Nutritional Potential and Low Heavy Metals Content of Oryctes monoceros (Olivier, 1789) and Rhynchophorus phoenicis (Fabricius, 1801) Adults, Two Coleopteran Species Consumed in Togo

Abstract

Oryctes monoceros (Olivier, 1789) (Scarabaeidae) and Rhynchophorus phoenicis (Fabricius, 1801) (Curculionidae) are two insects generally known as formidable pests of oil palms and coconuts trees. Although little known, different developmental stages of these insects are consumed. The aim of this study is to determine the composition of these adult Coleopteran species in order to promote their consumption as a strategy for enhancing food security. Chemical analyses were carried out on adults of both species. Samples of O. monoceros and R. phoenicis were collected in three localities in Togo. The ash, protein, vitamin, and lipid contents were determined according to the AOAC reference methods. The fiber contents were obtained by the method of Weende. The minerals and heavy metals were analyzed by atomic absorption spectrophotometry and colorimetry. Fatty acid composition was determined by gas chromatography. The results showed the average protein content ranges from 44.32 ± 0.83 to 45.89 ± 0.83%. The lipid level is between 15.06 ± 0.28% and 14.64 ± 0.54. Their lipids contain unsaturated fatty acids, notably oleic (40.84 ± 0.112 vs. 40.84 ± 0.11%), linoleic (4.49 ± 0.00 vs. 5.07 ± 0.02%), and α-linolenic (5.07 ± 0.02 vs. 6.35 ± 0.01%) acid. They are excellent sources of minerals and vitamins. They are also free of heavy metals. These species could, therefore, contribute to the nutritional balance of consumers. They deserve to be better promoted for human consumption, as they could make a significant contribution to the fight against malnutrition and constitute a novel food source.

1. Introduction

The evolution of environmental pollution in general, and soil and plant pollution in particular, has influenced perspectives on sustainable resource development [1,2,3]. Some sustainable resources are linked to the food industry, where, in recent years, due to their high nutritional content, researchers and producers have focused on the safety and benefits of consuming insects in various forms [4,5]. Plants in the Arecaceae family (oil palms and coconut trees) represent a significant mass of organic matter, which can provide a very favorable environment for the development of several polyphagous parasitic species attached to the plants, including various species of Coleoptera, such as weevils and beetles, according to several studies [6,7,8]. Unfortunately, empirical studies to determine the extent of the economic damage caused by pests of oil palm and coconut trees are generally not conducted. The larvae of weevils and beetles, which are well known as formidable pests of palm and coconut plantations, develop in the living or decomposing tissues of these plants [9]. Coleoptera are not the only pests of Arecaceae; oil palms and coconut trees are also vulnerable to attacks by other pests, particularly Lepidoptera, Orthoptera, and Homoptera, and may be infested by fungal diseases. To mitigate this economic damage, many farmers resort to the use of pesticides; however, these pesticides, especially fungicides, contain heavy metals [10]. Weevils and beetles in plantations have both harmful and beneficial economic effects [8]. On the positive side, some developmental stages of these insects are edible. In fact, several species of weevils and beetles, including Rhynchophorus ferrugineus (Olivier, 1790), Rhynchophorus palmarum (Linnaeus, 1758), Rhynchophorus phoenicis (Fabricius, 1801), Oryctes rhinoceros (Linnaeus, 1758), and Oryctes monoceros (Olivier, 1789), which are known to be harmful to Arecaceae crops, are among the most popular edible insects in tropical areas, particularly in Africa [7]. Although adults are consumed, they are often ingested in their immature stages (larvae), which are more highly valued [11]. Consequently, several studies have focused on the larvae of these Coleoptera [12,13,14,15]. These studies have shown that the larvae of various weevils and beetles have very high nutritional content, particularly essential fatty acids, amino acids, vitamins, and minerals [16,17]. Therefore, the consumption of these larvae is of particular interest to people suffering from protein-energy and micronutrient malnutrition. Adults of these species are not generally studied due to a lack of data on their chemical composition in the international scientific literature. Furthermore, the pesticides and chemicals used in the plantations of oil palms and coconut trees can accumulate in the weevils and beetles that develop in these areas via the food chain. According to Kokoete et al. [11], insects collected from palm trees treated with pesticides are unfit for consumption. In fact, edible insects may pose a potential risk to human health, especially when they are wild-harvested, as they can be contaminated with pesticides, particularly insecticides, herbicides, and fungicides [18]. Studies have shown that insects collected in forested areas are generally free of chemicals. In contrast, insects from agricultural fields sometimes contain pesticides and heavy metals [19,20]. However, the scientific literature on insect food safety is sparse. To promote insects in human nutrition worldwide, it is necessary to assess the dietary risks of pesticides and chemicals, particularly heavy metals, in edible insects, which are considered highly hazardous environmental pollutants due to their persistence and tendency to bioaccumulate in organisms through the consumption of contaminated insects. A better understanding of the composition of edible insects will promote their consumption by humans, as this will contribute not only to food security but also to safe biological control, benefiting both humanity and our natural ecosystems. The objective of this study is, therefore, to determine the nutritional value and heavy metal composition of adult O. monoceros and R. phoenicis consumed in Togo, with a view to promoting their consumption.

