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Nutritional Assessment of Aiélé (Canarium schweinfurthii) and Refined Palm (Elaeis guineensis) Oils in Wistar Strain Rats (Rattus norvegicus)

Chatigre Kouamé Olivier, Méité Alassane, Fofana Ibrahim*, Kati-Coulibaly Séraphin

Training and Research Unit (faculty) of Agriculture, Fisheries Resources and Agro-food industry, University of San Pedro, BP 1800 San Pedro, Côte d’Ivoire

Abstract: Refined palm oil (palm olein) is widely used in the diet of Côte d’Ivoire. However, populations traditionally consume oilseeds from spontaneous trees, including the aiélé. The purpose of this study is to compare the effects of ingestion (for 4 weeks) of 15% crude aiélé (unrefined), refined palm and combined oil diets on normal growing rats. The physicochemical properties of the oils or oil mixtures were determined by standard methods and their fatty acid profile by gas chromatography after methylation of the fatty acids by Boron trifluoride-methanol (BF3 methanol). In addition, Diets containing 15% of fat were administered to growing Wistar strain rats for 28 days. The results indicated that the SFA, MUFA and PUFA levels of the crude oil of the aiélé are respectively 45; 34; 21% to 44; 44; 12 % and 13; 29; 58 % for refined oils of palm and corn. Three main fatty acids have been identified: palmitic, oleic and linoleic acids. Nutritional parameters assessed revealed that the crude oil of the aiélé diet is better appreciated than the refined palm oil diet despite the relatively high acid and peroxide values of the oil of the aiélé. However, the digestibility of its dry matter and lipids are relatively low compared to those of refined palm and corn oil diets. However, the combination of crude oil of aiélé with refined oil of palm tends to improve the nutritional performance of the lipids of the diet. Furthermore, no significant differences were reported between blood lipid parameters of the aiélé and refined palm oil diets.

Keywords: Aiélé, palm, oils, physicochemical properties, fatty acid composition, digestibility, blood lipids, growth, rat

Received July 29, 2022; Revised September 10, 2022; Accepted September 20, 2022

Citation: Chatigre Kouamé Olivier, Méité Alassane, Fofana Ibrahim, Kati-Coulibaly Séraphin, Nutritional Assessment of Aiélé (Canarium schweinfurthii) and Refined Palm (Elaeis guineensis) Oils in Wistar Strain Rats (Rattus norvegicus). American Journal of Food and Nutrition, 10 (2). 57-64. January 2022. doi:10.12691/ajfn-10-2-4

1. Introduction

Palm oil is the main vegetable oil produced in West Africa. Its production is estimated at 500000 tons of crude oil in Côte d'Ivoire [1]. The crude oil is processed into palm olein which is refined, bleached and deodorized oil for food use.

Palm olein is the most commonly consumed oil in Côte d'Ivoire due to its relatively low cost and availability. However, the continuous rise in its market cost could reduce, if not already, its consumption in favor of fats from collection products. Many oilseed fruits from spontaneous food trees are known to the population and are regularly consumed by them, especially in rural areas. Among these fruits is the fruit of the aiélé (Canarium schweinfurthii Engl.).

The fruit pulp of aiélé is edible after cooking. It is consumed in various regions of Sub-Saharan Africa according to eating habits and culinary practices of each people [2]. In central Côte d’Ivoire, it is frequently consumed with cassava during periods of shortage [3].

The pulp of the aiélé fruit is characterized by its relatively high lipid content, in the order of 30 to 50% in Côte d'Ivoire and Cameroon [4,5], and 68 to 70% in Congo [6]. The main fatty acids of its fat are palmitic, stearic, oleic and linolenic acids [4,5,7], with a predominance of SFA levels, particularly palmitic acid [4,5,7]. Various studies have been carried out on the physico-chemical characteristics and fat composition of aiélé fruit in Côte d’Ivoire and elsewhere in Africa [4,7,8,9].

