Abstract

Background and objectives: Green vegetables are considered an important source of some nutritionally constituents that have health benefits. Generally, food composition databases related to raw foods are available, but data on cooked foods in Cote d’Ivoire are still lacking. The current study aimed to evaluate antioxidant compounds, Fatty acids and determine nutritional profile using the LIM and SAIN system of Solanum nigrum leaves before and after boiling. Materials and Methods: The leaves were subjected to boiling in cooker for 10, 15 and 20 min. Fatty acids and carotenoids and were determined according to standard methods for nutritional guidelines. Results The polyunsaturated, unsaturated fatty, omega-6 and omega-3, were investigated and the results obtained were as follow: (880.52 ± 0.06 - 3634.32 ± 3.20 mg /100g), (1047.03±0.63-2466.76 ± 0.48 mg/ 100g), (177.96 ± 0.33 - 1415.42 ± 0.31 mg/100 g), (459.21 ± 0.31-969.29± 0.05 mg/100g). The Carotenoids, β-Carotene and lycopene contents were high with remarkable amount (65.70 ± 0.12 - 37.38 ±0.03 mg / 100g), (17.65 ± 0.12 - 26.37 ±0.31 mg / 100g) and (1.64 ± 0.03 - 6.33 ± 0.01 mg / 100g). All samples have score SAIN > 5 and LIM score <7.5, profile recommended for health. Conclusion: These results revealed that Solanum nigrum leaves was important source of some nutritionally constituent. However, longer time of boiling (higher than 10 min) caused negative impacts by reducing nutritive compounds. It suggested that the recommended time for domestic cooking must be less than 10 min for the studied leafy vegetables in order to contribute efficiently to the nutritional requirement and to the food security of Ivorian population.

1. Introduction

Green leafy vegetables occupied an important place among the food crops as they provide adequate amounts of many vitamins and minerals. The importance and awareness of nutrient in public health issues have resulted in the increase demand of knowledge of the nutrient in vegetables ¹. Their components are essential for rural subsistence livelihood, health and the most affordable sources of micronutrients and health promoting phytochemicals for human ^{2, 3, 4}. For human, they are rich sources of oil, carbohydrates, carotenes, ascorbic acid, retinol, riboflavin, folic acid and minerals depending on the consumed vegetable ⁵. Solanum nigrum Linn (Family Solanaceae) is generally used in the traditional medicine as a remedy for treating various diseases^{. 6}. This plant species also has medicinal significance among Africans who included decoction or extract of the leaves in some ethno medicinal preparations particularly for the treatment of dysentery, haemoptysis, haemorrhoids, wound sepsis, and laxatives ⁷. The leaves are used to heal open wounds and is known to possess hypotensive effect ⁸. It commonly consumed as cooked complement to the major staple food ⁹. However, cooking, such as boiling, steaming and frying may be caused deterioration of constituents ¹⁰. The impact of food transformations on final nutritional quality of food products is a major question that has been studied only partially ¹¹. Nutritional profiling consisted of a classification of foods based on their nutritional composition ¹². Nutrient profile concept implied that it is possible to discriminate between foods according to their contribution to a healthy diet on the basis of their nutrient contents of key component. ¹³. The SAIN and LIM system can be helped to choose the best food and contributed to reduce malnutrition ². The aimed of this study was to evaluate antioxidant compounds, fatty acids and determine nutritional profile using the LIM and SAIN system to of Solanum nigrum leaves before and after boiling.

2. Material and Methods

Solanum nigrum was previously authenticated by National Floristic Center (University Felix Houphouët-Boigny, Abidjan-Côte d’Ivoire). The leaves were collected fresh and at maturity from cultivated farmlands located at Dabou (latitude: 5°19′14″ North; longitude: 4°22′59″West) in the District of Abidjan.

Leaves were put into clean and dry containers and transferred to the laboratory of Food Biochemical and Tropical Products Technology (Nangui Abrogoua University, Abidjan, Côte d’Ivoire) and were cooked after cleaning and washing with water ¹⁴.

The boiling of leaves was carried out as described previously ¹⁵. One (1) l of water was brought to boil in 2-l beaker. The beaker was covered to prevent water loss to evaporation. Five hundred grams of Solanum nigrum leaves were boiled separately for 0, 10, 15 and 20 min. After cooking, the vegetables were drained, cooled for a few minutes at room temperature homogenized, and. were oven-dried at 40°C for 72 h, grounded into flour and stored in polyethylene bags for biochemical analyzes

The method of Nayek et al. ¹⁶ was used for total Carotenoid contents determination using Diethyl-ether as solvents. The determination of β-carotene and lycopene was done according to the method of Kumara et al. ¹⁷. Dried sample was extracted using methanol and extract (100 mg) was mixed with 10 ml of acetone-hexane mixture (4 :6) for 1 min and filtered. The absorbance was recorded at wavelengths of 453, 505 and 663 nm and calculated as follows:

(1)

(2)

The results were expressed with mg/100 g of dried matter.

