Chemical composition and nutritional evaluation of the seeds of Acacia tortilis (Forssk.) Hayne ssp. raddiana

Chemical composition and nutritional evaluation of the seeds of Acacia tortilis (Forssk.) Hayne ssp. raddiana

Food Chemistry 200 (2016) 62–68 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Chemica...

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Food Chemistry 200 (2016) 62–68

Contents lists available at ScienceDirect

Food Chemistry journal homepage: www.elsevier.com/locate/foodchem

Chemical composition and nutritional evaluation of the seeds of Acacia tortilis (Forssk.) Hayne ssp. raddiana Hassan E. Embaby, Ahmed M. Rayan ⇑ Food Technology Department, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt

a r t i c l e

i n f o

Article history: Received 9 August 2015 Received in revised form 29 December 2015 Accepted 6 January 2016 Available online 7 January 2016 Keywords: Acacia tortilis Seeds Chemical composition Antinutritional factors Functional properties

a b s t r a c t Chemical composition and nutritional evaluation as well as physicochemical and functional properties of seed flour of Acacia tortilis (Forssk.) Hayne ssp. raddiana were studied. The results indicated that seeds contained 5.30% moisture, 3.99% ash, 9.19% fat, 14.31% fiber, 27.21% protein and 45.30% carbohydrates. Potassium was the predominant element followed by calcium and then phosphorous. Phytic acid, tannins and trypsin inhibitor as antinutrients were detected. The amino acid profile compared well with FAO/ WHO recommended pattern except for cystine/methionine, isoleucine, tyrosine/phenylalanine, lysine and threonine. Also, the first limiting amino acid was lysine. Fatty acid composition showed that linoleic acid was the major fatty acid, followed by palmitic, stearic, oleic and arachidic acids. The seed oil showed absorbance in the ultraviolet ranges, thus it can be used as a broad spectrum UV protectant. For physicochemical and functional properties, acacia seeds flour had excellent water holding index, swelling index, foaming capacity and foam stability. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction The growth in food demand and need are the result of the effects of world population growth. In developing countries large groups of the population suffer from protein malnutrition, hunger, famine and their associated disease (Falade, Owoyomi, Harwood, & Adewusi, 2005). To meet these nutritional requirements and continued increases in population, studies are needed to investigate and explore new food sources. In this regard, more attention has been focused on lesser known useful plants as food for human and feed for animals (Ee & Yates, 2013; El-Adawy & Khalil, 1994; Embaby & Mokhtar, 2011). The genus acacia is a large group of woody species, including shrubs of the family Fabaceae. Also, acacia is one of the plants that have been frequently used as medicine to treat fever, diarrhea, leukorrhoea, haemoptysis and throat infections (Agrawal & Gupta, 2013). The seeds of some acacia species are an important food source for humans and recognized to have economic potential due to the high amount of protein and soluble carbohydrates. For instance, the seeds of both Acacia nilotica and Acacia leucophloea are known to be eaten by tribal people in India (Siddhwaju,

⇑ Corresponding author at: Food Technology Department, Faculty of Agriculture, Suez Canal University, Ismailia 41522, Egypt. E-mail address: [email protected] (A.M. Rayan). http://dx.doi.org/10.1016/j.foodchem.2016.01.019 0308-8146/Ó 2016 Elsevier Ltd. All rights reserved.

Vijayakumari, & Janardbanan, 1996; Vijayakumari, Siddhuraju, & Janardhanan, 1994). In Egypt, Acacia tortilis (Forssk.) Hayne ssp. raddiana is grown in the Sinai area and the common Arabic name is sayyal. The plant tends to grow in areas where temperatures vary from 0 to 50 °C and rainfall is anywhere from about 100–1000 mm (3.9–39.4 in) per year and the seeds are known to be used for animal feed. However, information on the chemical composition, physical properties and nutritive value of Acacia tortilis seeds is scanty. Therefore, this study investigated the chemical composition and nutritive value of Egyptian Acacia tortilis seeds and evaluated the physicochemical and functional properties of acacia seed flour and oil. This study will provide information on whether or not advisable to incorporate this seed into the human diets.