However, to date no nutritional study on the fruit has been undertaken in Côte d'Ivoire. In West Africa, very few nutritional studies have been carried apart from [10], who studied the effect of aielé oil consumption in rats receiving diets with a 5% lipid intake. However, in view of the consumption of the oil-rich pulp of this fruit, it is desirable to acquire as much information as possible on the nutritional characteristics of this oil, as well as those of its association with palm olein. Indeed, the digestive utilization of fatty acid mixtures, from pure lipid sources or from different origins, varies according to the ratio between saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs) [11]. More specifically, studies have shown that the digestibility of high melting point FAs (long and saturated FAs) is relatively low, in particular that of palmitic acid [12,13,14,15,16], and that these FAs are associated with fecal or urinary calcium losses [17,18,19].

In addition, at the blood level it is well known that inadequate lipid intake, in quantity and/or quality, can be the source of various pathological disorders related to cholesterol levels [20,21,22]. Numerous studies conducted to examine the influence of dietary lipids on blood cholesterol levels have shown that SFAs (but probably not stearic acid) increase plasma cholesterol levels, while the effect of PUFAs is to lower these levels [23,24]. Recently, [25,26] reported that the use of PUFA-rich fats results in lower LDL-cholesterol compared to SFA-rich fats in subjects with moderate hypercholesterolemia and high lipid intakes [27].

However, it is recognized that the cholesterol lowering effect depends on the overall unsaturation of the diet independently of the FA family [28].

Indeed, contrary to the negative opinion on palm oil due to its high level of SFA, especially palmitic acid, intervention studies [29,30] showed that the effect of palm olein (with a palmitic acid level of about 40%) on the level of the different fractions of blood cholesterol is comparable to that of olive oil (palmitic acid level of about 10%). The recent article by Jean-Michel Lecerf takes stock of the various works that contradict this negative opinion on palm oil [31].

Therefore, the purpose of this study is to evaluate the effects of aiélé oil and palm olein, isolated or combined, on growing Wistar rats fed 15% fat diets with respect to weight gain, feed efficiency, digestibility, calcium and phosphorus balances, organ weights, blood lipid profile, serum calcium and phosphorus, for comparison with those of refined corn oil.

2. Material and Methods

2.1. Sources and Preparation of Oils

The refined oils of palm (Palm(R)) and corn (Corn(R)) were purchased on the market.

The refined oil of palm (Palm(R)) or palm olein was from the company Sania Cie (Ivory Coast). It is the fluid part of crude palm oil, fractionated, bleached and deodorized. It is marketed under the brand name Dinor.

The refined corn oil (Maize(R)) used is that is marketed under the brand name Lesieur (France).

Aiélé (Aiélé(B)) crude oil came from fruits collected in the savannah of Didiévi, in the center of Ivory Coast. These fruits, after rinsing with cold water, were treated according to the method of [32], for the extraction of the oil.

The blending oils were prepared from the crude oil of Aiélé (Aiélé(B)) and the refined oil of palm (Palm(R)) in the equivalent proportions of 50% (W/W) for the blending oil ⁵⁰Aiélé(B)/⁵⁰Palm(R) and respective proportions of 75 and 25% (W/W) for the blending oil ⁷⁵Aiélé(B)/²⁵Palm(R).

All oils were stored in the cold room (0-5°C) in the dark.

2.2. Physico-chemical Analysis and Fatty Acid Profile of Oils

The physico-chemical properties of oils and oil mixtures were determined according to AFNOR standards [33,34].

Methylation of fatty acids was done by acid methanolysis using the method of [35]. The fatty acid methyl esters were analyzed by gas chromatography on a Thermo chromatograph (Trace GC ultra) equipped with a flame ionization detector (FID), an evaporator injector and equipped with a capillary column (WCOT) of molten silica whose length, internal diameter, external diameter and film thickness are respectively: 100m; 0.25mm; 0.39 mm and 0.20 µm. The temperatures used were 250°C and 280°C, respectively, for the injector and detector. The oven was programmed according to the following procedure: an initial temperature of 60°C for 1min followed by the following speeds: 8°C/min to 150°C (10 min), then 1.5°C/min to 200°C (15 min) and finally 5°C/min to 225°C (0.5 min). The carrier gas was helium at a constant pressure of 400 Kpa.

