African Journal of Food Science and Technology (ISSN: 2141-5455) Vol. 4(4) pp. 44-47, April, 2013 Available Online http://www.interesjournals.org/AJFST Copyright©2013 International Research Journals
Full Length Research Paper
A study of the oxalate, phytate and cyanide contents of selected Nigerian foods and diet in Akwa Ibom and Cross River states of Nigeria *a
Kolawole, Sunday. E and bObueh, Henrietta. O
a
National Open University of Nigeria, Benin Study Centre, Benin City, Edo State Nigeria Department of Biology, College of Education, P.M.B 1144, Benin City, Edo State Nigeria
b
Accepted April 10,2013
This study examined the anti-nutritional factors (oxalate, phytate and cyanide) of some selected foods and diet in Akwa Ibom and Cross River States in South-South Nigeria. Oxalate had the highest concentration while a phytate had the lowest concentration in all the foods and diets analyzed. The oxalate content varied between 0.1380± 4.716mg/kg, phytate content ranged from 0.09 to 0.33mg/kg and the cyanide content ranged from 0.265 to 2.95mg/kg. Soup+meat had the highest mean cyanide value of 2.0±0.16mg/kg. Roots had the highest mean oxalate value of 5.47±5.75mg/kg. Cereals had the lowest cyanide and oxalate contents with mean values of 0.32±0.08mg/kg and 0.518±0.47mg/kg respectively. Soups had the highest phytate concentration with mean value of 0.260±0.07mg/kg while fruits had the lowest phytate concentration with mean value of 0.168±0.11mg/kg. All the anti-nutritional factors detected had values lower than established toxic levels. Though the foods and diets have enormous nutritional potential, optimal food processing and cooking methods are necessary to reduce the effect on bioavailability of minerals by anti-nutrients. Keywords: Anti-nutritional factors, oxalate, phytate, cyanide, foods and diets, South-South Nigeria INTRODUCTION Anti-nutritional factors have been described as substances that block or inhibit important metabolic pathways, especially digestion (Theil et al., 1997). These substances generally reduce the bioavailability of nutrients such as proteins, vitamins and minerals. This causes a reduction in the ability of the body to use the nutrients even when they are present in the food. Many minerals and trace elements are inefficiently and variably absorbed from diet due to many factors which include the presence of anti-nutrients such as phytates, oxalates, tannins, cyanides and polyphenols in foods, fibre, competition with other nutrients and acidity of the intestinal environment (Fair-weather – Tait, 1977; Paul et al., 2004). The common foods consumed in Akwa Ibom and Cross Rivers States, South-South Nigeria are mainly grown and harvested from the locations. They include
*Corresponding Author E-mail:
[email protected]
fruits, vegetable, legumes, roots, cereals and other foods from animal origin. They are made into various delicacies so that nutrients can be obtained from a variety of foods and diets from different sources. But due to wide spread poverty in Nigeria, there is lack of adequate energy and a diet balanced in micro nutrients resulting in malnutrition. According to World Health Organization malnutrition is the cellular imbalance between the supply of nutrients and energy and the body’s demand for them to ensure growth, maintenance and specific functions (Tierney et al., 2010). Phytate is a storage form of phosphorous which is commonly found in plant seeds and in many tubers (Reddy et al., 1989). The presence of phytate in foods has been associated with reduced mineral absorption due to the structure of phytate which has high density of negatively charged phosphate groups which form very stable complexes with mineral ions causing nonavailability for intestinal absorption (Walter et al., 2002). In consequence, the consumption of great quantities of food containing high phytic acid levels could produce a