2. Materials and Methods

2.1. Biological Material

The insects used in this study were collected in August 2022 from oil palm plantations in three randomly selected locations in Togo (Assahoun (6°14′206′ N, 1°10′595′ E), Agbozomé (6°22′897′ N, 1°27′371′ E) and Yégué (8°10′600′ N, 0°39′340′ E)). Captured insects were cold-killed by placing them in a cooler with a cold accumulator containing ice [21].

2.2. Biochemical Assays

All determinations of heavy metals and minerals, except for phosphorus, were carried out at the Faculty of Engineering of Vasile Alecsandri University of Bacau, Romania. Fatty acid profiling was conducted at the Laboratoire National de Santé Publique (LNSP) in Abidjan, Côte d’Ivoire. The remaining analyses were performed at the Laboratoire de Biochimie de la Faculté des Sciences de l’Université de Lomé, Togo.

A SCALTEC electronic moisture analyzer (SM01 Instrument GmH) was used to determine the moisture contents of the samples. Fifteen grams (15 g) of fresh samples of adult O. monoceros from each of the three localities brought back to the laboratory was weighed and mixed to obtain an average sample. The same treatment was applied to adult R. phoenicis. The average samples were oven-dried at 40 °C until a constant weight was obtained and then ground in a General electric; interlabs moulinex. The ground samples were kept cool in a refrigerator for subsequent chemical analysis.

Fiber content was determined using the Weende method [22].

After acid hydrolysis followed by basic hydrolysis, the samples were dried at 150 °C for one hour and then incinerated at 550 °C for 6 h.

The compositions of ashes (mineral substances), lipids, and proteins were determined according to the methods of the AOAC [23].

Ashes were determined by incinerating the samples at 550 °C for 6 h.

Proteins were estimated by determining total nitrogen using the Kjeldahl method. After adding 0.2 g of selenium sulfate and 20 mL of sulfuric acid to 0.5 g of crushed insect, the mixture was heated until discoloration occurred. This discoloration indicates that all organic forms of nitrogen have been converted to ammonium sulfate. Ammonia was distilled by introducing the resulting mixture, along with methyl red and 75 mL of 40% sodium hydroxide, into the distillation apparatus. Heating the mixture released ammonia from the ammonium sulfate in a basic medium, which was then distilled off. An Erlenmeyer flask used to collect the distillate contained 20 mL of 0.1 N sulfuric acid and Tashiro’s reagent as a color indicator. Once the pH paper indicated an acidic pH for the distilling solution, the distillation was stopped, and the excess acid was neutralized with a 0.1 N sodium hydroxide solution until the Tashiro reagent turned yellow-green. The percentage of nitrogen (%N) in the sample was calculated using the following formula:

$$\mathrm{N}={\displaystyle \frac{0.14\left(20-\mathrm{V}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{e} \mathrm{o}\mathrm{f} \mathrm{s}\mathrm{o}\mathrm{d}\mathrm{i}\mathrm{u}\mathrm{m} \mathrm{h}\mathrm{y}\mathrm{d}\mathrm{r}\mathrm{o}\mathrm{x}\mathrm{i}\mathrm{d}\mathrm{e} \mathrm{s}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} \mathrm{u}\mathrm{s}\mathrm{e}\mathrm{d}\right)}{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s} \mathrm{o}\mathrm{f} \mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}}$$

(1)

The crude protein was calculated by multiplying percentage nitrogen by a constant factor of 6.25, i.e., % crude protein = % N × 6.25.

