Seed Characteristics of Wild Legume (Tetragonolobus palaestinus) as Compared With Lens culinarisand Pisum sativum

Abstract

The plant of Tetragonolobus palaestinus Boiss is described. Physical properties, chemical composition, and cookability of T. palaestinus seeds were compared with Jor-1 lentil cultivar (Lens culinaris) and pea landrace (Pisum sativum) seeds. Results showed significant variation among the seeds of the three species. T. palaestinus seeds were found to have lower 100-seed mass (1.6 g), water absorption percent (26.7–29.2) kg water/100 kg of initial mass, but had a higher one-liter mass (831.5 g). Also T. palaestinus seeds were found to have higher protein (31) kg/100 kg seeds, fiber (20.8) kg/100 kg seeds, crude fat (2.3) kg/100 kg seeds, ash (5.1) kg/100 kg seeds, and carbohydrate (51.3) kg/100 kg seeds contents. Results also showed high positive correlations between mass/plant of T. palaestinus and plant mass (r = 0.90), number of pods/plant (r = 0.77) and seed mass/plant (r = 0.92). Cookability data showed that the unsoaked T. palaestinus seeds required 75 min to cook very well in distilled water at 100°C, whereas lentil and peas required 40 and 70 min respectively. Soaking the seeds for 18 h did not reduce the cooking time for T. palaestinus but reduced the cooking time for lentil and peas to 20 and 30 min, respectively.

Introduction

Dry legume is an important grain source in the diets of people of Mediterranean countries. It contributes a significant amount of protein, carbohydrate, vitamins, and minerals to the diet.2 5 Lentil (Lens culinaris Medik) is a major food legume crop in Jordan. Lentil is relatively free of anti-nutritional factors, low in flatulence, and it is an excellent source of proteins and amino acids.3 Thus, it is a good complement to cereal proteins, particularly bread, which is the most often consumed in Jordan. Legume yield improvement through breeding programs has been the major effort of scientists in Jordan. Tetragonolobus palaestinus Boiss (Jalaton is the local name) is a wild dry legume species found in the highlands of Jordan. The soft pods and seeds are consumed by Jordanian people before it reaches the dry stage.

Food legumes, together with cereals, account for as much as two-thirds of total dietary intake of the vast populations of many developing countries in the Mediterranean region.2 Food legumes, with their high protein content, offer the most practicable means of eradicating protein malnutrition in the cereal based diet of people of Mediterranean areas. This implies that increasing the supply of food legumes rather than organizing costly feeding programs based on protein-rich foods of animal origin should boost protein availability in these areas.

The search for new adapted legume such as T. palaestinus will help in providing new food source. The physical properties, chemical composition, and cooking characteristics of lentils have been studied.3 4 8 10 In addition, physical properties, chemical composition, and cookability of dry peas have been investigated.5 6 11 The literature search showed no information about T. palaestinus. The results of this work might encourage farmers to domesticate this wild legume species to be cultivated and used as legume food; it can be utilized as lentil, peas, and chickpeas. The purpose of this work is to report on the characteristics of T. palaestinus seeds and to compare their physico-chemical and cooking characteristics with a newly developed lentil cultivar (Jor-1) and a local pea landrace.

Materials and Methods

Plant Material and Cultural Practices

The seeds of the three species were provided by the National Center for Agricultural Research and Technology Transfer, Amman, Jordan. The three species were planted in 4 × 2.4 m plots and spaced by 0.4 m in a randomized complete block design with three replications during 2000/2001 and 2001/2002 growing seasons at Maru Agricultural Experimental Station located 34°40′ N; 590 m altitude. The soil type is silty clay (fine, montmorillonic, thermic, Entic Chromoxret) with low levels of organic matter (1.2%) and pH 7.9. This location has typical Mediterranean climate. Long term average rainfall is 370 mm. Phosphorus fertilization was applied at the rate of 30 kg P ha⁻¹. The seeds were grown under rainfed conditions. Plants were harvested at dry stage and manually threshed. Seeds were kept in nylon bags at 0°C until analysis time.

Measurements

The agronomical plant measurements (Table 1) were recorded only for T. palaestinus. Ten plants were evaluated every season and the average was recorded.

Table 1 Characteristics of T. palaestinus plants

	Mean±Standard error
Traits	2000/2001	2001/2002
Plant mass (g)	15.5±3.44	13.4±2.601
Number of pods/plant	17.0±2.50	9.9±1.426
Number of branches/plant	4.8±0.47	3.6±0.400
Number of seeds/plant	132.8±25.97	75.3±10.189
Seeds mass/plant (g)	6.8±1.40	3.9±0.567
100-Seed mass (g)	5.0±0.10	6.0±0.10
Pod mass (g)	0.8±0.017	0.9±0.075
Pod coat mass (g)	0.2±0.007	0.4±0.039
Seeds mass/pod	0.6±0.015	0.5±0.041
Number of seeds/pod	9.7±0.396	8.9±0.379
Pod length (cm)	4.2±0.062	4.5±0.122

