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Postharvest physicochemical properties of the pulp and seed oil from Annona squamosa L. (Gishta) fruit grown in Darfur region, Sudan
⁎Corresponding author at: School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China. Fax: +86 511 88790958. mhl@ujs.edu.cn (Haile Ma)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
The purpose of this study was to investigate on the postharvest physicochemical properties of Annona squamosa fruits. Changes in physicochemical parameters during ambient storage of the fruits for 9 days were determined. The fruits seeds’ chemical composition and physicochemical characteristics of the seeds oil were also studied. Results indicate that the seeds contain higher amounts of protein (18.34%) and oil (30.41%) than the fruit pulp. Levels of K, P and Mg are higher in the fruits and levels of Ca, Na, Cu, Zn and Fe are higher in the seeds. Moisture content, total sugar, reducing sugar, sucrose, titratable acidity and total soluble solids of the fruits increased significantly (p < 0.05) during the storage, while ascorbic acid and pH declined. Accordingly, a maximum of 6 day-storage period for the fruits is satisfactorily. The seed protein contains leucine, lysine, methionine, phenylalanine, threonine, valine and histidine comparable to World Health Organization (WHO) reference patterns. Iodine and saponification values of the seeds oil are higher but the acid value and the peroxide value are lower. The high iodine value suggests susceptibility of the oil to autoxidation. Oleic acid is the major fatty acids in the oil, followed by linoleic, palmitic and stearic acids, respectively. In conclusion, the fruits’ physicochemical attributes suggest its adequacy for human nutrition. The seeds oil could also be useful for edible purpose.
Keywords
Annona squamosa fruits
Postharvest storage
Fruits seeds
Seeds oil
Physicochemical properties
1 Introduction
Fruits have become important for human nutrition due to their nutrients and potential beneficial health effects (Albuquerque et al., 2016). Annona squamosa is a large evergreen tree, up to 7 m in height. It bears fruit commonly known as Custard apple in English and Sharifa in Hindi. The tree is cultivated all over many tropical countries (Salman and Senthilkumar, 2015). In Sudan, the fruit is locally known as Gishta (in Arabic) and it is grown in Darfur and Kordofan regions. The fruits have an edible soft granular juicy and sugary pulp with mild flavor and slight acidity. On the other hand, the demand for the fruits’ oils is increasing due to the nutritional needs and industrial requirements. The lack of information on the composition and utilization of many oil seeds indigenous to Sudan is problematic. The physicochemical properties of mango fruits (Abdualrahman, 2013) and apple fruits (Abdualrahman, 2015) from Darfur region have been studied due to their importance for human nutrition. Postharvest studies on fruits provide information that shows variations of fruits’ properties and the best beneficial time for consumption of the fresh fruits (Othman et al., 2014). To date, there are no studies on the common fruits such as papaya, Annona squamosa, and Cordia Africana grown in Darfur. Therefore, this study aimed to assess the effect of postharvest storage on the fruits’ physicochemical properties. The chemical composition of the seeds and the physicochemical characteristics of the seeds oil are also evaluated.
2 Materials and methods
2.1 Materials and chemicals
Annona squamosa fruits were collected from Nyala, Darfur region, Sudan. The fruits were sorted out, and cleaned. To investigate on the postharvest changes, fresh harvested fruits were stored at ambient temperature (25 °C) for a period lasting in 9 days. Stored fruit samples were withdrawn at 3 days intervals. Fresh and stored fruits were peeled off, seeds were removed and the pulps were kept at 4 °C for subsequent analyses. The seeds were dried under the shade for 10 days and then milled to pass 0.5 mm-mesh size using an electric grinder (Fritsch, idar-oberstein Germany) and then kept at 4 °C for further studies.
