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Storage Stability of Taro (Colocasia esculenta)
and Tannia (Xanthosoma Spp)

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presented by

Iloki, Ignace

 

 

 

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STORAGE STABILITY OF TARO (COLOCASIA ESCULENTA)

 

AND TANNIA (XANTHOSOMA SPP.)

 

BY

Ignace Iloki

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Food Science and Human Nutrition

1984

5/512

33‘!»

ABSTRACT

STORAGE STABILITY OF TARO (COLOCASIA ESCULENTA)

AND TANNIA (XANTHOSONA SPP.)

BY

Ignace Iloki

The purpose of this study was to develop fundamental
information concerning qualitative and quantitative
carbohydrate content in two trOpical tubers commonly consumed
in the People's Republic of The Congo (Congo Brazzaville)
and relate them to storage stability to assist in the
design of appropriate diets of the population.

Taro (Colocasia esculenta) and Tannia or ¥autia

 

(Xanthosoma E223) were stored at high and low temperatures
and 90-95% relative humidity for eight weeks and analyzed
for maltose, sucrose, glucose and fructose content by the
method develOped in our laboratory using High Performance
Liquid Chromatography (HPLC).

The amounts of glucose and fructose increased with
storage and both sugars were present in both tubers in
approximately equal amounts. Interrelationships were found
to exist beween shrinkage, decrease in moisture contents
and increase in glucose and fructose contents of Tannia

tuber.

Ignace Iloki

The extent of decay was also investigated. It was
observed that during storage Taro tubers were attacked
by various rots.

The results of this study also suggest that low
level quantitation of sugar (0.07%) in Tannia appears

promising by HPLC.

ACKNOWLEDGEMENTS

The author is greatly indebted to Dr. C. M. Stine for
his effective help, guidance and patience throughout the
course of this study and preparation of this THESIS and
graduate program.

Acknowledgement is given to Dr. J. R. Brunner, Departm
ment of Food Science, Dr. S. Thompson, Department of Food
Science, and M. L. Richmond, School of Packaging, for their
critical reading of this manuscript.

Appreciation is also extended to A. C. Cameron, Assistant
Professor of Horticulture for his particular concern and for
supplying the storage facilities used. To Dr. N. Z. Agbo,
Department of Biochemistry (University of Ivory Coast); Dr.

P. Markakis, Professor of Food Science; my brothers, C.
Iloki-Dimi, O. Iloki—Niamongui, my friends, M. Dzabatou-
Babeaux, A. Moyikoua, A. Molamou, my wife Nadala, my children,
Carry and Nachyr, for their wise advice and encouragement

in many ways.

To the Government of The People's Republic of The Congo
(Congo—Brazzaville) and to The African American Institute of
New York, the author is also indebted for the financial grant

which made this study possible.

ii

TABLE OF CONTENTS

Page

LIST OF TABLES I O O ........... O O O O O O O O O O O O O O O O O O O O O O O O O 0 iv

LIST OF FIGURES 0 O ..... O O O O O O O O O O O ...... O O O O O O O O O O O O O O O V
IIJTRODUCTIOIJO O I O O O O O O O O O O ..... O O O O O O O O O O O 0 O O O 0 O O ......
LITERATURE REVIEW. 0 O O O 0 O O O O O O O O O 0 O O O O O O O O O O O O O O O 0 O O O O 0
world PrOduction O O O O O I O O O O O O O O O O O O O O O I O O O O O O O O .1. O O O
comPOSition. O O O O O O O O O O O O O O I O O O O O C O O O O O I O O O O O O O O O O I O
Carbohydrates of Taro and Tannia or Yautia.........

StarCh—Sugar TranSfOImation......o................. ll
Storage....o......................o..o............. ll

meow oh I--'

meERIALS AND I'IETHODSOOOOCOOOOOOOOOOOOOOOOOOOOOIOOOOOO 14

Analysis of Extent of Decay of Taro and Tannia
Tubers............................................. 16
Moisture Determination............................. 17
Calculation........................................ 17
Sugars............................................. 17
Extraction Procedure............................. 17
Methods of Quantification... ....... .............. 19

RESULTS AND DISCUSSION ...... ............... ....... .... 21
Storage-.0000...0......OO..0OCOCOOOOOOOOOOOOOOOOOOO 21
Extent Of Decay. O I I C O O O O O O O O O O O O O O O O O O O O O O O C O O O O O C O 25
SproutingOOOOO00.0.00....00...O'COOOOOOOOOOOOOOOOOO 29
Moisture Analysis....... ..... .. ................... . 31

SUGARS....OOOOOOOOOOOOIOOOOOOOOO.QOOOOOOOOIOOOOOOOOOOO 34
Standard Chromatograms.. ..... ................ ...... 34
Glucose content. 0 O O O O O O O O O O O O O O O O O O I O I O O O O O O O O O O O O O 39
Fructose content. 0 O O O O O I O O O O O O O O I O O O O O O O O O O O ...... O 41
Sugar and Moisture Contents of Tannia ....... ....... 45

SUMMARY. 0 O O 0000000000000000000000000 O O O O O O O O O O O O O O O O O O 46

SUGGESTIONS ................................. .... ...... 47

BIBLIOGRAPHY .......................... . ........ ....... 48

iii

TABLES

Mean Annual Production Figures for Cocoyams for 2322
the 1965—1974 Period .......... ...................... 6
Recent Trends in World Production of Cocoyams ....... 7
Composition of Taro and Potatoes ............ . ..... .. 8
Composition of Yautia and Potatoes ....... ...........10
Moisture Content of Tannia after 3 Week Storage at
7.2°C (45°F), 10°C (50°F), 25°C (77°F) and 90-95%

RH ......... . ....... ..... ...... . ...... . .............. 32

Glucose content of Taro (Colocasia esculenta)

 

 

during storage at 4.4°C (40°F, 10°C (50°F), 20°C
(71°F), 25°C (77°F) and 30°C (86°F) and 90-95% RH...40

Glucose content of Tannia or Yautia (Xanthosoma

 

Sagittifolium) during storage at 7.20C (45°F), 10°C

 

(50°F), 15.6°C (60°F), and 25°C (77°F) and 90-95%
RH....... ..... .... ................ . ................. 40

Fructose content of Taro (Colocasia esculenta)

 

during storage at 4.4OC (40°F),10°C (50°F) 209C
(71°F), 25°C (77°F), and 30°C (86°F) and 90-95% RH..42

Fructose content of Tannia or Yautia (Xanthosoma

 

§E~> during storage at 7.2°c (45°F), 10°C (50°F),

15.6°C (60.0°F), and 25°C (77°F), and 90-95% RH ..... 42

iv

LIST OF FIGURES

Figure Page
1. Taro and Tannia Tubers ..... .......... ...... ... 15

2. Black discolorations of Taro developing under"
neath the skin ....... ............... .......... 26
3. Typical Sprouting of Taro tubers and Tannia
Tubers........................................ 30
4. Chromatogram of Aqueous Standard Containing

the following sugars: 1 - Sucrose, 2 - Maltose

3 - Glucose — 4 Fructose............. ........ 35
5. Typical Chromatograms of Taro. ............... 36
6. Typical Chromatograms of Tannia ..... ......... 37

INTRODUCTION

 

Taro (Colocosia esculenta) and Tannia or Yautia
(Xanthosoma sagittofolium) are among the staple food crops
consumed in the PeOple's Republic of Congo (Congo-Brazza-
ville) even though cassava remains the staple food which
enjoys high prestige among the basic foods in the Congolese
diets.