2. Materials and methods 2.1. Materials Dry mature seeds of Acacia tortilis (Forssk.) Hayne ssp. raddiana were collected from three different areas including Ismailia (from the campus of the Suez Canal University), South Sinai and North Sinai, Egypt. Whole seeds from each area were separately ground using an electric mill then used for chemical composition and nutritional evaluation analyses. The coarsely ground seeds were passed through a 0.25 mm sieve to obtain the flour which will be

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used for physicochemical and functional properties determination. At least two determinations were conducted for each sample (from each area) and the range which represents the highest and the lowest value for each component was given. All chemicals and reagents used in this study were of analytical grade and purchased from Sigma–Aldrich Co. (St. Louis, Mo., USA). 2.2. Proximate analysis Proximate composition of the acacia seeds was determined by using the standard Association of Official Analytical Chemists (AOAC) procedures (2005). Moisture content was evaluated by the loss of weight upon drying in an oven at 100 °C to a constant weight. Ash was assessed by incineration at 550 °C of known weights of the samples in a muffle furnace (Method No. 930.05) (AOAC, 2005). Crude fat was found out by exhaustively extracting a known weight of sample in petroleum ether (boiling point, 60– 80 °C) in a Soxhlet extractor (Method No. 930.09) (AOAC, 2005). Protein amount (N  6.25) was measured by the Kjeldahl method (Method No. 978.04) (AOAC, 2005). Crude fiber quantity was ascertained after digesting a known weight of fat-free sample in refluxing 1.25% sulfuric acid and 1.25% sodium hydroxide (Method No. 930.10) (AOAC, 2005). Carbohydrates were calculated by difference. 2.3. Minerals analysis Samples were digested with concentrated nitric acid and perchloric acid (4:1, v/v) and heated to 70–90 °C for 10 min and cooled before injection. Minerals including iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn) were estimated in the digested acacia seeds sample, using an Atomic Absorption spectrophotometer (Thermo Electron Corp., S series, AA spectrometer, Type S4 AA system, assembled in China). Potassium (K) and sodium (Na) contents of the digests were determined colorimetrically using Flame photometer model (Jenway Clinical PFP7, Jenway Ltd, Felsted, Dunmow, Essex, UK). Phosphorus (P) content was measured by using the phosphomolybdovanate method (AOAC, 2005). Calcium (Ca) and magnesium (Mg) were assessed by using the titration method with a 0.02 M EDTA solution, according to Chapman and Pratt (1961). 2.4. Antinutritional factor analysis Phytic acid was determined by the method of Latta and Eskin (1980), as modified by Vaintraub and Lapteva (1988). One gram of the sample was extracted with 50 ml 2.4% HCl for 1 h at ambient temperature and centrifuged at 3000g for 30 min. The clear supernatant was used for the phytate estimation by using the Wade reagent (0.03% solution of FeCl3  6H2O containing 0.3% sulfosalicylic acid in water) and the absorbance was measured at 500 nm using a spectrophotometer (model 6505 UV/Vis, JENWAY, UK). The concentration of phytate was calculated from the standard curve (using phytic acid), and the results were expressed as gram phytic acid per 100 g (dry matter). Tannins content was detected using the Folin–Denis reagent according to the method of AOAC (1984). Two hundred milligrams of the sample were extracted with 10 ml of 70% aqueous acetone (v/v) for 24 h. The extracts were centrifuged at 3000g for 20 min and the supernatant was used for the tannins estimation. After adding the saturated Na carbonate solution and the Folin– Denis reagent, the absorbance was measured at 760 nm. Tannic acid was used as a standard compound and the results were expressed as gram per 100 g (dry matter). Trypsin inhibitor activity (TIA) was evaluated using the procedure of Kakade, Rackis, McGhee, and Puski (1974). One gram of

defatted sample was mixed with 100 ml of 0.009 M HCl with shaking at ambient temperature for 2 h. After the centrifugation at 10.000g for 20 min, the clear supernatant was used for inhibitor activity estimation. Trypsin inhibitor activity was determined by using the trypsin solution and the substrate solution (BAPNA), the reaction was stopped by the addition of acetic acid (30%, v/ v). The absorbance was measured at 410 nm by using the spectrophotometer and the obtained values from the sample extract were subtracted from the trypsin standard. The trypsin inhibitor content was calculated from the following equation.

