Nutrient composition of five varieties of commonly consumed Nigerian groundnut ( Arachis hypogaea L . )

14 thiamin (0.73-0.98mg/100g), niacin (14.00-16.03mg/100g) and tocopherol (18.62-21.07mg/100g) activities; with boro red having significantly (P <0.05) higher values in all but β-carotene. Heavy metals like Co, As, Cd and Pb were not detected in any of the samples and the other minerals vary with K>P>Mg>Ca>Mn>Cu>Na>Zn>Fe>Al>Se in most of the varieties. Boro red also had the highest elemental contents in most of the minerals analyzed. Thus, these groundnuts can be considered useful foodstuffs in minimizing proteinenergy malnutrition (PEM) and micronutrient deficiencies in Nigeria. However, the boro red variety is most recommended. The outcome of this research is a contribution to the food composition table.


INTRODUCTION
Groundnut (Arachis hypogea L.) is among the major world oil seed crops.For some years now, China, India, the United States and Nigeria have been the major producers of the groundnut (~70% of the world production).During 2010-2011, approximately 35 million metric tons of groundnuts were harvested worldwide, where 42.81, 17.01, 5.36 and 4.39% came from China, India, the United States and Nigeria respectively (USDA-FAS, 2011).Its seeds are rich source of edible oils and provide a more valuable source of fat, protein, carbohydrate, minerals and some vitamins than any other nut, yet they are often the least expensive as well (Reddy et al., 2003).
Groundnut is an underexploited nut largely consumed by the western and most populations in Africa and known to a lesser extent as earthnut, monkeynut, and goobers.It is not a true nut but rather an annual legume much like the bean or a pea (Nwokolo, 1996).It has a high energy value and suitable for wide variety of agro ecological conditions (Karthikeyan et al., 2007).It is now grown in all tropical and subtropical countries primarily as an oil seed (Izge et al., 2007).It is used for different purposes: food (raw, roasted or boiled, cooking oil), animal feed (pressings, seeds, green material, straw), and industrial raw material (Onyeike and Oguike, 2003).

SUMMARY Nutrient composition of five varieties of commonly consumed Nigerian groundnut (Arachis hypogaea L.)
The nutrient composition of the five major varieties of groundnut (Arachis hypogaea L.) commonly consumed in the south-western part of Nigeria was investigated.Raw dryshelled samples were analyzed for proximate (moisture, ash, protein, fat, fiber and carbohydrate), 'vitamins' (β-carotene, thiamine, niacin and tocopherol) and minerals (Na, K, Ca, P, Mg, Fe, Mn, Zn, Cu, Se, Co, Al, As, Cd and Pb).Results showed that the groundnuts had 4.12-9.26%moisture, 2. 77-3.31% ash, 24.26-26.35% protein, 45.41-48.14%cardiovascular disease (Kris-Etherton et al., 1999), colon, prostate and breast cancer (Awad et al., 2000) as well as Type II diabetes (Jiang et al., 2002).It also seems to reduce osteoporosis and deficiencies in protein intake (Messina, 1999).Recently, it has been associated with metabolic benefits in the context of counteracting metabolic dysfunction associated with the increasing prevalence of obesity and metabolic syndrome (Coates and Howe, 2007).
Several studies have been carried out on groundnuts globally; some of which are highlighted subsequently.The chemical composition of groundnut from Argentina and Turkey had been determined by Grosso et al. (2000) and Ozcan & Seven (2003) respectively.Campos-Mondragon et al. (2009) reported the nutritional composition of six new peanut cultivars grown in Mexico.Asibuo et al. (2008) also reported the chemical composition of 20 groundnut varieties from Ghana and, Aslam Shad et al. (2009) reported the biochemical and phytochemical composition of some groundnut varieties from Pakistan.The fatty acid profile of some Nigerian groundnut oils had been analyzed (Anyasor et al., 2009).Furthermore, the chemical composition of groundnuts from Nigeria was also evaluated by Atasie et al. (2009) and Musa et al. (2010).However, in most of these studies, the varieties analyzed are not the commonly consumed ones (rather, they are mostly improved varieties from research institutes) and when they are commonly consumed, few varieties are considered.
Therefore, this study aimed at determining the nutrient composition of the five major varieties of groundnut commonly consumed in the southwestern part of Nigeria.We reported the proximate, vitamins and minerals found in these five varieties.

Materials
Seeds of five varieties of Arachis hypogaea L. were purchased, each from 3-5 stores, in Mile 12 market, Lagos, Nigeria (Ela, Campala, Boro light and Boro red) and Oje market, Ibadan, Nigeria (Mokwa) in February 2009.Lagos and Ibadan are located in southwestern Nigeria.The seeds were stored in a polythene bag and transported to the laboratory for analysis.They were identified by Ogunwenmo, K.O.(PhD) (Professor, Biosystematics, Cytogenetics & Environmental Science, Chemical and Environmental Sciences Department, Babcock University).They were de-shelled and stored in sterile airtight bottles at 4°C until analysis.
Calcium, potassium and sodium were determined using a Jenway flame photometer.Phosphorus was determined by the vanado-molybdate spectrophotometric method.Magnesium, iron, zinc, copper, manganese, aluminum, cobalt, arsenic, cadmium, lead and selenium were determined spectrophotometrically using a Buck 210 atomic absorption spectrometer (AOAC, 968.08).All mineral determinations were done after dry ashing of the samples and according to the AOAC official method (2005).

Statistical Analysis
Data were analyzed by one way ANOvA with an SPSS version 15.0 and differences were considered to be statistically significant at P<0.05.An LSD test was further carried out to establish the pairs that showed significant differences.