The average yearly consumption of roots and tubers per
capita in the Congo in 1975-1977 included 147 kg. of cassava,
72 kg. of cassava flour, 15.8 kg. of sweet potatoes and 14.5
kg. of other roots and tubers including Taro, Tannia or
Yautia (FAO, 1980).

In the district of Mossaka (Cuvette Congolaise), Maken-
engue and Libala are the areas most strongly associated with
dependence on Taro and Tannia for subsistence. Within the
district when families are running short of cassava, which is
the major staple subsistence food, during the annual flood
(November to March) Taro and Tannia or Yautia are emergency
foods.

Among Ndjems, the residents of the Sangha region, Taro
and Tannia have their greatest value when plantain and cassava
in the barn or in the field have been exhausted (Mendo, 1984).

Unlike cassava, potatoes and sweet potatoes, the import-

ance of which have been already recognized by Congolese

research institutions, Taro and Tannia, or Yautia, are still
neglected crops despite their importance in solving the
current shortage Congolese food supply.

In other parts of the world (Kay, 1973; Lambert, 1970;
Coursey, 1968) as well as in the Congo, tubers of Taro and
Tannia or Yautia are prepared like potato, sweet potato and
yam, diced, boiled, baked, roasted and are eaten with fish
or meat. In the District of Mossaka, they are usually either
cooked with fish or meat along with other cooked ingredients
such as peppers, oil, salt and onion or pounded and kneaded
into a dough and eaten with fish and meat. Young leaves are
prepared like spinach and are mixed with fish or meat during
cooking

The lack of transportation and storage facilities for
these commodities seems to be the major handicap for their
distribution throughout the country because they are likely
to rot before they reach the consumer or at best arrive in
an unattractive condition.

The experiment reported in this study deals with a
limited trial invoIVing storage of these root crops. The
purpose was to determine within the time constraints of
this work and the available facilities how long the products
tested can be successfully held in storage by means feasible
to both Congolese farmers and the government. The effects
of storage temperature and relative humidity on

--the extent of decay of Taro

--moisture content of Tannia and as well as on the
transformation of carbohydrates in Taro and Tannia
tubers were investigated.

Carbohydrate analyses were determined by High Perform-

ance Liquid Chromatography (HPLC).

LITERATURE‘REVIEW

 

The origin and the history of Taro (Colocasia) and

 

Tannia or Yautia (Xanthosoma) as well as the varieties of

 

the two crops have been extensively reviewed by Wang (1983),
Rodrigez-Sosa and Gonzalez (1977), Kay (1973) and Plucknett
(1970).

The origins of these tubers are placed by numerous
authors in India, West Indies and Tropical America (Gooding
and Campbell, 1961; Oyenuga, 1968; Chang, 1958; Catherinet,
1965). However, there are stories of African traditions
suggesting that these crops are indigenous to Africa. Nwana
and Onochie (1979) stated that stories of Nigerian traditions--
feasts and folklores are associated with the discovery of
these commodities as items of human food, implying that they
are indigenous to Nigeria.

When or how these crops came to the People's Republic of
Congo (Congo—Brazzaville) is not known. It is believed by
local farmers of the wet, swampy, river region of the District
of Mossaka that they are indigenous. They have a long history
of cultivation in the district where they have dominated the
diet of the population especially of the Makenengue and Libala
for many centuries (Iloki, 1984). In addition to that any
source of their introduction has not been found or documented.

It is well known that during the Fifteenth Century when the

Portuguese established a number of trading and missionary
posts along the coast of the Congo River, the only crOps
introduced in the People's Republic of Congo were corn and

Cassava (manioc).

WCrld Production:

 

It has been reported by Morton (1972) that the root

crOps Tannia or Yautia (Xanthosoma) are generally discussed

 

jointly with Taro (Colocasia esculenta) and this practice

 

tends to obscure the distinction between the two crops (Kay,
1973). In the literature on root crops the name "Cocoyams"
is applied to both Tannia and Taro and production figures
are no longer reported separately by FAO (Anonymous, 1978).
The production figures for Cocoyams in the 1965-1974
decade are summarized in Table 1. It can be seen that Africa
accounts for much of the world production of Cocoyams. The
data in Table 2 also reveal that the production of Taro and
Tannia or Yautia over the last 20 years has shown a continuous
increase in terms of area under cultivation and production.
Most of the Cocoyams (Taro and Tannia) produced in the
world today are consumed locally in the Congo, for example,
only small quantities are found in local markets. Therefore,
statistical information relating to both Taro and Tannia or
Yautia in the Congo is not readily available, even at Divinie

(Mossendjo) where they have recently emerged as a new plant of

commerce. World trade statistics indicate that almost no
international market exists; Saint Vincent Islands and Fiji
are among the few regions exporting these crops (Onwuene,

1978; Chandra, 1979; Kay, 1973).

Table 1. Mean Annual Production Figures for Cocoyams for
the 1965-1974 Period

 

Region Production % of World Production % of World Yield

 

 

or Area (1,000 Production (1,000 Production (kg hec-

Country hectares) . Area Tons) tare’l)
World 689 100 3831 100 5559
Africa 607 88 3061 80 5038
Asia 61 9 660 17 10794
Oceania l9 3 93 2 4925
Nigeria 281 41 1613 42 5769
Chana 129 19 1011 26 7813
Japan 39 6 534 14 13571
Ivory Coast168 24 ’ 176 5 1050
Papua New 15 2 86 2 5345
Guinea

 

From Onwuene (1978)

Table 2. Recent Trends in World Production of Cocoyams-

 

 

Production Area Yield
Year (1000 MT) (1000 hectares) (kg.hectare'l)
1962 3317 636 5213
1963 3426 603 5684
1964 3455 637 5421
1965 3465 643 5386
1966 3495 618 5656
1967 3656 669 5460
1968 3503 630 5557
1969 4033 731 5518
1970 3641 626 5815
1971 2961 720 5504
1972 4088 742 5508
1973 4252 786 5408
1974 4356 810 5377
1975 4502 816 ‘5520

 

Sources: Data from Food and Agriculture Organization of the
United Nations Production Yearbook, 1973 (Rome, 1974); and
Food and Agriculture Organization of the United Nations
Production Yearbook, 1975 (Rome, 1976).

Composition

 

The composition of Taro and Tannia or Yautia have been
reported by various investigators (De la Pena, 1970; Coursey,
1969; MacCaughey, 1917; Miller 1927 and Bell and Favier, 1979).

Results of Taro analyses as well as of comparable food
plants were compiled by Chatfield and Adams (1913) (Table 3).
The data in Table 4 show the composition of the two varieties
of Yautia or Tannia reported by Barret (1905) and include for
purposes of comparison the chemical composition of irish
potato and common sweet potato.

