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Changes in the composition and carbohydrate constituents of okra (Abelmoschus esculentus, Linn.) with age
Food
ChemistryII(1982)27-32
CHANGES IN THE COMPOSITION AND CARBOHYDRATE CONSTITUENTS OF OKRA (ABELMOSCHUS ESCULENTUS, LINN.) WITH AGE OYEBIODUN G. LONGE,* B. L. FETUGA* 3k M. E. AKEN'OVA~
* Division of Nutritional Biochemistry, Department of Animal Science. t Department of Agronomy, University of lbadan, lbadan, Nigeria (Received: 18 September, 1980)
ABSTRACT
Changes which occurred in the proximate composition, concentrations of free sugars, high molecular weight carbohydrates (water-soluble polysaccharides, starch hemicellulose and cellulose) and lignm in four varieties of okra when harvested at different ages have been studied. Samples were collected from the field at 1, 4, 7 and lOdays after flowering. Crude protein, which initially ranged from 19"9 to 24"7 g/lOOg DM, decreased with age whilst crude fibre, 12"5-16"7 g/lOOg DM, increased with age. Ether extract varied between 1"60 and 2"19 g~100 g D M whilst ash was 8.00-8.59 g/ lO0 g DM. Available carbohydrates (starch + sugars) ranged from 11.2 to 13.1g/lOOg DM whilst unavailable carbohydrates increased Ji'om 33"9--42"Og/100g DM to 51"9-59"7g/lOOg DM. Overall varietal differences were apparent for ethanol-soluble sugars and the structural carbohydrates while differences among the means due to age were significant (P < 0"05).
INTRODUCTION
Okra (Hibiscus esculentus, Linn., now classified as Abelmoschus esculentus, Linn.), or lady's finger, is self pollinating and, like a number of other commonly eaten green vegetables, is available almost throughout the year in Nigeria. It is usually cut into pieces for use in soup or boiled and drained to be served as vegetables with starchy foods such as rice and yams. The fruits of most cultivated local varieties are ready for harvest 2-3 months after sowing although there are varieties which are either early or late maturing. The first harvest for consumption takes place about 3 days after flowering and this can continue regularly for the next 7 days or more. 27 Food Chemistry 0308-8146/82/0008-0027/$02.75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain
28
OYEBIODUN G. LONGE, B. L. FETUGA, M. E. AKEN+OVA
Information is available on the chemical composition of mature okra fruits (FAO, 1968; Oyenuga, 1968; Longe, 1981). Apart from being appreciable in protein content, a major component of okra is carbohydrate, most of which is fibrous in nature. The seed, as distinct from the whole fruit, is also a potential source of oil varying between 15 and 22 ~ (Oyenuga, 1968) and the residual protein after oil extraction was found to compare favourably with cottonseed cake when fed to rats. Mucilage isolated from the whole fruit has also been fed to rats by Woolfe (1977) to test its effect on plasma cholesterol level. Knowledge of changes in the carbohydrate composition of okra is rudimentary. It is generally noted that older fruits lose their tenderness and the slimy texture possessed by young okra fruits when cooked disappears with advancing age. The purpose of this study is to contribute to a better knowledge of the changes which occur in the chemical composition of okra harvested at different ages with particular reference to the carbohydrate fractions. Information concerning varietal differences in chemical composition does not appear to be available even though differences in physical characteristics such as fruit colour, length, shape and seed number are well recognised (Van Epenhuijsen, 1974). Two imported and two local varieties, selected on the basis of fruit yield, have therefore been employed in the present analysis to show varietal contribution to the differences in nutrient content with advancing age. MATERIALS AND METHODS
Description of materials Four promising accessions in the okra world collection maintained by the Department of Agronomy, University of Ibadan, Nigeria, were used. Two of these, UI 92 and UI 104, were local accessions developed through selection from an accession collected from parts of Nigeria (Fatokun et al., 1978). UI 92 exhibits facultative short-day response to daylength, and UI 104 is similar, but to a lesser degree. The remaining two varieties, UI 72-11 and UI 72-262, are introductions from Asia and are day-neutral.
