Comparative Study of Proximate, Chemical and Physicochemical Properties of Less Explored Tropical Leafy Vegetables

Introduction

African leafy vegetables are of great nutritional importance as they supply vital nutrients required by human body.They are majorly grown and abundant in the rainy season and become scarce in dry seasons(Kamela et al., 2016).Different varieties of these vegetables range from wild to semi-wild and they form important parts of our daily diets.Leafy vegetables are the simplest sources of proteins, vitamins, minerals and fibers (Mepba et al., 2007; Fasuyi, 2006).They are rich sources of β-carotene, ascorbic acid, riboflavin and folic acid and the minerals calcium, iron and phosphorous (Gupta et al., 2005).African leafy vegetables contain high levels of vitamin A, vitamin C,iron, calcium and protein and are valuable sources of nutrition in rural areas where they contribute substantially to protein, mineral and vitamin intake(Abukutsa-Onyango, 2003).Vegetables are also good sources of poly unsaturated fatty acids and it is believed that sufficient consumption of vegetable is preventive against cardiovascular diseases (Murcia et al., 1992).

Although, the list of tropical vegetables is enormous, only few had been properly identified,underutilized ones are confined to rural areas where they are not consumed in great quantity (Smith and Eyzaguirre, 2007).They are neglected because they are thought to be high in the anti-nutritional factors(alkaloids, phytate, cyanide, nitrates and oxalates) and due to the flavor and unfamiliar taste impacted on the food.The bioavailability of essential nutrients could be reduced by the presence of the anti-nutritional factors like oxalates and cyanogenic glucoside (Akindahunsi and Salawu, 2005).This phenomenon had limited the importance of vegetables in nutrition.

The nutritional importance of any given food is a function of its nutrient and anti-nutrient composition(Prohp et al., 2006).Some vegetables have been the base of human diets for decades providing consumers with vital micronutrients needed for sustainability and to maintain health and promote immunity against infections (Flyman and Afolayan, 2006).The promoting health attributes of vegetables are associated with their nutritional and phytochemical properties(Oulai et al., 2014).Example of such component is glucosinolate found in Brassica vegetables which is effective against cancer and heart disease (Adebooye and Opabode, 2004).

Underutilized vegetables have immense potential in contributing to the economic growth of developing nations through sustainable food production and food security since they are tolerant to adverse climatic conditions and can be grown with lower management costs on marginal land (Sheela et al., 2004).These vegetables are easier to grow and more resistant to pests.In order to improve utilization of these vegetables, it is important to critically evaluate their nutritional values and their implications for consumers.This study was designed to evaluate the nutritional and anti-nutritional contents of some tropical underutilized green leafy vegetables.

接触交代型铁矿床是山西第二主要类型。该类型矿石品位w(Tfe)平均41.4%，最高可达54%(如壶关县照阳沟铁矿区)，属规模相对小，但品位较高的铁矿床。因此，要想寻找“小而富”的铁矿床，应重点放在狐堰山、塔儿山及虹梯关南部一带，即主要在省内寻找既有灰岩出露又有岩体出露地区。由于碳酸盐受热液热液影响会产生围岩蚀变，即矽卡岩化，因此寻找围岩蚀变带是良好的找矿标志。在野外注意观察有无断裂构造及岩体出露情况。狐堰山地区出露岩体多为二长斑岩，塔儿山一带为二长岩及正长闪长岩类，平顺一带为闪长岩类，因岩体本身铁质含量较高，通常岩体大，所发现矿体越大。

Materials and Methods

Sample collection and preparation

Ascorbic acid contents of samples were determined using 2, 6-dichlorophenol indophenols titration method.Carotene was extracted from randomly chosen 100 g of each sample.Twenty mL of acetone was added while grinding.After the third extraction,water was added.The filtrate was transferred to a separate funnel.The extraction of the acetone phase with a small volume of petroleum ether was continued until no color was visible.The petroleum ether extract was filtered through anhydrous Na2SO4.Extraction with petroleum ether was repeated, until the alcoholwater layer was colorless.The intensity of the color at 452 nm was measured using 3% acetone in petroleum ether as blank.The concentration of β-carotene was determined.

