252 journal homepage: www.fia.usv.ro/fiajournal Journal of Faculty of Food Engineering, Ştefan cel Mare University of Suceava, Romania Volume XIII, Issue 3 – 2014, pag. 252 - 262 STUDY OF ROASTING EFFECT ON NUTRITIVE AND ANTIOXIDANT PROPERTIES OF LEAFY VEGETABLES CONSUMED IN NORTHERN CÔTE D’IVOIRE Patricia D. OULAI1, *Lessoy T. ZOUE1, Athanase K. OTCHOUMOU1, Sébastien L. NIAMKE1 1Laboratoire de Biotechnologies, UFR Biosciences, Université Félix Houphouët-Boigny, 22 BP 582, Abidjan 22, Côte d’Ivoire. y.lessoy@yahoo.fr *Corresponding author Received September 14th 2014, accepted September 29th 2014 Abstract: African leafy vegetables (ALVs), also known as African spinach, contribute significantly to household food security and add variety to cereal-based staple diets. Five leafy vegetable species (Amaranthus hybridus, Andasonia digitata, Ceiba patendra, Hibiscus sabdariffa and Vigna unguiculata) that are used for sauce preparation in Northern Côte d’Ivoire were subjected to roasting in order to evaluate the impact of this non conventional processing method on their nutritive value and antioxidant properties. This study showed that longer time (higher than 2 min) of roasting at 180- 200°C caused negative impact with nutrients losses but positive impact by reducing anti-nutrients such as oxalates and phytates. The registered losses at 2 min were as follow: ash (0.09 – 6.58 %), proteins (1.22 – 29.31 %), vitamin C (77.56 – 89.01 %), carotenoids (11.24 – 45.16%) oxalates (2.30 – 20.51 %) and phytates (5.20 – 63.82 %). Roasting processing of the studied leafy vegetables highlighted a significant increase (4.77 – 32.71 %) of polyphenols contents coupled with increasing of antioxidant activity. Moreover, after 2 min of roasting time, the residual contents of minerals were: calcium (294.78 - 879.74 mg/100g), magnesium (175.87 - 480.54 mg/100g), potassium (159.72 - 371.33 mg/100g), iron (15.54 - 84.97 mg/100g) and zinc (13.27 - 38.85 mg/100g). All these results suggest that roasting of leafy vegetables (less than 2 min) may be used as alternative method of cooking in order to minimize nutrients losses and to contribute efficiently to the food security of Ivorian population. Keywords: antioxidant properties - roasting processing - leafy vegetables - nutritive value 1. Introduction Leafy vegetables are plants which leafy parts (young stems, flowers and young fruits) are used as vegetables. These plants have a unique place among vegetables because they are rich sources of many nutrients and antioxidant compounds [1,2]. Socio-economic surveys conducted in various parts of Africa indicate that ALVs are important commodities in household food and nutrition security [3]. Indeed, African leafy vegetables (ALVs) are the cheapest and most readily available sources of micronutrients and they provide also important sources of employment in peri - urban areas because of their short labour-intensive production system [4,5]. Leafy vegetables are obtained by harvesting or cultivation and their high moisture render them perishable and seasonal availability limits their utilization all round the year. Hence, there is a need to preserve this nature's store house of nutrients through proper processing techniques for safe storage with efficient nutrient retention [6]. To extend the period during which they are available, different ways of preserving Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 253 these vegetables have been developed. The two main methods are the sun-drying of fresh leaves and the sun-drying of blanched or cooked leaves. Both of these methods transform the leafy vegetables into dry products that have long shelf lives [7]. Electrification of the rural areas has introduced new preservation technology, including