Evaluation of Effect of Dietary Supplementation with Dacryodes edulis G.Don Pulp Oil on Serum Lipid Parameters in Wistar Albino Rats

INTRODUCTION

The African pear (Dacryodes edulis G. Don) fruit is one amongst the many indigenous tropical fruits greatly cherished and appreciated for its pulp. The plant belongs to the Burseraceae family and possesses many medicinal and nutritional properties. In Nigeria, when is season, the fruit pulp which is contained in a pod is traditionally consumed raw or after tenderization in hot water, hot ash or roasted (Isaac and Ekpa, 2009). Sometimes, it may be enjoyed with roasted or boiled corn (Iyawe et al., 2007).

Several studies have focused on the chemical composition of the D. edulis fruit pulp. The percentage fatty acid composition of the lipid yield includes palmitic acid (30- 62), linoleic acid (15-24), oleic acid (18-60), stearic acid (1.3-5.5) depending on the geographical location of the tree (Mbofung et al., 2002; Kinkela et al., 2006; Ikhuoria and Maliki, 2007; Ajibesin, 2011). Nutritionally important mineral elements such as phosphorus, sodium, zinc and manganese are also found in Eastern Nigeria varieties (Ajayi and Adesanwo, 2009). The essential oils of the pulp as reported by Jitrovetz et al. (2004); included x-pipene, β-pipene and myrcene. Bioactive compounds such as saponins, tannins, alkaloids and flavonoids have been identified in various parts of the plant (Okwu and Nnamdi, 2008) and these have been suggested to be responsible for the enormous ethno-medical applications of D. edulis in the treatment of skin diseases, inflammation, bacterial and fungal infections (Okwu and Nnamdi, 2008; Ajibesin, 2011).

The implication of high total cholesterol, Low-Density-Lipoprotein (LDL)-cholesterol, triacylglycerol and low High-Density Lipoprotein (HDL)-cholesterol in the development of cardiovascular disorders such as hypertension, artheriosclerosis, stroke and heart failure can never be over emphasized (Ghasi et al., 2000). There has been tremendous increase in the use of functional foods and, or nutraceuticals due to their beneficial effects on human health. For instance, cardiovascular activity of D. edulis oil in rats was reported by Ajibesin (2011). Oil extracted from prickly pear seeds oil has been found to exhibit hypoglycaemic and hypocholesterolemic effects (Ennouri et al., 2007). Changes in the lipoprotein composition of the plasma or serum could be attributed to the type of fat ingested in the diet. The present study was therefore designed to investigate the effect of continuous dietary intake of D. edulis fruit pulp oil (DFPO) extracted in n-hexane on serum lipid parameters of Wistar albino rats (Ratus norvegicus).

MATERIALS AND METHODS

Plant materials: Healthy African pear (D. edulis) fruits were collected from Abagana, Anambra State, Nigeira, in January, 2011. They were identified and authenticated of by Prof. R. Okigbo, of the Department of Botany, Nnamdi Azikiwe University, Awka. Voucher specimen (herbarium No. N.A.U.H No 112) was prepared and deposited in the herbarium.

The fruits were washed and the fruit pulps separated from the seeds, air-dried at room temperature, wrapped in polyethylene bags and stored in desiccators until needed. The dried fruit pulp was later pulverized using a grinding machine. Three hundred gram quantity of the sample was transferred into a thimble and oil content extracted for 2 h using normal hexane in vacuo with soxhlet apparatus. At the end of the extraction, the extracting solvent (n-hexane) was evaporated using rotary evaporator leaving the concentrated oil sample which was used for the experiments. The percentage oil yield was determined gravimetrically.

Animal materials: Sixteen apparently healthy Wistar albino rats weighing between 100.0 to 120.0 g were purchased from the Faculty of Veterinary Medicine, University of Nigeria, Nsukka. The animals were kept in cages in the animal house of the Department of Applied Biochemistry, Nnamdi Azikiwe University, Awka, for one week to allow for acclimatization.