Physical Measurement

The mass of 100 seeds, water absorption, and the mass of one liter were performed as described by Ereifej and Shibli.8

Chemical Analysis

Namely 50 g seed sample from each plot were milled on a Tecator 1093 Cyclotic sample mill (Tecator, Sweden), the milled product was passed through a 0.5 mm screen and used for chemical analysis. Moisture, protein (N × 6.25), crude fat, crude fiber, and ash were determined according to AOAC1 procedures. Glucose, sucrose, and fructose contents were determined according to Dubois et al.6 Starch content was determined according to McCready et al.12

Cookability

Seeds of the three species were soaked in distilled water for 18 h at room temperature. The cooking time for soaked and unsoaked seeds was determined according to the procedures outlined by Nikkuni et al.13 and Ereifej and Shibli.8 Namely 50 g seeds were soaked in 200 mL of distilled water and the seeds were weighed after 18 h of soaking, the increase in weight was computed and the percentage was calculated. The average of absorbed water as kg water/kg initial weight was recorded. Soaked and unsoaked seeds were cooked in distilled water until the cooked seed was easily smashed by thumb pressing; the cooking time was recorded.7

Statistical Analysis

The collected data of the two years were statistically analyzed, using MSTATC computer program (Michigan State University), as combined factorial randomized complete block design, using one factor (species), and the means were separated by Duncan's Multiple Range Test. Analysis of variance was performed to compare the characteristics of the investigated legumes. Simple correlation coefficients between the agronomical characteristics of T. palaestinus plant were estimated according to Steel and Torrie.14 The two years data for cooking times were analyzed as combined factorial randomized complete block design with two factors (species and seed soaking). Means and standard error were computed according to Steel and Torrie.14

Results and Dicussion

The description of lentil and pea plants are well known. Table 1 shows the description of T. palaestinus plants grown for two seasons. Plant mass, number of pods, number of branches, and number of seeds per plant decreased during 2000/2001 season, probably that was due to variation in rainfall (370 mm in 2000 and 330 mm in 2001). Other plant properties (seed, pod, coat mass per pod, and pod length) were similar in both seasons, which might have phenotypic stability over years.

Correlation coefficients between these traits are shown in Table 2. As expected, there are a moderate to high positive correlations between plant mass and number of pods, branches, and seeds per plant. In addition, pod length is positively correlated with pod mass, coat mass, seed mass, and number per pod. Results showed moderate to high correlations between grain yield and grain yield components in lentil, these results are in agreement with those values reported by Tikka et al.,15 on lentil.

Table 2 Correlation coefficients between T. palaestinus plant characteristics

Traits	2	3	4	5	6	7	8	9	10	11
1—Plant weight (g)	0.79b	0.71b	0.80b	0.90b	0.27	0.28	0.19	0.35	0.3	0.36
2—Number of pods/plant		0.80b	0.92b	0.91b	0.001	−0.12	−0.31	0.16	0.28	0.01
3—Number of branches/plant			0.77b	0.77b	−0.12	−0.33	−0.4	−0.09	0.08	−0.12
4—Number of seeds/plant				0.92b	0.11	−0.1	−0.21	0.24	0.4	0.14
5—Seeds weight/plant (g)					0.16	0.03	−0.11	0.27	0.41	0.23
6—100-Seed weight (g)						0.53a	0.57b	0.2	0.4	0.51
7—Pod weight (g)							0.90b	0.69b	0.36	0.68b
8—Pod coat (g)								0.36	0.18	0.65b
9— Seeds weight/pod									0.61b	0.55b
10—Number of seeds/pod										0.54a
11—Pod length (cm)

^aSignificant at p ≤ 0.05.

^bSignificant at p ≤ 0.01.

Physical and chemical properties of T. palaestinus did not vary significantly during both seasons except for fiber, fat, and carbohydrate content (Table 3). Also lentil did not show year-to-year variation for all traits except for 100-seed and one-liter mass. More seasonal variation was observed in one-liter mass, protein, carbohydrate, glucose, sucrose, and fructose contents of pea seeds. Species influenced significantly most of seed physical properties (100-seed mass, water absorption percent, and hectoliter) and chemical composition (fiber, fat, carbohydrate, glucose, sucrose, fructose, and starch). But the species and growing season interaction influenced the hectoliter, protein, fiber, carbohydrate, and fructose content of the seeds of the three legume species. The results demonstrate variation in physical and chemical properties. Lentil seeds absorbed more water than pea and T. palaestinus seeds which absorbed the least (26.7–29.2%). The one liter mass of T. palaestinus seeds was the highest (831.8–835.1 g) among the investigated legume species due to its smaller seed size. Ereifej and Shibli8 reported slightly higher values for a lentil landrace and three newly developed lentil cultivars. Similarly, peas data agree with Ereifej and Al-Karaki7 reported on pea lines characteristics. Although the chemical composition of the three species varied during seasons, the chemical analysis of T. palaestinus (Table 3) indicates that its seeds are rich in protein (30.4–31.0%) content which is similar to lentil (30.4–30.5%) and higher than peas protein (25.3–30.3%) content. Also the T. palaestinus seeds are richer in fiber (18.0–20.8%), fat (1.9–2.3%), and carbohydrates (43.7–51.3%). The sugar contents (glucose, sucrose, and fructose) are the lowest in T. palaestinus, whereas, peas have the highest concentrations. However, T. palaestinus has higher ash content than other species. The chemical analysis of T. palaestinus seeds indicates the importance of this species as a new human food source. These values were found coparable with values reported by Ereifej et al.9 on chickpea cultivars. The Jordanian people have experienced eating the soft green pods and immature seeds of T. palaestinus without any health problem, which indicates the importance of breeding to develop high yielding lines.