deficit in the absorption of some dietary minerals (Reddy and Pierson, 1994). Phytates are generally found in food high in fibre especially whole grains and legumes (Lori, Thava and James, 2001). Phytic acid is widely distributed in commonly consumed foods. It is found in high concentrations in the seeds of grains, pulses and oleaginous products and in lesser amounts in tubers and garden produce (Alabaster et al., 1996). In addition, complex formation of phytate with some proteins may inhibit the enzymatic digestion of the proteins. However, they are easily removed by cooking and soaking (Kumar et al., 2010). Oxalic acid and its salts occur as end products of metabolism in a number of plant tissues. When these plants are consumed by humans they may exert adverse effects because oxalates can bind to calcium and other minerals rendering these minerals unavailable for normal physiological and biochemical roles such as the maintenance of strong bones, teeth, nerve impulse transmission and as clothing factor in the blood (Ladeji, 2004, Noonan and savage 1999). The ingestion of 4-5 gm of oxalate is the minimum dose capable of causing death in an adult but reports have shown that 10-15 gm is the usual amount required to cause fatalities (Noonan and Savage, 1999). Calcium binds to free oxalate to form insoluble calcium oxalate. This may give rise to a functional hypocalcaemia with tetany in acute cases (Hughes and Norman, 1992). Calcium and free oxalate can precipitate in the urine and may form kidney stones. Oxalate crystallizes with calcium in the renal vasculature and infiltrates vessels walls causing renal tubular obstruction, vascular necrosis and haemorrhage which leads to anuria, uraemia, electrolyte disturbance or even rupture (Noonan and Savage), 1999). It has been reported that fermentation decreases the oxalate content of foods. Antai and Obong (1992) reported a significant decrease in Icacinia manni (a starch tuber) upon fermentation. Oxalates are present in vegetables (Dahouenon-Ahoussi, et al., 2012) Many edible plants contain cyanogenic glycosides. Consumption of food containing cyanogenic glycosides has been linked to several different diseases affecting mainly the nervous systems, such as tropical ataxic neuropathy in Nigeria. Cyanides have also been implicated in tobacco-alcohol amblyopia and thyroid effects such as goiter and even cretinism (Osuntokun, 1972, 1980; Tylleskar et al’ 1994; Boivin, 1997; Lantum, 1998; Ernesto et al; 2002). The minimum lethal dose of hydrogen cyanide taken by man through mouth is reported to be between 0.5mg and 3.5mg/kg body weight (Fawomola, 2010). Cyanide can also cause peripheral numbness, light –headedness, mental confusion, stupor, cyanosis and convulsion in man (Akyildiz et al., 2010). The most prudent nutritional strategies combine a rational balance of good diet and judicious supplementation. For the healthy population, consumption of a nutritionally adequate diet balanced
with regards to major nutrients generally is relied upon to provide an adequate and safe intake of trace elements. This study was carried out to determine the antinutritional factors (oxalate, phytate and cyanide) of some selected Nigeria foods and diets. MATERIALS AND METHODS Collection of Samples Samples of commonly eaten foods and diets were purchased from local restaurants and markets in five experiment areas (Calabar, Ikot Okpora, Ikom, Uyo and Oron) in Cross River and Akwa Ibom States, SouthSouth Nigeria for anti-nutritional factors analysis. The samples were mixed together to give each composite sample which was used for the analysis. (Dahouenon – Ahoussi et al., 2012) Antinutritional factors analysis Oxalate was determined as described by Day and Underwood (1986). Phytate was determined using the method of Reddy and Love (1999). The cyanide content was determined by the alkaline titration method (AOAC, 1990). Statistical Analysis The statistical analysis of the data was done with Statistical Package for the Social Science (SPSS) software. The values obtained from the study were expressed as mean and standard deviation. RESULTS The cyanide, oxalate and phytate contents of the selected foods and diets are shown in table 1. The result in table 1 showed that the oxalate concentrations in the selected foods and diets ranged from 0.138 to 4.716 mg/kg. The highest concentrations were found in roots with a mean oxalate value of 5.47±5.75 mg/kg. The oxalate content of cocoyam (Colocasia esculenta) was particularly high at 11.56 mg/kg. The lowest concentrations of oxalate were found in cereals with mean value of 0.518 ± 0.47 mg/kg. The phytate content of the selected foods and diets ranged from 0.09 to 0.33 mg/kg. The highest concentrations were found in soups with mean value of 0.260±0.07 mg/kg. The lowest concentrations were found in fruits with mean value of 0.168±0.11 mg/kg. The cyanide contents of the selected foods and diets varied between 0.265 to 2.95mg/kg. The highest concentrations were
Table 1. Oxalate, Phytate and Cyanide Contents of Foods and Diets (mg/kg)