Ti; mg=g of sample ¼

Astd-Asam 0:019  sample wt:; g dilution factor  1000  sample size; ml

2.5. Amino acid analysis Amino acid composition was analyzed using High-Performance Amino Acid Analyzer (Biochrom 20, Auto sampler version, Amersham Pharmacia Biotech., Sweden). The sample (100 mg) was hydrolyzed with 5 ml of 6 M HCl in a sealed tube at 110 °C in an oven for 24 h. The hydrolyzed sample was re-dissolved in Na citrate buffer (pH 2.2) and filtered using a 0.2 lm membrane filter then injected into the amino acid analyzer (Baxter, 1996). The contents of the various recovered amino acids were presented as grams per 100 g of protein and were compared with the FAO/ WHO (1990) reference pattern. 2.6. Fatty acid analysis Fatty acid methyl esters (FAME) analyses were prepared according to the method of O’Fallon, Busboom, Nelson, and Gaskins (2007). Fatty acid analysis was performed using a Hewlett Packard Gas Chromatograph (HP 6890 series), equipped with a flame ionization detector and a capillary column, HP5, (30 m; i.d. 0.32 mm; 0.5 lm film thickness). The column temperature was programmed from 150 °C for 1 min then elevated to 235 °C at a rate of 17 °C/min and then raised to 245 °C at a rate of 1 °C/min and hold at 245 °C for 5 min. The injector and detector temperatures were 260 and 275 °C, respectively. Nitrogen was the carrier gas at a flow rate of 1.5 ml/min. Identification of the peaks was achieved by retention times and by comparing them with authenticated standards analyzed under the same conditions. 2.7. Morphological analysis of the defatted acacia seed flour Scanning electron microscopy (SEM) of Acacia tortilis seed flour was carried out using a JSM-5800 LV microscope (JXA-840A ELECTRON PROBE MICROANALIZER, JEOL, TOKYO, JAPAN). Flour samples were sprinkled on adhesive tape, attached to specimen studs and coated with gold (S150A SPUTTER COATER). 2.8. Physicochemical and function properties of acacia seed flour Bulk density was determined according to the method described by Nwosu (2010). A clean, dry, measuring cylinder was filled with the flour sample and the bottom of the cylinder was tapped on a table until the level could fall no further at the 100 ml mark. The weight of the flour (W), which occupied the 100 ml was measured and expressed as a ratio of the volume (V). The bulk density was given by:

Bulk density ¼

W ðgÞ V ðmlÞ

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The water absorption index (WAI) was determined according to the method of Anderson, Conway, and Peplinski (1970). Distilled water (10 ml) was added to 1 g of flour sample in a weighed centrifuge tube. The tube was agitated for 2 min and then centrifuged for 15 min at 3000 rpm. The supernatant was poured into a tarred evaporating dish. The remaining gel was weighed and the WAI was calculated as:

WAI ¼ mg =ms where: mg is the weight of the hydrated gel (g) and ms is the weight of sample (g). The water solubility index (WSI) was calculated from the amount of dry solids recovered by evaporating the supernatant from the water absorption test as:

WSI ¼ ðmds =ms Þ  100 where: mds is the weight of dry solids from the supernatant (g) and ms is the weight of the sample (g). Oil absorption index (OAI) was measured according to the method of Liadakis, Floridis, Tzia, and Oreopoulou (1993). Refined corn oil (6 ml) was added to 1 g of flour sample in a graduated centrifuge tube. The tube was agitated for 1 min, left for 30 min and centrifuged for 20 min at 3000 rpm; the volume of the free oil was recorded. OAI was calculated as:

OAI ¼ V oil =ms where: Voil is the volume of absorbed oil (ml) and ms is the weight of the sample (g). Swelling index was carried out according to Amiri, Ebrahimizadeh, Amiri, Radi, and Niakousari (2009). Three gram portions (dry base) of flour were transferred into clean, dry, graduate (50 ml) cylinders. Flour samples were gently leveled and the volumes noted. Distilled water (30 ml) was added to each sample; the cylinder was swirled and allowed to stand for 60 min while the change in volume (swelling) was recorded every 15 min. The swelling power of each flour sample was calculated as a multiple of the original volume. Foaming capacity and stability were determined by the procedure of Nwosu (2010). Two grams of the sample were whipped with 100 ml distilled water in a micro blender at high speed for 5 min and quickly transferred carefully into a 250 ml graduated cylinder. The total volume of foam was noted and expressed as a ratio of the volume before blending. It was expressed as a percentage and was given by:

Ultraviolet–visible profiles of oil solution in hexane were obtained from scans (k = 200 to 290) of oil diluted 1:100; from scans (k = 290 to 400 nm) of oil diluted 1:100; and from scans (k = 400 to 800 nm) of oil diluted 1:10.

3. Results and discussion 3.1. Proximate composition The result presented in Table 1 shows that the moisture content of Acacia tortilis seeds is low (5.30%) indicating excellent storing quality for this seed. This result was similar to that reported for A. leucophloea (Vijayakumari et al., 1994). Ash content of A. tortilis seeds was 3.99%, which was quite similar to that reported for A. leucophloea (Vijayakumari et al., 1994). The fat yield (9.19%) was higher than that reported for A. leucophloea but fell within the range reported for A. colei and A. tumida (Adewusi, Falade, & Harwood, 2003). The relatively high level of crude fat in A. tortilis seed indicates that the seed would be a good source of energy. The content of crude fiber (14.31%) was higher than that recorded for A. leucophloea (Vijayakumari et al., 1994), but was similar to that reported for A. nilotica (Siddhwaju et al., 1996). Therefore, acacia seeds can be considered as a good source for dietary fiber. In fact, the dietary fiber has an important role in the human nutrition in that fiber helps to maintain the health of the gastrointestinal tract, but in excess may bind trace elements, leading to deficiencies of iron and zinc (Siddhwaju et al., 1996). The results show that A. tortilis seeds had a high protein content (27.21%), which was closely resembled that reported for A. leucophloea (Vijayakumari et al., 1994) but was higher than the protein content determined for A. colei and A. tumida (Falade et al., 2005). These results indicate that acacia seeds can be included in food formulations as a source of protein. Regarding the carbohydrate content, A. tortilis seeds contained 45.30% carbohydrate. This level of the carbohydrate was lower than that reported for A. leucophloea (Vijayakumari et al., 1994) and A. tumida (Falade et al., 2005), due to the higher levels of crude protein, crude fat and fiber in the seed. Therefore, the chemical composition of A. tortilis seeds

Table 1 Proximate, minerals and antinutritional factors composition of Acacia tortilis seed (dry weight).

Va  Vb 100 Foam capacity ð%Þ ¼  Vb 1 Va = volume of liquid and foam; Vb = volume of mixture before whipping. The foam stability was measured in terms of how stable the formed foam lasted at room temperature. The cylinder containing the sample was left undisturbed following the foam capacity experiment. At intervals (20 min/1 h) the foam volume was recorded. The foam stability was determined by measuring the foam volume at time (T). (T = life span of foam = 1 h) and expressed as the ratio of the foaming volume at the beginning. 2.9. Color and ultraviolet (UV) visible profile of acacia oil The CIELab coordinates (L⁄, a⁄, and b⁄) were directly read with a spectrophotocolorimeter (Konica Minolta Sensing, Inc. Osaka, Japan). In this coordinate system, the L⁄ value is a measure of lightness, ranging from 0 (black) to 100 (white), the a⁄ value ranges from 100 (greenness) to +100 (redness), and the b⁄ value ranges from 100 (blueness) to +100 (yellowness).