The peaks corresponding to the different fatty acids were identified using a standard solution of methylated fatty acids (NU-CHEKPREP, IN) of known chromatogram. The levels of fatty acids (as % of total methyl esters) were directly determined by a computerized data system.

2.3. Animal Testing

2.3.1. Animals and Diets

The experiments were carried out on young rats (male or female) aged between 45 and 60 days, of Wistar strain, from the pet store of the Biosciences, Training and Research Unit at Félix Houphouët-Boigny University.

After 2 days of adaptation to the environment where they were fed with the standard food, a commercial pellet purchased from FACI® (Ivorian Compound Food Manufacturing Company) the rats, numbering 36 and weighing on average 65.2 g were distributed on the basis of their more or less homogeneous weight in individual cages with metabolism, due to six per diet. The cage system used allowed separate collection of urine and feces. The cages were placed in a room set up, under ambient temperature conditions (28 to 30°C).

Table 1. Composition of experimental diets (%, DM)

Rats were fed six experimental diets containing 13% protein (based on fish meal Herring or Clupea harengus, de-oiled) for 28 days, prepared according to the [36] data sheet. It is a lipidoprive or fat-free diet (to determine metabolic fat in feces) and 5 diets with 15% (W/W, DM) fat. The 5 lipid diets differed only by the nature and/or proportions of the oils incorporated. These are: the “Corn” diet based on Corn(R) oil, considered as the reference diet, “Palm” diet based on Palm(R) oil, considered as a national reference diet (palm oil being the most consumed dietary fat in Côte d’Ivoire); ‘Aiélé’ diet based on Aiélé(B) oil; the ‘⁷⁵Aiélé/²⁵palm’ diet based on mixture oil ⁷⁵Aiélé(B)/²⁵Palm(R); the ‘⁵⁰Aiélé/⁵⁰palm’ diet based on blending oil ⁵⁰Aiélé(B)/⁵⁰Palm(R). The composition of the diets is given in Table 1.

The main source of carbohydrates was starch from a commercial corn flour (maizena) and all diets were balanced in vitamins and minerals with the U.A.R. 200 vitamin and U.A.R. 205 mineral mixtures, respectively.

The energy value of each diet (determined on the basis of the theoretical energy intakes of 4, 4 and 9 Kcal/g of DM, respectively for carbohydrates, proteins and lipids) was 443 Kcal/100 g of DM, with the exception of that of the private lipid (lipidoprive) diet equal to 368 Kcal/100 g of DM.

Diets were prepared once a week and stored in a refrigerator (5°C). They were served as porridge. The amount of distilled water was added at the time of use. Tap water, frequently renewed, and feed were served ad libitum to the animals. The feed consumption (expressed in DM) of each rat was daily determined was and the animals were weighed twice weekly.

2.3.2. Sampling and Analysis

During the balance-sheet period (the last 5 days of the experiment), the feces and urine of each rat were also collected and daily weighed. The feces were dried in an oven at 70°C. for 24 hours, then they were collected by rat and ground. The urine was also collected by rat and stored in a freezer (-20°C) after acidification (pH 3 - pH 4) by addition of a few drops of 0.1N hydrochloric acid.

Total fecal lipids were extracted from the dried feces using a chloroform-methanol mixture (2/1; V/V) and determined by colorimetry on a spectrophotometer (Humalyser 2000 Human) according to the Biomérieux Lipid Kit procedure [37].

Total nitrogen was determined in diets, feces and urine by the Kjeldahl method [38] using an automatic distiller (FOSS TECATOR).

The growth and digestibility parameters were evaluated according to the methods described by [39].

At the end of the experiment, the rats were overnight fasted (12 hours) and then sacrificed the next day. The blood was immediately removed and centrifuged. The collected serum was stored in the freezer at -20°C. for the various analyzes. The heart, liver and kidneys were also extracted and weighed. The weights were expressed as a percentage of the live weight of the animal, based on the ratio of the organ weight to the live weight of the animal.