The Taro and Yautia (Tannia) do not differ greatly in
composition from potatoes (Coursey, 1968); Barret, 1910) but
it is significant to point out that the content of carbohy—
drate is of great importance. Taro and Tannia or Yautia
contain a considerably larger amount of sugar than irish
potato. Young (1924a) states that the sugar content of the
Dasheen (Taros) is 1.75 percent, which accounts for the
noticeably sweeter taste of this vegetable.

Table 3. Composition of Taro and Potatoes

 

Vr

 

 

Taro Water Pro- Fat ASH Carbohydrate Starch Fuel
and % tein % Total Fiber Sugar Value
Potatoes (NX by Per
6.25 differ— Pound
% ence in- (Cal-
cluding cries)
fiber
Taro 75.1 2.0 .2 1.17 21.5 .8 1.42 18.2 435
S. Pot. 68.5 1.8 .7 1.55 16.3 1.00 5.35 20.2 565
Potato 77.8 2.0 .1 .99 19.1 .4 .87 14.7 385

 

From Chatfield and Adams (1913).

Carbohydrates of Taro and Tannia or Yautia.

 

The data in Tables.3and 4 show clearly that carbo-
hydrates and polysaccarides constitute the chief nutrient
material of these two root crops.

The composition of the carbohydrate fraction of Taro

(Anon, 1933) is:

%
Starch 77.91
Pentosans 2.58
Crude Fiber 1.42
Dextrin 0.52
"Reducing sugars" 0.52
Sucrose 0.11

Amin (1955) reported that the starch of Taro tubers contains
28% of amylose which has 490 glucose units per molecule while
the amylopectin has 22 glucose units per molecule. He con-
cluded that these results were similar to those for potato
starch. Murray (1977) and Onwuene (1978) have reported that
the diameter of the Taro starch grain ranges from 1 to 4 uM,
implying that the starch granules are easily digestible.
Previous works on the hydrolysis of the mucilages of
Taro have indicated that 8 sugars and their derivatives were
identified including glucosamine, galactose, glucose, sorbose,
arabinose, ribose, rhamnose and glucolactose (Amin, 1955;

Wang, 1983).

Table 4. Composition of Yautias and Potatoes

 

 

 

Total

Carbohydrates Fuel
Yautia Sugar, Crude Value per
and Water Protein Fat Starch, Fiber Ash Pound
Potatoes (%) (%) (%) etc. (%) (%) (Calories)
White
Yautia 70.0 1.7 0.2 26.3 0.6 1.2 529
Yellow
Yautia 70.1 2.5 .2 26.1 .6 .6 538
Irish
Potato 78.3 2.2 .1 18.0 .4 1.0 385
Sweet
Potato 69.0 1.8 .7 26.1 _1.3 1.1 570

 

From D. W. Barret (1905).

Studies carried out by Treche and Guion (1979) reveal

that the carbohydrate fraction of Tannia or Yautia is made

of
Starch 80.2 - 86.3%
Soluble Sugar 0.9 - 2.6%
Pentosans 0.4 - 0.5%

Onwuene (1978) and Barret (1910) state that the carbo-
hydrates present in Tannia or Yautia consist mostly of
starch.Onwuene (1978) mentions also that the starch has
relatively large grains with average diameter of 17 - 20
pM. He concluded that Tannia or Yautia would be expected

to be less readily digested than Taro.

10

StarCheSugarFTransformation

The levels of reducing sugars in young Taro plants are
higher than those of nonreducing sugars (Wang, 1983). In
their study, Hashad, et al. (1956a, 1956b) have indicated,
a reversal of this relationship as the plants age. They
reported that on storage, sugar content (reducing, nonreduc—
ing and totals) increases for 10 to 15 weeks and then may
drop or continue to rise. Hirshi and Balagopal (1979) have
observed a gradual reduction in starch and an increase in
total sugar with appreciable reduction in moisture. Results
reported by Sanches-Nieva and Hernandes (1977) have shown
that during storage, Tannia (Yautia) tubers showed no change
in total or reducing sugar even though starch content dropped
from 28.2 to 16.1 percent. They also observed a marked

decrease in moisture content under these conditions.

Storage

The storage of Taro and Tannia(Yautia) has not received
adequate attention despite the fact that such studies benefit
both the producer and consumer by improving availability of
the tubers to consumers throughout the year.

flooding and Campbell (1961) and Rodrigez-Sosa and
Gonzalez (1977) noted that very little information was present
in the literature on storage stability of Tannia and that
no methods had been developed for storing Tannia for extended

periods. However, Rodrigez-Sora and Gonzalez (1977) claimed

11

Tannia could be stored satisfactorily for several weeks at
ambient conditions. Barret (1910), Coursey (1968), and
Catherinet (1965) pointed out the roots of high quality Taro
and Tannia resist decay fairly well if kept dry after harvest.
Small packages of tubers could be kept six months in a dry
atmosphere without losing much of their vitality.

Experiments in Trinidad have shown that Tannia of good
keeping qualities can be kept on wire racks in dry, well vent-
ilated storage at an average temperature of 79°F and humidity
for 79% for 9 weeks. In refrigerated storage at 45°F with 80
percent relative humidity, they will remain in good condition
for 18 weeks or more (Gooding and Campbell, 1961).

Storage facilities are often inadequate or nonexistent

in producing areas such as Nigeria, the Pacific Islands,
Asia, Egypt, Ghana, Congo, Cameroon (Wang, 1983; Karikari,
1979; Warid, 1970; Praquin and Miche, 1971). In some of these
countries, Tannia and Taro are often left in the field unhar-
vested until needed. After harvesting, farms may bury the
cormels in the ground with occasional watering. Under such
conditions, they store longer and are less susceptible to
dehydration before they are removed for consumption (Karikari,
1971; Iloki—Niamongui, 1984). Pit storage in which high
humidity is maintained is also traditionally used in Nigeria.
(Okeke, 1976; Nwana and Onochie, 1979).

More detailed investigations on storage losses of Taro

and Tannia have been made more recently by Gollifer and Booth

12

(1973); Posnette (1945); Praquin and Miche (1971) and Okeke
(1976). Such losses are due primarily to disease, dry and
soft rots, fungal or viral infection. Dehydration and

sprouting also contribute to loss in storage. Karikari (1971)

has also mentioned that cuts and bruises during harvesting

encourage early rotting during storage.

13

MATERIALS AND i-IL‘THODS

 

Taro (Colocosia esculenta,L Schott) and Yautia or

 

Tannia (Xanthosoma sagittifolium,L Schott) used in this study

 

were obtained from the local market (Fig. 1). They were de-
livered in nylon mesh bags to the Horticulture and Food
Science Departments.

Upon arrival Taros were stored at 20°C (70°F) and 57
percent relative humidity and Yautia at 4.4°C (40°F) and 90-95
percent relative humidity (RH) for three days respectively
after being aired for about 2 hours.

Three tubers of each cultivar were immediately selected
at random for duplicate extracts used for fructose, glucose,
sucrose and maltose determinations by the method developed in
our laboratory using High Performance Liquid Chromatography
(HPLC).

The remaining tubers of the two cultivars were separated'
into as many groups as there were storage conditions. The
tubers were graded so there were in each group tubers of equi-
valent size distribution.