the freezing of leafy vegetables [8]. Among the twenty hundred and seven (207) leafy vegetables widely consumed in tropical Africa, about twenty (20) species of leafy vegetables belong to 6 botanical families, are widely consumed and cultivated by Ivorian population [9,10]. Furthermore, the consumption of these leafy vegetables is linked to the region and ethno-botanical studies have stated that most people in Northern Côte d’Ivoire consume indigenous green leafy vegetables such as Amaranthus hybridus “boronbrou”, Andasonia digitata “baobab”, Ceiba patendra “fromager”, Hibiscus sabdariffa “dah” and Vigna unguiculata “haricot” [10,11]. Earlier reports have highlighted the nutritive potential of these fresh leafy vegetables [12]. For these species, the tender leaves are prepared as potherbs or as relishes, primarily to accompany starchy paste foods as cassava, maize and sorghum. These leafy vegetables may be prepared from a single species or from a combination of them. For cooking, the mature and freshly leaves are boiled in water for about 30 min in order to reduce bitter taste and then used, after discarding boiled water, for sauce preparation. In a lesser extent, blanching is also used to inactivate oxidative enzymes, destroy vegetative microbial cells, reduce or eliminate the bitterness and to remove any residual pesticides [13,14]. Even if some adverse effects such as nutrient losses have been reported [15,16] by using boiling or blanching processing, there is any scientific data with regards to the effect of roasting (oven-cooking) processing on the physicochemical and nutritive characteristics of leafy vegetables consumed in Northern Côte d’Ivoire. Therefore, the aim of this study is to evaluate the effect of roasting on the nutritive value of these selected leafy vegetables in order to provide necessary information for their wider utilization and contribution to food security of Ivorian population. 2. Material and methods 2.1. Samples collection Leafy vegetables (Amaranthus hybridus, Andasonia digitata, Ceiba patendra, Hibiscus sabdariffa and Vigna unguiculata) were collected fresh and at maturity from cultivated farmlands located at Dabou (latitude: 5°19′14″ North; longitude: 4°22′59″West) (Abidjan District). The samples were harvested at the early stage (between one and two weeks of the appearance of the leaves). These plants were previously authenticated by the National Floristic Center (University Felix Houphouët-Boigny, Abidjan-Côte d’Ivoire). 2.2. Samples processing The fresh leafy vegetables were rinsed with deionized water and the edible portions were separated from the inedible portion. The edible portions were chopped into small pieces (500 g) and allowed to drain at ambient temperature. Each sample was divided into two lots. The first lot (raw, 250 g) was dried in an oven (Memmert, Germany) [17], ground with a laboratory crusher (Culatti, France) equipped with a 10 μm mesh sieve. The powdered samples were stored in a clean dry air-tight sample bottle in a refrigerator (4°C) until further analyses. The second lot (250 g) was roasted (oven-cooking) for 2, Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 254 4 and 6 min at 180-200°C. The roasted samples were cooled at ambient temperature and subjected to the same treatment using for raw samples. 2.3. Chemicals All solvents (n-hexane, petroleum ether, acetone, ethanol and methanol) were purchased from Merck. Standards used (gallic acid, β-carotene) and reagents (metaphosphoric acid, Folin-Ciocalteu, DPPH) were purchased from Sigma- Aldrich. All chemicals used in the study were of analytical grade. 