Calcium and phosphorus in the serum and urine were directly assayed by colorimetry on an automaton (COBAS, INTEGRA 400). At the food and feces level, dry mineralization (550°C for 12 hours) was performed prior to the determination of calcium [40] and phosphorus [41] by atomic absorption spectrometry on a VARIAN spectrophotometer (SpectrAA110).

The different markers of lipid metabolism (total cholesterol (TC), triglycerides (TG), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C)) were quantified using colorimetric enzyme methods on the COBAS analyser (INTEGRA 400).

2.4. Data Analyzes

The statistical treatments for the various parameters studied were based on the arithmetic mean of the individual values and the standard deviations and on the differences between the groups by analysis of variance (ANOVA). For significant differences (p < 0.05) between groups, the Student-Newman-Keull test was used to determine the specific differences among the averages. Three determinations were made per sample.

3. Results

3.1. Physicochemical Studies and Fatty Acid Profile of Oils

The physicochemical properties of the used oils are presented in Table 2. The melting ranges of Palm(R) (13-17°C) and Aiélé(B) (28-31°C) oils are different and markedly superior to that of Corn(R) oil (below -5°C).

Table 2. Physicochemical properties of dietary oils and some related standards

The refractive indices of all the oils tested are close. They ranged from 1.455 (Aiele(B)) to 1.466 (Corn(R)). The saponification values (Si) are also similar. They range from 192.2±0.4 (Corn(R)) to 196.1±0.9 (Aiele(B)). The value of Palm(R) oil is 194.8±0.5. However, at the level of the iodine value, Corn(R) oil is distinguished from others by a very high iodine index (114.3±2.7), almost double that of others whose values are between 55.5±0.6 (Palm(R)) and 59.2±0.9 (Aiele(B)). The acid (12.9±0.3 mg KOH/g) and peroxide (12.7±0.2 mEq O2/Kg) value of Aiélé(B) oil are very high compared to those of refined oils: Palm(R)(0.1 mg KOH/g and 8.7±0.2 mEq O₂/Kg) and Corn(R)(0.1 mg KOH/g and 1.5±0.1 mEq O₂/Kg).

The total fatty acids (FA) composition of the oils used is presented in Table 3. Chromatographic analysis indicates the presence of three dominant fatty acids. These are palmitic (16:0), oleic (18:1n-9) and linoleic (18:2n-6) acids. They alone account for approximately 90% of the total FAs contained in each of these oils. However, from one oil to another, the dominant fatty acid is different. These are palmitic (43.81±0.27%), oleic (40.11±0.58%) and linoleic (57.57±0.38%) acids, respectively, for crude aiélé (Aiélé(B)), refined palm (Palm(R)) and refined corn (Corn(R)) oils. For the two blending oils, palmitic acid remains the dominant fatty acid with contents of 42.35±0.25% and 40.90±0.24% respectively for blending oils ⁷⁵Aiélé(B)/²⁵Palm(R) and ⁵⁰Aiélé(B)/⁵⁰Palm(R).

Thus, it is apparent that the fatty acid profiles of the 3 oils are different, but the Aiélé(B) and Palm(R) oils, as well as their blending oils have similar levels of SFA, of the order of 44% compared with approximately 13% for the Corn(R) oil. Corn(R) oil (28.63 ± 0.34%) also remains the lowest in monounsaturated fatty acid (MUFA); the highest level is Palm(R) oil (44.22 ±1.08%). Conversely Corn(R) oil has the highest level of PUFA (58.02±0.55%). Aiélé(B) oil (21.21 ± 0.15%), although lower than Corn(R) oil, is about twice as high as Palm(R) oil (11.69 ± 0.23%).

Table 3. Physicochemical qualities and average FA composition (% of total FA) of dietary oils

Overall, the ratios of SFA/ MUFA/ PUFA rates obtained are different from oil to oil. They are around 13:29:58; 45:34:21 and 44:44:12, respectively, for Corn(R), Aiele(B) and Palm(R) oils. Mixing oils have ratios between those of these two oils used for the mixtures, namely 45:36:19 and 44:39:16, respectively, for the blending oils ⁷⁵Aiélé(B)/²⁵Palm(R) and ⁵⁰Aiélé(B)/⁵⁰Palm(R) (Table 3).