Chemicals used: Analytical chemicals were used and all were products of British Drug House (BDH), Poole England. Triacylglycerol total cholesterol, LDL-cholesterol and HDL-cholesterol diagnostic Kits were obtained from Randox Laboratories Ltd., Ardmore, U.K.

Experimentation: The animals were divided into two groups of eight rats each in accordance with their weights and housed in separate cages.

The first group was fed with the control diet compounded with 10% groundnut oil, whereas the second group of rats was kept on the test diet compounded with 10% D. edulis fruit pulp oil. The chemical compositions of both diets were as illustrated in Table 1. The body weights of animals and feed intake were recorded at two days interval for a period of six weeks.

Table 1:	Composition of the control and Dacryodes edulis fruit pulp oil diets (g 100 g^-1 diet)

Vitamin mixture according to Rao et al. (1991), Salt mixture according to Rao et al. (1991), This diet (100 g) containing 26 g of casilan provided 18.5% of the protein, DFPO Dacryodes edulis fruit pulp oil

The daily feed intake was calculated using the equation:

where, Da is the amount placed in the bin feed and Db is the amount remaining after 2 days. 8 corresponds to the number of animals in each cage.

All the animals were allowed free access to feed and drinkable water ad libitum.

At the expiration of six weeks period of feeding, the animals were anaesthetized with chloroform and blood samples collected through cardiac puncture for the determination of serum lipid profile. The sera samples were obtained as the supernatant after centrifuging the coagulated blood samples at 3,000 r.p.m for 15 min. Serum total cholesterol, LDL-cholesterol, HDL-cholesterol and triacylglycerol levels were determined using diagnostic kits from Randox Laboratories, U.K.

Lipid extraction from serum and liver: The total lipids of sera samples (500 μL) and liver (2 g) were extracted with chloroform: methanol (2:1, v/v) according to the method of Folch et al. (1957). The quantities of total lipids in the sera and liver samples were measured gravimetrically after evaporating the extracting solvent in the sera and liver extracts.

Physicochemical studies: The physicochemical properties of the DFPO were determined immediately by the AOAC (1975).

Fatty acid composition of the oil: Fatty acid profile of the oil was obtained using a high-performance-liquid chromatographic technique (HPLC).

Proximate composition of the diets: The proximate composition of both control and test diets were determined using the method of AOAC (1984).

Statistical analysis: Arithmetic mean and standard error of mean were calculated and all the data obtained were analyzed statistically using Analysis of Variance (ANOVA). Statistical analyses were made by a SPSS for Windows version 13.0 packaged statistics program. All results represented were Mean+Standard Error of mean (SEM) of six determinations.

RESULTS AND DISCUSSION

Findings from our study showed that Dacryodes edulis (G.Don) pulp yielded a pale yellow oil (26.4±0.81% yield) with an agreeable odour. The oil existed in the semisolid state at laboratory temperature of 29°C. The percentage oil yield of 26.4 indicates that the pulp is a rich source of lipids. This is comparable to other reports by Lam et al. (1987) and Ajibesin (2011). Supplementation of DFPO (10%) into the diet did not cause any significant difference in body weight gain between the control and the test groups since the p. value (0.11) was greater than 0.05. The average body weight increased from 183.51±2.3 g to 190.47±0.6 g after six weeks of feeding (Table 2).

The type of lipids ingested in the diet could provoke the deposition of fats in the body tissues and for this reason we also estimated the total quantities of extractable lipids in the serum and liver of the experimental animals. Insignificant (p>0.05) variations in the amount of serum and liver lipids were observed after the six weeks duration of feeding. Also, the relative weights of the vital organs (the liver, pancreas, kidney and heart) were not statistically different irrespective of whether the animals were fed with groundnut oil or DFPO (Table 2). Slight but insignificant (p>0.05) increases in the weights (g 100 g^-1 BW) of the liver (2.91±0.17 to 3.38±0.25), kidney (0.36±0.06 to 0.40±0.02) and heart (0.32±0.02 to 0.33±0.04) were observed in the test group. This implies that accumulation of lipids in these organs, particularly the liver which plays a pivotal role in lipid metabolism, as a result of the supplementation of the diet with DFPO was negligible.