The method of AOAC. ¹⁸ was used for lipid extraction. The lipid extract was subjected to acidic methanolysis to prepare fatty acid methyl esters as described previously ¹⁹. One (1) μL of oil converted to methyl ester was injected into GC coupled with MS to obtain individual peaks of the fatty acid methyl esters. The amounts of each of the fatty acids were calculated from the areas of the internal standards (heptadecanoic acid) ²⁰. The contents of the particular fatty acids are expressed as percentages of the sum of all of the fatty acids analysed.

The determination of water-soluble vitamin (folic acid) was carried out by high-performance liquid chromatography according to Miglio et al ²¹. Vitamin C, Iron, Calcium, protein, fiber, saturated fatty acid, sodium and sugar were determined according to standard methods for nutritional guidelines and SAIN and LIM scores were calculated using the nutrient profiling system of the French Food Safety Agency ^{11, 13}.

Analyses were made in triplicate and the mentioned values were the average ± standard deviation (SD). These experimental data were subjected to Analysis of Variance (ANOVA) and Duncan’s multiple range test for mean separation at P = 0.05 in STATISTICA software version 7.1.

3. Results and Discussion

The total carotenoids, β-carotene and lycopene contents of Solanum nigrum L. leaves are presented in Figure 1. In this study, the boiling significantly (p 0.05) increased initially from raw to 10 min (53.95 ± 0.38 to 65.70 ± 0.12 mg/100g) and decreased (65.70 ± 0.12 - 37.38 ± 0.03 mg/100g) at 10 and 20 min of boiling. The β-Carotene content of the uncooked leaves initially increased from raw to 10 min (18.17 ± 0.01 to 26.37 ±0.31mg/100g) and decreased (26.37 ±0.3 to 17.65 ± 0.12 mg/100g) at 10 to 20 min of boiling. For lycopene contents, significant (P= 0.05) differences were observed for all samples. Lycopene content was significantly increased initially from raw to 10 min (1.64 ± 0.03 - 6.33 ± 0.01 mg / 100g) and decreased (6.33 ± 0.01 - 3.58 ± 0.08 mg/100g) at 10 and 20 min of boiling.

The fatty acids contents of the boiled and raw leaves were presented in Figure 2. The fatty acids parameters generally differed significantly (p < 0.05) from boiled to fresh leaves. The polyunsaturated fatty acids content of the uncooked leaves initially increased from raw to 15 min (880.5 to 3702.80 mg/100g) and decreased (3400.70 mg/100g) at 20 min of boiling unsaturated fatty acids contents after 10 min of boiling decreased significantly (P = 0.05) compared with the fresh leaves and ranged from 2466.77 ± 0.47 to 1047.03 ± 0.61 mg/100g (boiled at 20 min). Omega 6 content was decreased significantly (P = 0.05) from all boiled samples with the values of 1415.50 ± 0.36, 987.70 ± 0.10 and 177.96 ±0.92 mg/100 g respectively for uncooked, boiled at 10, 15 min and became null after 20 min of cooking. The Omega 3 content after 10 min of boiling decreased significantly (P = 0.05) compared to the fresh leaves and ranged from 157.45±2.73 to 73.82±1.22 mg/100 g (boiled at 20 min).

The impact of boiling on vitamins (vitamin B₁ and B₂) contents is depicted in Figure 3. The vitamins contents generally differed significantly (p < 0.05) from boiled to fresh leaves. Vitamin B₁ contents after 10 min of boiling decreased significantly (P = 0.05) compared to the fresh leaves and ranged from 2.58 ± 0.00 to 0.18 ± 0.00 g/100 g (boiled at 20 min). The Vitamin B₂ contents were significantly different (P = 0.05) in all samples with the values of 0.26 ± 0.00, 0.07 ± 0.00, 0.05 ± 0.00 and 0.04 ± 0.00 g/100 g respectively for uncooked, boiled at 10 min, 15 min and 20 min. Figure 4 shows the LIM and SAIN scores of S. nigrum leaves at different cooking time. All samples have LIM scores below 7.5 and SAIN scores above 5.