Taro tubers were maintained at 4.4°C (40°F), 10°C(500F),300(85fi?)
and 25°C (77°F) and about 95 percent and 92 percent RH respect-
ively and at 20°C (71°F) and about 57 percent RH. Taro tubers
stored at 4.4°C (40°F), 25°C (77°F) and 20°C (71°F) were

wrapped in individual paper bags whereas the ones at 10°C

14

 

1 Taro Tubers

Fig.

 

Tannia Tubers

1

Fig.

15

(50°F) and about 95 percent RH in nylon mesh bags.

Yautia or Tannia tubers maintained at 7.2 (45°F),
10°C (50°F) and 15.6°C (60°F) and about 95 percent RH were
stored in nylon mesh bags and those held at 25°C (77°F) and
about 92 percent RH wrapped as stated above.

In order to reduce high rate of fungal infections ob—
served on Taros held at 30°C and 25°C and to extend the
storage life of tubers two times during the two first weeks
of the storage, tubers were brushed, washed with a very dilute
detergent solution, rinsed with tap water, wiped with clean
paper towel, air-dried for less than 30 minutes and wrapped
in individual paper bags. The above treatment was carried
out a day after sampling.

While in storage Taro tubers were examined from time to
time and each'iot was freed of spoiled roots in order to prevent

spread of infection in the stored tubers.

Analysis of Extent of Decay‘of Taro and Tannia Tubers

 

Tubers of Taro with any soft spots were removed and
analyzed for the extent of decay. Cross sections of tubers
were made in order to provide an analysis of the color of
diseased tissues, starting points of decaying tissues and
location of mold growth. Similar observations were made on
Tannia tubers. No attempts were made to determine the causal
factors of deCay which have been widely reviewed by Gollifer

and Booth (1973) and Posnette (1945).

16

Moisture Determination

 

The percentage moisture of Tannia at 25°C (77°F)
10°C (50°F) and 7.6°C (45°F) and 90-95 percent RH was deter-
mined in duplicate. An accurately weighed 2 g sample of
Tannia was dried for 24 hours in a vacuum oven at 70°C to
80°C, removed and cooled in a dessicator for about 30 minutes
and weighed into an analytical balance. The loss in weight

was calculated and reported as percent moisture.

Calculations

 

Sample weight (gm) - dry weight, gm x 100
sample weight, gm

 

% moisture:

Sugars

Extraction Procedure

 

Transverse thin slices were cut from the center of the
tube and diced into small cubes. A 5.0 9 sample was immed-
iately weighed on a tOp loading METTLER balance into a clean
preweighed plastic container containing 20 m1 of hot (70°C)
95 percent ethanol (EtOH) to yield a final alcohol concentra-
tion of 80 percent. The sample was blended in a Waring
blender for one to two minutes. The slurry was transferred
quantitively into a plastic centrifuge tube. The centrifuge
tube was stoppered and the slurry shaken with wrist action
shaker for 15 minutes and centrifuged at 3,000 rpm for 5 min.

The supernatant was decanted and transferred into another

17

plastic centrifuge tube. The residue was homogenized,
diluted with 10 ml of 80 percent ethanol, shaken (to assure
quantitative extraction), centrifuged, and the supernatant
liquid decanted and transferred as above. Clarification of
samples was carried out using a modification of the method of
Agbo (1982) and taking into account observations made by
Triebold .and Aurand (1963).

The first step of sample clarification was performed
by treating the extract with 1 m1 lead acetate (10 percent
w/v). The sample was thoroughly mixed for 5 to 10 seconds
and centrifuged at 3,000 rpm for 3 min to precipitate protein
materials. The supernatant was then deleaded with 1 m1 of
oxalic acid 10% w/v thoroughly mixed for 5 to 10 seconds
centrifuged as above and decanted. (If visual observation
of the extract after centrifugation revealed a cloudy appear-
ance, 0.5 ml of lead acetate was added to the extract which
was thoroughly mixed for 5 to 10 seconds and centrifuged as
above.)

Since at each storage temperature three tubers were
analyzed in duplicate, six final extracts, were obtained.
Then two representative samples were obtained by combining
one extract from each of the three tubers.

The combined extracts were filtered through S. & S.
filter paper (Schleicher & Schuell Co., Keene, New Hampshire)
into a 100 m1 volumetric flask, thoroughly mixed and made
to mark with 80 percent EtOH.

A 25.0 ml aliquot of each diluted solution was

18

pipeted into a round bottom flask, reduced to dryness on a
rotary evaporator at <1 mm Hg pressure, transferred to a
10 m1 volumetric flask with distilled water, made to mark
and filtered through a Waters Sep-Pak C18 cartridge.
Finally both water clear and reddish extract samples from

Tannia and Taro respectively were analyzed by HPLC.

Chromatography Equipment

 

The chromatography equipment used in this study
consisted of a Waters M-45 solvent delivery system, a U6K
Septumless injector, and a model RI-401 differential refracto-
meter, and a model 730 Data Module. The column was a Bio-Rad
Aminex Carbohydrate HPX-87 Column (300 mm x 7.8 mm) main-
tained at 80°C by a 30 cm Alltech Associates water jacket
(Cat #9502) and a Haake Model L. thermoregulated, circulating
water bath. A Bio-Rad Laboratories Aminex A-25 (40 mm x 4.6'
mm) Microguard Anion/OH cartridge (Cat #125-0130) was used
as a guardcolumn to remove unwanted anions and to prolong
analytical column life. The eluting fluid was water purified
by reverse osmosis followed by monobed ion exchange and
vacuum degassing. The purified water was stored at 50°C to
minimize resorption of oxygen. A Hamilton 50 pl syringe was

used to inject 30 pl sample volumes.

Methods of Quantitation

 

External standard and repetitive injection techniques
(Waters Associates, 1981) were used. They consisted of:

First, preparing aqueous standards of individual analytical

19

grade sugars (maltose, sucrose, glucose and fructose) of
known amount. Second, injection of individual sugars separate—
ly to determine the retention times of each sugar; third,
a sample of mixed standard solutions were then chromatographed;
fourth, the retention times as well as the known amount (con-
centration) of the sugars were put in calibration into the
computer Data Module according to the technique of Waters
Associates (1981); fifth, the unknown samples injected onto
the HPLC column were then quantitated by comparison with the
standard sugars put in calibration previously.

The percentage of the individual sugars extracted from
the Taro and Tannia used in this study were calculated

according to the following formula:

% sugar - amount shown on data module mg/ml x 0.266
or
% sugar = amount on data module mg/ml x

10 m1 x 100 m1
, mg x m

X 100

Where
- 15,000 mg (5,000 mg x 3) is the sample weight
resulted by combining one extract of each of the three
tubers (see sugars - Extraction procedure).
- 100 ml is the first dilution volume.
- 25 m1 is the volume of aliquot of the diluted
solution reduced to complete dryness.

- 10 m1 is the second dilution volume.