Field experiment The varieties described above were planted in May, 1978 at the University of Ibadan Teaching and Research Farm and fertiliser was uniformly applied to all treatments at the rate of 56 kg N/ha as urea, 25 kg K/ha as murate of potash and 15 kg P/ha as triple superphosphate. Each variety was randomly allocated a plot, 5.4m long, within the experimental area. Each plot consisted of six rows and the spacing was 90 x 45 cm. Flowers were tagged as they opened with date of opening and pods were harvested at 1-, 4-, 7-, and 10-day intervals from the five inner of the seven plants in each row of each of the four inner rows. Harvested pods were freed of stalks and receptacles to obtain the edible portions. These were dried prior to milling.
CARBOHYDRATES OF OKRA AT DIFFERENT AGES
29
Analytical procedure Dry matter, crude protein, c r u d e fibre, ether extract a n d total ash e s t i m a t i o n was carried o u t according to the m e t h o d s of A O A C (1970) a n d the nitrogen-free extractives estimated by difference. T h e total soluble sugars o b t a i n e d by exhaustive extraction with hot 80 % (v/v) e t h a n o l were d e t e r m i n e d by the m e t h o d of D u B o i s et al. (1956). Starch was d e t e r m i n e d after extraction of the e t h a n o l - s o l u b l e sugars by the m e t h o d o f T h i v e n d et al. (1972) a n d e t h a n o l - s o l u b l e sugars a n d starch were s u m m a t e d as available c a r b o h y d r a t e s . Unavailable carbohydrates of cell wall origin were estimated (after elimination of soluble sugars a n d starch) by acid hydrolysis (Southgate, 1969) after which total sugars in-hydrolysates were estimated ( D u b o i s et al., 1956). D a t a o b t a i n e d were analysed statistically (Steel & Torrie, 1960). RESULTS AND DISCUSSION
P r o x i m a t e composition The p r o x i m a t e chemical c o m p o s i t i o n o f the four varieties harvested at different ages is presented in T a b l e 1. C r u d e p r o t e i n c o n t e n t decreased as harvesting TABLE 1 EFFECT OF AGE AT HARVEST ON THE PROXIMATE COMPOSITION OF FOUR VARIETIES OF OKRA
Variety UI 92
UI 72-11
UI 104
UI 72-262
Age in days
Crudefibre
Crudeprotein
! 4 7 10 Mean SD i 4 7 10 Mean SD 1 4 7 10 Mean SD
15.0 20-1 23.0 23-2 20-3 +3.8 12.5 15.6 20.7 23.6 18.1 +5.0 16-7 17.9 20.0 21.1 18.9 -t-2.0
24.7 22"0 18.2 18.6 20.9 +3.1 20.0 23.8 16-6 14.4 18.7 -t-4-1 19.9 19.5 18.4 18.8 19.2 +0.7
1 4 7 10
15.93 16.56 18.62 20.74 17-96 +2-18
24.5 16.1 18-7 17.06 19.1 +3-8
Mean
SD S D = standard deviation.
Ether extract
(g/100g
DM)
Ash
NFE
1-60 1"69 1"77 1-86 1-73 _0.11 1.96 2.12 2.07 2-11 2-07 +0.07 2.19 2.25 2.37 2.37 2.30 +0-09
8.59 8-88 9"02 9-19 8.92 +0-25 8.00 8.46 9.23 9.11 8-70 +0.58 8.10 8-25 8-54 8-72 8-40 +0-28
49.9 47.4 48.1 47.2 48.1 +!.3 57.6 50.0 51.3 50.8 52.4 +3.5 53-1 52-2 50.7 49.1 51.3 + 1-7
1-67 1.78 1.79 1-82 1-77 +0.07
8.27 8-45 8-58 8.66 8.49 +0-17
49.7 57.1 52.3 51-7 52.7 +3.1
30
OYEBIODUN G. LONGE, B. L. FETUGA, M. E. AKEN'OVA
advanced whilst crude fibre content increased. At day 1 after flowering, fibre content varied between 12 and 17 9/0 but rose to 21-23 9/00by the tenth day. Ash and ether extract increased gradually with time for all varieties. Analysis of variance gave no indication of real differences in crude protein and crude fibre between the four varieties although values varied significantly with age.