The following analytical reagents were used: sulfuric acid, petroleum ether, sodium hydroxide, copper (II) sulfate, sodium sulfate, sodium bicarbonate, sodium arsenate dibasic heptahydrate, sodium thiosulphate, boric acid, metaphosphoric acid, 2.6-dichlorophenol-indophenol, ethanol, potassium iodide, carbon tetrachloride, hydrochloric acid, potassium hydroxide, phenolphthalein, toluene, nitric acid, acetic acid, oxalic acid, iodine chloride, chloroform, potassium sodium tartrate, ammonium molybdate and caproic acid. All chemicals were used of analytical grade (Sigma Chemicals Co., St. Louis, MO, USA). Arium 67316 reverse osmosis (Sartorius Stedim Biotech GmbH, Germany) was used to treat the distilled water.
2.2 Proximate composition
Contents of crude oil (Soxhlet method), total nitrogen (micro-Kjeldahl method), ash, and total carbohydrates (by subtraction) of the fruit pulp and the dried seed samples were determined according to the official methods of AOAC (2005). Moisture content was determined by drying a sample at 105 °C overnight. Crude protein was calculated as N% × 6.25. The crude oil was extracted with petroleum ether (boiling point, 60–80 °C) for 16 h. Crude fiber content was measured by the acid/alkali digestion method (Southgate, 1976).
2.3 Mineral analysis
Five grams from each of fruit pulp and seeds was placed in 2 crucibles and then incinerated at 600 °C for 24 h. Ash was obtained, dissolved in diluted HCl (1:3 HCl: distilled water, v/v) and then a few drops of concentrated nitric acid were added. The crucibles were heated on a sand bath. The contents were cooled and made up to 50 mL with distilled water. Na content was determined by a flame photometer (Corning, model 403, UK) (Abdualrahman et al., 2015). Ca, Mg, P, K, Fe, Zn and Cu were determined using atomic absorption spectrophotometer (Perkin-Elmer model 403, USA) (Ekpete et al., 2013).
2.4 Determination of the physicochemical properties of the fruits during ambient storage
The following physicochemical properties were determined in triplicate directly after arrival of the fresh fruits (zero time) at the laboratory and at intervals of three days from the day of harvest to the 9th day of storage.
2.4.1 Moisture content
The moisture content was determined following the official method described in Section 2.2.
2.4.2 Ascorbic acid
Ten grams of fruit pulp was mixed with 50 mL of 3% metaphosphoric acid solution. The mixture was made up to 100 mL with 3% metaphosphoric acid and then filtered. Ten milliliters of the filtrate was added to 1.0 mL of 40% formaldehyde and 0.1 mL of HCl. After standing for 10 min, the mixture was titrated with 2.6-dichlorophenol-indophenol dye to an end point of pink color. Dye factor was calculated by titrating 10 mL of standard ascorbic acid solution (0.1 mg/mL) with the dye (Kulkarni et al., 2015). The amount of ascorbic acid (mg/100 mL) was calculated as follows:
2.4.3 Total sugars
The total sugars content was determined by the phenol–sulfuric acid method (Wang et al., 2009). Hereby, 0.6 g of fruit juice was mixed with 0.6 mL of 5% phenol solution and 1.0 mL of concentrated sulfuric acid. The mixture was left to stand for 30 min and then the absorbance was read at 490 nm, using a UV spectrophotometer (Beijing Instrument Co. Ltd., China). Distilled water was used as a blank and glucose as standard for calibration.
2.4.4 Reducing sugars
The reducing sugar content was determined following the Nelson-Somogyi method (Green et al., 1989) with minor modifications. In short, 1.0 g of fruit juice was mixed with 1.0 mL of copper reagent comprised of 4.0 mL of KNa tartarate:Na2CO3:Na2SO4:NaHCO3 (1:2:12:1.3, w/w, dissolved in 75 mL distilled water) and 1.0 mL of CuSO4.5H2O:Na2SO4 (1:9, w/w, dissolved in 50 mL distilled water) and 1.0 mL of arsenomolybdate reagent (25 g ammonium molybdate in 450 mL H2O + 21 mL H2SO4 + 3 g Na2HASO4.7H2O in 25 mL H2O) in a test tube. The tube was vortexes thoroughly and boiled in a water bath for 10 min. After cooling, the tube was adjusted to 25 mL with distilled water. After 10 min, the diluted sample was filtered through a filter paper and the absorbance was measured at 600 nm in a UV spectrophotometer. Distilled water was used as a blank and glucose as standard for calibration.
