Geometric Characteristics and Chemical Composition of Okra (Hibiscus esculentus L.) Grown Under Semi-arid Conditions

Abstract

A Landrace and seven foreign genotypes of okra (Hibiscus esculentus L.) were grown in a randomized complete block design at Jordan University of Science and Technology (JUST) Experimental Station in northern Jordan during the 1997 and 1998 growing seasons. The pods were studied for their physical properties, chemical composition, and mineral content. Geometric characteristics of okra fruits were significantly influenced by genotypes. Mosel and Steen had higher protein content than the Landrace, being 23.19, 22.43, and 19.96% respectively. The average fruit mass of different genotypes showed a trend similar to that found in fruit volume; Vigorpak had the highest fruit mass and volume, whereas Mosel had the lowest. Number of pods per plant showed very wide range for all genotypes, which ranged between 17 and 31. Data demonstrated that the variability within individual okra genotypes may be was due to environmental effects. High variability was observed in chemical composition among different genotypes. However, the genotype having high carbohydrate content showed low fiber content. All mineral contents (Ca, Na, Cu, Mn, Zn, Mg, P, and K) varied significantly among the genotypes except for Fe content, which showed no significant differences between genotypes. Mosel genotype was found superior in its mineral contents, whereas other genotypes might be considered good source for proteins, fiber, carbohydrate and minerals. The investigated genotypes seem to be a good source of minerals for human diet. The variation in mineral contents is probably due to genotype, environment and/or genotype environment interaction.

Keywords:

• Okra, Hibiscus esculentus
• Chemical composition
• Mineral
• Geometric characteristics

Introduction

Okra (Hibiscus esculentus L.) is a warm season vegetable crop widely grown throughout the tropical and sub-tropical regions of the world.12 15 Okra is grown primarily for the immature fruits to be used as fresh green, frozen, canned or in the dry state. In Jordan, okra is widely grown and has increasing production area 5874.2 dunum in 1999.2 The Landrace is widely used in the Jordanian cultivation. However, other genotypes are very limited in Jordan due to consumer preferability.

There has been a lack in information about geometric characteristics, chemical composition of Landrace and foreign cultivars as well. The most recent information's about okra nutritional value are those dealing with seed as a new source of protein.11 Analysis of okra seed meal from which the oil had been extracted with hexane showed values for crude protein, 13.56%; fat, 1.92%; carbohydrate, 31.5%; ash, 8.19%; CaO, 0.37%; P₂O₅, 3.47%; and thiamine, 4.72–5.78 µg g⁻¹.7 Analysis of the okra seed hulls found to have crude protein, 12.33%; ash, 3.83%; CaO, 0.27%; and P₂O₅, 0.76%.7 Other workers concentrated on the dietary fiber1 showing the importance of fiber in human diet and health. The objectives of this study were to investigate the chemical composition, geometric characteristics and mineral contents of a Landrace and seven okra genotypes.

Materials and Methods

Plant Material and Cultural Practices

This investigation was carried out at Jordan University of Science and Technology (JUST) Experimental Station in northern Jordan. A Landrace and seven foreign genotypes were used in this study. Landrace, Pakistani, Mosel, Bonanza, Modesto, Steen, Ohlsenseke, and Asgrow Vigorpak okra seeds provided by JUST Experimental Station were grown on 4 m long rows and 90 cm wide at 30 cm spacing during the 1997 and 1998 growing seasons. All okra genotypes were arranged in a randomized complete block design with three replications. After complete emergence, plants were thinned to two plants. Irrigation, fertilization, insect and disease control were followed as recommended for commercial farming.

The okra pods (fruits) were collected during the growing season (5 days after anthesis), total yield ton ha⁻¹, yield gm plant⁻¹, number of pods (1000 ha⁻¹) number of pods plant⁻¹, and average pod weight were recorded. Ten pods were randomly taken from each plot in each harvesting time, data were recorded, and the means were computed to obtain average pod length, mass, diameter, and volume. The 10 pods from each plot were cut, mixed together and dried at 80°C, and sent to the laboratory for analysis.