20

RESULTS AND DISCUSSION

 

Storage

Within the time limitations of this study, it has been
found that Taros stored at 20°C (71°F) and 57 percent RH
dehydrated and decayed within three weeks even though the
skin remained intact. Those maintained at 25°C (77°F) lasted
6 weeks and the tubers stored at 30°C (86°F), 4 weeks.
Sprouting occurred at 25°C (77°F) after four weeks storage
but did not occur at either 30°C (86°F) or 10°C (50°F). At
90-95 percent RH tubers held at 30°C (86°F) decayed faster
than those stored at 25°C (77°F). At either temperature
larger tubers decayed faster than smaller ones. The rate of
decay was slower at 10°C (50°F) than at 25°C (77°F) and
30°C (86°F), respectively.

Yautia or Tannia tubers kept well for 8 weeks at 7.2°C
(45°F) and 25°C (77°F) and 90-95 percent RH respectively.
The tubers maintained at 10°C (50°F) and 15.6°C (60°F) began
to shrink after 3 weeks storage and were completely dried
out after 5 weeks storage. Tannia tubers stored at 25°C
(77°F) sprouted after 6 weeks storage; those maintained at
10°C (50°F) 15.6°C (60°F) and 7.2°C (45°F) did not sprout.

The storage tests of Taros and Yautia or Tannia have

21

been reported by Okeke (1976); De la Pena (1970); Gooding
and Campbell (1961); and Baybay (1922).

Onwuene (1978) stated that Taro and Tannia can best
be stored in cool, dry, well—ventilated surroundings. The
best temperature for prolonged storage is about 7°C at 85%
RH. Under these conditions Yautia or Tannia in Trinidad,
Kay, 1973) and Taro in Egypt (Hashad, et al., 1956) did not
deteriorate in storage over 3.5 months. Similar results
were found in storage tests carried out during this study
where Yautia or Tannia tubers maintained at 7.6°C (45° F)
and about 95% RH were stored well for 8 months while those
stored at 15.6°C (60°F) and 10°C (50°F) lasted only 5 weeks.
It is interesting to mention that the storage conditions
prevailing in this study differed somewhat from those
reported by Kay (1973) and Onwuene (1978) in regard to Tannia
or Yauta storage.

The results of this study also indicate that Tannia
stored at 25°C (77°F)’ and about 92% RH lasted as long as
the ones maintained at 7.2°C (45°F) and about 95% RH.
However, Tannia stored at 7.2°C (45°F) started to decay
after 7 weeks. The above two storage conditions when consid-
ered together, seem to refute a direct relationship between
temperature and relative humidity. However, comparing the

Tannia (Yautia) maintained at 7.2°C (45°F) and those at

15.6°C (50°F) and 10°C (50°F) and about 95% RH on the

22

one hand and the Taro stored at 4.4°C (40°F), 10°C (50°F),

25°C (77°F) and 30°C (86°F) and 92-95% RH on the other hand,

it becomes apparent that the higher the temperature the shorter
the storage. This is in agreement with the observations

made by Onwuene (1978) who mentioned that higher temperatures
are not satisfactory for long storage.

At the same storage conditions it was difficult to in—
dicate which of the two roots exhibited better keeping
quality. However, it was apparent Tannia tubers did not
decay at 25°C (77°F) and about 92% RH and lasted longer than
Taro tubers. The reverse was found at 10°C (50°F) and 95%
relative humidity. However, both tubers kept well for six
weeks at 4.4°C (40°F).

These findings are in total disagreement with investi-
gations reported by De la Cruz (1970) who mentioned that
Taro (Colocasia)doesrmn:keep well after harvesting and will
usually keep for about two weeks if stored in a cool, well-
ventilated and shady place. Results of this study tend to
support those published by Gooding and Campbell (1961) which
indicate that cold storage can considerably assist in length-
ening the availability of Tannias for market and certain
clones can be kept under normal conditions at least two
months.

Taro tubers held at 25°C (77°F) and about 92% RH under-
went the shortest period of storing (5 weeks) compared to

Tannia tubers (8 weeks). This could be explained by the

23

drop in temperature from 25°C (77°C) to 5°C (41°F) which
occurred after the 5th week of Taro storage and which lasted
about 36 hours followed by a subsequent increase of temper-
ature from 5°C (41°F)' to 25°C (77°F)-. This fluctuation
of temperatures had certainly a damaging effect on Taro
tissues and this was immediately followed by a rapid decay.

This supposition is supported by previous works
(Uritani, 1978; Lyons, 1973; Young, 1924b) which reveal that
in tropical and subtropical plants, the tissues after harvest
suffer from chilling injury during cold storage. Such chill-
ing injury in storage causes cytological and metabolic a1-
terations and when cold stored tissues are transferred to a
normal temperature room, some secondary metabolites are
accumulated and the tissues are easily attacked by some sap-
rophytic microorganisms (Ogata, 1977). Young (1924a) stated
that the Dasheens (Taros) appear to be able to withstand
short exposure to lower temperatures, even near freezing, but
prolonged exposure to a temperature of 5°C (41°50 result
in death and consequent decay.

The results of these storage tests have shown that
when a higher temperature is chosen for storage of Tannia
and Taro corms, it should be recognized that the storage

life will be correspondingly shortened.

24

Extent of Decay

 

The results have indicated that at any time of storage,
tubers of Taro were attacked by various rots. The softening
of the tubers was mainly observed as a result of extensive
mold growth either through bruises or the skin. The cross-
section of Taro tubers showed that the boundary between
diseased and healthy tissues was clearly defined. The color
of the diseased tubers ranged from charcoal black, cream
brownish to crumbly gray. Cross-sections of Taros maintained
at 20°C revealed a spongy, cheesy and chalky, dry consistency
with advanced darkening of the tissues.

At either storage temperature, the tissues had a cooked
appearance. Ring types of rots were also observed and were
likely to occur at random. Colors of ring rots ranged from
grayish brown to dark. Soft rots seemed to spread through
rings. They started either at one end and proceeded toward
the opposite end or from the skin toward the center. Black
discolorations developed underneath the skin and progressed
toward the center. (Fig. 2)

Cut sections of Tannias revealed that the firmness of
tubers maintained at 7.2°C (45°F) and at 4.4°C(40°F) did not
always indicate the presence of healthy tissue. Decay some-
times started underneath the skin and spread longitudinally
through the tuber.

It has been reported by previous workers (Hashad et

al.,1956; Gollifer and Booth, 1973; Posnette, 1945),that

25

 

Fig. 2. Black discolorations of Taro developing
underneath the skin.

 

26

when the terminal buds sprout or the corms of Taro and
Tannia begin to deteriorate, storage is no longer effective.

Gollifer and Booth (1973) mentioned that storage rots
of Taro corms in the Solomon Islands prevent storage for
longer than 1-2 weeks. In this study it was found that ;.
corms of Taro maintained at 30°C (8601?) and 25°C (77°F0
were badly rotted during the two first weeks of storage. The
storage tests conducted by Gollifer (1970) showed that most
corms developed unidentified rots after a two-week period at
ambient temperatures and humidities. His observations con-
firm the results of our study which indicate that the treat-
ment given to Taro tubers in the early days of this study
had possibly extended the storage life of these commodities
to 4 weeks and 6 weeks respectively. It was also reported
(Anonymous, 1978) that no rot occurred at low humidity. This
report does not agree with the results of our study where it
had been observed that Taro tubers stored at 20°C and about
57% RH decayed within 3 weeks even though they were apparent-
ly intact.

