJIMAet al.15) who concluded this phenomenon wasclosely related with linamarase activity, andsuggested that linamarase had played a primaryrole in regulating the levels of cyanogenic glu-coside in cassava roots.For cv. 'Vassourinha' cassava roots, the

changes in sugar constituents during storage

are shown in Table 2. The moisture content

of cv. 'Vassourinha' root was 10% higher than

that of cv. 'Lakan'. This may explain why the

cv. 'Lakan' kept a healthy condition throughout

all 28 days of storage, while the cv. 'Vas-

sourinha' could maintain its health for only 18

days; the total sugar content of cv. 'Vas-

sourinha' also was higher than that of cv.'Lakan' . Concering the ratios of various sugars

to total sugar content, cv. 'Vassourinha' showed

the same tendency as cv. 'Lakan' up to the

14th day; but by the 18th day, the glucose

ratio for cv. 'Vassourinha' became the highest.


The increase of limamarin content in the first

7 days were also shown, but as with cv.

'Lakan' it almost disappeared prior to decay .

The changes in sugar constituents of yambean

root during storage are shown in Table 3.

The moisture content decreased slightly from

88.5% to 86% during storage, and even though

the moisture content is high, the moisture-loss

was less shown in yambean than in cassava.

The total amount of sugars varied from about

1800 to 5300mg per 100g of root. The ratio

of sucrose content to total sugar was lower

than that of glucose or fructose. Glucose con-

tent was the highest, in a range of about 41

～51% of total sugar . No other sugars than

these three were found in yambean root.

Effect of heat treatment on sugar constit-

uents of roots and leaves

Both cassava roots and cassava leaves are

commonly eaten after subjection to one or

several methods of pre-cooking and/or cooking.

In this study, three types of heat treatment

were used: a) boiling, b) roasting, and c)

drying. The sugar constituents of the heat-

treated samples were then determined andcompared with the raw samples. As shown inTable 4, the total sugar content (dry-weightbasis) of the roots tended to increase regardlyof the treatment method. It was only linamarinthat showed a marked decrease because of heattreatment. On average, 40% of the originallinamarin content of these roots was removedby the various treatments. This is consistentwith WOOD3), COOK et al.4) and FUKUBA et al.5)who considered in their reports that cyanogenic

glucosides decomposed and diminished as aresult of heat treatment.In cassava leaves there is a much higher

concentration of linamarin than found in theroots. Therefore, the changes in linamarin con-tent of these leaves caused by boiling in waterwas studied and is shown in Table 5. After5 minuites of boiling, the linamarin contentof whole leaves did not change so much.However when the leaves were first finely-chopped, boiling caused total sugar content todecrease by about 75%, and about 73% ofthe linamarin content was removed. It was

Table 4 Effect of heat treatment on the sugar constituents of cassava root (cv. 'Lakan')

Table 5 Effect of boiling on the sugar constituents of cassava leaves (cv. 'Datu')


Fig. 2 Effect of storage on the galacturonic acid

of cassava root (cv. 'Lakan')

observed that in using young leaves as food-stuffs, expansion of the cut surface area is animportant technique for dissolving linamarinin boiling water.

Effect of storage and heat treatment on the

pectic substances of rootsPectic substances are the main constituents

of the middle lamella of root-cell walls and, assuch, give dynamic properties like hardness,elasticity, plasticity, and so forth to the cellstructure. It is known that during storagecassava root tissue, becomes soft from physio-logical deterioration, but reports on changesin those pectic substances which contribute tothe tissue structure canntot be found.Changes in the galacturonic acid content of

cv. 'Lakan' cassava roots during storge areshown in Fig. 2. The total content of galac-turonic acid ranged from about 1570 to 2150mg

per 100g fresh weight. After two days storage,the amounts of total galacturonic acid and ofH-S fraction had sharply increased, but there-after, held to a roughly constant level. Amongthe fractions, W-S tended to increase only overthe last 12 days. P-S and K-S declined slight-ly. It was considered16) that the W-S fractionwas water soluble pectinic acid and pectic acid;the P-S fraction had water insoluble salts of

pectinic and pectic acids; and the H-S and

Fig. 3 Effect of storage on the galacturonic acid

content of cassava root (cv. 'Vassourinha')