Chemical Analysis

A sample of 100 g from each replication were grounded to pass a 0.5 mm screen using a Cycotec mill and used for chemical and mineral analysis. Moisture, crude protein (N×6.25), crude fat, fiber, and ash contents were determined according to standard procedures.3 Carbohydrate content was calculated by difference. Phosphorus was determined colormetrically.20 Concentration of Mn, Fe, Cu, Zn, Na, K, Mg, and Ca were determined using an atomic absorption spectrophotometer (Pye Unicam, model SP9, UK) after wet digestion with a mixture of nitric, sulfuric, and perchloric acid (10:1:4) as described previously.9

Statistical Analysis

The collected data were subjected to analysis of variance as randomized complete block design and means were separated according to least significant differences (LSD P≤0.05) to determine the significance in differences between the means.19

Results and Discussion

Data on physical characteristics of okra fruits are presented in Table 1. The analysis of variance revealed that total yield, as well as total yield ton ha⁻¹, yield gm plant⁻¹, number of pods 1000 ha⁻¹, number of pods plant⁻¹, average pod weight, average pod length, diameter, and volume were significantly different and were influenced by genotypes.

Table 1 Fruit geometric properties, yield and yield components of okra genotypes.a

Genotypes	Length (cm)	Mass (gm)	Diameter (cm)	Volume (cm^3)	Yield wt (ton ha^−1)	Number of pods (1000 ha^−1)	Yield (g plant^−1)	Pods (plant^−1)
Landrace	5.79 bc*	3.56 c	1.13 d	4.90 c	7.2 d	1390 a	119.0 d	23 b
Pakistani	7.50 ab	5.08 bc	1.22 cd	6.52 bc	9.5 bc	1876 a	159.1 bc	31 a
Mosel	3.34 d	3.16 c	1.48 b	4.20 c	7.2 d	1447 a	122.2 d	17 c
Bonanza	5.21 c	4.97 c	1.32 bcd	6.65 bc	11.2 ab	1740 a	185.8 ab	29 a
Modesto	5.16 c	4.20 c	1.23 cd	5.93 c	12.1 a	1825 a	202.2 a	30 a
Steen	7.19 ab	7.55 ab	1.39 bc	10.10 ab	12.4 a	1824 a	209.2 a	31 a
Ohlsensenke	4.76 cd	4.27 c	1.23 cd	6.10 c	11.2 ab	1726 a	186.0 ab	29 a
Vigorpak	7.78 a	7.99 a	2.62 a	11.50 a	8.9 cd	1388 a	149.8 cd	23 b
SEb	0.826	1.186	0.109	1.71	0.849	239.16	14.49	2.01
LSD P<0.05	1.772	2.543	0.233	3.659	1.82	513	30.95	4.32

^aValues are average of three replications.

^bStandard error.

*Means followed by the same letter are not significantly different at P≤0.05.

Fruit length has been classified by the International Board for Plant Genetic Resources (IBPGR) into three classes: less than 7 cm, 8–15 cm, and more than 15 cm.5 Fruit length of okra genotypes exhibited a wide variation ranged from 3.34 to 7.78 cm. Landrace, Mosel, Bonanza, Modesto, and Ohlsenseke fruits were less than 7 cm in length but Pakistani, Steen, and Asgrow Vigorpak had more than 7 cm. Pod length is genetically controlled, which did not change irrespective of the environment.14

The average fruit diameter was varied significantly among genotypes. At the edible age, 5 days from anthesis, fruit diameter ranged from 1.13 to 2.62 cm. The Landrace was the smallest whereas Asgrow Vigorpak had the largest fruit diameter, which is not preferable by Jordanian consumer. Pod width of okra cultivars is used to distinguish okra genotypes.18 The variation in okra pod width indicated that the immature fruit diameter is quantitatively inherited with few genes involved in controlling this trait.16