The rots of Taro and Tannia are reported as being of

three types: Dry rot caused by Fusarium solani; spongy black

 

rot, caused by Botgyodiplodia theobromae; and a Sclerotium

 

 

rot due to S. rolfsii. Under humid conditions all three
fungi could penetrate and rot undamaged corms, although most
natural infection is thought to occur through wounds. (Okeke,

1976; Jackson and Gollifer, 1975; Gollifer and Booth, 1973).

The color of the diseased tubers revealed by visual observations

27

of the cross section of tubers carried out during this study
was probably caused by these fungi. (Fig. 2)

The charcoal rot as well as Sclerotium rot disease of
"Cocoyams" (which includes both Tannia and Taro) are of
major economic importance to Nigeria (Okeke, 1976) where
losses in storage may mount to 50 percent. This explains
why these diseases have become a limiting factor not only to
satisfactory storage but also to the maintenance in many
warm regions, such as in the Congo where Tannia and Taro are
grown. The soft rot observed during this study has been
reported by Posnette (1945), and Alvarez-Garcia and Cortes-
Monllor (1971). It is due to the genus Erwinia.

Results of this experiment revealed that decay was
favored by both high temperature and relative humidity. But
it was also apparent that antifungal treatment, as well as
cold storage, could possibly extend the storage of Taro and
Tannia. The use of fungicides against post harvest decay in
stored Taro has been shown by Jackson, et a1. (1979) to sub-
stantially reduce rots caused by phycomycetous fungi (Phytoph-

thora colocasia and _ Pythium splendes in the early days of

 

 

storage. But by 10 days most corms had become infected by

B. theobromae, and at 20 days they were completely decayed.

 

Young (1924a) reported that prolonged exposure of Taros
(Dasheens) to a temperature of 5°C (41°F) resulted in
deathand consequently decay in periods as long as six weeks

to two months. Taros stored at 4.4°C (40°F), in our

28

laboratory lasted six weeks before decay was noticeable.
Whereas, Tannia maintained at 4.4°C (40°F), and 7.2°C
(45°F) respectively started to decay after 7 weeks. In both
cases decay was favored by prolonged storage.

All the above observations suggest the need for a sur-
vey to ascertain the seriousness and extent of damage done

by these diseases.

Sprouting

 

The post harvest losses of Tannia and Taro appear
similar to that of Irish potatoes, except for the sensitivity
of Tannia and Taro to cold temperatures. There is little
quantitative information on post-harvest losses on storage
of Taro and Tannia due to sprouting.

However, in their trials in storage of Taro and Tannia,
Praquin and Miche (1971) reported that when sprouting occurs
soon after harvest, over 50 percent loss was observed after
2 months and 95 percent after 5 months. Borgstrom (1968)
states that these losses are not always readily apparent and
are difficult to assess as to their consequence. He mentions
that cooling is the chief measure against this kind of stor-
age loss.

It was found during this study that Taro and Tannia
maintained at higher temperature 25°C} (77°EU sprouted and

none of the tubers stored at lower temperatures 10°C (SOOIU'

29

 

Fig. 3. Typical sprouting of Taro tubers

 

Fig. 3. Typical sprouting of Tannia tubers.

30

7.2°C (45°F) and 4.4°C (40°F) respectively Sprouted
during the same period. (Fig. 3). Similar results were
obtained by Anonymous (1978) on potatoes,and Gooding and
Campbell (1961) on Tannia. They reported that refrigerated
storage inhibits sprouting.

Results of this experiment also suggest that cold

proved to be preferable for long storage periods.

 

Moisture Analysis

Moisture determinations were made on Tannia samples
maintained at three different storage temperatures: 25°C
(77°F), 10°C (50°F) and 7.2°C (45°F) respectively to observe
if a correlation could be made with the change in sugar con?
tent.

Based upon the results summarized in Table 5, it appears
that the moisture content for all samples was at a maximum
initially then began to decrease. Further analysis of the
results indicate that the loss of moisture was higher in
Tannia stored at 10°C (50°F) than in those maintained at
25°C (77°F) and 7.2°C (45°F), respectively. A marked de-
crease in moisture content was observed mostly between the
2nd and 3rd week of storage for tubers stored at 25°C
(77°F) and 10°C (50°F),respectively, where 6.2 to 9.2% loss
in moisture was recorded. Results also suggest that moisture
content of tubers maintained at 7.2°C (45°F) seems to

decrease at a rate of about 2% every week.

31

Table 5. Moisture content of Tannia after 3 week storage at
7.2°C (45°F), 10°C (50°F), 25°C (77°F) and 90-

 

 

 

95% RH
Weeks of o o %OMoistgre o o
St°rage . 7-2 C (45 F) 10 c (50 F) 25 c (71 F)
0 70-0* 70.0* 70.0*
1 69.4 68.3 68.1
2 67.1 65.2 55,8
3. . .65-°_. 161.8 f 63.8

.....

 

*Initial Moisture content.

Even .though moisture determinations were conducted on
Tannia to find out if a correlation could be made with
changes occurring in the sugars, in our study it was observed
that Tannia tubers stored at 10°C (50°F) lost moisture faster
than those maintained at 25°C (77°F). This observation is
also supported by the storage tests which revealed that Tannia
tubers maintained at 10°C (50°F) as well as those held at
15.6°C (60°F) began to shrink after 3 weeks and were completely
dried out after 5 weeks storage. The relationship between
the shrinkage and the decrease in moisture content was clearly
established. It appears from results summarized in Table 5
that the marked decrease in moisture content of about 9.2% was
noticed between the second and 3rd week of storage when the
shrinkage of tubers began to occur.

Further analysis of these results suggest that roots

of tubers maintained at 10°C (50°F) as well as at 15.6°C

32

(60° F) had probably developed high respiration rates and that

the variety used in this study was possibly susceptible to
low temperatures. This supposition is supported by data
published by Lewis and Morris (1956) who reported that the
respiration rate of sweet potatoes increased during chilling.
In their respiration studies on Russet Burbank potato tubers
Boe et al., (1974) have reported that storage at 48° F (8.9° C)
gave low respiration rates early in the storage season equiv—
alent to those of tubers at 42° F (5.6° C) and 45° F (7.2° C).
A gradual increase occurred and the CO2 evolution reached
levels several times greater than tubers stored at 42° F

(5.6° C) and 45° F (7.2° C).

The great loss in moisture noticed at 10° C (50° F) is
an anomaly when compared to the moisture loss at higher
temperature and suggest a metabolic breakdown. This break-
down was probably accompanied by the shrinkage and finally by
the drying out of the tubers.

Further study is needed to determine the exact physio-
logical causes for this low temperature reaction in Tannia

tubers.

33

SUGARS

Standard Chromatggrams

 

Initially aqueous standards of individual sugars were
chromatographed separately to determine the retention times
of each sugar. Mixtures of aqueous sugars were then chroma-
tographed.

An aqueous standard Chromatogram containing a mixture
of sugars is illustrated in Fig. 4. Typical Chromatograms
of Taro and Tannia (same chromatographic conditions as
Fig. 4), are also illustrated in Fig. 5 and Fig. 6.