K-S fractions mainly included protopectin inwhich pectic substances were combined withcellulose. The increase of W-S fraction after21 days is related to the softening phenomenonof root tissue.In Fig. 3 is shown the content of galacturonic

acid in four fractions from cv. 'Vassourinha'cassava roots during storage. The total galac-turonic acid content of cv. 'Vassourinha' islower than that of cv. 'Lakan', and the H-Sratio is also somewhat lower. This is con-sidered to be related to the dynamic propertiesof root tissue structure which, together withamounts of moisture and sugar content, producea profound effect upon the deterioration ofstored roots.Changes in the galacturonic acid content of

cassave and yambean roots, as caused by roast-ing, are shown in Table 6. All samples showeda tendency for increasing ratios of W-S afterroasting. FUCHIGAMI and OKAMOTO17) noted thatchanges in the firmness of vegetable rootsduring cooking is influenced by the quantity


Table 6 Effect of heat treatment on the galacturonic acid of cassave and yambean roots

[mg/100g fresh weight]

Fig. 4 Scanning electron photomicrographs of cassava roots


and quality of pectic substance. The resultsin Table 6 show that water soluble pecticsubstances increased by pyrolyzer during cook-ing.

Scanning electron microscopy (SEM) of roottissueThe changes in appearance occurring in cas-

sava (cv. 'Lakan') root tissue during storagewere observed through SEM; typical photo-

graphs of these observations are shown inFig. 4-1 and 4-2. Destruction of the root-cellwalls was observed to have occurred after 28days of storage. The SEM appearance of rawcassava (cv. 'Datu') root is shown in Fig. 4-3.The appearance of the same root after boilingfor 1 hour is shown in Fig. 4-4, where itcan be seen how starch granules in the tissuebecame gelatinized and swollen, and also howsome of the graunles have ruptured.

Summary

Roots of two cassava cultivars (cv. 'Lakan'and cv. 'Vassourinha'), and one cultivar of

yambean were stored under ambient conditionsfor 18 to 28 days. The following results wereobtained:

(1) Sugar content was determined by a highperformance liquid chromatography (HPLC).The total sugar contents essentially increasedduring the first one or two weeks, whereaslinamarin content of the cassava roots increasedmarkedly in 7 days, continued to increase forseveral days, then decreased gradually andalmost disappeared before decay. Root dete-rioration was observed to occur faster in cv.'Vassourinha' than in cv. 'Lakan'. In yambeanroot moisture content was more than 80% andthe amount of total sugar was higher than thatof cassava roots.

(2) The total sugar content of cassava rootswas increased by heat treatment. Linamarincontent, however, decreased significantly, aswas empirically foreseen.

(3) The pectic substances were extractedfractionally into four fractions from the roots.The water soluble pectin (W-S) tended toincrease, while protopectin showed a slightdecrease at the end of storage. The changesin appearance that occurred in cassava roottissue during storage were observed under a

scanning electron microscope.

Acknowledgements: The authors would like to ac-

knowledge the continuing guidance and encourage-ment of Dr. Hiroyasu FUKUBA, Professor of Ochano-

mizu Women's University, and to express their thanks

to Ms. Naomy SABINIANO, Virgie ALMENTEROS, LucilleABAD, and the other staff of the Food Chemlstry

Laboratory, Institute of Food Science and Technologyof the Philippines at Los Banos, for their assistancein the experiments.

References

1) BOOTH, R.H., DE BUKLE, T.S., CARDENAS,

O.S., GOMEZ, G. and HERVAS, E.: J. FoodTechnol., 11, 245 (1976).

2) RICHADRA, J.E. and COURSEY, D.G.: Trop.