Also supporting the above inferences is the fact that supplementation of the diet with DFPO did not produce any remarkable alterations in the serum total-cholesterol, LDL-cholesterol, HDL-cholesterol, VLDL-cholesterol and triacylglycerol levels of the animals (Table 3). All the observed values were within the normal ranges for total cholesterol (g L^-1) (0.69±0.07), LDL-cholesterol (g L^-1) (0.21±0.03), HDL-cholesterol(g L^-1) (0.37±0.05) and triacylglycerols (g L^-1) (0.56±0.07) in the serum of adult albino rats (Alonso et al., 2001; Gaiva et al., 2003).

Table 2:	Body weights, feed intakes and relative weights of some vital organs after six weeks of feeding in control and DFPO groups

Each value represents the mean of eight rats±standard error of mean. No significant difference between groups was noted. p>0.05, DFPO Dacryodes edulis fruit pulp oil

Table 3:	Serum lipid profile of rats fed control and DFPO diets

Values are Mean±SEM of eight observations. No significant difference between groups was found at 95% level of significance. p>0.05 for all figures in the same row, Atherogenic index (A.I) = Total cholesterol-HDL-cholesterol, HDL-cholesterol, Deguchi and Ogata (1991), DFPO Dacryodes edulis* fruit pulp oil

Table 4:	Chemical properties of DFPO extracted with n-hexane

Values are Mean±SEM of eight observations, DFPO Dacryodes edulis fruit pulp oil

Table 4 shows the chemical properties of the D. edulis fruit pulp oil. Acid value is a parameter that is used to indicate the suitability of oil for consumption. The acid value of DFPO was 18.51"2.38. This is similar to that of the conventional palm kernel oil, 14.04±0.022 (Akubugwo and Ugbogu, 2007; Igbum et al., 2012) and Landolphia owariensis, 15±0.38. (Pearson, 1976). High iodine value of 50.32±0.63 observed in this study is a clear indication of high level of unsaturation of the fatty acid components of DFPO. High-performance-liquid chromatographic (HPLC) analysis of the oil also revealed the presence of appreciable quantities of oleic acid (12. 94%) and linoleic acid (28.57%). Omega-3 fatty acid, linolenic acid (1. 65%) was also detected (Table 5). The health benefits associated with the consumption of oleic acid (18:1), linoleic acid (18:2) and linolenic acid (18:3) have been well documented (Ennouri et al., 2007, 2005; Chattopadhyay and Bandyopadhyay, 2005; Ezekwesili et al., 2010). particularly in alleviating cardiovascular, inflammatory and autoimmune disorders.

Table 5:	Fatty acid profile of DFPO extracted in n-hexane as given by HPLC

DFPO Dacryodes edulis fruit pulp oil

However, since the iodine value is also a parameter that indicates the capacity of the oil to go rancid (Amoo et al., 2004), adequate protection should be ensured during storage of DFPO in order to prevent lipid peroxidation.

The peroxide value serves as an index to assess the deterioration of oils. Freshly prepared oils usually have values that are equal to or less than 10, whereas higher ranges (20-40) indicate rancidity of the oils (Akubugwo and Ugbogu, 2007). The peroxide value of DFPO was 0.00. This may suggest that DFPO have antioxidants that resist rancidity by preventing lipid peroxidation.

The iodine value and fatty acid profile of DFPO are very similar to those found in the conventional oil palm oil (from Elais guineensis variety). The oil contains approximately equal amounts of saturated (50.85%) and unsaturated (49.14%) fatty acids Lam et al. (1987).

CONCLUSION

Data obtained from this study demonstrated that Dacryodes edulis (G. Don) fruit pulp is a high oil-yield fruit producing nutritionally, biochemically and medicinally important oil. Supplementation of animal diet with this oil did not cause any significant alteration in the serum lipid profile of the experimental animals.