The leafy vegetables Amaranthus spinosus L., Basella alba Linnaeus, Corchorous tridens L., Cyrtosperma senegalense (Schott), Erigeron floribundus Sch, Ho-slundia opposite Vahl, Lagenaria siceraria (Molina)Standl, Ocimum basilicum L., Solanum aethiopicum L.and Talinum portulacifolium (Forssk.) Asch.ex Schweinf were obtained from and authenticated at the Institute of Agricultural Research and Training, Moor Plantation, Ibadan (latitude 7°33'N and longitude 3°56'E), Nigeria.Samples were washed with potable water.Samples were sorted into mature leaves and stalk and analyzed separately.

Analyses

All the analyses were done in three replicates.Data were subjected to analyses of variance and means separated with Duncan's Multiple Range Test (SAS,2001).

Protein contents were determined with Kjeldhal method (AOAC, 2005) and values multiplied by 6.25 to obtain the total nitrogen.The total fat contents were determined by using soxhlet extraction method (AOAC,2005) and crude fiber content were determined.Samples were ashed to a constant weight and the weight was determined.Moisture contents were determined gravimetrically at 105℃ for 8 h. Carbohydrate was calculated by subtracting the sum of protein, ash,crude fiber, crude fat and moisture contents obtained from 100.i.e [100- (protein+ash+ crude fiber+crude fat+moisture contents)]%.

可它刚跳到半空，一只黑乎乎的、长着红眼睛的家伙就将它扑倒在地，张开满口尖牙的大嘴，准备将它撕碎。那东西竟然是老鼠！

To determine magnesium content, the ash content was digested by adding 5 mL of hydrochloric acid to the ash in crucibles and heating to dryness on a heating mantle.Five mL of hydrochloric acid was added and the mix heated to boil and filtered through a Whatman No.1 filter paper into a 100 mL volumetric flask.The filtrate was made up to mark with distilled water and concentration of magnesium determined with a Jenway Digital flame photometer.

Saponin was determined using Brunner (1984)method.Ten g of finely ground sample was weighed into a 250 mL beaker and 100 mL of isobutyl alcohol added.The absorbance of samples and standards were determined with a Jenway V6300 spectrophotometer(Cole-Parmer Ltd., Staffordshire, United Kingdom)at a wavelength of 380 nm.Phytate was determined using Maga (1982) method.Two g of sample was weighed into a 250 mL conical flask.A hundred mL of 2% hydrochloric acid was added and the sample was left to stand for 3 h.The mix was filtered through a double layer of hardened filter paper.Fifty mL of each filtrate was placed in 250 mL conical flask and 100 mL of distilled water was added into each solution.Titration was with a standard iron (III) chloride solution containing 0.00195 g · mL-1 of iron.

首先对于道路桥梁施工图纸进行充分的熟和了解，同时详细的了解伸缩缝施工的操作流程以及需要注意的细节，根据工程施工的实际情况制定出施工方案并报告给相关部分经检查合格之后再进行施工。同时对于施工人员应该明确每一个施工人员的工作任务以及工作责任，将施工中所使用的机械设备进行合理的分配，并对所有设备进行必要的测试，确保可以正常使用，严格对每一道施工工序进行监管，避免出现质量问题。

Iron and iodine contents were determined from digests with 5 mL of hydrochloric acid solution and heated to dryness on a heating mantle.Diluents were aspirated into a Buck 200 Atomic Absorption Spectrophotometer (Buck Scientific, Norwalk) through the suction tube.Each trace element was read at the respective wavelength.

Oxalate was determined using Chai and Liebman(2005) method.Two g of sample was boiled in 40 mL of water for 30 min in a re flux condenser and 10 mL of 20% Na2CO3 was added and the mix boiled for another 30 min.The liquid extract was filtered and washed with hot water until the wash water did not show any alkaline reaction.The combined wash water and filtrate were concentrated to a small volume and cooled.An aliquot of this filtrate was transferred into a 400 mL beaker, and diluted with water to 200 mL.The filtrate was titrated against 0.05N KMNO4 solution and was reported as oxalic acid.

Cyanide content was determined using Bradbury et al.(1999) method.One g of sample was weighed into a flat bottom plastic bottle with a screw-capped lid.A 0.5 mL of 0.1 mol · L-1 phosphoric acid at pH 6 was added to the sample and a yellow picrate paper attached to a plastic strip and placed in the bottle.The cap of the bottle was closed.A blank was prepared as the above.The absorbance of all the solutions, including linamarin standards, was measured against a blank on a Spectronic 2ID spectrophotometer at 510 nm.

pH and titratable acidity were determined using Illand et al.(2000) method by using a pH meter with pH buffer solutions of pH 4, 7 and 9.