Lipids were extracted with hexane using a Soxhlet extractor and the extracts evaporated under vacuum at 35 °C using a Buchi R114 Rotavapor. Phosphorus content was determined by colorimetry using the phosphovanado molybdate method [24], and absorbance was assessed using a colorimeter (Jenway model 6300, Fisher Scientific, Göteborg Sweden). Other minerals (calcium, magnesium, potassium, sodium, iron, manganese, copper, and zinc) and heavy metals (cadmium, mercury, lead, arsenic, and nickel) were analyzed by atomic absorption spectrophotometry [25]. Solubilization of the insect crushers was performed by acid attack on a sand bath, using two concentrated solutions: nitric acid and hydrogen peroxide. One gram of each grind was introduced in a Teflon container to which 1 mL of hydrogen peroxide and 8 mL of nitric acid were added. After stirring, the Teflon containers were heated on a sand bath for about 2 h at a temperature of about 150 °C. The recovery of the products obtained after heating was performed with 2 mL of distilled water. After cooling, the solution obtained after digestion was transferred to a 100 mL volumetric flask and supplemented with demineralized water. After homogenization, the solution was filtered through a Wattman paper. Thus, the filtrate was collected in a closed bottle. The determination of TMEs was carried out from this filtrate using a flame atomic absorption spectrophotometer Agilent 7500 ICP-MS cu UP 213 (GenTech Scientific, New York, NY, USA) using the standard solutions. The real concentrations were determined with the following formula [26]:

$$RC={\displaystyle \frac{CS\times DV}{M}}$$

(2)

where RC is the real concentration, CS is the analyte concentration, DV is the dilution volume, and M is the mass of the test sample.

To assess the nutritional quality of each species, the Ca/P, Ca/Mg, and Na/K ratios were calculated.

The percentage of carbohydrates and the metabolizable energy values of the samples were calculated.

The percentage of carbohydrates was calculated by difference with the percentages of the other total constituents according to the following formula [26]:

Carbohydrate = 100 − (Moisture + Protein + Fat + Ash + Fiber)

(3)

The metabolizable energy (EM) values of the samples were calculated from the protein, lipid, carbohydrate, and fiber values by applying the energy conversion factors using the following formula [26]:

EM = 17 × Protein + 37 × Fat + 17 × Carbohydrate + 8 × Fiber

(4)

The fatty acid composition of the lipids was obtained by gas chromatography and the omega-6/omega-3 ratio was calculated.

An HP 6890 Series GC System gas chromatograph (Agilent Technologies Inc., Santa Clara, CA, USA) was used for the analysis. The instrument is equipped with a flame ionization detector and an HP-5 (cross-linked 5% ME siloxane) capillary column (length: 30 m; film thickness: 0.25 μm; internal diameter: 0.32 mm). The oven temperature was programmed to increase from −60 °C to +325 °C at a rate of 1 °C/min. The injector temperature was set at 275 °C, and the detector was set at 325 °C. The inlet nitrogen pressure, used as the carrier gas, varied from 6.90 to 47.6 kPa. The flow rate was maintained at 1 cm³/min, and the dead time was 1 min 15 s (hydrogen at 40 cm³/s). All fatty acids (saturated, unsaturated, cis, trans) were analyzed in the samples.

Chromatographic profiling of fatty acids was carried out in two stages: sample preparation and determination by gas chromatography. Sample preparation was conducted in accordance with procedure [27]. Five grams of fat was placed in a flat-bottomed flask, and 2.5 g of liquid sodium hydroxide (NaOH 1 N) was added. A few grains of pumice stone were included to prevent excessive crackling. A cooler was fitted to the flask, and the mixture was heated under reflux over low heat until a crust formed. Slowly, 20 mL of 20% (v/v) sulfuric acid was added, and the mixture was heated until a translucent solution appeared. Next, 80 mL of the methanol–sulfuric acid mixture was added to the translucent solution, and the mixture was boiled under reflux for 2 h.

After 2 h of reflux boiling, the esterified fat was decanted into a separating funnel until the non-esterified phase was completely removed. A volume of 0.5 mL of the esterified sample was mixed with 2.5 mL of hexane, then decanted to obtain a solution of methyl esters. Gas chromatographic determination was carried out in accordance with ISO 5508 [28] by injecting one microliter (1 µL) of the methyl ester solution obtained. The peaks representing the methyl esters were identified using reference standards (methyl esters) by comparing the retention times of each peak in the chromatogram with those obtained for the standards.