a b

Component

Valuea

Rangeb

Proximate composition Moisture (%) Ash (%) Fat (%) Crude fiber (%) Protein (%) Carbohydrates (%)

5.30 ± 0.65 3.99 ± 0.32 9.19 ± 0.58 14.31 ± 0.57 27.21 ± 1.24 45.30 ± 1.74

(4.68–6.41) (3.61–4.37) (8.44–9.93) (13.2–14.7) (25.7–28.7) (43.3–48.1)

Minerals Ca (mg/100 g) P (mg/100 g) K (mg/100 g) Mg (mg/100 g) Na (mg/100 g) Mn (mg/100 g) Cu (mg/100 g) Zn (mg/100 g) Fe (mg/100 g)

70.5 ± 1.29 67.8 ± 5.89 448 ± 12.5 56.5 ± 3.22 48.0 ± 4.47 3.89 ± 0.27 0.74 ± 0.09 3.76 ± 0.47 6.79 ± 0.54

(69.0–72.0) (64.0–71.0) (435–465) (55.0–58.0) (45.0–55.0) (3.48–4.25) (0.63–0.86) (3.11–4.30) (6.31–7.63)

Antinutritional factors Phytic acid (g/100 g) Tannins (g/100 g) Trypsin inhibitor (mg/g)

2.48 ± 0.31 0.98 ± 0.22 1.48 ± 0.21

(2.30–3.07) (0.67–1.20) (1.14–1.65)

Results are mean of three different determinations ± standard deviation. Range represents the lowest and highest observed values.

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was determined to be nutritious and incorporating this seed into the human diets will improve the nutrition status. 3.2. Minerals composition

Table 2 Amino acid composition and essential amino acid score of Acacia tortilis seed compared to the essential amino acid pattern suggested by FAO/WHO (g/100 g protein).

Plants are known to provide the required vitamins and minerals important for human health. Table 1 shows the minerals composition of A. tortilis seeds. Potassium was the predominant mineral; this result was in good agreement with the findings of BrandMiller and Maggiore (1992) and Vijayakumari et al. (1994) for different species of acacia seed samples. Other elements in descending order by quantity were Ca, P, Mg, Na, Fe, Mn, Zn and Cu. Also, the contents of Fe, Mg, Na, Ca, P, Zn, Mn and Cu fell within the range reported for 34 acacia species (Aganga, Tsopito, & Adogla-Bessa, 1998; Brand-Miller & Maggiore, 1992). Based on the above results, A. tortilis seeds are a good source for minerals, especially K, Ca, P, Mg and Na. Since some flours used in commercial baking are deficient in one or more element, addition of acacia seed flour might improve their nutritional properties. 3.3. Antinutritional factors composition Antinutritional factors in plant foods are responsible for deleterious effects related to the absorption of nutrients and micronutrients. However, some antinutrients may actually have beneficial health effects at low concentrations. For example, phytic acid, tannins and protease inhibitors have been shown to reduce the availability of nutrients and cause growth inhibition. However, when used at low levels, they have also been shown to reduce cancer risk, blood glucose and insulin responses to starchy foods and/or reduce plasma cholesterol and triglycerides. This reveals that antinutrients might not always harmful even though they lack general nutritive value (Gemede & Ratta, 2014). The levels of different antinutritional factors for A. tortilis seeds are listed in Table 1. The content of phytic acid (2.48 g/100 g) was higher than that of A. nilotica (Siddhwaju et al., 1996). However, this level was within the range reported for other seeds (Embaby & Mokhtar, 2011). The level of tannins (0.98 g/100 g) was slightly higher than that of A. leucophloea seed (Vijayakumari et al., 1994), but was lower than that reported for A. nilotica seed (Siddhwaju et al., 1996). On the other hand, the obtained result fell within the range reported for other seeds such as lupin (Embaby, 2010) and nabak seeds (Embaby & Mokhtar, 2011). The trypsin inhibitor activity (TIA) of A. tortilis (1.48 mg/g) was similar to those reported for some several common legume seeds (Embaby, 2010; Martin-Cabrejas et al., 2009). 3.4. Amino acid composition The amino acid profile and essential amino acid score (EAS) for A. tortilis seeds are listed in Table 2. The potential food value of the seed proteins (as a source of amino acids) can be justified by comparison with the FAO reference pattern (FAO/WHO, 1990). The amino acid profile of A. tortilis seeds revealed that both leucine and histidine had higher levels than those listed in FAO/WHO reference pattern. Also, the level of valine was very similar to that of the FAO/WHO reference pattern. However, the other essential amino acids had lower levels when compared with those of the FAO/WHO reference pattern. Moreover, the result of EAS indicated that the most limiting amino acids were lysine (57) and cystine/ methionine (66). 3.5. Fatty acid composition The fatty acid profile of A. tortilis seed oil is shown in Table 3. Linoleic acid was the predominant fatty acid (66.57%), followed