As shown from (Table 1), the average fruit mass of okra genotypes showed a similar trend to that found for fruit volume, Vigorpak had the highest fruit mass and volume whereas Mosel had the lowest. On the other hand, no large differences were detected among other okra genotypes in regard of fruit volume and mass. Baladi variety in Egypt produced small pods with low weight, which preferred by consumer.6

Okra pods are sold based on number instead of weight in African markets.14 Number of pods per plant showed significant differences among genotypes and the average pods per plant ranged from 17 (Mosel) to 31 (Pakistani) and Steen (Table 1). For each genotype, number of pods per plant showed very wide range for all genotypes. That variability within individuals may be due to environmental effects. Number of pods per plant showed low heritability estimate, which support the environmental factors affect number of pods per plant.4

Significant differences in yield (per plant) were detected among different genotypes. The average yield per plant ranged from 119 g (Landrace) to 209.2 g (Steen). The Steen genotype gave the highest average yield per plant followed by Modesto genotype 202.2 g. The lowest value was 119 and 122.2 for Landrace and Mosel respectively. This variation may be attributed to environment, genotype, and/or genotype environment interaction. Yield of pods had a positive and significant association with the number of pods per plant.17 The pod yield per plant was based on number of pods per plant and weight in gram per pod.6

High variability was observed in chemical composition among different genotypes under investigation (Table 2). Mosel and Steen had higher protein content than the Landrace, being 23.19, 22.43, and 19.96% respectively. It was found that Mosel and Steen had 3.2 and 2.4% more protein content than the values were previously reported.13

Table 2 Protein, fat, fiber, ash, carbohydrate, and moisture contents of okra genotypes (% on dry-weight basis).a

Genotypes	Ash	Fiber	Fat	Protein	CHO	Moisture
Landrace	9.31 b*	18.21 b	2.573 cd	19.96 c	49.95 b	83.5 a
Pakistani	10.35 a	21.56 ab	1.858 e	18.86 c	47.37 bc	81.3 a
Mosel	10.72 a	20.85 ab	2.316 de	23.19 a	42.93 d	82.0 a
Bonanza	9.30 b	20.93 ab	1.935 de	20.21 bc	47.62 bc	84.1 a
Modesto	8.53 c	22.34 a	4.187 a	18.72 c	46.23 bcd	83.1 a
Steen	8.65 c	22.05 ab	3.205 bc	22.43 ab	43.66 cd	84.9 a
Ohlsensenke	8.67 c	20.85 ab	3.405 b	19.92 c	47.16 bcd	82.3 a
Vigorpak	8.61 c	8.76 c	3.381 b	18.88 c	60.36 a	87.1 a
SEb	0.2658	1.878	0.3316	1.138	2.026	2.76
LSD P<0.05	0.5702	4.028	0.7113	2.440	4.346	5.93

^aValues are average of three replications.

^bStandard error.

*Means followed by the same letter are not significantly different at P≤0.05.

The fat content varied significantly among genotypes, it ranged from 4.19% for Modesto to 1.86% for Pakistani. All genotypes had higher fat content than those values reported on okra.13 Ash content varied significantly among different okra genotypes, being 8.53 (Modesto) and 10.72% (Mosel).

As shown in Table 2, there was a significant variation among genotypes in their fiber content, being 8.78 (Vigorpak)–22.34% (Modesto). All genotypes except Vigorpak had higher fiber content than those reported earlier.13 Our results are in agreement with previous reports about differences in fiber content among okra genotypes.10 Fiber content in okra fruit is an important quality attribute where higher fiber content of a genotype is related to progress in age. The carbohydrate content also varied significantly among different genotypes; Vigorpak had the highest carbohydrate content (60.36%) followed by the Landrace (49.95%). On the other hand, Mosel found to have the lowest carbohydrate content (42.93%) as compared with other investigated genotypes. All genotypes had lower carbohydrate content than those values reported on okra.13 Our results are in agreement with previous reports that indicated differences in fiber, ash, and carbohydrate contents among okra cultivars.8