The percentages of saturated and unsaturated fatty acids (monounsaturated and polyunsaturated) lipids were obtained by summing the contents of the fatty acids concerned. The omega-6 fatty acid found in the lipids of the insect species studied was linoleic acid, and the omega-3 fatty acid found was α-linolenic acid. The omega-6/omega-3 ratio was calculated based on the levels of these fatty acids in the samples.

Vitamins were assayed using AOAC [29] methods.

Vitamins in the various samples were determined by colorimetry. Optical density was measured using a Jenway Model 6300 colorimeter. Calibration curves were obtained from the preparation of a range of solutions of the corresponding vitamin molecule. The samples were prepared as follows:

Retinol (A): One gram of the sample was placed into a 250 mL flask. After adding 5 mL of pyrogallol solution, 35 mL of ethanol, and 10 mL of potassium hydroxide solution, the mixture was heated for 30 min at 70–80 °C under a reflux condenser, then allowed to cool under a stream of water. After cooling, 40 mL of distilled water and 100 mL of petroleum ether were added. Extraction was performed by stirring for 3 min. The mixture was then left to settle, and the upper phase was transferred to a separating funnel. The ethereal phase was washed to neutrality with three 50 mL portions of water and filtered through filter paper. A 5 mL sample of the ethereal phase was transferred into a 50 mL flask and diluted with petroleum ether. The retinol concentration of this solution was determined by measuring its optical density at 325 nm.

Thiamine (B1): The thiamine content of the samples was determined by adding 50 mL of 0.1 N sulfuric acid to one gram of each sample in a 100 mL volumetric flask. The mixture was heated in a water bath at 100 °C for 30 min, with frequent stirring. Five milliliters of 2.5 N sodium acetate solution was added to the contents, and the mixture was left to cool. After cooling, the flask was capped and placed in a water bath at 45–50 °C for 2 h. The resulting solution was made up to 100 mL with distilled water and filtered through filter paper. A 10 mL volume of the filtrate was transferred and mixed with 5 mL of potassium chloride solution. Absorbance was measured at a wavelength of 285 nm.

Riboflavin (B2): One gram of each sample was weighed into a 250 mL volumetric flask. To this, 5 mL of 0.1 N sulfuric acid and 5 mL of dichloroethane were added, followed by 90 mL of distilled water. The mixture was stirred and heated on a sand bath for 30 min to extract the riboflavin. Afterward, the mixture was cooled and made up to 250 mL with distilled water, then filtered through filter paper. A 2 mL volume of the filtrate was transferred into another 250 mL volumetric flask and topped up with distilled water. The riboflavin concentration of the solution was determined by measuring its absorbance at 460 nm.

Niacin (B3): Five grams of the sample were extracted with 50 mL of distilled water. Extraction was performed by repeated stirring for 30 min. The mixture was then left to settle, and the upper phase was recovered and filtered. This operation was repeated three times with the same amount of distilled water (100 mL). Five milliliters of the combined filtrates were transferred into a 100 mL volumetric flask and topped up with distilled water. The absorbance of the resulting colored solution, measured at a wavelength of 385 nm, was used to determine the nicotinic acid content of the sample.

Tocopherol (E): One gram of the sample was weighed and placed in a 250 mL flat-bottomed flask. A solution of 10 mL of ethanol and 20 mL of 1 N sulfuric acid was added. The flask was wrapped in aluminum foil and heated under reflux for 45 min. The resulting solution was cooled for 5 min, followed by the addition of 50 mL of distilled water and transferred to an aluminum foil-covered separating funnel. The unsaponifiable matter in the mixture was extracted five times with 50 mL of dimethyl ether each time. The combined extract was washed with 1 N sulfuric acid solution and dried over anhydrous sodium sulfate. The evaporated extract was immediately dissolved in 15 mL of ethanol, 1 mL of concentrated sulfuric acid, and 1 mL of concentrated nitric acid. The resulting solution was placed in a water bath at 90 °C for 30 min. After cooling, the tocopherol content of the extract was measured by ultraviolet absorption at 470 nm.

2.3. Statistical Analyses

Trials were performed in triplicate. The mean values of the components were calculated on the basis of the three repetitions. Their standard deviations (SDs) were added. One-way analysis of variance (ANOVA-1) was used to compare two means using the SPSS 20.0 software. Differences observed between two means were considered statistically significant at the 5% level.

3. Results

3.1. Compositions of Organic and Mineral Constituents of O. monoceros and R. phoenicis

The composition of adult O. monoceros and R. phoenicis are shown in

Table 1. Proximate compositions (% wet weight) and their energy value (KJ/100 g) of O. monoceros and R. phoenicis.