Available and unavailable carbohydrates Among the four varieties studied, average values for available carbohydrates for the different ages were 11-2 to 13.1 g/100 g D M and, for unavailable carbohydrates, 44.2 to 50.9g/100g DM (Table 2). Significant age differences were found in all carbohydrate fractions studied but overall varietal differences were apparent for the cell wall carbohydrates only. A significant age x variety interaction for all carbohydrates, however, suggests varietal differences for the different ages. This was similar to the crude protein and crude fibre of the okra varieties for the different harvesting periods. Free sugars declined gradually with age for UI 92 and about 40 9/0 of the sugars disappeared by the tenth day. Starch content was least among the carbohydrates and starch synthesis reached a peak by the seventh day. Apart from a rise in concentration between the first and fourth days, subsequent increases were very slight. The water-soluble fraction followed the same trend as the free sugars. The watersoluble carbohydrate content progressively decreased except in two varieties, UI 92 and UI 72-262, where there was a slight increase within the first four days, after which the values declined. Despite the fall in the concentration of free sugars and water-soluble carbohydrates with advancing age, hemicellulose, cellulose and lignin values increased. With the exception of the cellulose in UI 72-262 and hemicellulose of UI 104, cell wall carbohydrates in all varieties increased sharply from the first to fourth day and thereafter slowly in an almost linear fashion. Results obtained to date from the four varieties suggest that the carbohydrates of the fibre fraction, with the exception of the water-soluble fraction, are synthesised rapidly between days 1 and 4 so that they accumulate steadily and probably reach a maximum between the seventh and tenth days. It is possible, however, that the free sugars are degraded by an enzyme system before polysaccharide synthesis. The water-soluble polysaccharides may have been converted to insoluble structural carbohydrates, i.e. hemicellulose and cellulose. As maturation proceeds, lignification increases. All these observations may explain the 'woody' nature (Van Epehuijsen, 1974) and hard texture of late harvested okra fruits. The individual sugars of okra have already been quantified (Longe, 1981) but nothing is known concerning the metabolism of these sugars. Metabolic processes affecting change in carbohydrate fractions merit examination. Further studies are also necessary in order to understand fruit development. Studies of other parts of the plant, apart from the fruit alone, may have to be undertaken in order to obtain such a
1 4 7 10 Mean SD
1 4 7 10 Mean SD
1 4 7 10 Mean SD
UI 72-11
UI 104
UI 72-262
11.2 11.8 8.88 8.01 9-86 + 1.30
10.8 9.96 9.48 8.82 9.76 +0.82
11.2 11.0 8.70 8.10 9.76 + 1.59
9-21 8.76 8.07 5.58 7.91 +1.61
Free sugars
2.37 2.44 2.72 3.93 2.87 _+0"73
2.49 3.18 3.81 3.95 3.36 -+0.67
2.58 3.27 3.50 3.69 3.26 -+0.48
2.33 3.29 3.62 3.83 3.27 +0.66
Starch
13.5 14.2 11.6 11.9 12.8 _+ 1.25
13.3 13.1 13.3 12.8 13.1 +0.24
13.8 14.3 12.2 11.8 13.0 -+ 1.21
11.5 12.1 11.7 9-41 11.2 +1.19
Available carbohydrates
14.3 16.6 1 i.5 11.2 13.4 _+2.57
23.7 19.7 16.1 14.2 18.4 +4.19
15.6 13.5 16.3 10.9 14.1 +2.44
19'6 18.7 10.8 7.46 14.2 +6.05
Watersoluble carbohydrate*
11.7'" 14.7 16.0 16.3 14.7 _+2.08
10.4 9.59 11.8 16.3 12.0 -+2.97
6.22 12.2 13.1 14.5 11.5 +3.65
8.05 18.3 22.8 21.2 17.6 _+6.62
Hemicellulose
SD = standard deviation. * Water-soluble carbohydrate determined after removal of starch and ethanol soluble free sugars.