2.4. Nutritive properties 2.4.1. Proximate analysis Proximate analysis was performed using official methods [18]. The moisture content was determined by the difference of weight before and after drying the sample (10 g) in an oven (Memmert, Germany) at 105°C until constant weight. Ash fraction was determined by the incineration of dried sample (5 g) in a muffle furnace (Pyrolabo, France) at 550°C for 12 h. The percentage residue weight was expressed as ash content. For crude fibres, 2 g of sample were weighed into separate 500 mL round bottom flasks and 100 mL of 0.25 M sulphuric acid solution was added. The mixture obtained was boiled under reflux for 30 min. Thereafter, 100 mL of 0.3 M sodium hydroxide solution was added and the mixture were boiled again under reflux for 30 min and filtered through Whatman paper. The insoluble residue was then incinerated, and weighed for the determination of crude fibres content. Proteins were determined through the Kjeldhal method and the lipid content was determined by Soxhlet extraction using hexane as solvent. Carbohydrates and calorific value were calculated using the following formulas [19]: Carbohydrates: 100 – (% moisture + % proteins + % lipids + % ash + % fibres). Calorific value: (% proteins x 2.44) + (% carbohydrates x 3.57) + (% lipids x 8.37). The results of ash, fibres, proteins, lipids and carbohydrates contents were expressed on dry matter basis. 2.4.2. Mineral analysis Minerals contents were determined by the ICP-MS (inductively coupled argon plasma mass spectrometer) method [20]. The dried powdered samples (5 g) were burned to ashes in a muffle furnace (Pyrolabo, France). The ashes obtained were dissolved in 10 mL of HCl/HNO3 and transferred into 100 mL flasks and the volume was made up using deionized water. The mineral composition of each sample was determined using an Agilent 7500c argon plasma mass spectrometer. Calibrations were performed using external standards prepared from a 1000 ppm single stock solution made up with 2% nitric acid. 2.4.3. Anti-nutritional factors Oxalates content was performed using a titration method [21]. One (1) g of dried powdered sample was weighed into 100 mL conical flask. A quantity of 75 mL of sulphuric acid (3 M) was added and stirred for 1 h with a magnetic stirrer. The mixture was filtered and 25 mL of the filtrate was titrated while hot against KMnO4 solution (0.05 M) to the end point. Phytates contents were determined using the Wade’s reagent colorimetric method [22]. A quantity (1 g) of dried powdered sample was mixed with 20 mL of hydrochloric acid (0.65 N) and stirred for 12 h with a magnetic. The mixture was centrifuged at 12000 rpm for 40 min. An aliquot (0.5 mL) of supernatant was added with 3 mL of Wade’s reagent. The reaction mixture was incubated for 15 min and absorbance was measured at 490 nm by using a Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 255 spectrophotometer (PG Instruments, England). Phytates content was estimated using a calibration curve of sodium phytate (10 mg/mL) as standard/ 2.5. Antioxidant properties 2.5.1 Vitamin C and carotenoids determination Vitamin C contained in analyzed samples was determined by titration [23]. About 10 g of ground fresh leaves were soaked for 10 min in 40 mL metaphosphoric acid- acetic acid (2%, w/v). The mixture was centrifuged at 3000 rpm for 20 min and the supernatant obtained was diluted and adjusted with 50 mL of bi-distilled water. Ten (10) mL of this mixture was titrated to the end point with dichlorophenol- indophenol (DCPIP) 0.5 g/L. Carotenoids were extracted and quantified by using a spectrophotometric method [24]. Two (2) g of ground fresh leaves were mixed three times with 50 mL of acetone until loss of pigmentation. The mixture obtained was filtered and total carotenoids were extracted with 100 mL of petroleum ether. Absorbance of extracted fraction was then read at 450 nm by using a spectrophotometer (PG Instruments, England). Total carotenoids content was subsequently estimated using a calibration curve of β-carotene (1 mg/mL) as standard. 