SAMPLES FRUITS Ndiya (Cola rostrata) Plantain (Musa paradislaca) Pineapple (Ananas conosus) Banana (Musa sapientum) Pawpaw (Carica papaya) Orange (Citrus) Mean ±S.D LEGUMES Cooked Beans (Vigna unguiculata) Groundnut (roasted) (Arachis hypogeal) Mean±S.D CEREALS Boiled rice (Oryza sativa) Pap(fermented yellow maize (Zea mays) Mean ±S.D ROOTS Eba (Manihot utilisima) Boiled cocoyam (Colocasia esculenta) Pounded yam (Discorea rotundata) Means ±S.D SOUPS Oha (Pterocarpus milbreadi) Edikanikong(Telfaria occidentalis) Melon (Citrullus vulgaris Schrad) Afia efere Mean ±S.D SOUP + MEAT Afang + Beef (Gnetum Africana) Ntong + Goat meat (Ocimum Basillieum) Shaki + Banga soup (Offais + Elaeis guinensis kernel soup) Mean ±S.D
OXALATE
PHYTATE
CYANIDE
2.276 1.099 3.216 1.115 0.422 1.044 1.54±1.04
0.090 0.330 0.120 0.230 0130 0.110 0.168±0.11
0.953 0.455 0.459 0.556 0.526 0.294 0.540±0.22
2.933 3.855 3.39±0.65
0.290 0.210 0.25±0.05
0.373 0.425 0.39±0.04
0.185 0.852 0.518±0.47
0.280 0.100 0.19±0.13
0.265 0.375 0.32±0.08
0.138 11.560 4.716 5.47±5.75
0.240 0.250 0.250 0.247±0.03
0.819 2.953 1.774 1.85±1.19
1.946 2.063 1.037 1.054 1.525±0.56
0.220 0.330 0.230 0.250 0.260±0.07
1.561 2.521 1.821 0.314 1.186±0.83
2.411 2.103 3.025 2.513±1.095
0.24 0.13 0.31 0.227±0.06
1.898 2.209 2.01 2.039±0.16
Figure 1. Mean values of anti-nutrients in selected foods and diets
found in soups+meat with a mean cyanide value of 2.04±0.16 mg/kg. The lowest concentrations were found in cereals with mean value of 0.32±0.08 mg/kg.
Figure 1 showed the mean values of the anti-nutrients in the selected foods and diets. The phytate concentration was lowest in all the selected foods and diets while the
oxalate concentration was highest in all the foods and diets.
effects of the anti-nutrients especially oxalate in roots and tubers.
DISCUSSION
REFERENCES
All the selected foods analyzed for anti-nutrient factors were the commonly eaten foods and diets in South-South Nigeria. The values for oxalate ranged from 0.138 to 4.716mg/kg and were within the acceptable limit. Oxalate decreases mineral absorption. It forms complex with calcium thereby making it unavailable when eaten in foods and more so high oxalate diets can increase the risk of renal calcium absorption. (Osagie and Eka, 1998). With detoxification through processing, the roots (cocoyam) which had the highest oxalate values can be consumed. Phytate, like oxalates limit the availability of minerals such as magnesium, iron and calcium (Groff et al., 1995). According to (Oke, 1969), a phytate diet of 1 to 6% over a long period decreases the availability of mineral elements in monogastric animals. Phytate values were lowest in all the selected foods and diets. This could be due to the destruction of phytates by enzymes called phytases during certain food processes such as wasting, soaking, cooking, fermentation etc (Kolawole, 2008). Phytate content was highest in the soup. This could be due to the vegetables rich in fibre used to prepare the soup. Phytates are generally found in foods high in fibre (Norhaizan and Nor Faizadatul Ain, 2009). Though fibre-rich foods protect against diseases such as cardiovascular disease, colon and breast cancer (Ensminger and Ensminger, 1996), it indirectly reduces bioavailability of mineral. The cyanide content was below the established toxic level. The highest level of cyanide was found in soups + meat and the lowest level was found in the cereal. The high cyanide level in soups + meat could be attributed to the inclusion of different condiments used in the preparation of the soups + meat. The cyanide in the cereals was low in agreement with a study carried out by (Hassan et al., 2005). The values of oxalate were exceptionally higher than the values of other anti-nutrient factors. The lethal dose of oxalate is between 200mg/100g and 500mg/100g (Pearson, 1973). CONCLUSION From the results of this study, it is clear that the foods and diets analysed have enormous nutritional potentials because of their low concentrations of anti-nutrients. The low content of phytate, oxalate and cyanide in the selected foods and diets consumed by humans in Cross River and Akwa Ibom States make them harmless and in addition reduces their inhibitory effect on the bioavailability of minerals. It is however recommended that optimal food processing and cooking methods should be chosen to reduce the contents and thus the adverse
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