a b

Amino acid

Valuea

Rangeb

FAO/WHO reference

Essential amino acid score

Essential Cystine Methionine Valine Isoleucine Leucine Tyrosine Phenylalanine Histidine Lysine Threonine

1.64 ± 0.26 0.00 3.49 ± 0.55 2.25 ± 0.63 10.4 ± 1.36 2.78 ± 0.33 3.12 ± 0.39 3.41 ± 0.14 3.32 ± 0.56 2.76 ± 0.16

(1.38–1.91)

2.5

66

(2.92–4.02) (1.65–2.92) (9.45–12.0) (2.59–3.16) (2.84–3.57) (3.31–3.57) (2.76–3.89) (2.60–2.92)

3.5 2.8 6.6 6.3

100 80 158 94

1.9 5.8 3.4

179 57 81

Nonessential Aspartic acid Proline Serine Glutamic acid Glycine Alanine Arginine

3.01 ± 0.21 1.14 ± 0.17 3.03 ± 0.24 3.29 ± 0.54 2.04 ± 0.20 1.65 ± 0.27 4.22 ± 0.39

(2.84–3.24) (0.95–1.29) (2.76–3.24) (2.84–3.89) (1.89–2.27) (1.42–1.94) (3.78–4.54)

Results are mean of three different determinations ± standard deviation. Range represents the lowest and highest observed values.

Table 3 Fatty acid composition of Acacia tortilis seed oil (% of total fatty acids).

a b

Fatty acid

Valuea

Rangeb

Palmitic (C16:0) Stearic (C18:0) Oleic (C18:1) Linoleic (C18:2) Arachidic (C20:0) Total unsaturated fatty acids Total saturated fatty acids

12.31 ± 0.83 11.88 ± 0.42 7.740 ± 0.30 66.57 ± 0.36 1.500 ± 0.12 74.31 25.69

(11.90–13.72) (11.37–12.36) (7.540–8.190) (66.14–66.96) (1.410–1.640)

Results are mean of three different determinations ± standard deviation. Range represents the lowest and highest observed values.