2.4.5 Titratable acidity, total soluble solids (TSS) and pH
Ten grams of fruit pulp was mixed with 200 mL of distilled water, boiled for 1 h and then cooled. A known volume of 10 mL of the filtrate was titrated against 0.1 N NaOH. The titratable acidity was expressed as percentage of citric acid. The TSS was measured as °Brix at 20 °C using a refractometer (Atago, N1, brix 0–32, Japan). The pH was determined by a pH meter (PHS-3C Precision pH-meter, China) at 25 °C (Kulkarni et al., 2015).
2.5 Determination of the physicochemical characteristics of the oil from fruits seeds
2.5.1 Oil extraction
Soxhlet method (AOAC, 2005) was employed to extract the crude oil from seeds. Petroleum ether (boiling point, 60–80 °C) was used as the extraction solvent. Extraction was performed for 16 h and the petroleum ether was separated from the oil by distillation. Traces of petroleum ether were evaporated at 100 °C in an air oven for 1 h. The oil was cooled in a desiccator to room temperature (25 °C), put into a dark glass bottle, and stored at 4 °C for further analysis.
2.5.2 Specific gravity
A dry density bottle (volume capacity of 25 mL) was weighed accurately, filled with distilled water and weighed again. Similarly, another pre-weighed dried density bottle was filled with oil and re-weighed. Experiment was repeated three times (Kukeera et al., 2015). The specific gravity was calculated as follows: where Wb+o is the weight (g) of bottle filled with oil, Wb+w is the weight (g) of bottle filled with water and Wb is the weight (g) of empty bottle.
2.5.3 Refractive index
Refractive index is a measure of the deviation of the beam of light as it passes from one medium to another (Hussain et al., 2015). The refractive index of the seeds oil was determined with a digital refractometer (Atago, N1, brix 0–32, Japan).
2.5.4 Acid value
Five grams of oil was put into 250 mL conical flask containing 50 mL of neutralized alcohol and boiled. Then 5 drops of phenolphthalein were added. The oil solution was titrated with 0.1 M NaOH using phenolphthalein as an indicator (Ogungbenle and Omodara, 2014). where N is the normality of NaOH, and TB and TS are the titer volumes of blank and sample, respectively.
2.5.5 Iodine value
An amount of oil (0.20 g) was dissolved in 10 mL of carbon tetrachloride and then 25 mL of Wijs solution was added. The mixture was stored in the dark for 30 min at 25 °C. Thereafter, 15 mL of potassium iodine solution and 100 mL of distilled water were added and mixed thoroughly. The mixture was titrated with 0.1 M sodium thiosulphate using 1% starch as an indicator (Ogungbenle, 2014). where N is the normality of sodium thiosulphate, and TB and TS are the titer volumes of blank and sample, respectively.
2.5.6 Peroxide value
Two grams of oil was dissolved in 20 mL of petroleum ether and the mixture was heated for 30 s in a water bath. Then, 20 mL of 50% potassium iodide and 25 mL of distilled water were added and the mixture was titrated with 0.002 M sodium thiosulphate (Ogungbenle, 2014). where N is the normality of sodium thiosulphate, and TB and TS are the titer volumes of blank and sample, respectively.
2.5.7 Saponification value
Two grams of oil and 25 mL of ethanolic potassium hydroxide solution were placed in a conical flask and heated under reflux for 30 min. After cooling, 2.0 mL of phenolphthalein was added to the saponified mixture and then titrated with 0.5 M HCl (Ogungbenle and Afolayan, 2015). where N, is the normality of HCl; W, is the weight of oil; and V1 and V2 are the titer volumes of blank and sample, respectively.