第一，从服务的内容上看，烹调、保洁、操持家务、婴幼儿保育、照料长者、看护病人、护理孕妇、家务管理、家庭教育和娱乐等，均属于家政服务的内容，也应该是未来家政行业所要涉及的领域。

Statistical analyses

Proximate analyses

Results and Discussion

Crude fiber content was the highest in B.alba and the lowest in C.tridens; these values were lower than that in Ipomea batatas Lam, Piper guineense and Vernonia amagydalina (Akindahunsi and Salawu,2005; Antia et al., 2006).Non-starchy vegetables were the richest sources of dietary fiber (Agostoni et al.,1995) and were employed in treatment of obesity,diabetes, cancer and gastro-intestinal disorders(Swaminathan, 1995).The required dietary allowance of fiber for children, adults, pregnant and lactating mothers were 19-25, 21-38, 28 and 29 g, respectively (Akubugwo et al., 2007).The vegetables studied were capable of contributing to daily requirements when l00 g dried leaves were consumed and could be a valuable source of dietary fiber in human nutrition.

当前我国的水治理要更好地发挥政府的作用，关键是转变政府职能。政府需要从微观事务管理更多地转向宏观管理和社会管理，从水利工程的建设更多地转向制度建设和公共服务，从行政手段为主转向法律、行政、经济、教育等多种手段并用并更加重视依法行政。例如，政府从直接调配水资源转向实施水权管理调控水资源配置，从直接投资建水利工程转向大规模利用社会资本办水利，从直接管理水务设施转向制定标准和强化监管保障水安全，从全方位提供各种水服务转向重点提供水利基本公共服务，从主要依靠行政手段协调水事主体的利益冲突转向依靠规划、法规、标准等规则来规范各种水事关系。

Proximate compositions in all the samples analyzed differed (Table 1).Protein was the highest in C.tridens and the lowest in E.floribondus.The range of the values (2.10%-5.93%) fell within those for selected commonly consumed tropical green vegetables (Bailey, 1992; Akindahunsi and Salawu,2005).According to Aberoumand (2012), plants that derived more than 12% of its calorific values from proteins were a good sources of proteins which made vegetable good sources of proteins.Gupta et al.(2005)reported a high protein content of 7.1 and 4.3 g · 100 g-1 in Delonix elata L and Digera arvensis Forsk, respectively.Similar values had been reported for the protein contents of some tropical leafy vegetables of Nigeria (Aletor and Adeogun, 1995).

The highest fat content was for H.opposita and the least for E.floribondus.Fat contents of these vegetables compared favorably to that for edible green leafy vegetables of southern India and Nigeria(Midmore et al., 1991).A diet providing 1%-2% of its calorie as fat was sufficient for humans, as excess fat consumption was implicated in certain cardiovascular disorders such as arteriosclerosis and cancer.

Proximate analysis

Ash content was the highest in A.spinosus and the lowest in B.alba (Table 1).Ash was an index of the total mineral content.The highest carbohydrate content was for B.alba and the lowest for C.tridens.Though generally low, when compared to some carbohydrates, the studied vegetables could meet required dietary allowance of children (130 g), adults(175 g), and pregnant and lactating mothers (210 g)(Akubugwo et al., 2007).Moisture content was the highest in C.tridens and the lowest in H.opposita;the values were within the range for some Nigerian leafy vegetables and pacific green leafy vegetables(Akindahunsi and Salawu, 2005; Gupta et al., 2005;Akubugwo et al., 2007).

For tannin, 10 g of sample was measured into a 50 mL beaker and 2 mL of 50% methanol was added and the beaker was covered with paraffin, placed in a water bath at 77-80℃ for 1 h and shaken to ensure a uniform mixing.The extract was filtered using double layered Whatman No.4 filter paper in to a 100 mL volumetric flask.Absorbance of tannic acid standard solution and the samples were read after color development on a 21D spectrophotometer (Michigan,USA) at a wave length of 760 nm.

Table 1　Proximate composition of some tropical under-utilized vegetables

Values with different letters within column are significantly different at p＜0.05.Values expressed are means of three replicates.The same as below.