Chemical Composition
The mean chemical compositions of five varieties of groundnut (Arachis hypogaea L.) are presented in Table 1.The groundnut had 4.12-9.26%moisture, 2.91-3.45%ash, 26.64-27.57%protein, 48.06-50.66%fat, 2.76-3.07%fiber and 17.03-18.51%carbohydrate.Boro red had the highest levels of ash, fiber and carbohydrate; while ela and boro light had the highest levels of protein and fat respectively.The significantly higher (P<0.05)moisture content (9.26%) of mokwa would likely lower its shelf life compared with other varieties.
The ash contents reported in this study are higher compared to the report of Campos-  (Musa et al., 2010).This shows that our values (48.06-50.66%)are within the ranges found in the literature.The high fat content in groundnuts indicates high energy density that promotes fat soluble vitamin absorption without adding to the bulk of the diet (Atasie et al., 2009).The fiber of groundnut varieties has been reported as 6.1%, 3.7% and 3.3-4.4% by Paul and Southgate (1978) and 18.9-23.4%respectively as the carbohydrate contents of groundnuts, which are higher than the one we obtained from the groundnut varieties analyzed.This trend might also be due to the fact that improved varieties from research institutes were analyzed by Asibuo et al. (2008) and Campos-Mondragon et al. (2009) as different from the local varieties we analyzed.This calls for a need to circulate more improved varieties to our local farmers for cultivation and distribution to Nigerian groundnut consumers.

Vitamin Composition
The mean concentrations of β-carotene, thiamin, niacin and tocopherol in the five varieties of groundnut (Arachis hypogaea L.) are summarized in Table 2.All the groundnut varieties showed activities of the β-carotene and vitamins determined.They had 63.32-65.35mg/100g of β-carotene, 0.73-0.98mg/100g of thiamin and 14.00-16.03mg/100g of niacin and 18.62-21.07mg/100g of tocopherol.All values were reported on dry weight basis.There is a paucity of information on the levels of vitamins in groundnut varieties.This result indicates the richness of these commonly consumed foodstuffs.They have the potential of supplying these micronutrients to a malnourished populace, especially in the developing world.
Nut consumption is associated with a protection effect against coronary heart disease, partly due to its high antioxidant content (Davis et al., 2007).The β-carotene value of the boro light variety (63.32mg/100g: 5.28mg/100g vitamin A) for example, is higher than the vitamin A value (0.71µg/100g) of the almond nut reported by Christian and Ukhun (2006).Both vitamin A and tocopherol have important roles as antioxidants which may reduce the risk of those cancers initiated by free radicals and other strong oxidants (Willett and Stampfer, 2001;Devlin, 2006).The levels of thiamin and niacin in all the varieties, especially the boro red, indicates that individuals consuming them can derive substantial amounts of these B-vitamins, which are essential for the metabolisms of carbohydrates, proteins, and fats.

Mineral Composition
Nuts play a significant role in human nutrition especially as sources of vitamins and minerals (Wargovich, 2000).The mean concentrations of the minerals evaluated for the five groundnut varieties in this study are presented in Table 3.The result shows that Co, As, Cd and Pb were not detected in the samples.Other minerals vary with K>P>Mg>Ca>Mn>Cu>Na>Zn>Fe>Al>Se, in most varieties.In all minerals evaluated, boro red had the highest contents followed mostly by ela; while makwa normally had the least contents.This trend is clearly reflected in the ash contents of these groundnut varieties (Table 1).The data obtained in this study for K, P and Ca are similar to previous data from bamabara groundnut reported by Amarteifio et al. (2006).However, most of the minerals are lower compared with those reported by Asibuo et al. (2008) from 20 improved varieties of groundnut.This further calls for the need to invest resources in the development, production and distribution of improved groundnut varieties for Nigerians.Minerals serve as cofactors for many physiological and metabolic functions.The presence of a substantial amount of Ca and P in all the groundnut varieties is a good indication that they are rich in minerals that play a role in bone formation, blood coagulation and muscle contraction along with other metabolic processes.It has also been hypothesized that chronic groundnut consumption would improve serum Mg concentration, thus reducing the risk of cardiovascular disease (CvD) (Alper and Mattes, 2003).Mn, Cu, Zn and Se, which are parts of the human antioxidant defence systems (Wardlaw and Hampl, 2007), were present in all the varieties analyzed, especially the boro red variety.Therefore, they can boost the antioxidant status of individuals consuming them.Consequently, they can positively minimize the effects of oxidative stressrelated diseases in individuals consuming them.

CONCLUSION
Groundnuts can be considered as good sources of protein and fats, which make them useful for enhancing growth and supplying energy to humans and animals when added to the diet.All the groundnut varieties analyzed are potential micronutrient (vitamins and minerals) sources and thus will facilitate various metabolic processes and improve growth and development in their consumers.However, boro red is the most recommended variety due to its relative macro and micronutrient richness.The outcome of this research is a very useful contribution to the food composition table.There is a need to release the already developed improved varieties of groundnuts in Nigeria to farmers for mass production, distribution and consequent positive impact on their consumers.
Mondragon et al.

Table 1 Chemical Composition (g/100g dry weight ** ) of Five Varieties of Groundnut (Arachis hypogaea L.)
Determination was on wet weight basis values with different superscript along the same column are significantly different (P<0.05).

Table 2 Vitamin composition (mg/100g dry weight) of five varieties of groundnut (Arachis hypogaea L.)
COMPOSITION OF FIvE vARIETIES OF COMMONLy CONSUMED NIGERIAN GROUNDNUT (ARAChiS hYPOGAEA L.) NUTRIENT

Table 3 Mineral Composition (mg/100g dry weight) of Five Varieties of Groundnut (Arachis hypogaea L.)
values are expressed as mean  Standard Deviation, n=3.values with different superscript along the same column are significantly different (P<0.05).ND -Non-detectable