2.5.8 Unsaponifiable matter
The unsaponifiable matter was determined following the official method (AOCS, 1997). In brief, 30 mL of ethanol and 5 mL of 50% aqueous KOH were added to 5 mL of oil. The mixture was refluxed for one hour in boiling water bath and then transferred to a separating funnel. Extraction of unsaponifiable matter was done using petroleum ether (500 mL), washed with distilled water (1000 mL) and finally evaporated to dryness at 105 °C using a rotary evaporator (R-210, Buchi Labortechnik AG, Switzerland). The unsaponifiable matter was calculated as a percent of oil.
2.6 Fatty acids composition
Twenty milligrams of oil were placed into 10 mL screw-top glass bottle, and 4.0 mL of fresh solvent comprised of methanol, concentrated sulfuric acid and chloroform (1.7:0.3:2.0, v/v/v) was added. Oil transesterification was done at 100 °C for 30 min. After cooling, the bottle was weighed and then 1.0 mL of distilled water was added and swirled for 1 min. The mixture was separated into two phases. The lower phase, containing fatty acid methyl esters (FAME), was transferred into a clean 10 mL bottle and dried with anhydrous Na2SO4. A 1.0 μL of caproic acid (C6:0) methyl ester in chloroform (1:499 v/v) was added to 0.5 mL of the dried solution as a standard. The fatty acids content was determined using a gas chromatography (Shimadzu GC-14A, Kyoto, Japan). The fatty acid was calculated as a percentage of the single peak area of the fatty acid to the total peak area (Indarti et al., 2005).
2.7 Amino acid composition
Total amino acid composition of the seeds (weight equivalent to 4% protein) was assayed by first hydrolyzing a sample with 6.0 N HCl in a sealed glass tube at 110 °C for 24 h (Abdualrahman et al., 2015). After hydrolysis, the sample was filtered and adjusted to 50 mL with distilled water. A 1.0 mL of diluted sample was filtered with a 0.22 μm membrane and analyzed using amino acid analyzer (S433D; Sykam Co. Ltd, Eresing, Germany).
2.8 Statistical analysis
Data from triplicate analysis for the same sample were subjected to one way ANOVA. Means were separated at the significance level of P < 0.05. The statistical analysis was performed using OriginPro 8.0 (Origin Lab Corporation, MA, USA).
3 Results and discussion
3.1 Proximate composition
Moisture is an important parameter when considering fruits’ quality because it significantly affects texture, taste, shelf life, and growth of the microbes. As seen in Table 1, the fresh harvested Annona squamosa fruits contain 78.54% moisture. This value is comparable to the moisture contents reported for the Tanzanian and Nigerian soursop fruits (Ekpete et al., 2013; Othman et al., 2014). The contents of ash and oil are lower than the values of some edible fruits (Boakye, 2013), but higher than the values of Nigerian soursop fruits (Ekpete et al., 2013). The low oil content indicates that the fruits are not considered as a good source of energy; they are useful for maintaining weight and lowering blood pressure (Othman et al., 2014). Fiber content of the fruits agrees with the findings reported in the literature (Albuquerque et al., 2016). Except for moisture, all other nutrients in the seeds are significantly (p < 0.05) higher than those in the fruits. Because of its high content of oil (30.41%), the seeds can be classified as an oilseed (Kukeera et al., 2015).
