Oil from T. conophorum kernels was obtained by cold pressing using a KOMET screw oil expeller DD85G, number 200666 manufactured in 1991 (Germany) [30] . Refined corn oil (Lesieur, France) was purchased at a local market. To avoid oxidation, the oils were packaged in dark bottles and kept in the refrigerator until use.

Fatty acids were determined by the analytical methods described by Focant et al. [31] . Fatty acids were converted to fatty acid methyl esters (FAMEs) before being analyzed. The FAMEs were prepared using 10 mL of 1M sodium hydroxide in methanol. Then, 4 mL of 1.2M hydrochloric acid in methanol was added to the mixture. After extraction of methyl ester, the chromatograph Thermo Finnigan, type TRACE GC was used to identify fatty acids (Milan, Italy). The capillary column used was RESTEK Rt-2560 (100 m length, 0.25 mm internal diameter, 0.20 µm film thickness) (Supelco, Bellefonte, PA, USA). Gas chromatography conditions were: a flow rate of 1 mL/min with an initial temperature of 140˚C held for 5 min. The column temperature was then increased to 250˚C at a rate of 2˚C/min, and then held at 250˚C for 15 min. Fatty acid peaks were identified using pure methyl ester standards (Larodan, Belgium).

Healthy male Wistar rats (20 - 21 weeks old, 300 - 310 g weight) were provided by the animal house of the Bioprocess Laboratory (IUT, University of Ngaoundere, Cameroon). The rats were acclimatized for a 1 week in a standard environmental atmosphere (at a 12-hours light/dark cycle, 25 ± 2˚C temperature, 50 ± 5% humidity) with a normal diet ( Table 1 ) and water ad libitum in a simple cages.

After this period, the rats were randomly assigned into seven groups, 6 rats per group. The TC5, TC10 and TC20 groups consumed respectively 5%, 10% and 20% of T. conophorum oil while the CO5, CO10 and CO20 groups consumed 5%, 10% and 20% of corn oil respectively. One control group (T) received a standard rat diet. Animals were housed individually in the cages. Body weight was performed once a week, water and food consumption was estimated daily. Diets were prepared inthe Biopress laboratory and details of their compositions are presented in Table 1 . Formulations were based on the modified AIN-93 protocol [32] . This study was approved by the institutional animal research committee of the Faculty of Sciences of the University of Ngaoundere.

The following parameters were calculated:

At the end of the experiment, animals were fasted for 12 hours with free access to drinking water. The rats were then anesthetized using Diazepam (10 mg/Kg) according to the recommendations for the anaesthesia of experimental animals. Blood samples were collected from the caudal vein and stored in dry tubes and stabilized for 15 to 30 minutes to ensure that it could clotted at room temperature (25˚C). Serum was prepared from blood by centrifugation at 3000 rpm for 10 min. This serum was used to carry out the dosages. The liver, heart, kidneys, and epididymal and abdominal fats were removed and weighed to calculate the hepatosomatic index, viscerosomatic indices, and adiposity index, respectively.

The total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and triglyceride levels in the serum were performed using kit assay methods (FORTRESS, Northern Ireland) as per the manufacturer’s instruction. Serum low density lipoprotein cholesterol (LDL-C) concentration and very low density lipoprotein cholesterol (VLDL-C) were determined using Friedwald formula, where LDL-C = TC − (HDL-C + VLDL-C) and VLDL-C = TG/5 [33] . Castelli risk indices I (CRI-I) and Castelli risk indices II (CRI-II) were calculated using the Castelli formula, where CRI-I = LDL-C ÷ HDL-C and CRII = TC ÷ HDL-C [34] .

Blood glucose level was evaluated directly after the sacrifice of the rats on an automatic biochemical analyzer using enzymatic colorimetric tests (FORTRESS, Northern Ireland).

The colorimetric method described by Gornall et al. [35] was used to estimatethe protein content in the blood. Peptide bonds in proteins react with Cu²⁺ in alkaline solution to form a colored complex which absorbance, proportional to the protein concentration in the specimen at 550 nm. Biuret reagent contains sodium potassium tartrate, which complexes cupric ions and maintains their solubility in alkaline solution [36] .

Results were expressed as means ± standard deviation. For each group, the result obtained was the mean for 6 rats. All results were analysed using a one-way analysis of variance. Duncan’s Multiple Range test was performed to evaluate differences between groups. Differences between means were considered to be significant at p < 0.05.

In Table 2 , fatty acids composition of the two oils is presented. Corn oil contains nearly 56.13 ± 0.30% linoleic acid and only 1.07 ± 0.02% ofα-linolenic acid, compared to T. conophorum oil with nearly 70 % α-linolenic acid and 10.56 ± 0.18 of linoleic acid. The ω-3/ω-6 ratio of T. conophorum oil is 6.52 while this ratio is 0.01 for corn oil. Both oils are rich in essential fatty acids; which is a great advantage in diet formulations the risks of cardiovascular diseases.

Figure 1 shows the evolution of body mass (in g) of rats fed with the different diets over a 5-week period. In the first two weeks, there was no change in body masses compared to starting day. From week 3 to week 5, the increase of body mass was inversely proportional to the amount of oil in the feed. Thus, groups T, CO5 and TC5 evolved together, as do groups CO10, TC10 and CO20. The body mass of the TC20 group decreased from the first week till the end of the experiment compared to the other groups, and the difference between this group and the other groups was significant (p < 0.05).

Daily feed intakes after 5 weeks of feeding are summarized in Table 3 . Irrespective of the type of oil, feed intake decreased with increasing oil content (p < 0.05). One can agree that fats slow down the digestion process and leave a prolonged feeling of satiety in the stomach. Thus, the quantity of oil consumed per rat per day is 0.75 for the 5% diets compared to 1.35 for the 10% diets and 2.5 for the 20% diets.