3.2. Growth and Balance Sheet Parameters

Rats’ food consumption, expressed as total dry matter of the ingested food (TDMI), showed no significant difference (P>0.05) in the Corn, Lipidoprive and Aiélé diets with higher intakes (P<0.05) compared to the 3 Palm(R) oil diets. Rats fed blended oils had the lowest intakes: 5.52±0.63 g/d/rat and 5.91±0.36 g/d/rat respectively for the ⁷⁵Aiélé/²⁵Palme and ⁵⁰Aiélé/⁵⁰Palme diets (Table 4). However, all animals recorded weight gains. Mean daily weight gains (DWG) in rats fed the Corn (3.19 ± 0.40 g/d/rat) and Palm (2.94 ± 0.40 g/d/rat) diets were significantly (P<0.05) higher than in other animal batches; the batch of rats subjected to the Lipidoprive diet with the lowest DWG value (1.74 ± 0.13 g/d/rat) (Table 4).

The ratio of daily weight gain (DWG) to consumption (TDMI), or alimentary efficacy coefficient (AEC), was used to distinguish three significantly different dietary groups (P<0.05). These are, in ascending order of AEC, the Lipidoprive (0.22±0.02) and Aiélé (0.25±0.03) diets, followed by the Corn (0.38±0.04), ⁷⁵Aiélé/²⁵Palm (0.35±0.09) and ⁵⁰Aiélé/⁵⁰Palm (0.40±0.06) diets, and finally, the Palm diet (0.47±0.03) (Table 4).

With regard to the apparent digestive utilization coefficients (aDUC) of the dry matter (DM) of the diets (Table 4), the results showed that the diets based on crude oil of aiélé (Aiélé: 88.30±1.42%; ⁷⁵Aiélé/²⁵Palm: 88.67±2.50% and ⁵⁰Aiélé/⁵⁰Palm: 88.04±1.64% diets) had a significantly identical (P>0.05) and close to that of the Palm diet (90.33±1.68%), but lower (P<0.05) than those of the Lipidoprive (92.17±0.76%) and Corn (92.72±0.99%) diets.

For the digestive use of dietary oils, the aDUC values obtained indicate that Aiélé(B) oil (56.53±7.58%) and blending oils (⁷⁵Aiélé(B)/²⁵Palm(R)): 63.61±10.94%; ⁵⁰Aiélé(B)/⁵⁰Palm(R): 57.96±11.07) have a significantly lower digestibility (P<0.05) than those of Palm(R) (77.99±6.42) and Corn(R) (74.72±4.83) oils. On the other hand, at the tDUC level, the values obtained significantly vary, more or less, from one batch to another. The tDUC of Aiélé(B) oil (66.77±8.31) was significantly lower than that of the others. However, there is a trend to improve dietary lipid digestibility when combining Aiélé(B) and Palm(R) oils, although there are no significant differences (P>0.05).

Calcium and phosphorus excretions are shown in Table 4. Rates significantly varied (P<0.05) from 20.32±4.38 (Palm diet) to 69.01±9.52% (Lipidoprive diet) for phosphorus and from 31.93±14.54 (Corn diet) to 71.52±18.66% (⁵⁰Aiélé/⁵⁰Palm diet) for calcium. Apart from the calcium excreted by the animals subjected to the ⁵⁰Aiélé/⁵⁰Palme diet, it appears from these results that the oils used significantly decrease (P<0.05) the total excretions of these two minerals.

Table 4. Mean values of Total Dry Ingested Matter (TDMI), Daily Weight Gain (DWG) and Coefficients of Dietary Efficiency (AEC) and Digestibility (DUC) of diets and oils and calcium and phosphorus balance

The different blood biochemical parameters determined in the animal batches are recorded in Table 5.