Components
Fruit pulp
Seeds
Moisture
78.54 ± 0.14a
6.65 ± 0.05b
Ash
2.84 ± 0.21a
5.24 ± 0.04b
Crude protein
1.13 ± 0.02a
18.34 ± 0.03b
Crude oil
0.79 ± 0.03a
30.41 ± 0.03b
Crude fiber
5.90 ± 0.05a
17.56 ± 0.11b
Total carbohydrates
10.80 ± 0.06a
21.80 ± 0.12b
Energy value (kJ/100 g)∗∗
51.79 ± 0.26a
434.49 ± 0.23b
3.2 Mineral composition
Minerals are important for the maintenance of body health. Minerals that required in large amounts in our diet (>100 mg/day) are known as macro-elements and those required in small amount (<100 mg/day) are known as micro-elements (Lugwisha et al., 2016). Results show that the contents of K, Na, Ca, Mg, P, Fe, Zn and Cu in the fruit pulp are 371.45, 12.27, 33.85, 22.37, 40.80, 0.77, 0.37 and 0.29 mg/100 g, respectively (Table 2). Most of the contents of macro- and micro-elements in the fruits coincide with the findings in the literature (Ekpete et al., 2013; Hiwale, 2015). In this study, all contents of minerals in the fruits are higher than those of Chilean apple fruit tissues (Henríquez et al., 2010). The levels of K, Na, Ca, Fe and Zn in the fruits are lower, while the level of Cu is higher compared to Tanzanian sugar apple fruits (Lugwisha et al., 2016). The differences in minerals contents might be due to the variation in their presence in soil and their different rates of absorption by the plants, microbial activity (Henríquez et al., 2010), type of charge in soil colloids, the degree of complexations with ligands, and the soil’s relative surface area (Chibuike and Obiora, 2014). Moreover, the contents of Fe and Cu in the fruits are lower than the recommended dietary allowance (RDA), while the level of Zn is below the FAO/WHO permitted level (Hellen et al., 2014). Except for K, Mg and P, all other elements in the fruits are significantly (p < 0.05) lower when compared to those in the seeds. The contents of Ca, Mg, K and Na in the seeds coincide with their contents in Annona muricata seeds from Congo-Brazzaville (Kimbonguila et al., 2010).
Mineral
Fruit pulp
Seeds
Calcium (Ca)
33.85 ± 1.30a
187.12 ± 0.26b
Magnesium (Mg)
22.37 ± 0.06a
16.22 ± 0.05b
Phosphorus (P)
40.80 ± 0.11a
32.75 ± 0.04b
Potassium (K)
371.45 ± 1.50a
355.84 ± 0.23b
Sodium (Na)
12.27 ± 0.12a
28.27 ± 0.11b
Iron (Fe)
0.77 ± 0.10a
20.84 ± 0.08b
Zinc (Zn)
0.37 ± 0.03a
22.17 ± 0.04b
Copper (Cu)
0.29 ± 0.01a
23.91 ± 0.05b
3.3 The effect of postharvest storage on the physicochemical properties of the fruits
Contents of total sugars, reducing sugars, sucrose, ascorbic acid, moisture, titratable acidity, and total soluble solids (TSS) and pH of the fruit pulp are presented in Table 3. As can be seen, the moisture content of the fresh harvested fruits is 78.54%. During ambient storage, the initial moisture content increased significantly (p < 0.05) to 85.50% at the 6th day of storage, and then decreased significantly (p < 0.05) to 83.47% at the 9th day. Similar downward/upward trend in moisture content during storage is reported in Annona squamosa fruits (Othman et al., 2014). The increase in the moisture content increases the fruits’ juiciness; and might be becomes more palatable to consumers. The decrease in the fruits moisture content after 9 days might be due to the evaporation process. Therefore, 6 days of storage can be considered the maximum period for keeping the fruits full turgid. In contrast, Lugwisha et al. (2016) reported a significant increase in moisture content of sugar apple fruits during ripening from the day of harvest (64.0%) to the 8th day of storage (73.10%), which ascribed that to the loss in dry matter due to the decrease in total carbohydrates.