These Chromatograms show that under conditions of this
study maltose and sucrose co-eluted, making the quantitation
of these disaccharides impossible. Changing the chromato—
graphic conditions of this study by either slowing the flow
rate or using a ternary solvent system such as acetonitrile/
water/ethanol should probably provide an acceptable resolution
of these two disaccharides.

The effects of changing (slowing) the flow rate of
eluent on the resolution of carbohydrates in dairy products
for Aminex HPX-87 resin have been reported by Richmond, et a1.
(1982). In their study they found that sucrose and lactose
co—eluted when water purified by reverse osmosis followed
by ion exchange was used as eluent. By slowing the flow

rate, they were able to resolve sucrose and lactose. Within

34

[,2

 

 

 

 

5 3 IO 20
TIME UWN)

Fig. 4. Chromatogram of an aqueous standard contain-
ing the following sugars: 1. Sucrose, 2. Maltose,

3. Glucose, 4. Fructose. Chromatographic conditions:
Bio-Rad HPX-87, Carbohydrate column (80°C), Aminex A-25
Micro-guard Anion/OH cartridge, solvent H 0; flow rate

.7 ml/min injection volume 30 ul/min, injgction volume
30 ul, attenuation 4X.

35

3n?

 

 

 

 

 

 

 

 

l [.2 7 U L~—

l I A

1 L__L L A
0 5 I 0 l7 0 5 IO /7
TIME (MIN) TIME (MW)

 

Fig. 5. Typical Chromatograms of Taro (Colocasia exculenta
at 25°C (left) and at 44°C (rightk Containing: 1. Unknown,
2. Unknown, 3. Sucrose, 4. Maltose, 5. Glucose, 6. Fructose,
7. Unknown. Same chromatographic conditions as Fig. 4.

36

 

 

 

5 3 fo 7? 5 5 i0 17
TIME (Ml/V) TIME (MIN )

Typical Chromatograms of Tannia (Xanthosoma S22.)
1. Unknown,

7. Unknown..

Fig. 6.
at (left) and at 15.6°C (right).containing:

2. Sucrose, 4. Maltose, 5. Glucose, 6. Fructose,
Same chromatographic conditions as Fig. 4.

37

the time limitations of this work, no attempt was made

to resolve sucrose and maltose. Further studies are needed

in order to maximize the resolution of these two disaccharides
by changing other chromatographic conditions while maintain-
ing column temperature at 80°C. Although it is recommended
(Anon, 1979) that the Aminex HPX—87 carbohydrate column be
Operated at 85°C, Richmond, et a1. (1982) reported that there
was little improvement from increasing column temperature from
80 to 85°C. They also indicated that operating at 80°C
shortened start-up time and also may relieve stress on the

system operated over long times.

38

Glucose Content

 

Results of glucose analysis by HPLC of Taro (Colocasia

 

esculenta) and Tannia or Yautia (Xanthosoma sagittifolium)

 

 

are summarized in Tables 6 and 7 respectively.

Based upon the results given in Table 6, it appears
that in Taro corms stored at 4.4°C (40°F)~ glucose decreased
gradually at a rate of about 0.01% during the two first weeks
of storage and finally increased again at a rate of about
0.03% during the three last weeks of storage.

Glucose content of Taro corms maintained at 10°C
(50°F) and 25°C (77°F) respectively increased during storage
even though glucose content of Taro corms stored at 10°C,
(50°F) started to decrease after the 5th week of storage.

There was no significant increase in glucose in Taro
corms maintained at 30°C (86°F), during the first three weeks
of storage even though there was an increase of sugar of
about 9.02% between the third and 4th week of storage.

Further analysis of data reveals that there was a con-
tinuous decrease of sugar at a rate of about 0.01% every week
in Taro corms stored at 20° C (77°F).

Data summarized in Table 7 show that at either temper-
ature of glucose content in Tannia or Yautia corms increased
during storage. Glucose content seemed to increase at a rate
of about 0.01% every week in Tannia stored at 10°C (50°F)
and 15.60 C (60°F),_ respectively, and at a rate of about 0.01%
to 0.04% weekly in Tannia maintained at 7.20 (45°F) and 25°C

(77°F),, respectively.

39

 

 

 

 

Table 6. Glucose content of Taro (Colocasia Esculenta)
during storage at 4.4°C (40°F), 10°C (50°F), 20°C
(71°F), 25°C (77°F) and 30°C (86°F) and 90-95% RH.
% Glucose
Week 4.4°C 10°C 20°C 25°C 30°C
0 0.19 0.19 0.19 0.19 0.19
l 0.18 0.50 0.25 0.20 0.31
2 0.17 0.51 0.24 0.24 0.31
3 0.26 0.47 0.23 0.12 0.31
4 0.33 0.57 * 0.30 0.33
5 0.36 0.72 * 0.32 *
6 0.39 0.48 * 0.35 *

 

*Analysis terminated because of spoilage

Table 7. Glucose content of Tannia or Yautia (Xanthosoma
Sagittifolium) during storage at 7.2°CTYES5F), 10°C
(50°F), 15.6°C (60°F), and 25°C (77°F) and 90-95% RH.

 

 

% Glucose

 

vv

 

Week 7.2°C 10°C 15.6°C 25°C
0 0.07 0.07 0.07 0.07
1 0.13 0.11 0.08 0.13
2 0/13 0.12 0.10 0.13
3 0.22 0.13 0.11 0.16
4 0.16 0.14 0.12 0.17
5 0.16 0.12 0.20 0.15
6 0.19 * * 0.22
7 0.23 * * 0.25
8 0.24 * * 0.26

 

*Analysis terminated because of spoilage.

40

Fructose Content

 

Results of fructose analysis by HPLC of Taro (Colocasia

Esculenta) and Tannia of Yautia (Xanthosoma sagittofolium

 

 

are given in Tables 8 and 9 respectively.

It is clear from Table 8 that fructose content increased
during storage in tubers maintained at 44°C (40°F), 10°C
(50°F), 20°C (71°F) and 25°C (77°F), respectively. These
results also show that fructose content of corms stored at
44°C (40°F) and 25°C (77°F), respectively, had doubled during
storage from 0.17% to about 0.34 - 0.36%. Whereas, an in-
crease of fructose content of 0.68% was observed in Taro
maintained at 10°C (50°F). Further analysis of the data
indicate that fructose content of Taro held at 30°C (86°F)
increased at first from 0.17% to 0.35% and finally started to
decrease at a rate of about 0.02% to 0.16%.

The data in Table 9 indicate that fructose content of
Tannia maintained at 7.2°C (45°F), 10°C (50°F) and 15.6°C
(60°F) respectively,increased during storage. Further analy-
sis of these results reveal that during the first 6 weeks of
storage at 25°C (77°F) fructose seemed to accumulate most
rapidly and upon prolonged storage, it started to decrease.
Results summarized in Table 9 also show that after 4 weeks
storage, a marked increase of fructose concentration of about

0.20% was observed in Tannia maintained at 15.6°C (60°F).