Table 5. Dietary influences on levels of triglyceride (TG), HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), total cholesterol (TC), calcium (Ca) and phosphorus (P) in the serum of animals

No significant differences (P>0.05) were found in triglyceride (TG) levels, ranging from 0.54±0.19 g/l (Corn lot) to 0.86±0.49 g/l (⁵⁰Aiele/⁵⁰Palm lot). However, in terms of HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C) and total cholesterol (TC), rats on the Lipidoprive (g/l; C-HDL: 0.50±0.04; LDL-C: 0.50±0.04; CT: 0.68±0.09 and Corn (g/l; C-HDL: 0.56±0.07; LDL-C: 0.08±0.07; CT: 0.75±0.08) diets had similar (P>0.05) and significantly lower (P<0.05) values than other animal batches.

The significantly (P<0.05) higher lipid parameters were obtained with animals subjected to the Palm (HDL-C: 0.64 ± 0.05 g/l), Aiélé (LDL-C: 0.23±0.08 g/l) and ⁵⁰Aiélé/⁵⁰Palm (LDL-C: 0.23±0.06 g/l and TC: 1.03±0.08 g/l) diets.

The results indicate that the TC/C-HDL ratios of Palm (1.54±0.09) and Aiélé (1.68±0.17) lots are close (P>0.05) to those of Corn (1.37±0.16) and Lipidoprive (1.33±0.12). However, at the level of the LDL-C/HDL-C ratio, that of the Aiélé batch (0.42±0.16) is significantly higher than those of these two batches (Corn: 0.14±0.13; Lipidoprive: 0.09±0.08). Furthermore, it should also be noted that ⁵⁰Aiélé/⁵⁰Palm lot had the significantly highest (P<0.05) ratios (TC/HDL-C: 2.06 ±0.61 and LDL-C/HDL-C: 0.43 ±0.09).

Concerning the phosphatemia, the administration of the oils did not result in any significant change (P>0.05) in plasma phosphorus concentrations. The concentrations obtained are from 91.61±4.89 (Palm diet) to 99.31±5.43 mg/l (Corn diet).

On the other hand, in terms of serum calcium, intake of Palm(R) oil alone (Palm diet) or in combination (⁷⁵Aiélé/²⁵ Palme and ⁵⁰Aiélé/⁵⁰Palme diets) appears to significantly increase plasma calcium concentrations. The values obtained ranged from 108.50±5.36 mg/l (Lipidoprive diet) to 118.17±3.19 mg/l (Palm diet).

The relative weights (in % of live body weight) of the organs of the batches of animals subjected to the different diets were determined. The results are presented in Table 6. No significant difference (P>0.05) was found in the heart. However, in the liver and kidney, administration of blending oils (⁷⁵Aiélé/²⁵Palm and ⁵⁰Aiélé/⁵⁰Palm diets) to animals induced a significant increase (P<0.05) in the relative weights of these two organs.

Table 6. Organ weight (% live weight)

4. Discussion

The physicochemical characteristics of refined corn (Corn(R)) and palm (Palm(R)) oils are in accordance with FAO standards [43]. In Aiélé(B) oil, the high acid and peroxide values are due to the fruit harvesting and storage conditions which have probably promoted intense endogenous enzyme activities (lipases and lipoxidases). However, the values obtained remain comparable to those obtained by [44]. The same is true for the total FAs composition where the values obtained agreed well with those of [45,46], although they have worked on Cameroonian fruits. The 45/34/21 ratio of the SFA/MUFA/PUFA rates for Aiélé(B) oil is similar to that determined by the latter, which is 45/32/21 [45,46].

According to Deuel's recommendations [47], all the oils used can be considered digestible since they have melting ranges of less than 50°C. (compared with their melting ranges, all of which are less than 50°C).

For animal testing, the results indicated that the daily weight gain (DWG) obtained is not solely attributable to food consumption but mainly to diet quality, which varies in this study depending on the rate and nature of FAs in the diet. Indeed, it is apparent from the data obtained that the absence of fats (Lipidoprive diet) or the presence of high palmitic acid and low oleic acid (Aiélé diet) in the diet led to the lower DWGs despite a high food consumption. Hence, significantly (P<0.05) lower AECs were observed in these two groups of rats.

