Physicochemical and functional properties of dried okra (Abelmoschus esculentus L.) seed flour

Abstract The physicochemical and functional properties of dried okra seed flour of two genotypes Agbagoma and Balabi were evaluated. The samples Agbagoma and Balabi had 8.90%–9.00% moisture, 16.80%–17.40% protein, 47.80%–48.00% fat, 7.70%–7.80% ash, and 18.20%–18.40% carbohydrate. The mean values of functional properties revealed significant differences (p < .05) between okra seed flour samples studied. The samples’ bulk density range was 0.80–0.83 g/ml. Water absorption capacity and oil absorption capacity ranged from 511.65% to 504.32% and 88.38 to 160.67%, respectively. The solubility was 14.10% for Agbagoma and 10.97% for Balabi, whereas swelling power was 16.37% and 14.68% for Agbagoma and Balabi, respectively. All pasting properties except peak time and pasting temperature of Agbagoma seed flour were higher than those of Balabi seed flour. The study revealed that dried okra seed flour is rich in nutrients, which could be used for baking and fortification of foods.

Okra pods can be consumed in many ways as fresh (raw), dried, cooked, frozen, fried, and pickled. Utilization of okra seeds is numerous. In Turkey, mature okra seeds are roasted, ground, and used as a coffee substitute (Calisir & Yildiz, 2005). In Africa, often okra seeds are dried and used to prepare vegetable curds (Moekchantuk & Kumar, 2004). Adelakun and Oyelade (2011) opined that okra seed flour has huge potential of being used to enrich foods to improve daily nutritional needs. Okra has industrial applications and is used in confectionary products (Adetuyi, Badejo, Ikujenlola, & Omosuli, 2009). In Egypt, okra seed flour has been used to supplement corn flour to produce better quality dough (Kumar, Patil, Patil, & Paschapur, 2009).
In Ghana, the major okra genotypes identified in Ghana with high seed contents include Agbagoma and Balabi. However, literature is limited on the physicochemical and functional properties of the seed flour to explore alternative uses in food systems. In addition, pectin is commercially extracted from the okra pods  leaving the seeds wasted, which can be utilized in the production of seed flour. The objective of this work was to determine the physicochemical and functional properties of the dried seed flour of Agbagoma and Balabi genotypes cultivated in Ghana.

| Materials and reagents
All chemicals used were analytical grade reagents. Two okra genotypes Agbagoma and Balabi were cultivated at Akrofu in the Volta Region of Ghana, and all agricultural practices including thinning, weed control, and watering were carried out under controlled environmental conditions. The okra pods were harvested after 3 months of cultivation.

| Preparation of okra seed flour
Harvested Agbagoma and Balabi okra genotypes were sorted, cleaned, and washed with distilled water and cut opened using a stainless knife to remove seeds. Seeds were then sun-dried for 6 hr.
The sun-dried seeds were ground into powder of particle size less than 450 µm using a grinding mill (Christy and Norris Ltd., Surrey, UK) and packaged in zip-lock bags and stored at −20°C in a freezer (Protech PRCF-500, China) for further analysis.

| Proximate analysis
Proximate composition of moisture, crude protein, ash, and crude fat of the dried okra seed flour samples was determined according to AOAC (2005). Protein was calculated from total nitrogen using the conversion factor 6.25. The percentage of total carbohydrate content of okra seed flour sample was calculated by subtracting the percentage of moisture, ash, protein, and fats obtained from 100.

| Determination of pH, color, and bulk density
The pH was determined by the method as described by AOAC (2005).
Two grams (2.0 g) of okra seed flour was poured into three beakers containing 20 ml of distilled water and allowed to stand for a while and an electric digital pH meter (BECKMAN Φ340 pH/Temp. Meter) was used to determine the pH of the samples. The pH meter was dipped into the sample and the reading was taken after about 4 min when it was stable.
The color of the okra seed flour was measured using the CR-400 Chroma Meter which is a handheld, portable measurement instrument designed to evaluate the color of objects.
The color meter coordinates system L* a* b* values were recorded, and the Light index was calculated as (100/0). The white tile used for calibrating the Hunter L* a* b* color scale had L* = + 97.51, a* = + 0.29 and b* = 1.90 as standards.
Bulk density was determined by modifications of the gravimetric method by Asoegwu, Ohanyere, Kanu, and Lwueke (2006). Fifty grams (50 g) of okra seed flour sample was weighed into 100 ml measuring cylinder. The bottom of the cylinder was tapped repeatedly on a firm pad on a laboratory bench until a constant volume was observed. The packed volume was recorded. The bulk density (BD) was calculated by using a ratio of sample weight to constant volume obtained as:

| Determination of water and oil absorption capacities
Water and oil absorption capacity was determined by the method of Beuchat (1977). One gram (1 g) of okra seed flour sample was mixed with 10 ml distilled water for 30 s. The samples were then allowed to stand at room temperature (25 ± 2°C) for 30 min after which they were centrifuged at 3,000 rpm for 30 min. The volume of the supernatant was noted in a 10 ml graduated cylinder. Water absorption capacity (mg.mL -1 ) was calculated as the difference between the initial volume of water added to the sample and the volume of the supernatant. The same procedure was carried out to determine the oil absorption capacity as below; (1) Bulk Density = Weight of sample constant volume (2) Water Absorption Capacity∕Oil Absorption Capacity = Bound water∕oil weight of sample × 100

| Determination of swelling power and water solubility index
Swelling power and water solubility indices were carried out based on a modification of the method of Leach, McCoven, and Scoch (1959). One gram (1 g

| Statistical analysis
Two samples independent test was used for mean comparison to identify significant differences between the samples. Statistical significance was accepted at 95% confidence limit (p < .05).

| Proximate composition of okra seed flour
Moisture content of the okra seed flour samples ranged from 8.90% to 9.00% (Table 1). The Balabi had the lower average moisture content than Agbagoma genotype. The moisture content of flour studied (8.9%-9.0%) falls within the acceptable range of 0%-13% (James, 1995). This moisture content range has been reported to be unfavorable for spoilage organisms to thrive (James, 1995), therefore extending the shelf-life of flours and other food products. According to Uyoh, Ita, and Nwofia (2013), moisture content is an index of its water activity important for stability in foods.
Protein content was in the range of 16.80%-17.40% for the dried okra seed flour samples (

| Physicochemical properties of okra seed flour
The pH values of the okra seed flour samples ranged from 6.41 to 6.48 with no significant difference between all okra seed flour samples (Table 2). In a study by Ahmed, Shivhare, and Debnath (2002), the authors reported pH 5.08 for green chili puree.
Color value was between the ranges of 60.29 to 65.37 in all okra seed flour samples. The color (L* a* b*) values were significantly higher (p < .05) for Balabi as compared to Agbagoma okra seed flour samples ( Table 2). The color brightness coordinate L* measures the degree of whiteness, ranging between black (0) and white (100).
The chromaticity coordinate a* measures red when positive and green when negative, and b* measures yellow when positive and blue when negative. Consumer acceptability is affected by the presence of color in starch, which is an indication of low quality (Galvez & Resureccion, 1993). The color brightness (L*) of the Balabi seed flour was significantly higher (p < .05) than that of the flour from

| Functional properties of dried okra seed flour
The results of the functional properties of okra seed flour samples are presented in Table 3.
According to Kinsella (1979) The low swelling power value could be attributed to the low carbohydrate content of the okra seed flour because the ability to swell is a function of the carbohydrate content.
There was significant difference (p < .05) between okra seed flour samples in terms of solubility index. Often, the solubility and

| Pasting properties of okra seed flour
The pasting property parameters of Agbagoma seed flour were higher than that of the Balabi seed flour (Table 4) The high peak viscosity of the Agbagoma seed flour shows that water molecules penetrate easily causing enormous granular swelling, which in turn weakens the associative forces of the flour hence makes them susceptible to breakdown as compared to the Balabi seed flour with lower peak viscosity (Etudaiye, Nwabueze, & Sanni, 2009).
Although the trough viscosity is the ability of starch to withstand long duration of hot temperature during processing or heating, the Agbagoma seed flour with high hot paste stability would preferably be used in food processing than Balabi seed flour.
According to Olufunmilola, Jacob, and Tajudeen, (2009), flours with low break down are more stable under hot conditions and have strong cross-linking within the granules. It therefore implies that there is stronger cross-linking within the granules of the Balabi seed flour. Agbagoma seed flour recorded higher final viscosity, which suggests its ability to form gel/paste during cooling (Shimelis, Meaza, & Rakshit, 2006) and more suitable in the processing of food products such as sauces, soups, and dressings.
As the setback value is a measure of gel stability and potential of retrogradation, the low setback value of the Balabi seed flour suggests its high resistance to retrogradation than the Agbagoma seed flour with a higher setback value. Balabi seed flour can be incorporated into wheat flour in the production of pastries such as bread, pie, and others (Adams et al., 2019).

| CON CLUS ION
The dried okra seed flours (Agbagoma and Balabi) revealed a high content of fat and proteins. The high protein content could be a valuable protein supplement for cereals based foods. The pH values of the okra seed flour were within the recommended range which is ideal for individuals with ulcers-related problems. The functional properties of okra seed flour were appreciable that could be exploited in food formulations such as cereals and wheat flour. All pasting properties except peak time and pasting temperature of Agbagoma seed flour were higher than that of Balabi seed flour suggestion that Balabi seed flour could be used as composite for baby foods because of its low viscosity whereas flour from Agbagoma could be used as composite for high viscous food.

CO N FLI C T O F I NTE R E S T
All the authors hereby state that there is no conflict of interest regarding this publication.