Parameters Analyzed	Average Content (±SD) *
	O. monoceros	R. phoenicis
Moisture (%)	9.36 ± 1.4 a	8.68 ± 0.31 b
Ash (%)	11.09 ± 1.37 a	10.45 ± 0.37 a
Protein (%)	44.32 ± 0.83 a	45.89 ± 0.28 b
Lipid (%)	15.06 ± 0.28 a	14.64 ± 0.54 a
Fiber (%)	10.04 ± 1.15 a	13.72 ± 0.46 b
Carbohydrate (%)	10.11 ± 0.80 a	6.59 ± 1.2 b
Energy (KJ/100g)	1563.11 ± 8.77 a	1543.99 ± 8.58 a

* Means followed by different letters in the same line are significantly different (ANOVA-1 comparison tests, p < 0.05).

. The mineral (11.09 ± 1.37 vs. 10.45 ± 0.37%) and lipid (14.64 ± 0.54 vs. 15.06 ± 0.28%) contents of the two species studied were not statistically different. On the other hand, the moisture (9.36 ± 0.54 vs. 8.68 ± 0.31%), protein (44.32 ± 0.83 vs. 45.89 ± 0.83%), fiber (10.04 ± 0.83 vs. 13.72 ± 0.46%), and carbohydrate (10.11 ± 0.80 vs. 6.59 ± 8.77%) contents of the two species were statistically different. The protein and fiber contents were higher for R. phoenicis, while the moisture and carbohydrate contents were higher for O. monoceros. The metabolizable energies of the species were not statistically different (1563.11 ± 8.77 vs. 1543.99 ± 8.58 KJ/100g).

Although the contents of these two species were not statistically different (Table 1), the contents of the majority of the mineral elements analyzed were statistically higher for R. phoenicis than for O. monoceros (

Table 2. Mineral composition (mg/100g) of O. monoceros and R. phoenicis.

Minerals	Average Mineral Content (±SD) *		Recommended Dietary Intake (RDI) [30]
	O. monoceros	R. phoenicis
Calcium	53.54 ±1.53 a	66.51 ± 0.10 b	700–1300
Magnesium	25.38 ± 0.55 a	40.73 ± 0.38 b	80–420
Phosphorus	47.82 ±1.31 a	73.90 ± 2.51 b	500–1250
Potassium	108.38 ±1.03 a	644.12 ± 0.98 b	3000–4700
Sodium	77.64 ±1.69 a	113.57 ± 1.63 b	1500–2300
Iron	8.08 ± 0.88 a	11.51 ± 0.06 b	7–18
Manganese	0.96 ± 0.34 a	1.26 ± 0.03 a	1.2–2.3
Copper	9.96 ± 0.72 b	1.33 ± 0.01 a	0.34–09
Zinc	0.85 ± 0.02 a	15.65 ± 0.04 b	3–11
Sodium/Potassium	0.71	0.17	<1
Calcium/Phosphorus	1.12	0.90	1–1.3
Calcium/Magnesium	2.1	1.63	2

* Means followed by different letters in the same line are significantly different (ANOVA-1 comparison tests, p < 0.05).

). The analysis of minerals (mg/100g), in particular, sodium (77.64 ± 1.69 vs. 113.57 ± 1.69), potassium (108.38 ± 1.03 vs. 644.12 ± 1.03), phosphorus (47.82 ± 1.31 vs. 73.90 ± 2.51), magnesium (25.38 ± 0.55 vs. 40.73 ± 0.38), calcium (53.54 ± 1.53 vs. 66.51 ± 0.10), iron (8.08 ± 0.88 vs. 11.51 ± 0.06), copper (9.96 ± 0.72 vs. 1.33 ± 0.01), zinc (0.85 ± 0.02 vs. 15.65 ± 0.04), and manganese (0.96 ± 0.34 vs. 1.26 ± 0.04), shows that these species contain variable and significant quantities of minerals. Table 2 shows that the sodium/potassium, calcium/phosphorus, and calcium/magnesium ratios were 0.71, 1.12, 2.1 for O. monoceros and 0.17, 0.9, 1.63 for R. phoenicis, respectively.

The percentages of saturated and unsaturated fatty acids (monounsaturated and polyunsaturated) in the lipids of O. monoceros and R. phoenicis are shown in

Table 3. Fatty acid content of lipids (% of all fatty acids) of O. monoceros and R. phoenicis.