2.5.2. Polyphenols determination Polyphenols were extracted and determined using Folin–Ciocalteu’s reagent [25]. A quantity (1 g) of dried powdered sample was soaked in 10 mL of methanol 70% (w/v) and centrifuged at 1000 rpm for 10 min. An aliquot (1 mL) of supernatant was oxidized with 1 mL of Folin–Ciocalteu’s reagent and neutralized by 1 mL of 20% (w/v) sodium carbonate. The reaction mixture was incubated for 30 min at ambient temperature and absorbance was measured at 745 nm by using a spectrophotometer (PG Instruments, England). The polyphenols content was obtained using a calibration curve of gallic acid (1 mg/mL) as standard. Antioxidant activity Antioxidant activity assay was carried out using the 2,2-diphenyl-1-pycrilhydrazyl (DPPH) spectrophotometric method [26]. About 1 mL of 0.3 mM DPPH solution in ethanol was added to 2.5 mL of sample solution (1 g of dried powdered sample mixed in 10 mL of methanol and filtered through Whatman No. 4 filter paper) and was allowed to react for 30 min at room temperature. Absorbance values were measured with a spectrophotometer (PG Instruments, England) set at 415 nm. The average absorbance values were converted to percentage antioxidant activity using the following formula: Antioxidant activity (%) = 100 – [(Abs of sample – Abs of blank) x 100/Abs positive control] Statistical analysis All the analyses were performed in triplicate and data were analyzed using EXCELL and STATISTICA 7.1 (StatSoft). Differences between means were evaluated by Duncan’s test. Statistical significant difference was stated at p < 0.05 3. Results and discussion The proximate composition of the roasted leafy vegetables is presented in Table 1. The physicochemical parameters generally differ significantly (p<0.05) from a roasting time of a leafy vegetable to another. The ash content after 2 min of roasting ranged from 8.19 ± 0.00% (A. hybridus) to 23.90 ± 0.24% (C. patendra). These values were closed to 7.66 ± 0.18% Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 256 and 21.69 ± 1.56% after 6 min of roasting. The observed decrease rate at 2 min of roasting ranged from 0.09 to 6.58 % in the following order: V. unguiculata (0.09%) > A. digitata (1.55%) > A. hybridus (4.65%) > H. sabdariffa (5.43%) > C. patendra (6.58%). These losses are lower than that (9.78 – 28%) reported for boiled Nigerian leafy vegetables [27]. Therefore, roasting processing could be advantageous for mineral quality preservation of leafy vegetables. As concern protein contents, roasting processing caused 1.22 to 29.31% reduction after 2 min. These proteins losses increased in the order: V. unguiculata (1.22%) > A. hybridus (3.16%) > H. sabdariffa (10.29%) > C. patendra (12.56%) > A. digitata (29.31%). This reduced protein contents could be attributed to the severity of thermal process (180-200°C) which leads to protein degradation [28]. However, this thermal processing could enhance the digestibility of proteins by degradation of anti-nutritional factors such as tannins [29]. With regards to their protein contents (12.78 – 21.69%) at 2 min, roasted leaves of the selected species could be considered as non negligible sources of proteins for human nutrition. Roasting of the studied leafy vegetables resulted in a slight increase (p > 0.05) in their crude fibres content (0.9 – 4.27%) after 2 min of heat application. Table 1. Proximate composition of raw and roasted leafy vegetables consumed in Northern Côte d’Ivoire Ash (%) Fibres (%) Proteins (%) Lipids (%) Carbohydrates (%) Calorific value (kcal /100g) H. sabdariffa Raw 10.30 ± 0.10a 14.27 ± 1.70b 14.47 ± 0.10a 4.75 ± 0.15a 56.21 ± 1.78b 275.71 ± 0.55a 2 min 9.74 ± 0.09b 14.40 ± 1.99b 12.98 ± 0.01b 4.87 ± 0.01a 59.73 ± 6.88a 271.28 ± 4.68a 4 min 9.60 ± 0.23b 14.67 ± 1.56b 12.36 ± 0.00b 4.92 ± 0.03a 59.11 ± 4.30a 276.85 ± 5.60a 6 min 9.26 ± 0.64b 16.00 ± 1.24a 12.15 ± 0.00b 4.95 ± 0.01a 54.64 ± 2.41b 266.13 ± 8.49b A. hybridus Raw 8.59 ± 1.34a 17.80 ± 0.30a 13.25 ± 0.13a 2.15 ± 0.01b 58.21 ± 1.78a 305.19 ± 7.73a 2 min 8.19 ± 0.00a 17.19 ± 2.21a 12.83 ± 0.04b 2.48 ± 0.03b 60.21 ± 2.26a 259.46 ± 7.85c 4 min 8.03 ± 1.43a 17.28 ± 1.24a 12.24 ± 0.00b 2.54 ± 0.06b 59.91 ± 3.87a 265.02 ± 3.34c 6 min 7.66 ± 0.18b 17.54 ± 0.84a 11.99 ± 0.06c 3.79 ± 0.03a 59.02 ± 2.41a 271.69 ± 2.41b A. digitata Raw 10.97 ± 0.40a 12.56 ± 0.45a 18.08 ± 0.10a 2.18 ± 0.03c 56.23 ± 1.25b 267.03 ± 4.00d 2 min 10.80 ± 0.12a 12.80 ± 3.49a 12.78 ± 0.40b 2.56 ± 0.01c 61.06 ± 3.77a 270.60 ± 2.37c 4 min 9.82 ± 1.39a 13.33 ± 1.15a 12.60 ± 0.00b 3.91 ± 0.03b 60.35 ± 0.28a 278.90 ± 0.75b 6 min 7.82 ± 0.22b 14.79 ± 1.51a 8.20 ± 0.28c 4.73 ± 0.04a 64.46 ± 5.96a 289.71 ± 2.34a V. unguiculata Raw 11.17 ± 0.25a 18.00 ± 0.92a 21.96 ± 0.30a 4.23 ± 0.25c 44.64 ± 1.72b 248.35 ± 1.33c 2 min 11.16 ± 0.14a 18.77 ± 0.94a 21.69 ± 0.08a 5.81 ± 0.04b 42.57 ± 0.93b 253.52 ± 2.76b 4 min 11.11 ± 0.15a 19.55 ± 2.47a 20.86 ± 0.12b 6.11 ± 0.01a 42.38 ± 2.76b 253.31 ± 9.43a 6 min 10.79 ± 0.02a 19.68 ± 1.15a 17.09 ± 0.00c 6.43 ± 0.03a 46.01 ± 1.11a 259.77 ± 4.18a C. patendra Raw 25.67 ± 1.12a 31.50 ± 1.50a 15.20 ± 0.05a 1.39 ± 0.22c 26.30 ± 0.11b 142.61 ± 7.74c 2 min 23.90 ± 0.24b 32.44 ± 2.28a 13.29 ± 0.41b 6.62 ± 0.03b 23.67 ± 2.09c 172.34 ± 8.69b 4 min 22.56 ± 0.00b 33.21 ± 1.70a 12.98 ± 0.14c 7.15 ± 0.03a 24.10 ± 2.88c 177.54 ± 7.94b 6 min 21.69 ± 1.56b 33.56 ± 1.09a 7.42 ± 0.00d 7.46 ± 0.05a 29.87 ± 2.70a 187.14 ± 7.48a Data are represented as Means ± SD (n = 3). Means in the column with no common letter differ significantly (p<0.05) for each leafy vegetable. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 257 Indeed, the increased temperature leads to breakage of weak bonds between polysaccharides and the cleavage of glycosidic linkages, which may result in solubilization of the dietary fibres [30]. With regard to their fibres content (12.80 - 32.44%) after 2 min, adequate intake of roasted leafy vegetables could lower the risk of constipation, diabetes, colon and breast cancers [31]. The relatively low values of lipids contents at 2 min of roasting (2.48 – 6.62%) in the studied leafy vegetables corroborate the findings of many authors which showed that leafy vegetables are poor sources of fat [32]. In addition, the estimated calorific values (172.34 – 271.28 kcal/100g) agree with general observation that leafy vegetables have low energy values due to their low crude fat and relatively high level of moisture [33]. Mineral composition of roasted leafy vegetables used in this study is shown in table 2. The residual contents of minerals after 2 min of roasting were significantly different (p < 0.05): calcium (294.78 - 879.74 mg/100g), magnesium (175.87 - 480.54 mg/100g), potassium (159.72 - 371.33 mg/100g), iron (15.54 - 84.97 mg/100g) and zinc (13.27 - 38.85 mg/100g). Compared to the values of raw leafy vegetables, these observed reductions may be due to the losses of ashes as observed previously. With regards to these values, the consumption of roasted leafy vegetables (2 min) could cover at least 50% of the standard mineral requirements for human. Table 2. Mineral composition of raw and roasted leafy vegetables consumed in Northern Côte d’Ivoire Ca Mg P K Fe Na Zn H. sabdariffa Raw 402.21±0.55a 295.93±0.41a 407.59±0.00a 816.19±1.12a 102.08±0.14a 23.46±0.03a 26.06±0.04a 2 min 371.84±2.43b 241.61±1.80b 371.33±5.16b 711.42±3.00b 56.18±3.41b 