The data on Ca, Na, Cu, Fe, Mn, Zn, Mg, P, and K are shown in Table 3. Mineral content varied significantly among the genotypes except for Fe, which showed no significant differences among genotypes. However, all genotypes had Fe content higher than those values reported on okra.13 Mineral level found to compare very well with those values reported on okra cultivars. Phosphorus levels ranged from 452.3 (Vigorpak) to 609.1 mg/100 g (Modesto), K concentration varied significantly and ranged from 2607 (Vigorpak) to 3620 mg/100 g (Mosel), calcium also ranged from 1006 (Vigorpak) to 1639 mg/100 g (Pakistani). Other minerals Mn, Cu, Zn, Na, and Mg also varied and their ranges were 3.224 (Vigorpak)–5.77 mg/100 g (Mosel); 1.1 (Steen)–1.7 mg/100 g (Mosel); 7.6 (Ohlsensenke)–11.6 mg/100 g (Mosel); 38.7 (Vigorpak)–65.8 mg/100 g (Mosel), and 386 (Vigorpak)–542.4 mg/100 g (Mosel), respectively. In general the uptake of nutrients by Mosel genotype was higher than that of other genotypes. This may be because of better adaptation of this genotype to northern Jordan. Mosel had the highest content of Mn (5.77 mg/100 g), Cu (1.70 mg/100 g), Zn (11.6 mg/100 g), Na (65.8 mg/100 g), K (3620 mg/100 g), and Mg (542.4 mg/100 g), whereas Pakistani was the richest in Ca (1639 mg/100 g) and Modesto had the highest P (609.1 mg/100 g) content. Calcium content was higher whereas sodium and phosphorus contents were lower than those reported previously.13 This might be the starting point for suggesting that the variation probably attributable to the regional differences (soil, climate, season, species). The investigated genotypes seem to be a good source of minerals for human diet and any of these genotypes can be adopted for okra production in the region.

Table 3 Mineral content (mg/100 g) of okra pods (on dry-weight basis).a

Genotypes	Mn	Fe	Cu	Zn	Na	K	Mg	Ca	P
Landrace	4.256 b*	12.7 a	1.6 ab	8.2 b	43.8 b	3051 bc	428.3 b	1120 c	497.8 bcd
Pakistani	4.602 b	34.4 a	1.5 ab	7.9 b	43.3 b	2908 cde	519.1 a	1639 a	488.9 cd
Mosel	5.777 a	14.6 a	1.7 a	11.6 a	65.8 a	3620 a	542.4 a	1460 b	593.5 ab
Bonanza	4.362 b	11.7 a	1.3 ab	8.2 b	53.1 ab	3253 b	446.3 b	1272 bc	579.3 abc
Modesto	3.289 c	14.1 a	1.6 ab	8.3 b	55.5 ab	2876 cde	415.9 b	1125 c	609.1 a
Steen	4.351 b	13.0 a	1.1 b	8.5 b	66.2 a	2932 cd	446.2 b	1206 bc	502.9 bcd
Ohlsensenke	3.799 bc	13.9 a	1.3 ab	7.6 b	48.3 ab	2710 de	401.1 b	1093 c	471.2 d
Vigorpak	3.224 c	25.2 a	1.4 ab	7.8 b	38.7 b	2607 e	386.0 b	1006 c	451.3 d
SEb	0.4442	11.44	0.27	0.96	8.681	147.55	31.46	124.66	46.508
LSD P<0.05	0.9528	24.54	0.578	2.07	18.62	316.5	67.48	267.4	99.76

^aValues are average of three replications.

^bStandard error.

*Means followed by the same letter are not significantly different at P≤0.05.

Conclusion

Investigated okra Landrace and genotypes grown under semi-arid conditions, showed significant variation in their geometric characteristics, proximate analysis, and mineral content. The variation in chemical composition and mineral content is probably due to genotype, environment and/or genotype environment interaction. However, Mosel genotype was found superior in its mineral contents, whereas other genotypes might be considered good source for proteins, fiber, carbohydrate, and minerals.