Degree of Fatty Acid Saturation	Percentage of Fatty Acids (±SD)
	O. monoceros	R. phoenicis
Total saturated fatty acids	50.35 ± 0.01	41.05 ± 0.03
Total monounsaturated fatty acids	40.84 ± 0.00	47.06 ± 0.03
Total polyunsaturated fatty acids	6.67 ± 0.01	11.42 ± 0.03
Total unsaturated fatty acids	47.51 ± 0.01	58.48 ± 0.06
Omega-6/Omega-3	2.06	0.80

. It appears that O. monoceros and R. phoenicis contain more than 45% unsaturated fatty acids. The results of this table show that the unsaturated fatty acid content of R. phoenicis (58.48 ± 0.06%) was higher than that of O. monoceros (47.51 ± 0.01%). The polyunsaturated fatty acids content of the insects studied was low (3.13 ± 0.01 vs. 3.13 ± 0.03%). Concerning the omega-6/omega-3 ratio of fatty acids in the insects studied, the values were 2.06 for O. monoceros and 0.08 for R. phoenicis.

The results of the chemical screening carried out on O. monoceros and R. phoenicis lipids are shown in

Table 4. Fatty acid composition of lipids (% of all fatty acids) of O. monoceros and R. phoenicis.

Fatty Acids	Percentage of Fatty Acids (±SD)
	O. monoceros	R. phoenicis
Lauric acid (C12: 0)	0.64 ± 0.00	0.58 ± 0.01
Myristic acid (C14:0)	Not detected	0.96 ± 0.00
Palmitic acid (C16:0)	39.95 ± 0.07	30.35 ± 0.03
Stearic acid (C18:0)	10.21 ± 0.06	9.16 ± 0.09
Oleic acid (Cl8:1 c(n-9)	40.84 ± 0.11	47.06 ± 0.08
Linoleic acid (C18:2 c(n-6))	4.49 ± 0.00	5.07 ± 0.02
α-Linolenic acid (C18:2 c(n-3))	5.07 ± 0.02	6.35 ± 0.01

. The lipids of the species studied contained saturated fatty acids like lauric acid (0.64 ± 0.00 vs. 0.58 ± 0.01%), myristic acid (0.96 ± 0.00% for R. phoenicis), palmitic acid (39.95 ± 0.07 vs. 30.35 ± 0.03%), and stearic acid (10.21 ± 0.06 vs. 9.16 ± 0.09%). The monounsaturated fatty acid present in these species was oleic acid (40.84 ± 0.11 vs. 47.06 ± 0.08%). The polyunsaturated fatty acids contained in the lipids were linoleic acid (4.49 ± 0.00 vs. 5.07 ± 0.02%) and α-linolenic acid (5.07 ± 0.02 vs. 6.35 ± 0.01%).

The two insect species studied had variable vitamin contents per 100 g dry weight (

Table 5. Vitamin contents (mg/100g dry weight) of insects.

Vitamins	Average Vitamin Content (±SD) *
	O. monoceros	R. phoenicis
Retinol (A)	0.04 ± 0.00 a	0.01 ± 0.00 b
Thiamine (B1)	1.35 ± 0.20 a	0.96 ± 0.11 a
Riboflavin (B2)	2.25 ± 0.19 a	2.33 ± 0.33 a
Niacin (B3)	8.18 ± 0.23 a	7.44 ± 0.3 b
Tocopherol (E)	3.43 ± 0.04 a	4.77 ± 0.01 b

* Means followed by different letters in the same line are significantly different (ANOVA-1 comparison tests, p < 0.05).

) as follows: retinol (0.04 ± 0.00 vs. 0.01 ± 0.00 mg), thiamine (1.35 ± 0.20 vs. 0.96 ± 0.11 mg), riboflavin (2.25 ± 0.19 vs. 2.33 ± 0.33 mg), niacin (8.18 ± 0.23 vs. 7.44 ± 0.3 mg), and tocopherol (3.43 ± 0.04 vs. 4.77 ± 0.01 mg).

3.2. Heavy Metal Composition of O. monoceros and R. phoenicis

The results of the heavy metal analyses show that the insect species studied did not contain cadmium, mercury or lead (

Table 6. Heavy metals content (mg/kg) of O. monoceros and R. phoenicis.