Sample Parameter Protein (%)　Fat (%)　Fiber 　Ash (%)　Carbohydrate (%)　Moisture (%)C.tridens　5.93a　0.28e　1.22g　1.91f　3.82j　88.04c T.portulacifolium　5.27b　0.34d　1.34e　2.21b　4.36i　87.84d L.siceraria　4.90c　0.46b　1.26f　2.16c　5.22h　87.26e O.basilicum　4.20d　0.35c　1.39d　2.04d　6.26g　87.15g A.spinosus　3.85e　0.37c　1.42c　2.27a　6.45e　88.02c S.aethiopicum　3.52f　0.34d　1.44c　1.90f　6.32f　87.20f H.opposite　3.15g　0.54a　1.47b　1.96e　7.16d　87.19fg C.senegalense　2.80h 　0.29e　1.37d　1.93e　7.64b　88.32a B.alba　2.45i 　0.48b　1.54a　1.89g　7.94a　87.24ef E.floribondus　2.10j 　0.25f　1.25f　2.23b　7.31c　88.11b

Anti-oxidant components and mineral contents differed for vegetable samples (Table 2).Ascorbic acid content was the highest in A.spinosus and the lowest in C.senegalense.All the samples had significant amounts of ascorbic acid.Gupta et al. (2005) reported large variations in the ascorbic acid contents of some green leafy vegetables.Ascorbic acid was an antioxidant which was used as additive in many processed foods to prevent nutrient loss and spoilage.Ascorbic acid found in these green leaves had the capacity in varying degrees to counteract free radicals.The highest β-carotene content was in A.spinosus and the lowest in O.basilicum.The values obtained were close to the values reported by Shokunbi et al.(2011). β-carotene was a precursor of vitamin A and needed for maintenance of skin mucous membrane, bones and teeth.The highest iodine level was in A.spinosus and the lowest in H.opposita.Iodine levels of the vegetables were within the range reported by Bailey (1992).Iodine was needed by the body to prevent goiter disease.

Table 2　Anti-oxidant and mineral contents of under-utilized tropical leafy vegetables

Sample Parameter Ascorbic acid (mg · 100 g-1)　　β-carotene (4 g · 100 g-1)　Iodine (mg · kg-1)　Iron (mg · kg-1)　Magnesium (mg · kg-1)C.tridens　92.43g　295.26g　29.10c　86.00b　483.00fg T.portulacifolium　104.30b　335.53b　28.35e　76.00cd　659.00a L.siceraria　87.77j　308.68f　28.88d　79.00c　486.00f O.basilicum　98.37d　273.79j　26.77h　74.00de　592.00d A.spinosus　108.12a　346.26a　31.42a　93.00a　588.00d S.aethiopicum　103.03c　311.37e　30.26b　89.00b　635.00b H.opposite　96.67e 　279.16i　25.92j　57.00i　416.00h C.senegalense　88.62i　316.74d　26.34i　65.00g　479.00g B.alba　 91.58h　292.58h　27.61g　69.00f　624.00c E.floribondus　94.98f　330.16c　27.83f　71.00ef　497.00e

The highest iron content was in A.spinosus and the lowest in H.opposita, but compared favorably with values reported for some green leafy vegetables(Antia et al., 2006; Akubugwo et al., 2007).Iron was an essential trace element for hemoglobin formation,normal functioning of the central nervous system and in the oxidation of carbohydrates, protein and fats (Adeyeye and Otokiti, 1999).The difference in nutrient concentration in these leafy vegetables may be due to environmental and genetic factors.Magnesium content was the highest in T.portulacifolium and the lowest in H.opposita.The magnesium contents of the studied vegetables were within the range reported by Antia et al (2006).This mineral is important, due to its connection with is chemic heart disease and calcium metabolism in bones.

The plants differed in contents of anti-nutritional compounds (Table 3).Values obtained for tannins in T.portulacifolium and C.senegalense were among the highest and there was few difference among other vegetables.Other types of plants had higher tannin levels (Vander-Poel, 1990; Apena et al., 2004).Tannin binds to exogenous and endogenous proteins including enzymes of the digestive tract and affects their utilization (Sotelu et al., 1995).Tannin is known to inhibit the bioavailability of proteins and mineral.

The saponin content in C.tridens was significantly higher than some of the other plants but similar to most.Saponin values were lower than those in bitter leaf (Vernonia amygdalina) as reported by Apena et al (2004).Saponins were practically non-toxic to man and could lower plasma cholesterol concentrations.High levels of saponin have been associated with gastro enteritis (Awe and Sodipo, 2001).