22.82±0.91a 17.32±9.38b 4 min 368.74±8.90c 111.98±1.53c 232.49±7.70c 629.75±7.23c 35.62±0.35c 21.30±3.81a 12.25±0.31c 6 min 257.32±3.51d 111.85±3.70c 208.79±2.85d 583.76±9.40d 32.43±0.74c 20.05±1.79a 10.12±0.10d A. hybridus Raw 932.6±0.55a 497.75±0.49a 368.69±0.00a 1989.32±2.12a 77.88±0.05a 94.39±0.04a 31.73±0.04a 2 min 879.74±6.44b 480.54±4.74b 366.74±4.36a 1943.57±8.65b 72.57±0.00b 94.38±0.00a 30.11±0.38b 4 min 843.65±0.00c 476.88±0.00c 356.28±0.00b 1826.41±0.00c 68.52±0.58c 94.37±1.33a 26.41±0.00c 6 min 755.01±0.00d 337.24±8.26d 274.86±4.92c 1690.04±1.71d 49.95±3.49d 90.33±5.64b 20.04±0.92d A. digitata Raw 496.26±2.20a 264.36±1.17a 761.63±0.00a 1856.90±8.23a 106.27±0.47a 37.13±0.12a 22.61±0.10a 2 min 464.74±8.39b 175.87±3.74b 275.88±5.54b 1571.84±4.90b 15.54±0.22b 37.00±2.46a 20.68±0.44b 4 min 439.84±4.80c 157.7±2.23c 269.01±3.80c 1496.44±2.14c 15.15±0.32b 35.97±1.36b 12.06±0.14c 6 min 407.66±5.88d 147.35±2.06d 249.03±5.29d 1370.45±6.98d 15.05±2.87b 32.17±1.11c 11.97±0.83c V. unguiculata Raw 439.54±0.56a 341.34±0.18a 309.04±0.00a 718.11±0.91a 91.45±0.12a 33.32±0.02a 40.83±0.04a 2 min 426.94±0.54b 315.39±0.25b 300.02±4.45b 678.50±2.03b 84.97±3.74b 31.75±0.17b 38.85±0.43b 4 min 424.92±5.57c 298.81±2.49c 297.34±0.46c 622.33±2.70c 82.38±0.33b 26.99±1.09c 31.52±0.39c 6 min 417.65±5.36d 293.19±2.46d 293.94±3.69d 549.18±1.44d 78.29±3.56c 25.59±1.07c 23.04±0.02d C. patendra Raw 997.02±0.55a 773.55±0.43a 570.85±2.11a 1585.58±0.87a 219.84±0.12a 42.69±0.02a 35.68±0.02a 2 min 294.78±5.63b 224.82±4.48b 159.72±2.34b 983.00±9.71b 20.74±4.19b 27.96±0.99b 13.27±2.68b 4 min 266.36±9.42c 191.69±0.00c 105.90±0.00c 854.30±0.00c 20.70±0.60b 22.06±4.46c 9.75± 0.00c 6 min 245.09±0.00d 162.08±6.20d 83.27±3.15d 729.74±2.60d 18.11±0.00c 21.08±0.00c 7.78± 0.26d Data are represented as Means ± SD (n = 3). Means in the column with no common letter differ significantly (p<0.05) for each leafy vegetable. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 258 Indeed, these standard requirements are: calcium (1000 mg/day); magnesium (400 mg/day), iron (8 mg/day) and zinc (6 mg/day) [34]. Calcium and phosphorus play important role in growth and maintenance of bones, teeth and muscles [35]. As concern magnesium, this mineral is known to prevent cardiomyopathy, muscle degeneration, growth retardation, congenital malformations and bleeding disorders [36]. Iron plays important role in prevention of anemia while zinc is important for vitamin A and vitamin E metabolism [37,34]. To predict the bioavailability of calcium and iron, anti- nutrients to nutrients ratios of blanched leafy vegetables were calculated (Table 3). The calculated [phytates]/[Ca] ratio in all the roasted species were below the critical level of 2.5 which is known to impair calcium bioavailability [38]. The effect of roasting on anti-nutritional factors (oxalates and phytates) contents is depicted in figure 1. Levels losses (p < 0.05) at 2 min were 2.30 – 20.51% and 5.20 – 63.82% for oxalates and phytates, respectively. Oxalates losses increased in the order: A. hybridus (2.30%) > A. digitata (12.30%) > V. unguiculata (13.49%) > H. sabdariffa (18.54%) > C. patendra (20.51%) while phytates losses increased in the order: A. digitata (5.20%) > V. unguiculata (20.92%) > C. patendra (24.54%) > A. hybridus (61.48%) > H. sabdariffa (63.82%).The reductions in oxalates and phytates contents during roasting could be advantageous for improving the health status of consumers. Indeed, oxalates and phytates are anti- nutrients which chelate divalent cations such as calcium, magnesium, zinc and iron, thereby reducing their bioavailability [39]. Table 3. Anti-nutritional factors/mineral ratios of raw and roasted leafy vegetables consumed in Northern Côte d’Ivoire Phytates/Ca Phytates/Fe