Components
Storage days∗
0
3
6
9
Moisture content (%)
78.54 ± 0.11a
83.29 ± 0.22b
85.50 ± 0.11c
83.47 ± 0.14d
Ascorbic acid (mg/100 mL)
31.22 ± 0.15a
26.41 ± 0.06b
23.85 ± 0.04c
17.65 ± 0.06d
Total sugars (%)
30.43 ± 0.13a
34.19 ± 0.05b
37.76 ± 0.06c
40.11 ± 0.11d
Reducing sugars (%)
17.96 ± 0.12a
22.31 ± 0.04b
30.25 ± 0.10c
38.62 ± 0.05d
Sucrose (%)
12.47 ± 0.05a
15.52 ± 0.13b
16.82 ± 0.03c
27.22 ± 0.07d
Titratable acidity (%)
0.24 ± 0.02a
0.35 ± 0.02b
1.17 ± 0.01c
1.34 ± 0.02d
Total soluble solids (°Brix)
23.10 ± 0.10a
25.47 ± 0.16b
27.15 ± 0.05c
29.77 ± 0.17d
pH value
5.54 ± 0.02a
3.87 ± 0.02b
3.52 ± 0.03c
3.29 ± 0.02d
The ascorbic acid content in the fruits decreased steadily from 31.22 to 17.65 mg/100 mL after the 9 days of storage. Gradual oxidation of ascorbic acid during storage is found responsible for the decrease observed (Sravanthi et al., 2014). Similar decrease in ascorbic acid during storage has been reported in soursop fruits (Othman et al., 2014), and sugar apple fruits (Lugwisha et al., 2016). According to RDA for vitamin C (Albuquerque et al., 2016) the Annona squamosa fruits could be an excellent source of antioxidant for human nutrition.
The total sugars, reducing sugars and sucrose contents in the fresh fruit pulp increased significantly (p < 0.05) after 9 days of storage by 31.81, 115.03 and 118.28%, respectively. Similar increase in total sugars, reducing sugars and sucrose during storage has been reported in soursop fruits (Othman et al., 2014) and sugar apple fruits (Lugwisha et al., 2016). The increase in total sugars and reducing sugars is good indicator to the fruits’ ripening (Benkeblia and Emanuel, 2014). It seems that the increase in sucrose is very important in improving the sweetness of fruits: a factor that is important for consumers’ preferences.
The titratable acidity of the fruits increased significantly (p < 0.05) from 0.24 to 1.34% after 9 days of storage, possibly resulting from production of more organic acids. In contrast, Lugwisha et al. (2016) reported a decrease in titratable acidity in Tanzania sugar apple fruits from 0.28 to 0.12% during ripening, which attributed that to utilization of constituent acids in the respiratory process. Fruit acidity plays an important role in the taste, color, maturity and microbial stability (Othman et al., 2014). Simultaneously, the pH of the fruits declined from 5.54 to 3.29 during the 9 days of storage. An increase in titratable acidity and a decrease in pH during storage are reported earlier (Sawant and Dongre, 2014; Munira et al., 2013) in some fruits. The TTS of fresh fruits (23.10 °Brix) increased significantly (p < 0.05) after 9 days of storage (29.77 °Brix). This result is higher than the finding reported for Chilean apple fruits (Henríquez et al., 2010) but agrees with some reports in the literature (Giménez et al., 2016; Manning et al., 2016). On the other hand, Marquez-cardozo et al. (2012) reported a rapid increase in TSS of Colombian soursop fruits from the first day of storage, reaching its maximum on the 6th day and then decreased, which is not in consistent with our result.
3.4 Physicochemical characteristics of the seeds oil
The physicochemical characteristics of oil identify the practical importance and provide bases for quality and suitability of oils in daily life (Barkatullah et al., 2012). The specific value of some oil properties provides an indication of both nutritional and physical qualities of the oil (Angaye and Maduelosi, 2015). Fats and oils are triglycerides with different compositions of the alkyl chains depending on their origin (Salimon et al., 2012). Physical state, color, specific gravity, acid value, iodine value, peroxide value, free fatty acids, saponification value and unsaponifiable matter of the seeds oil are shown in Table 4. The oil extracted from Annona squamosa seeds is a brown color liquid at room temperature (25 °C). The specific gravity of the seeds oil is 0.79, which is comparable to the specific gravities of oils from seeds of pumpkin (Kukeera et al., 2015), watermelon (Egbuonu et al., 2015) and African wild mango (Etong et al., 2014). Refractive index of the Annona squamosa seeds oil (1.454) is comparable to the refractive indices of the pumpkin seeds oil (Kukeera et al., 2015) and moringa seeds oil (Campas-Baypoli et al., 2014). Mean ± SD, n = 3.