1 4 7 10 Mean SD
Age in days
UI 92
Variety
4.56 6.84 12.6 14.8 9.70 +4.80
3.85 4.19 18-3 12.8 7.29 +4.20
6.06 17.8 19.5 24.3 16.9 +7.75
2.05 8.84 10.7 14.0 8.90 +5"05
Cellulose
9.50 11.2 15-5 16.3 13.1 +3.28
4.00 5.10 8.10 8.62 6.46 +2.26
6.00 6.52 6.81 10.0 7.33 +7.75
7.10 8.20 8.40 10.4 8.56 -+1.37
Lignin
TABLE 2 EFFECT OF AGE AT HARVESTON THE CARBOHYDRATECONSTITUENTSOF FOUR VARIETIESOF OKRA (g/100g DM)
40. ! 49.4 55.6 58.6 50.9 +8.15
42"0 38-6 44.3 51.9 44.2 + 5'65
33.9 49'6 55'6 59.7 49.7 +11-3
36.8 54.0 52.7 53-0 49.1 +8.27
Unavailable carbohydrate
m gM Z
,.q
O
O
,..]
O
32
OYEBIODUN G, LONGE, B. L. FETUGA, M. E. AKEN'OVA
c o m p r e h e n s i v e view. O n l y f o u r o f t h e n u m e r o u s varieties o f o k r a in e x i s t e n c e h a v e b e e n e x a m i n e d ; c a u t i o n s h o u l d t h e r e f o r e he exercised in d r a w i n g a g e n e r a l conclusion.
REFERENCES AOAC (1970). Official Methods of Analysis (I Ith edn.), Association of Official Analytical Chemists, Washington, DC. DuBoIs, M., GILL,S, K., HAMILTON,J. K., REBEl,S, P. A. & SMITH,F. (1956). Colorimetric method for determinations of sugars and related substances. Anal. Chem., 180, 350-6. FATOKUN,C. A., AKEN'OVA,M. E. & CHHEDA,H. R. (1978). Two new varieties of okra. Niger J. Genet., 2, IIO-II. FOOD ANDAGRICULTUREORGANIZATIONOF THE UNITEDNATIONS(FAG) (1968). Food composilionfor use in Africa, FAG, Rome, p. 113. LONGE,O. G.[(! 98 I). Effect of boiling on the carbohydrate constituents of some non-leafy vegetables. Fd. Chem., 7, 1-6. OYENUGA,V. A. (1968). Nigeria's foods andfeeding-stuffs. Their chemistry and nutritive value (3rd edn.), Ibadan University Press, Ibadan, Nigeria, 90. SOUTHGATE,D. A. T. (! 969). Determination ofcarbohydrates in foods, i I. Unavailablecarbohydrates. J. Sci. Fd. Agric., 20, 331-5. STEEL,R. G. D. & TORRIE,J. H. (1960). Principles and procedures of statistics. McGraw-Hill Book Co. Inc., London. THIVEND,,P., MERCIER,C. & GUILBOT,A. (1972). Determination of starch with glucoamylas¢. Vii. General carbohydrate methods. In: Methods in carbohydrate chemistry. (Whistler, R.L. & BeMiller, J.N. (Eds)), Academic Press, London and New York. VAN EPENHUIJSEN,C. W. (1974). Growing native vegetables in Nigeria. FAG, Rome, 65-7. WOOLFE,J. (I 977). The effect ofokra mucilage (Hibiscus esculentus, L.) on the plasma cholesterol level in rats. Proc. Nutr. Soc., 36, 59A.
ChemistryII(1982)27-32
CHANGES IN THE COMPOSITION AND CARBOHYDRATE CONSTITUENTS OF OKRA (ABELMOSCHUS ESCULENTUS, LINN.) WITH AGE OYEBIODUN G. LONGE,* B. L. FETUGA* 3k M. E. AKEN'OVA~
* Division of Nutritional Biochemistry, Department of Animal Science. t Department of Agronomy, University of lbadan, lbadan, Nigeria (Received: 18 September, 1980)
ABSTRACT
Changes which occurred in the proximate composition, concentrations of free sugars, high molecular weight carbohydrates (water-soluble polysaccharides, starch hemicellulose and cellulose) and lignm in four varieties of okra when harvested at different ages have been studied. Samples were collected from the field at 1, 4, 7 and lOdays after flowering. Crude protein, which initially ranged from 19"9 to 24"7 g/lOOg DM, decreased with age whilst crude fibre, 12"5-16"7 g/lOOg DM, increased with age. Ether extract varied between 1"60 and 2"19 g~100 g D M whilst ash was 8.00-8.59 g/ lO0 g DM. Available carbohydrates (starch + sugars) ranged from 11.2 to 13.1g/lOOg DM whilst unavailable carbohydrates increased Ji'om 33"9--42"Og/100g DM to 51"9-59"7g/lOOg DM. Overall varietal differences were apparent for ethanol-soluble sugars and the structural carbohydrates while differences among the means due to age were significant (P < 0"05).