Oxalates/Ca H. sabdariffa Raw 0.21 0.85 3.26 2 min 0.08 0.56 2.86 4 min 0.07 0.78 2.71 6 min 0.10 0.80 3.69 A. hybridus Raw 0.03 0.41 0.07 2 min 0.01 0.17 0.07 4 min 0.01 0.16 0.06 6 min 0.01 0.18 0.04 A. digitata Raw 0.04 0.19 1.57 2 min 0.04 1.21 1.47 4 min 0.03 1.09 1.25 6 min 0.03 0.90 1.11 V. unguiculata Raw 0.04 0.19 1.66 2 min 0.03 0.16 1.48 4 min 0.03 0.15 1.35 6 min 0.02 0.11 1.35 C. patendra Raw 0.04 0.17 0.78 2 min 0.10 1.39 2.10 4 min 0.09 1.22 1.46 6 min 0.09 1.30 1.34 Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 259 Roasting also resulted in a decrease of carotenoids and vitamin C contents in the studied leafy vegetables (Figure 2). For carotenoids, losses at 2 min were estimated to 11.24 to 45.16%. Carotenoids losses increased in the order: A. digitata (11.24%) > A. hybridus (15.28%) > H. sabdariffa (17.87%) > C. patendra (22.02%) > V. unguiculata (45.16%). The decrease in the concentration of total carotenoids could be attributed to the oxidation and isomerization of β-carotene [40]. For vitamin C content, a significant reduction (77.56 - 89.01%) was highlighted after 2 min during roasting processing (Figure 2). Figure 1: Oxalates (A) and phytates (B) contents of raw and roasted leafy vegetables consumed in Northern Côte d’Ivoire This decrease in vitamin C could be attributed to the fact that this important micronutrient is not stable at high temperature [41]. With regard to the vitamin C decrease, consumption of roasted leafy vegetables may be supplemented with other sources of vitamin C such as tropical fruits to cover the daily need for humans (40 mg/day) as recommended by food agriculture organization [34]. Figure 2: Vitamin C (A) and carotenoids (B) contents of raw and roasted leafy vegetables consumed in Northern Côte d’Ivoire Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Volume XIII, Issue 3 – 2014 Patricia D. OULAI, Lessoy T. ZOUE, Athanase K. OTCHOUMOU, Sébastien L. NIAMKE, Study of roasting effect on nutritive and antioxidant properties of leafy vegetables consumed in northern Côte d’Ivoire, Food and Environment Safety, Volume XIII, Issue 3 – 2014, pag. 252 – 262 260 The effect of roasting on polyphenols content and antioxidant activity of the selected leafy vegetables is depicted in figure 3. It was observed a high increase of polyphenols contents varying from 4.77 to 32.71%. The percent gain in the total phenol content during blanching may be due to the breakdown of tough cell walls and release of phenolic compounds trapped in the fibres of green leafy vegetables [42]. Polyphenols compounds of the roasted leafy vegetables could be advantageous for lower cellular oxidative stress which has been implicated in the pathogenesis of various neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis [43,44]. Figure 3: Polyphenols contents (A) and antioxidant activity (B) of raw and roasted leafy vegetables consumed in Northern Côte d’Ivoire 4. Conclusions Leafy vegetables consumed in Northern Côte d’Ivoire contain significant levels of nutrients that are essential for human health. The present study showed that roasting at 2, 4 and 6 minutes may increase their antioxidant activity and decrease the contents of proteins, mineral, vitamin C, carotenoids, and anti-nutritional factors (oxalates and phytates). The reduction of anti-nutritional factors might have a beneficial effect on bioavailability of minerals like calcium, iron and zinc. Thus, the study suggests that the recommended time of roasting leafy vegetables must be less than 2 min in order to contribute efficiently to the nutritional requirement and to the food security of Ivoirian population. 5. References [1]. GUPTA S., LAKSHMI J.A., MANJUNATH M.N. PRAKASH J. 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