Physicochemical properties
Seeds oil
Crude oil
30.41 ± 0.03
State at room temperature (25 °C)
Liquid
Color
Light brown
Specific gravity (25 °C)
0.79 ± 0.03
Refractive index (40 °C)
1.454 ± 0.01
Acid value (mg KOH/g oil)
0.83 ± 0.01
Free fatty acids (%) as oleic acid
0.89 ± 0.03
Iodine value (g/100 g oil)
107.18 ± 0.15
Peroxide value (meq O2/kg oil)
3.84 ± 0.04
Saponification value (mg KOH/g)
189.17 ± 0.12
Unsaponifiable matter (%)
1.24 ± 0.01
The seeds oil has an acid value of 0.83 mg KOH/g, which agrees with that reported for Sudanese Annona squamosa seeds oil (Mariod et al., 2010). This cid value is higher than that stated for Annona diversifolia seeds oil (Reyes-trejo et al., 2014) and lower than that for watermelon seeds oil (Egbuonu et al., 2015) and African wild mango oil (Etong et al., 2014). Low acid value indicates less susceptibility of the oil to hydrolytic rancidity. The free fatty acid content of the seeds oil is 0.89%. However, the free fatty acid content of seeds oil lies within the acceptable limits of 0.0–3.0% (Ogungbenle, 2014). The iodine value and peroxide value of seeds oil are 107.18 mg/100 g oil and 3.84 meq O2/kg oil, respectively. These values are lower than the iodine value and peroxide value reported for bitter apple oil (Riaz et al., 2015).
The saponification value and the unsaponifiable matter of the seeds oil are 189.17 mg KOH/g and 1.24%, respectively. The higher the saponification value indicates the higher the molecular weight fatty acid triglyceride (Esan and Fasasi, 2013).
3.5 Fatty acid composition
Fatty acid composition provides information about the total content of both saturated and unsaturated fatty acids, which are often used as health indicators to determine the oxidative stability of fat and oil (Ogungbenle, 2014). As shown in Table 5, oleic acid is the major fatty acids (48.54%), followed by linoleic acid (23.40%), then by palmitic acid (15.47) and at last by stearic acid (8.14). Similar fatty acid content has previously been reported in Sudanese Annona squamosa seeds oil (Mariod et al. (2010). The content of oleic acid also agrees with the value reported previously (Rana, 2014) for squamosa oil. The seeds oil is characterized by high amount of unsaturated fatty acids, representing 75.55% of the total studied fatty acids. However, oleic acid and linoleic acid represent 95.22% of the unsaturated fatty acids. Oils containing more unsaturated fatty acids than saturated fatty acids are more desirable as food and are found to lowering blood serum cholesterol (Ogungbenle and Afolayan, 2015). Means ± SD (n = 3). FA, Fatty acids.