INTRODUCTION
Okra (Hibiscus esculentus, Linn., now classified as Abelmoschus esculentus, Linn.), or lady's finger, is self pollinating and, like a number of other commonly eaten green vegetables, is available almost throughout the year in Nigeria. It is usually cut into pieces for use in soup or boiled and drained to be served as vegetables with starchy foods such as rice and yams. The fruits of most cultivated local varieties are ready for harvest 2-3 months after sowing although there are varieties which are either early or late maturing. The first harvest for consumption takes place about 3 days after flowering and this can continue regularly for the next 7 days or more. 27 Food Chemistry 0308-8146/82/0008-0027/$02.75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain
28
OYEBIODUN G. LONGE, B. L. FETUGA, M. E. AKEN+OVA
Information is available on the chemical composition of mature okra fruits (FAO, 1968; Oyenuga, 1968; Longe, 1981). Apart from being appreciable in protein content, a major component of okra is carbohydrate, most of which is fibrous in nature. The seed, as distinct from the whole fruit, is also a potential source of oil varying between 15 and 22 ~ (Oyenuga, 1968) and the residual protein after oil extraction was found to compare favourably with cottonseed cake when fed to rats. Mucilage isolated from the whole fruit has also been fed to rats by Woolfe (1977) to test its effect on plasma cholesterol level. Knowledge of changes in the carbohydrate composition of okra is rudimentary. It is generally noted that older fruits lose their tenderness and the slimy texture possessed by young okra fruits when cooked disappears with advancing age. The purpose of this study is to contribute to a better knowledge of the changes which occur in the chemical composition of okra harvested at different ages with particular reference to the carbohydrate fractions. Information concerning varietal differences in chemical composition does not appear to be available even though differences in physical characteristics such as fruit colour, length, shape and seed number are well recognised (Van Epenhuijsen, 1974). Two imported and two local varieties, selected on the basis of fruit yield, have therefore been employed in the present analysis to show varietal contribution to the differences in nutrient content with advancing age. MATERIALS AND METHODS
Description of materials Four promising accessions in the okra world collection maintained by the Department of Agronomy, University of Ibadan, Nigeria, were used. Two of these, UI 92 and UI 104, were local accessions developed through selection from an accession collected from parts of Nigeria (Fatokun et al., 1978). UI 92 exhibits facultative short-day response to daylength, and UI 104 is similar, but to a lesser degree. The remaining two varieties, UI 72-11 and UI 72-262, are introductions from Asia and are day-neutral.
Field experiment The varieties described above were planted in May, 1978 at the University of Ibadan Teaching and Research Farm and fertiliser was uniformly applied to all treatments at the rate of 56 kg N/ha as urea, 25 kg K/ha as murate of potash and 15 kg P/ha as triple superphosphate. Each variety was randomly allocated a plot, 5.4m long, within the experimental area. Each plot consisted of six rows and the spacing was 90 x 45 cm. Flowers were tagged as they opened with date of opening and pods were harvested at 1-, 4-, 7-, and 10-day intervals from the five inner of the seven plants in each row of each of the four inner rows. Harvested pods were freed of stalks and receptacles to obtain the edible portions. These were dried prior to milling.