四是2005年10月正式实施的《预包装食品标签通则》，这是一项食品标签的国家强制性标准。它对预包装食品必须标示的内容及基本要求做出了明确规定，并规定转基因食品的标识属于强制标识的内容，并且应当符合国务院行政管理部门的规定。

Phytate content was the highest in C.senagalense and the lowest in L.siceraria and A.spinosus.The values were comparable to those reported in other crops (Adeyeye et al., 2000; Apena et al., 2004).Vander-Poel (1990) obtained higher levels of phytic acid in other crops.The effect of high phytic acid consumption was induction of mineral deficiency through formation of insoluble salts with divalent metals, so that they were unavailable to the body(Iyawe, 2009).Oxalate values were generally similar for all the plants.The oxalate contents were lower than the lethal dose, 4-5 g, dose reported for adults (Rose et al., 1999).The major problem associated with excessive oxalate consumption was its ability to form water soluble salts with some mono- and divalent ions and reducing its bioavailability (Iyawe, 2009).The highest hydrogen cyanide (HCN) value was in A.spinosus and the lowest in L.siceraria.High dose of HCN could inhibit respiration (Onigbinde, 2005);however, the values obtained were very low and within the recommended value that must be present in a diet.

Table 3　pH, titratable acidity and anti nutrients composition of some under-utilized tropical leafy vegetables

* Parameters are in %.

Sample Parameter Tannin* (×10-3)　Saponin* (×10-3)　Phytate (%)　Oxalate* (×10-3)　HCN (mg · kg-1)　pH　TTA (%)C.tridens　0.40b　5.20a　0.12f　0.90b　 0.00h　6.38a　0.16j T.portulacifolium　 1.40ab 　1.40b　0.16d　3.70ab　147.84c　4.12f　0.22c L.siceraria　0.50b　1.80ab　0.05h　5.80a　 0.00h　6.26b　0.17i O.basilicum　0.90b 　1.20ab　 0.15ed　3.30ab　97.55g　4.39d 　0.19f A.spinosus　0.06b 　1.80ab　0.02h　1.60b　169.88a　3.56h　0.24a S.aethiopicum　0.30b 　1.20b　0.01e 　0.70b　 0.00h　6.18c　0.17h H.opposite　0.70b　1.90ab　0.08g　2.00ab　139.92d　4.23d　0.20e C.senegalense　5.70a 　1.50b　0.24a　3.70ab　156.82b　3.89g 　0.22b B.alba　0.90b　1.60ab　0.18c　2.50ab　105.87g　4.36d 　0.18g E.floribondus　1.20b 　1.90ab　0.21b　2.90ab　112.86c　4.06d 　0.21d

The highest pH was in C.tridens and the lowest in C.senegalense.Plants with no HCN, and low values of other anti-nutrients had high pH.Acidic and alkaline foods did not usually translate in to acid and alkaline yielding foods.Jack (2009) reported that citrus fruit and tomatoes were acidic, but had a net alkaline yield once their constituents got to the kidneys.Vegetables were rich in potassium salts, a natural buffer.Acidosis would decrease the body's ability to repair damaged cells, decrease ability to detoxify heavy metals, make tumor cells thrive, and make persons more susceptible to fatigue and illness (Jack, 2009).The total titratable acidity was the highest in S.aethiopicum and the lowest in A.spinosus.The total titratable acidity indicated acid content of vegetables, but not the strength of the acid.

由于预紧力损失和护表情况的不同，加木垫板后锚杆支护预应力场的峰值与扩散范围与金属托盘相比出现一定差异。以100 kN预紧力下加木垫板前后锚杆支护预应力场为例，锚杆支护预应力场沿对称面切片分布情况如图7所示。其中，0～1 200 mm为自由段，1 200～2 400 mm为锚固段。

Conclusions

The under-utilized leafy vegetables contain appreciable amount of proteins, fat, fiber, carbohydrate, vitamins A and C and mineral elements.All the analyzed vegetables were high in one nutritional attribute or two nutritional attributes.These vegetables could contribute to the nutrient requirements of human and should be used as a source of nutrients to supplement other sources.The anti-nutritional constituents in the vegetables included oxalate, phytate, tannin, saponin and cyanide at values lower than the established toxic levels and L.siceraria, C.tridens, S.aethiopicum,O.basilicum and B.alba had the least amounts of anti-oxidants.It is recommended that vegetables with higher levels of anti-nutrients be well processed before consumption.

由式(1)、式(3)和式(4)得到直线形全车速下转向助力函数表达式,利用Matlab绘制出直线形助力特性曲线的三维曲面图,如图4所示.

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