41

 

 

 

 

 

 

 

 

Table 8. Fructose content of Taro (Colocasia esculenta)
during storage at 4.4°C (40UFT_I05C’T505FTT—20°C
(71°F), 25°C (77°F), and 30°C (86°F) and 90—95% RH.

% Fructose

Week 4.4°C 10°C 20°C 25°C 30°C
0 0.17 0.17 0.17 0.17 0.17
l 0.20 0.48 0.13 0.30 0.35
2 0.21 0.48 0.20 0.27 0.33
3 0.31 0.48 0.26 0.27 0.18
4 0.31 0.63 * 0.27 0.18
5 0.32 0.80 * 0.33 *
6 0.36 0.84 * 0.34 *

*Analysis terminated because of spoilage.

Table 9. Fructose content of Tannia or Yautia (Xanthosoma
§2i1 during storage at 7.2°C (45°F), 10°C (50°F),
15.6°C (60.0°F), and 25°C (77°F), and 90—95% RH.

% Fructose
Week 7.2°C 10°C 15.6°C 2.5°C
0 0.07 0.07 9.07 0.07
l 0.12 0.12 0.10 0.12
2 0.12 0.11 0.08 0.10
3 0.15 0.10 0.08 0.18
4 0.20 0.13 0.09 0.16
5 0.16 0.14 0.21 0.20
6 0.20 * * 0.21
7 0.21 * * 0.19
8 0.21 * * 0.18

 

*Analysis terminated because of spoilage.

42

Little research has been reported in the literature in
recent years on maltose, sucrose, glucose and fructose

contents of both Taro (Colocasia esculenta) and Tannia or

 

Yautia (Xanthosoma sagittifolium). The available information

 

has dealt primarily with the chemical compositions of both
tubers (Bell and Favier, 1979; Doku, 1967; Barret, 1910;
Nicholls, 1951), the composition of the carbohydrate fraction
of Taro which include starch, pentosans, crude fiber, dextrin,
reducing sugars and sucrose (Anon., 1933; Payne et al., 1941)
and the carbohydrate fraction of Tannia or Yautia which is
made of starch, soluble sugar and pentosans (Treche and Guion,
1979).

Recently, Hashad et a1. (1956) and Sanches-Nieva and
Hernandes (1977) have conducted studies on transformation
of carbohydrates in Taro and Tannia corms during storage.
But compounds investigated included starch, reducing and
non-reducing sugars determined by AOAC Official Methods
(1935) and by Method of Moyer and Holgate (1948) respectively.

In this study the quantification of soluble carbohydrates,
glucose and fructose are achieved by means of HPLC. As stated
earlier, maltose and sucrose co-eluted and were not readily
quantifiable under chromatographic conditions of this study.
However, analysis of maltose and sucrose peaks reveal that
all samples analyzed contained variable amounts of these
two disaccharides. Visual inspection of peaks 3, 4 suggest

a continued decline in sucrose-maltose content. The rate and

43

extent of both increase or decrease of their peaks
(amounts) varied from one storage condition to another
(Fig. 6 and Fig. 7).

Based upon the results given in Tables 6 and 8 and
analyzing data obtained at 4.4°C (40°F)’ and 25°C: (77°F),
respectively, it is apparent that glucose and fructose were
present in Taro in approximately equal amounts. Similar
results were reported by Talburt and Smith (1975) who mention
that sucrose, glucose and fructose are usually present in '
the potato in approximately equal amounts. Data summarized
in Tables 9 and 7 at 7.2° C (45° F) and 25° C (77° F) also
agree with the findings reported by Talburt and Smith (1975).
Results of Taro corms obtained at 4.4°C (40°F) and at 30°C
(86° F) and summarized in Table 8 show that after two weeks
fructose accumulated preferentially in cold storage. This
phenomenon has also been observed previously (Samotus and
Schwimmer, 1962). Data given in Tables 6 and 8 show that
both glucose and fructose contents of Taro tubers stored at
10°C (500 F) were higher than those of Taro tubers maintained
at 4.4°C (40°F0.. The explanation is that the variety of
Taro stored at 10°Cr (50°F) differed from those maintained
at other temperatures. However, both varieties tended to
accumulate more sugar at low temperatures.

Analysis of Chromatograms illustrated in Figure 4
indicates that unidentified peaks occurred. They eluted

either before maltose and sucrose or after fructose. This

44

indicates that they were not solely maltose, sucrose,
glucose and fructose in samples Of Taro and Tannia analyzed.
As stated earlier, the known data on the soluble carbohydrate
content of both Taro and Tannia are very scarce and it was
also mentioned that within the time limitations of this
study, identity of sugars in both tubers other than maltose,
sucrose, glucose and fructose could not be established.

The results of this investigation revealed that low
level quantitation of sugar (0.07%) in Tannia (Tables 7 and

9)appears promising by HPLC.

Sugar and Moisture Contents of Tannia

 

The data in Tables 5, 7 and 8 show that a decreaSe of
moisture content was almost followed by an increase of glucose
and fructose contents at either storage temperature. As
expected, a correlation was then established. However, it
is interesting to mention that at 10°C (50°F) fructose
content of Tannia decreased with moisture whereas at the
same temperature glucose contents (Table 7) increased when
moisture decreased. The results of this study support those
published by .Hrishi and Balagopal (1979) who observed an
increase in total sugar with appreciable reduction in moisture
content during Taro storage and are in total disagreement
with those reported by Sanches Nieva and Hernandes (1977)
who stated that there was no change in total or reducing

sugar during Tannia storage.

45

SUMMARY

The results of this investigation indicate that upon
storage glucose and fructose contents of both Taro (Colocasia

esculenta) and Tannia (Xanthosoma Spp.) increased and were

 

 

present in both tubers in approximately equal amounts. Under
chromatographic conditions of this study, maltose and sucrose
co-eluted and were not readily quantifiable.

Storage tests revealed that Tannia or Yautia tubers were
kept in good condition for 8 weeks at 7.2°C (45°F) and
25°C (77°F) and 90-95% RH respectively. Taro tubers
maintained at 25°C (77°F) and 10°C (50°F) lasted 6 weeks
and those stored at 30°C. (86°F) 4 weeks and about 90-95%

RH respectively.

The analysis of the extent of decay indicated that at
any time of storage, Taro tubers were attacked by various
rots. Moisture determinations revealed that there was a
clear relationship between shrinkage, decrease in moisture
content (9.2%) and increase in fructose and glucose of

Tannia or Yautia tubers during storage.

46

SUGGESTIONS

l. The storage tests which covered a large range of
temperatures was an attempt to find out how long the products
tested could be successfully held in storage by means
feasible to both Congolese and the government. A more in~
tensified research of storage stability of these two
commodities is needed to meet the future demands for food
by the vast majority of the peOples of the People's Republic
of The Congo (Congo-Brazzaville).

2. The study on soluble carbohydrates of both Taro

(Colocasia esculenta) and Tannia or Yautia (Xanthosoma

 

 

SEE.) provided valuable information on existing sugars.
Further work on qualitative and quantitative analysis of
carbohydrate contents of these two commodities is needed to
assist in the design of appropriate diets of Congolese
people.

3. In future work in this area, it would be worth-
while to investigate the effect of chilling on Tannia and

Taro respiration and sugar content.

47

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