CARBOHYDRATES OF OKRA AT DIFFERENT AGES
29
Analytical procedure Dry matter, crude protein, c r u d e fibre, ether extract a n d total ash e s t i m a t i o n was carried o u t according to the m e t h o d s of A O A C (1970) a n d the nitrogen-free extractives estimated by difference. T h e total soluble sugars o b t a i n e d by exhaustive extraction with hot 80 % (v/v) e t h a n o l were d e t e r m i n e d by the m e t h o d of D u B o i s et al. (1956). Starch was d e t e r m i n e d after extraction of the e t h a n o l - s o l u b l e sugars by the m e t h o d o f T h i v e n d et al. (1972) a n d e t h a n o l - s o l u b l e sugars a n d starch were s u m m a t e d as available c a r b o h y d r a t e s . Unavailable carbohydrates of cell wall origin were estimated (after elimination of soluble sugars a n d starch) by acid hydrolysis (Southgate, 1969) after which total sugars in-hydrolysates were estimated ( D u b o i s et al., 1956). D a t a o b t a i n e d were analysed statistically (Steel & Torrie, 1960). RESULTS AND DISCUSSION
P r o x i m a t e composition The p r o x i m a t e chemical c o m p o s i t i o n o f the four varieties harvested at different ages is presented in T a b l e 1. C r u d e p r o t e i n c o n t e n t decreased as harvesting TABLE 1 EFFECT OF AGE AT HARVEST ON THE PROXIMATE COMPOSITION OF FOUR VARIETIES OF OKRA
Variety UI 92
UI 72-11
UI 104
UI 72-262
Age in days
Crudefibre
Crudeprotein
! 4 7 10 Mean SD i 4 7 10 Mean SD 1 4 7 10 Mean SD
15.0 20-1 23.0 23-2 20-3 +3.8 12.5 15.6 20.7 23.6 18.1 +5.0 16-7 17.9 20.0 21.1 18.9 -t-2.0
24.7 22"0 18.2 18.6 20.9 +3.1 20.0 23.8 16-6 14.4 18.7 -t-4-1 19.9 19.5 18.4 18.8 19.2 +0.7
1 4 7 10
15.93 16.56 18.62 20.74 17-96 +2-18
24.5 16.1 18-7 17.06 19.1 +3-8
Mean
SD S D = standard deviation.
Ether extract
(g/100g
DM)
Ash
NFE
1-60 1"69 1"77 1-86 1-73 _0.11 1.96 2.12 2.07 2-11 2-07 +0.07 2.19 2.25 2.37 2.37 2.30 +0-09
8.59 8-88 9"02 9-19 8.92 +0-25 8.00 8.46 9.23 9.11 8-70 +0.58 8.10 8-25 8-54 8-72 8-40 +0-28
49.9 47.4 48.1 47.2 48.1 +!.3 57.6 50.0 51.3 50.8 52.4 +3.5 53-1 52-2 50.7 49.1 51.3 + 1-7
1-67 1.78 1.79 1-82 1-77 +0.07
8.27 8-45 8-58 8.66 8.49 +0-17
49.7 57.1 52.3 51-7 52.7 +3.1
30
OYEBIODUN G. LONGE, B. L. FETUGA, M. E. AKEN'OVA
advanced whilst crude fibre content increased. At day 1 after flowering, fibre content varied between 12 and 17 9/0 but rose to 21-23 9/00by the tenth day. Ash and ether extract increased gradually with time for all varieties. Analysis of variance gave no indication of real differences in crude protein and crude fibre between the four varieties although values varied significantly with age.