by palmitic acid (12.31%), stearic acid (11.88%), oleic acid (7.74%) and arachidic (1.50%). These results were similar to profiles obtained by Rivett, Tucker, and Jones (1983) for seeds from three other Australian Acacias (A. alata, A. dealbata, A. drummondii). Also, the results of four subspecies of A. saligna indicated that the seed oil had relatively high levels of the essential fatty acid, linoleic acid, followed by oleic, palmitic and stearic acids (Ee & Yates, 2013). Moreover, the content of linoleic acid in A. tortilis seed oil was similar to that of sunflower oil and such linoleic acid rich oils including A. tortilis oil can play a significant role in reducing blood cholesterol levels when consumed regularly as a part of the diet, thus, indicating that the oil is highly nutritious (El-Adawy & Taha, 2001). In addition, the results indicated that A. tortilis seed oil contained 74.31% unsaturated fatty acids. This degree of the unsaturation was close to those of the common vegetable oils. The higher index of mono- and polyunsaturated fatty acids play an important role in human and animal health. 3.6. Morphological analysis of the defatted acacia flour Fig. 1 shows SEM micrographs of the defatted A. tortilis seed flour. A compact structure of densely cells of starch granules surrounded by a protein matrix can be observed at different magnification levels (600–5000). The starch granules appear to be round or oval in shape with smooth surfaces and with a wide size distribution. These shapes were similar to those observed for potato starch granules (Sujka & Jamroz, 2009).

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3.7. Physicochemical and functional properties of Acacia tortilis seed flour Knowledge of functional properties of unconventional and/or novel food ingredients is imperative to be able to successfully incorporate these components into existing food formulations. The bulk density of A. tortilis seed flour was low (0.519 g/ml) (Table 4). It was reported that the low values of bulk densities make the flour suitable for high nutrient density formulation of foods (Shad, Nawaz, Hussain, & Yousuf, 2011). The water absorption index (WAI) was 3.17 g/g (Table 4), and the high protein content of such samples (27.21%), surrounding the starch granules increased the capacity of the flour to adsorb more water. For that reason the WAI is used as a function of protein quality. Furthermore, WAI is an important processing parameter and has implications for viscosity. It is also important in bulking and consistency of products, as well as in baking applications (Niba, Bokonga, Jackson, Schlimme, & Li, 2001). The water solubility index (WSI) was 20.6%. Amiri et al. (2009) reported that the degree of solubility may depend on the type and species of starch and proteins present in the flour. The milling process causes the breakdown of starch granules, which further leads to an improvement in the solubility index. An increase in temperature facilitates the hydrolysis of starch leading to improved solubility. It seems that the solubility was affected by the carbohydrate content of the samples. The oil absorption index (OAI) of A. tortilis seed flour was 1.28 ml/g (Table 4). The major chemical component affecting OAI is protein,

Table 4 Physicochemical and function properties of acacia seed flour.

a b

Property

Valuea

Rangeb

Bulk density (g/ml) Water absorption index (g/g) Water solubility index (%) Oil absorption index (ml/g) Swelling index (ml/g) Foaming capacity (%) Foaming stability (%)

0.519 ± 0.014 3.17 ± 0.24 20.6 ± 3.18 1.28 ± 0.13 3.13 ± 0.18 7.17 ± 1.66 71.8 ± 5.76

(0.493–0.532) (2.92–3.46) (16.6–24.1) (1.10–1.50) (3.00–3.33) (5.76–9.80) (66.6–80.0)

Results are mean of three different determinations ± standard deviation. Range represents the lowest and highest observed values.

which is composed of both hydrophilic and hydrophobic parts. Non-polar amino acid side chains can form hydrophobic interactions with hydrocarbon chains of lipid and has implications in the functional properties of flours (Jitngarmkusol, Hongsuwankul, & Tananuwong 2008). The oil absorption index is important since oil acts as flavor retainer and increases the palatable texture of foods. Improvement of palatability and extension of shelf life particularly in bakery or meat products where fat absorptions is desired, are important to achieve. The swelling index (SI) of A. tortilis seed flour was 3.13 ml/g. The swelling index is thought to be a property of amylopectin and amylase is thus a diluent. Polysaccharide (amylose, amylopectin or both depending on the starch) leached from the granules is generally highly correlated with the extent of swelling for each starch (Tester & Morrison, 1990). The foaming capacity was observed

Fig. 1. Scanning electron microscopic (SEM) pictures of Acacia tortilis seed flour.