Food quality often deals only with the influences of primary production and industrial processing. Food preparation at home as final step of the chain has also great influence on quality determining parameters ²². The effect of boiling on carotenoids, β-carotene and lycopene contents of Solanum nigrum leaves is given in Figure 1. All parameters significantly (p 0.05) increased initially from raw to 10 min and decreased at 10 and 20 min of boiling. The temperature, instead of the presence of water, was the major factor influencing the carotenoids stability ²³. In green vegetables, β-carotene is incorporated in the carotenoid-protein-complexes in the chloroplasts. Cooking led to a softening of the plant tissue and the denaturation of proteins so that the carotenoids can be extracted much easier ²⁴. β-carotene, and more recently lycopene and other specific carotenoids, have been the subject of many observational studies assessing their association with chronic diseases ²⁵. β-carotene from fruits was more effective in increasing plasma levels of β-carotene ²⁶. High circulating levels of their biomarkers (carotenoids), have been associated with a relatively low incidence of cardiovascular disease, cataract, cancer and prevent Alzheimer’s disease pathogenesis ^{27, 28, 29}. In addition, high levels of circulating lycopene have been associated with cholesterol serum levels decreasing and have been shown to be effective against several common diseases including atherosclerosis, and heart disease ^{30, 31}. The fatty acids content of the boiled and raw leaves was presented in Figure 2. The fatty acids parameters generally differed significantly (p < 0.05) from boiled to fresh leaves. The unsaturated fatty content of the uncooked leaves initially increased from raw to 15 min and decreased at 20 min of boiling. During cooking, the oils and fats are exposed to high temperature which may result in changes in their chemical properties ³². It is an triester of fatty acids and glycerol heating oil at a temperature above its smoke point results in breaking down its triglyceride to glycerol and fatty acids. Furthermore, heating break-down the glycerol to acrolein which ends up in losing flavour and nutritional value of the specific oil. In addition, the heating of oils and fats without catalysts produces secondary lipid peroxidation abducts such as carbonyls and cyclic fatty acids which are toxic to human body ³³. The amount of polyunsaturated, omega-3 and omega-6 of boiled leaves, significantly (p<0.05) decreased during boiling compared to the control. The long-chain of polyunsaturated are susceptible to oxidation during heating and other culinary treatments ³⁴. The polyunsaturated fatty acids are essentials in human diets and their deficiency leads to a slowing of growth and development, an alteration of the integrity of the skin and kidney ³⁵. α-linolenic acid is part of the n-3 series present in many plants ³⁶. Intake of omega-6 fatty acids shifts the physiological state to one that is prothrombotic, whereas omega-3 fatty acids have anti-inflammatory, antithrombotic, anti-arrhythmic, hypolipidemic and vasodilatory properties ³⁷. Omega-3 fatty acids are essential for normal growth and development and may play an important role in the prevention and treatment of coronary artery disease, hypertension, diabetes, arthritis, other inflammatory, autoimmune disorders, and vasodilatory discover ³⁸. The effect of boiling on vitamins composition of Solanum nigrum leaves is given in Figure 3. The residual contents of vitamins after 10 min of cooking were: Vitamin B₁ (1260-180 mg/100 g) and vitamin B₂ (70-40 mg/100 g). Vitamin B₁ and B₂ are water-soluble vitamins, the reduction of vitamin content may be due to leach into the boiling water ³⁹. Water-soluble vitamins are essential compounds for adequate functioning of the human body. In metabolic processes, several B-group vitamins act mainly as coenzymes to produce energy and play important roles ⁴⁰. Also, they are involved in the processes of normal metabolism and cell regulation, and they are necessary for growth and development; thus, they are chemicals that we all need to stay healthy ⁴¹. Figure 4 showed the LIM and SAIN scores. All samples have high SAIN (SAIN> 5) and low LIM (LIM <7.5). SAIN and LIM system can be helped to choose the best food and contribute to reduce malnutrition ². The food which have higher SAIN high and lower LIM are a good profile and recommended to prevent diseases ^{2, 42}. However, boiling impact significantly nutritional quality of leaves. Boiling at 10 min was considered the best to preserve Solanum nigrum leaves contents.

4. Conclusion

Solanum nigrum leaves are good source of essential fatty acids, carotenoids, β-carotene and lycopene which could contribute to their medicinal value. Their leafy leaves if consumed in sufficient amount would contribute greatly to the human nutritional requirement for normal growth and adequate protection against diseases arising from malnutrition. Boiling has great influence on quality determining parameters. It caused the loss of nutrients, this might be due to leaching during heat application. It was noted a significant reduction of nutrient content of leaves after boiling. Thus, the study suggests that the time of domestic boiling must be less than 10 min for the studied leafy vegetables in order to the nutritional requirement and to the food security of Ivorian population.

References