Available and unavailable carbohydrates Among the four varieties studied, average values for available carbohydrates for the different ages were 11-2 to 13.1 g/100 g D M and, for unavailable carbohydrates, 44.2 to 50.9g/100g DM (Table 2). Significant age differences were found in all carbohydrate fractions studied but overall varietal differences were apparent for the cell wall carbohydrates only. A significant age x variety interaction for all carbohydrates, however, suggests varietal differences for the different ages. This was similar to the crude protein and crude fibre of the okra varieties for the different harvesting periods. Free sugars declined gradually with age for UI 92 and about 40 9/0 of the sugars disappeared by the tenth day. Starch content was least among the carbohydrates and starch synthesis reached a peak by the seventh day. Apart from a rise in concentration between the first and fourth days, subsequent increases were very slight. The water-soluble fraction followed the same trend as the free sugars. The watersoluble carbohydrate content progressively decreased except in two varieties, UI 92 and UI 72-262, where there was a slight increase within the first four days, after which the values declined. Despite the fall in the concentration of free sugars and water-soluble carbohydrates with advancing age, hemicellulose, cellulose and lignin values increased. With the exception of the cellulose in UI 72-262 and hemicellulose of UI 104, cell wall carbohydrates in all varieties increased sharply from the first to fourth day and thereafter slowly in an almost linear fashion. Results obtained to date from the four varieties suggest that the carbohydrates of the fibre fraction, with the exception of the water-soluble fraction, are synthesised rapidly between days 1 and 4 so that they accumulate steadily and probably reach a maximum between the seventh and tenth days. It is possible, however, that the free sugars are degraded by an enzyme system before polysaccharide synthesis. The water-soluble polysaccharides may have been converted to insoluble structural carbohydrates, i.e. hemicellulose and cellulose. As maturation proceeds, lignification increases. All these observations may explain the 'woody' nature (Van Epehuijsen, 1974) and hard texture of late harvested okra fruits. The individual sugars of okra have already been quantified (Longe, 1981) but nothing is known concerning the metabolism of these sugars. Metabolic processes affecting change in carbohydrate fractions merit examination. Further studies are also necessary in order to understand fruit development. Studies of other parts of the plant, apart from the fruit alone, may have to be undertaken in order to obtain such a
1 4 7 10 Mean SD
1 4 7 10 Mean SD
1 4 7 10 Mean SD
UI 72-11
UI 104
UI 72-262
11.2 11.8 8.88 8.01 9-86 + 1.30
10.8 9.96 9.48 8.82 9.76 +0.82
11.2 11.0 8.70 8.10 9.76 + 1.59
9-21 8.76 8.07 5.58 7.91 +1.61
Free sugars
2.37 2.44 2.72 3.93 2.87 _+0"73
2.49 3.18 3.81 3.95 3.36 -+0.67
2.58 3.27 3.50 3.69 3.26 -+0.48
2.33 3.29 3.62 3.83 3.27 +0.66
Starch
13.5 14.2 11.6 11.9 12.8 _+ 1.25
13.3 13.1 13.3 12.8 13.1 +0.24
13.8 14.3 12.2 11.8 13.0 -+ 1.21
11.5 12.1 11.7 9-41 11.2 +1.19
Available carbohydrates
14.3 16.6 1 i.5 11.2 13.4 _+2.57
23.7 19.7 16.1 14.2 18.4 +4.19
15.6 13.5 16.3 10.9 14.1 +2.44
19'6 18.7 10.8 7.46 14.2 +6.05
Watersoluble carbohydrate*
11.7'" 14.7 16.0 16.3 14.7 _+2.08
10.4 9.59 11.8 16.3 12.0 -+2.97
6.22 12.2 13.1 14.5 11.5 +3.65
8.05 18.3 22.8 21.2 17.6 _+6.62
Hemicellulose
SD = standard deviation. * Water-soluble carbohydrate determined after removal of starch and ethanol soluble free sugars.
1 4 7 10 Mean SD
Age in days
UI 92
Variety
4.56 6.84 12.6 14.8 9.70 +4.80
3.85 4.19 18-3 12.8 7.29 +4.20
6.06 17.8 19.5 24.3 16.9 +7.75
2.05 8.84 10.7 14.0 8.90 +5"05
Cellulose
9.50 11.2 15-5 16.3 13.1 +3.28
4.00 5.10 8.10 8.62 6.46 +2.26
6.00 6.52 6.81 10.0 7.33 +7.75
7.10 8.20 8.40 10.4 8.56 -+1.37
Lignin
TABLE 2 EFFECT OF AGE AT HARVESTON THE CARBOHYDRATECONSTITUENTSOF FOUR VARIETIESOF OKRA (g/100g DM)
40. ! 49.4 55.6 58.6 50.9 +8.15
42"0 38-6 44.3 51.9 44.2 + 5'65
33.9 49'6 55'6 59.7 49.7 +11-3
36.8 54.0 52.7 53-0 49.1 +8.27
Unavailable carbohydrate
m gM Z
,.q
O
O
,..]
O
32
OYEBIODUN G, LONGE, B. L. FETUGA, M. E. AKEN'OVA
c o m p r e h e n s i v e view. O n l y f o u r o f t h e n u m e r o u s varieties o f o k r a in e x i s t e n c e h a v e b e e n e x a m i n e d ; c a u t i o n s h o u l d t h e r e f o r e he exercised in d r a w i n g a g e n e r a l conclusion.
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