Conversely, it could be noted that the Palm(R) oil diet, which is richer in oleic acid, although less appreciated by animals, had the highest AEC. In addition, its combination with Aiélé(B) oil (case of blended oils) significantly improved the dietary efficiency, as well as the digestibility of the lipids in the diet. Palm(R) oil was characterized by the highest digestive use coefficients (apparent and true) (aDUC and tDUC).

Moreover, it appears from the results obtained that the corn(R) oil diet, which has the highest level of UFAs, induced relatively low calcium excretion rates in the animals which ingested it compared with those subjected to the diets with the aiélé and/or palm oils, which are richer in (SFAs). At the phosphorus balance, all animals fed lipid diets had excretion rates ranging from 20 to 48%, i.e. absorption rates ranging from 52 to 80%. In humans, 50% of the dietary phosphorus is absorbed. This absorption may be increased in the presence of vitamin D or decreased if the diet is rich in calcium [48,49].

All the data obtained seem to illustrate the gains made with regard to lipid nutrition. Indeed, it is known that the digestive use of fats varies according to the ratio between SFAs and UFAs [11]. More specifically, studies have shown that the digestibility of long and saturated FAs is low, particularly that of palmitic acid [12,13,14,15,16]. However, the digestibility of a diet rich in palmitic acid (16:0) can be improved in the presence of UFAs, in particular by a high intake of oleic acid [11,50,51].

With regard to intestinal calcium absorption, it is recognized that excess fat (especially SFA) and fat malabsorption (steatorrhea) are accompanied by high calcium excretion rates by the formation of calcium salts of insoluble fatty acids [19,48,52]. In rats, the formation of insoluble soaps is essentially based on long and saturated FAs [53]. For example, significant increases (P<0.05) in kidney and liver weights observed in animals fed mixed oil diets (⁷⁵Aiélé(B)/²⁵Palm(R) and ⁵⁰Aiélé(B)/⁵⁰Palm(R) diets) may be due to the presence of excess insoluble fatty acid salts, including calcium palmitate salts (long fatty acid soap). Removal of these organs would likely have required an additional activity, which resulted in increased organ weights. Similar facts have been reported by [39,49] who observed that the disposal of excess nitrogen waste could lead to an increase in kidney weight, due to high kidney activity [39,54].

In addition, it is noted that the calcium and phosphorus excretion rates of the batches of rats fed the Corn(R) and Palm(R) oil diets, respectively, are comparable to those of the [55] study, obtained in Wistar rats fed 15% soybean or peanut oil diets [55].

In terms of lipid parameters, the results expressed in terms of the ratio TC/HDL-C and LDL-C/HDL-C give significantly high values (P<0.05) at the level of the batches of animals ingesting the diets rich in SFAs. In humans, these ratios (TC/HDL-C and LDL-C/HDL-C) are related to a risk factor for coronary heart disease; the risk increases as they increase. Overall, this risk is low when the LDL-C/HDL-C ratio is less than 3.5. For the TC/HDL-C ratio, the standard risk is 4.5 [48,56]. The absence of the significant difference (P>0.05) in triglyceridaemia appears to be explained by the fact that the different oils incorporated in the diets are free of PUFAs of the series (n-3), only FAs capable of significantly decreasing on this parameter [57,58,59].

Finally, neither the presence nor the nature of the oils in the diets significantly (P>0.05) influenced blood phosphorus levels. Phosphoremia disorders are non-nutritional anyway [48]. On the other hand, at the calcemia, the diets containing refined palm oil, alone or in a mixture (diets with Palm(R) oils and with blending oils), significantly increase (P<0.05) this parameter.

5. Conclusion

Overall, neither the physicochemical study nor the nutritional study carried out mention any significant adverse indications or marked pathological effects due to the crude oil of aiélé (unrefined oil) compared to the refined fats used; this reassures the food use of this oil. However, the results suggested that palmitic acid is a determinant of the declining nutritional performance of crude oil of aiélé compared to refined palm or corn oils. Thus, further work to reduce the level of this fatty acid can be carried out to improve the nutritional quality of the crude oil of aiélé.

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