The consumption index makes it possible to determine feed consumption in relation to growth rate. This index is low for TC diets compared to CO diets.

Overall, water consumption is proportional to the amount of oil, so the more the oil content of a feed, the more the water consumption. Thus, the water consumption is 6.87, 5.30, 8.08 and 8.55 respectively for regimes T, TC5, TC10 and TC20. Water consumption therefore depends on the palatability stimulated by the type of oil.

Hepatosomatic, adiposomatic and viscerosomatic indices are determined to better appreciate the effect of the quantity of different oils on organ development.

Ratios of liver weight to body weight in rats (hepatosomatic index) (HSI) of the seven study groups are shown in Table 4 . Data analysis shows that there was no significant difference (p < 0.05) between the control group and the other groups, irrespective of oil type and quantity.

It was found that the adiposomatic index (ASI) decreased with increasing oil quantity for the T. conophorum diet groups, but the difference was not significant (p < 0.05). Furthermore, the lowest values were observed for the T. conophorum diet (p < 0.05) compared to the corn oil diet, whatever the oil percentage.

Note: Means ± SD (n = 6) followed by different letters are significantly different (p < 0.05) as determined by Duncan’s multiple range test. T: Control group; CO5: Group of 5% of corn oil; CO10: Group of 10 % of corn oil; CO20: Group of 20% of corn oil; TC5: Group of 5% of T. conophorum oil; TC10: Group of 10 % of T. conophorum oil; TC20: Group of 20% of T. conophorum oil.

Note: Means ± SD (n = 6) followed by different letters in the same column are significantly different (p < 0.05) as determined by Duncan’s multiple range test. T: Control group; CO5: Group of 5% of corn oil; CO10: Group of 10% of corn oil; CO20: Group of 20% of corn oil; TC5: Group of 5% of T. conophorum oil; TC10: Group of 10% of T. conophorum oil; TC20: Group of 20% of T. conophorum oil.

These indices vary from 1.7 - 1.8 for the TC groups compared to 2.3 - 3.4 for the CO groups.

There was no significant difference between the different groups studied in terms of viscerosomatic indices (heart and kidney weight to body weight ratios).

Glycemia in this study provides information on the influence of lipids consumed on glucose metabolism. Regardless of the type of oil, glucose levels in fasting rats decreased as the amount of oil in the food increased. However, the decrease is more marked with diets rich in T. conophorum oil, but significant for both CO10 and TC10 groups ( Figure 2 ).

The total cholesterol in the blood of rats was determined and the results are presented in Figure 3 . At 0% oil, total cholesterol was 80 ± 3 mg/dl. The addition of oils in the diets resulted in a decrease in serum total cholesterol (p < 0.05) depending on the oil type and the concentration. The drop was −18 mg/dL, −15 mg/dL, −46 and −45 mg/dL respectively for the CO10, CO20, TC10 and TC20 groups. There was no significant difference between TC10 and TC20.

The levels of LDL and HDL cholesterols were evaluated in the serum of rats fed with CO and TC oils, and the results are illustrated on Figure 4 .

There was a significant drop in serum LDL-C levels at the different treatment levels compared to group T (p < 0.05) ( Figure 4(a) ). These reductions were as follows: −4, −42 and −30 mg/dL respectively for 5%, 10% and 20% corn oil, compared to −18, −42 and −47 mg/dL for T. conophorum oil with the same oil percentages. T. conophorum oil induced a significant reduction in LDL levels compared to corn oil. There was no difference between the TC10 and TC20 groups.

The results also mentioned that, irrespective of the oil percentage in the diet, HDL cholesterol levels were significantly (p < 0.05) higher with the corn and T. conophorum oil diet groups compare with the control diet ( Figure 4(b) ). This increase was proportional to the percentage of oil for CO5 and CO10. The results also indicate that TC diets induced a significantly augmentation of higher serum HDL-C compare to CO diets. This increase was 29, 46 and 45 md/dL respectively for TC5, TC10 and TC20 diets. There was no difference between the TC10 and TC20 diets.

Triglycerides can come from the diet or from endogenous synthesis. Their measurement is generally used to classify different types of lipoproteinemia.

Changes in triglyceride levels after 5 weeks of experimentation are shown in Figure 5 . Regardless of oil type and percentage, triglyceridemia decreased.

Castelli risk indices (CT/HDL (CRI-I) and LDL/HDL (CRI-II)) are the best markers for identifying and minimizing the risks of cardiovascular disease. These indices also allow early management of cardiovascular diseases [37] . The CRI-I is also called cardiac risk indices. The higher it is, the greater the risk of developing cardiovascular diseases. The results depicted in Figure 6 show that for all the groups supplemented with oil, CRI-I is less than 3.5, which is the favorable limit [38] . In this work, the values are lower for the TC regimes than for the CO regimes. Moreover, this ratio decreases at 5% oil (p < 0.05) and remains constant between 10 and 20% for TC oil.

The LDL/HDL or CRI-II ratio is used makes to justify a predisposition to atherosclerosis. It is favorable when its value is less than 3 [38] , which is the case for all groups receiving corn oil and T. conophorum oil ( Figure 6 ). Regardless of the type of oil, CRI-II decreases with increasing oil content; values remain constant between 10 and 20% oil. This reduction is more represented with TC diets than CO diets.

Serum assays carried out on the rats after 5 weeks of experimentation were used to determine the protein levels in each group of rats ( Figure 7 ). Protein levels increased with 5% oil, then decrease between 10 and 20% for all types of oils; but there is no significant difference (p < 0.05) between the CO and TC groups whatever the oil content.