Heavy Metals	Average Heavy Metals Content (±SD) *
	O. monoceros	R. phoenicis
Cadmium	<0.0005	<0.0005
Mercury	<0.0005	<0.0005
Lead	<0.01	<0.01
Arsenic	0.0364 ± 0.00 a	0.0073 ± 0.00 a
Nickel	0.0209 ± 0.00 a	0.0767 ± 0.00 b

* Means followed by different letters in the same line are significantly different (ANOVA-1 comparison tests, p < 0.05).

); however, they did contain nickel and arsenic. The nickel content of these species varied from 0.0209 to 0.07671638 mg/kg and the arsenic content from 0.0209 to 0.0767 mg/kg.

4. Discussion

This study revealed that adults of the two Coleopteran species consumed in Togo (O. monoceros and R. phoenicis) are not just a traditional dish but are also a rich source of essential nutrients (e.g., results presented in Table 2, Table 3, Table 4 and Table 5).

The results of this study show that adults of both species have very low moisture contents compared with conventional meat and fish commonly consumed in West Africa. The average moisture content of these meats and fish varies from 65 to 75% [29]. These contents are also very low compared with those of the larvae of these species, which average 64% [31]. On the other hand, the moisture content of the two species studied corroborates the results of certain studies carried out on adult Orthoptera, Coleoptera, and Isoptera consumed in Togo [32,33] and Nigeria [34,35]. The moisture content of the insects studied is low, which is advantageous for their preservation because moisture is a constituent related to difficulties encountered in food preservation [36].

The protein content of R. phoenicis adults (45.89 ± 0.28%) was significantly higher than that of O. monoceros (44.32 ± 0.83%). The protein percentages of O. monoceros and R. phoenicis adults were higher than those obtained by several authors [17,31,37] for the larvae of the same species, which contain more lipids; however, they contained lower amounts of protein than the larvae of Allomyrina dichotoma Linnaeus,1771 (Coleoptera: Dynastidae), Tenebrio molitor Linnaeus,1758 (Coleoptera: Tenebrionidae), and the adults of two species of Orthoptera of the family Gryllidae (Gryllus bimaculatus (De Geer, 1773) and Teleogryllus emma (Ohmachi and Matsuura, 1951)) [38]. They also contained lower amounts of protein than the adults of Chondacris roseum (De Geer, 1773) (Orthoptera: Acrididae) and Brachytrupes orientalis (Burmeister, 1838) (Orthoptera: Gryllidae) [39]. Protein is essential for the development and renewal of muscular tissues, body tissues such as nails, hair and body hair, the bone matrix, and the skin [40]. The high protein content of the adults of O. monoceros and R. phoenicis can adequately supply essential protein to the growing population in developing countries. Indeed, insects can significantly contribute to the daily protein requirements of populations, which range from 23 to 56 g [41]. Therefore, consuming less than 125 g of any of these Coleopteran species is sufficient to meet the daily protein requirement. Hence, the consumption of these insects could serve as a cheap and nutritious substitute for the expensive protein sources found in conventional foods.

The mineral composition (data from Table 2) of the insect species studied was not statistically different from, but was higher than, that of beef, poultry, and fish, with values of between 1 and 2.5% [26]. These values are quite similar to those obtained by Ghosh et al. [38] for adults of two Orthopteran species, G. bimaculatus and T. emma, in South Korea. The Coleopteran species studied contained significant quantities of minerals, as generally reported in the literature for insects consumed [32,42,43]. The insects studied are a good source of minerals (Ca, Mg, P, K, Na, Fe, Cu, Zn, and Mn) that are involved in different physiological functions. Sodium and potassium were the most dominant minerals in these insects compared to the other minerals. They are essential for human health. Potassium, for example, plays an essential role in the body’s cellular biochemical reactions, energy metabolism, normal growth, and building of muscle [44]. It is also essential for the proper function of all cells in the human body [45]. However, to meet the Recommended Dietary Intake (RDI) for these minerals (potassium and sodium), it is important to include other complementary food sources in the diet based on O. monoceros and R. phoenicis. On the other hand, a daily intake of 100 g of O. monoceros and R. phoenicis would satisfy the full RDI for trace elements such as iron, copper, and manganese, according to the recommendations by the Dietary Guidelines Advisory Committee [30]. R. phoenicis also represents a promising source of zinc in this study, which plays an important role in regulating gene expression and intracellular signaling [46].

Given the large quantity of mineral elements contained in the Coleopteran species studied, they can make a significant contribution to combating micronutrient deficiency in developing countries.