Table 3. Physical characteristics and chemical composition of T. palaestinus Boiss, Lens culinaris Medik, and P. sativum L. seeds.*

	T. palaestinus Boiss			L. culinaris Medik			P. sativum. L.
Seed characteristic	2000/2001	2001/2002	2000/2001	2001/2002	2000/2001	2001/2002	LSD1	CV (%)2	EMS3
100-Seed mass (g)	1.6^d #	1.6^d	4.7^b	3.7^c	15.8^a	16.2^a	0.87	6.4	0.212
Water absorption (%)	29.2^c	26.7^c	112.0^ab	120.6^a	107.1^ab	99.6^b	15.6	0.0	68.683
One-liter mass (g/L)	831.8^ab	835.1^a	815.2^b	793.3^c	747.0^d	821.9^ab	18.6	1.2	7.999
Protein (%)	30.4^a	31.0^a	30.4^a	30.5^a	30.7^a	25.3^b	3.5	6.3	3.506
Fiber (%)	18.9^b	20.8^a	5.6^d	5.7^d	7.7^c	6.7^cd	1.2	5.7	0.390
Fat (%)	2.3^a	1.9^b	1.3^c	1.2^c	0.8^d	0.6^d	0.36	4.4	0.037
Carbohydrate (%)	43.7^d	51.3^c	59.1^b	58.8^b	57.9^b	63.9^a	3.8	3.6	4.046
Ash (%)	5.1^a	4.3^ab	3.6^bc	3.7^bc	2.8^c	2.9^c	0.83	11.8	0.195
Glucose (%)	0.3^c	0.5^c	4.5^b	4.6^b	10.8^a	9.9^a	2.9	30.0	2.349
Sucrose (%)	1.4^b	2.1^b	3.5^b	3.5^b	8.3^a	7.8^b	2.4	28.3	1.574
Fructose (%)	1.8^d	2.0^d	4.0^c	3.9^c	9.1^a	5.9^b	1.5	17.3	0.591
Starch (%)	21.7^b	22.2^b	15.4^b	15.2^b	36.8^a	38.5^a	7.3	15.6	15.144

*Values are average of three replications on dry weight basis.

¹LSD—Least significant difference.

²CV (%)—Coefficient of variation percent.

³EMS—Error mean square.

^#Numbers within row having same superscripts are significantly different according to Duncan's Multiple Range Test (DMRT) at p ≤ 0.05.

The analysis of variance for weight in grams required to smash the cooked seeds and the time (min) to cook very well at 100°C showed significant variation in weight and time within the three species. These were influenced by species, and soaking treatment. The unsoaked seed of T. palaestinus required 75 min and P. sativum required about 70 min to cook very well, but L. culinaris required only 45 min (Table 4). Soaking the seeds for 18 h in distilled water reduced greatly the cooking time for lentils and peas but did not influence the cooking time for T. palaestinus due to its hard seed coat that prevent water imbibition. However, hard seed coat dormancy might help the plant to survive the harsh environment in the semiarid lands and makes seed storage more economic.

Table 4 Cooking time (min) means for legume seeds cooked in distilled water at 100°C.a

	Soaked seeds	SE	Unsoaked seeds	SE
T. palaestinus Boiss	72.5	±2.9	75.0	±4.8
L. culinaris Medik	25.0	±7.5	45.0	±9.1
P. sativum L.	38.8	±8.9	70.0	±4.8

SE—Standard error.

^aValues are average of three replications.

Similar cooking times for lentil cultivars were reported previously.8 The cooking time for pea seeds is comparable to Ereifej and Al-Karaki7 results on some pea lines. The search for new food legume sources will continue. The T. palaestinus might be an excellent addition to the food legumes.

Conclusion

The investigated wild T. palaestinus, Lens culinaris, and P. sativum seeds found to have different genetic backgrounds for almost all the traits tested. Data showed that chemical composition of T. palaestinus as compared with lentils and peas can offer to the nutritionists the possibility of using T. palaestinus along with Lens culinaris and P. sativum as source for protein, carbohydrate, fiber, starch, sugar, and minerals. The growing season and legume species found to influence the chemical composition of the seeds and seed characteristics. The significant correlations reported in this article can offer to the breeders the possibility of indirect selection for any of these quality characters.