H.E. Embaby, A.M. Rayan / Food Chemistry 200 (2016) 62–68

A

3.8. Color and ultraviolet–visible profile of acacia oil

35 30

Values

25

20 15 10 5 0

L

-5

a

b

2

Absorbance

B

1.5 1 0.5 0 200

230

260

290

λ (nm)

Absorbance

1 0.8 0.6

0.4 0.2 0 290

310

330

350

370

390

λ (nm) 0.8

Absorbance

67

Fig. 2(A) demonstrates the CIELab coordinates (L⁄, a⁄, and b⁄) of the oil extracted from A. tortilis seeds. The levels of L⁄, a⁄ and b⁄ of A. tortilis seed oil were 29.5, 1.6 and 12.8, respectively, indicating that this oil was light yellow in color. Also, the L⁄, a⁄, and b⁄ values of the A. tortilis seed oil were lower than those reported for common vegetable oils such as sunflower, olive, and corn oils (Hsu & Yu, 2002). Acacia tortilis seed oil showed some absorbance in the UV-C (100–290 nm), UV-B (290–320 nm), UV-A (320–400 nm), and visible (400–800 nm) range (Fig. 2(B)). In the UV-B and the UV-A ranges, the wavelengths of the UV light are responsible for most of the cellular damage (Oomah, Ladet, Godfrey, Liang, & Girard, 2000). As indicated by the absorbance at 290–400 nm, Acacia tortilis seed oil shields against UV-B and UV-A radiation. Thus, it could be used in the formulation of UV protectors that provide protection against both UV-A and UV-B. Similar results had been reported for raspberry seed oil (Oomah et al., 2000), and Lantana and sweet pepper seed and nabak seed kernel oils (Embaby & Mokhtar, 2011). Embaby and Mokhtar (2011) also stated that these oils can shield against UVA-induced damage by scattering (high transmission), as well as by absorption. The high absorption at or above 230 nm may be due to the conjugation of double linkers resulting from the oxidation of polyunsaturated fatty acids and hydroperoxides of the linoleic acid produced by the oil autoxidation (Embaby & Mokhtar, 2011). Furthermore, the studied oil contained yellow color similar to Nabak seed kernel oil (Embaby & Mokhtar, 2011), but was more yellow colored than date palm seed oil (Nehdi, Omri, Khalil, & Al-Resayes, 2010) under the same conditions. The yellow color of A. tortilis seed oil, which includes carotenoids, is beneficial, since it enhances the appearance of dairy products without the use of primary colorants, such as carotenes and annattos, which are generally used in the oil and fat industry (Besbes, Blecker, Deroanne, Drira, & Attia, 2004).

0.6

4. Conclusion

0.4 0.2 0 400 440 480 520 560 600 640 680 720 760 800

λ (nm) Fig. 2. (A) CIELab coordinates (L⁄, a⁄, and b⁄) of oil extracts from Acacia tortilis seeds. (B) Ultraviolet–visible spectra of Acacia tortilis seed oil.

The present study on the chemical composition and nutritional value of Acacia tortilis seeds suggests that these seeds could be useful as a new source of food ingredients especially for adding protein, lipid, fiber and minerals. However, this seed contained some antinutrients, which must be reduced or removed before using. Also, the seed flour had physicochemical and functional properties, making it suitable for several food formulations. References

to be 7.17% (Table 4). The foamability of the flour depends on the proportion of the flexible protein molecules in the flour, which may decrease the surface tension of water (Sathe, Desphande, & Salunkhe, 1982). The foaming stability of acacia seed flour was 71.8%. It was reported that there was an inverse relationship between foaming capacity and foaming stability. Flours with high foaming ability could form large air bubbles surrounded by a thinner, less flexible protein film. These air bubbles might be easier to collapse and consequently lowered the foaming stability (Jitngarmkusol et al., 2008). In general, the levels of these properties are within the ranges reported for other common legume seeds such as pinto beans, lima beans, red kidney beans, mung beans and lentils (Du, Jiang, Yu, & Jane, 2013). It is worth mentioning that there are no data reported in the literature regarding the physicochemical and function properties of acacia species seeds flour.

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