Fatty acid
Seeds oil
Capric acid (10:0)
0.17 ± 0.03
Myristic acid (14:0)
0.67 ± 0.01
Palmitic acid (C16:0)
15.47 ± 0.17
Sapienic acid (C16:1)
1.43 ± 0.03
Stearic acid (C18:0)
8.14 ± 0.04
Oleic acid (C18: 1)
48.54 ± 0.13
Linoleic acid (C18:2)
23.40 ± 0.06
Linolenic acid (C18:3)
2.18 ± 0.03
Saturated FAs (%)
24.45
Unsaturated FAs (%)
75.55
Oleic/linoleic ratio
2.074
3.6 Amino acid composition
Amino acids (AAs) are nutritionally classified into essential and nonessential depending on whether they are manufactured by the body or only supplied by the diet (Aboagarib et al., 2014). Amino acid composition of the Annona squamosa seeds is listed in Table 6. Glutamic acid is the major AA, accounting for 13.50 g/100 g protein and then followed by aspartic acid (7.90 g/100 g protein). Similar level of glutamic acid is found in the seeds of guddaim fruits, African yam bean and wild melon (Aboagarib et al., 2014; Esan and Fasasi, 2013; Umar et al., 2013), respectively. The levels of the essential AAs leucine, lysine, phenylalanine and isoleucine in the Annona squamosa seeds are 5.50, 3.90, 3.72 and 3.50 (g/100 g protein), respectively. These results are higher than the findings reported by Mariod et al. (2010) for Sudanese Annona squamosa. The contents of leucine and lysine are comparable to the reported results (Umar et al., 2013) in some fruits’ seeds. Total content of the essential AAs is satisfactory when compared to the WHO/FAO reference pattern (WHO, 2007). The total essential amino acids (43.86%) of the seeds is lower when compared to 59.20% for the Sudanese A. squamosa seeds (Mariod et al., 2010), while the sulfur-containing amino acids (methionine and cystine) and aromatic amino acids (phenylalanine and tyrosine) are higher than the values reported by Mariod et al. (2010). The contents of leucine, lysine, methionine, phenylalanine, threonine, valine and histidine of the seeds are in line with the WHO/FAO for adult human’s requirements and lower than those for child’s requirements (WHO, 2007). The ratio of the essential AAs to the nonessential AAs is 1:1.3, which is considered adequate for an ideal protein structure. Mean ± SD, (n = 3). Daily requirements for child and adult (WHO, 2007).
Amino acids
Composition
WHO
Child
Adult
Isoleucine
3.50 ± 0.02
2.80
1.30
Leucine
5.50 ± 0.05
6.60
1.90
Lysine
3.90 ± 0.04
5.80
1.60
Cysteine
1.60 ± 0.01
–
–
Methionine
2.52 ± 0.02
2.70
1.70
Tyrosine
3.11 ± 0.03
–
–
Phenylalanine
3.72 ± 0.03
6.30
1.90
Threonine
2.83 ± 0.04
3.40
0.90
Valine
3.65 ± 0.03
3.50
1.30
Histidine
2.90 ± 0.05
1.90
1.60
Arginine
6.08 ± 0.03
Aspartic
7.90 ± 0.03
Glutamic
13.50 ± 0.1
Serine
2.70 ± 0.05
Proline
3.27 ± 0.02
Glycine
4.26 ± 0.06
Alanine
4.82 ± 0.03
Total AAs
75.76
Total essential AAs
33.23
33.00
12.20
Aliphatic AAs
25.00
Aromatic AAs
6.83
Neutral AAs
31.05
Acidic AAs
21.40
Basic AAs
12.88
Sulfur-containing AAs
4.12
4 Conclusion
In this study, the data indicate that the proximate nutrients and the content of minor elements are significantly (p < 0.05) higher in the seeds than the pulp of Annona squamosa fruits. The nutritional composition of fruits indicated that soursop fruits could be a good source of nutrients to the human body. The changes in the physicochemical properties (moisture, sugars, titratable acidity and TSS, ascorbic acidized and pH) of the fruits during postharvest ambient storage indicate continuity of the fruits ripening. Therefore, 6 days after harvest is the maximum period for the fruits to be in good quality for consumption. The high contents of oil and protein raised the nutritive and economic values of the seeds. Due to its high iodine value, the oil is more susceptible to autoxidation. On the other hand, the high content of oleic and linoleic acids may lend validity to the oil for use in edible purposes. The results of this research open up new prospects in the future in-depth study of the Annona squamosa fruits and the seeds with aim of their incorporating in the food system.
Acknowledgments
The authors wish to extend their gratitude to the National Public sector Special Science and Technology (No. 201303071) and National Nature Science Foundation of China (No. 31471698) for their valuable support.
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