Sci., 23. 1 (1981).3) WOOD. T.: J. Sci. Food Agric., 17, 85 (1966).4) COOK, R.D., HOWLAND, A.K. and HAHN, S.K.:

Exp. Agric., 14, 365 (1978).5) FUKUBA, H., IGARASHI, O., BRIONES, C.M. and

MENDOZA, E.M.T.: "Tropical Root Crops:Postharvest Physiology and Processing" ed. by

Uritani. I. and Reyes, E.D., Nagoya Univ.,NRI, Tokyo Univ. of Agric. p. 225 (1984).

6) CONN, E.E.: Anal. Biochem., 77, 310 (1977).7) KURIHARA, Y., SATOH, T. and UMINO, M.: Toyo

Soda Hokoku, 24, 115 (1980).8) SAWAYAMA, S., UCHIMURA, Y. and KAWABATA,

A.: J. Home Econ. Jpn., 35, 242 (1984).

9) BLUMENKRANTZ, N. and ASBOE-HANSEN, G.:Anal. Biochem. 54, 484 (1973).

10) ONWUEME, I.C.: "The Tropical Tuber Crops."

John Wily and Sons, Chichester, p. 234 (1973).11) YOSHIMURA, K.: Bull. Kagoshima Imp. Coll.

Agric. For., 7, 125 (1929).12) NACAHAMA, T.: Bull. Fac. Agric. Kagoshima

Univ., 14, 1 (1964).13) DELANGE, F., ITEKE, F.B. and ERMANS, A.M.

(ed.) "Nutritional Factors Involved in theGoitrogenic Action of Cassava" 100 p., Inter-

national Development Research Center, Ot-tawa, Canada, IDRC-184 (1982).

14) ERMANS, A.M., MBULAMAKO, N.M., DELANGE,F. and AHUWALIA, R. (ed.): "Role of Cas-

sava in the Etiology of Endemic Goitre andCretinism" 198 p., International Development

Research Center Ottawa, Canada, IDRC-1362

(1980).15) KOJIMA, M., IWaTSUKI, N., DATA, E.S., VIL-

LEGAS, C.D.V. and URITANI, I.: Plant Phy-

siol, 72, 1986 (1983).


16) MIURA, H., HAGIHARA, K. and MIZUTA, T.:J. Jpn. Soc. Hortic. Sic., 32, 27 (1963).

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(Received Sep. 13, 1985)

キャッサバおよびヤムビーン根茎の構成糖に及ぼす

貯蔵と加熱処理の影響

川端晶子*・澤山茂*・リカードR.デル

ロザリオ**,マリサG.ノエル**

(* 東京農業大学農学部栄養学科〒156 東京都世

田谷区桜丘 1-1-1)

(** フィリピン大学ロスバニオス校食品工学研究所)

キャッサバおよびヤムビーン根茎の収穫直後,貯蔵中

および加熱処理による構成糖の変化を高速液体クロマト

グラフを用いて定量し,検討した.根茎類は室温(28～

32℃,相対湿度66～88%)で,18～28日間貯蔵された.

キャッサバ根茎中の合計糖含量は,貯蔵初期2週間に顕

著な増加を示した.合計糖含量に対する比率では,シュ

クロースの含量が最も高かった.貯蔵期間中,フラクト

ースとグルコースが漸増するのに対し,シュクロースは

漸減した.リナマリン(青酸配糖体)は,貯蔵1週間目

に顕著な増加を示したが,その後減少し,貯蔵終期には

殆んど消失していた.ヤムビーン根茎中からは,シュク

ロース,フラクトース,グルコースの3種の糖のみが定

量された.4画分に分別定量したペクチン質では,少量

ながら,貯蔵終期において水溶性ペクチンの増加の傾向

が認められた.走査型電子顕微鏡によって組織を観察し

た結果,収穫直後に比べて,貯蔵28日後の細胞組織は

崩壊し,また,加熱によるデンプンの変化などをとらえ

ることができた.

Documents

Effect of Storage and Heat Treatments on the Sugar