The balance between sodium and potassium on the one hand and between calcium and phosphorus on the other is fundamental. When the sodium/potassium ratio in food is less than 1, as is the case for O. monoceros and R. phoenicis, the intake of these elements is beneficial for health. When the sodium/potassium ratio is favorable, it reduces blood pressure and consequently cardiovascular accidents [47], protects renal function, and prevents lithiasis and osteoporosis [48]. The calcium/phosphorus ratio should preferably be between 1 and 1.3. The ratios for both species are within this range. Calcium and phosphorus are the main elements involved in bone formation; however, an imbalance between these two minerals can be harmful, as a balanced supply of calcium and phosphorus is important for bone formation and skeletal integrity [49]. With regard to calcium and magnesium, the calcium/magnesium ratio for the two insect species studied is close to 2, which is the recommended value in food. This ratio enables significant calcium fixation in the body [50].

The insect species studied are rich in fats, which are well known for their importance in nutrition and energy production. Fats are also vital for the structural and biological functioning of cells and for carrying fat-soluble vitamins [51]. The high proportion of unsaturated fatty acids in these lipids determines the nutritional quality of the lipids in the two Coleopteran species studied. The lipids of both species are characterized by a high content of oleic acid, a monounsaturated fatty acid. Oleic acid has been shown to be beneficial to health. This fatty acid is involved in the prevention of several diseases, in particular, type 2 diabetes and metabolic syndrome [52]. The lipids in O. monoceros and R. phoenicis also contain small amounts of the so-called essential polyunsaturated acids, in particular, linoleic acid and α-linolenic acid. Womeni et al. [53] also found a high proportion of polyunsaturated fatty acids in six insects consumed in Cameroon: larvae of raphia weevil (Rhynchophorus phoenicis), crickets (Homorocoryphus nitidulus), grasshopper (Zonocerus variegatus), termites (Macrotermes sp.), a variety of caterpillars (Imbrasia sp.), and an unidentified caterpillar from the forest (UI caterpillar), with particular representation of linoleic and α-linolenic acids. These essential fatty acids also play an important nutritional role. Linoleic acid is involved in the prevention of atherosclerosis [54]; α-linolenic acid helps regulate cholesterol [55]. These essential fatty acids are the precursors of the two families of fatty acids (omega-6 and omega-3). The species studied have an omega-6/omega-3 ratio below 5. This underlines the nutritional quality of this insect oil, because this ratio value reduces the risk of cardiovascular disease [56].

All the insect species studied contained appreciable quantities of the desired vitamins, making them species of good nutritional quality. According to several authors [57,58], vitamins like retinol, thiamine, riboflavin, niacin, and tocopherol have been found in edible insects. These vitamins have several functions in the body. Vitamins A and E are antioxidants, while B vitamins are co-enzymes [59]. The presence of vitamins in the insect species studied makes them good sources of food supplements for people suffering from micro-nutritional malnutrition.

The results of the heavy metal analyses show that the insect species studied do not contain heavy metals like cadmium, mercury or lead and have only small quantities of nickel and arsenic. The quantities found were lower than those measured in common animal products [60]. Our results suggest that it is possible to consume these insect species harvested in Togo without additional risks compared to the most commonly consumed animal products. However, the European Food Safety Authority (EFSA), in its scientific opinion on the risk profile related to the production and consumption of insects for food and feed [61], points out that certain factors (like production methods, substrates used, insect species, and processing methods) may influence the potential presence of chemical contaminants. Indeed, depending on their growth stage, insects can accumulate anti-nutritional substances present in the environment or diet, like pesticides and heavy metals. However, there is limited quantitative or qualitative data on the accumulation of pesticides by insects. Some studies have shown that insects can bioaccumulate pesticides [18,62,63]. Several other studies have highlighted the presence of heavy metals in insects: lead and cadmium in crickets and silkworms in Canada [64], and lead, cadmium, and nickel in Acheta domesticus (Linnaeus, 1758) (Orthoptera: Gryllidae), T. molitor, Zophobas morio (Fabricius, 1776) (Coleoptera: Tenebrionidae), Schistocerca gregaria (Forsk, 1775) (Orthoptera: Caelifera) in the Czech Republic [65]. It is, therefore, clear that further studies are needed on O. monoceros and R. phoenicis collected from palm plantations in Togo to assess the impact of agricultural practices on the sanitary quality of different stages of O. monoceros and R. phoenicis. This study also has several notable limitations. Since the analyses were not conducted on a site-by-site basis, we were unable to perform statistical comparison tests to identify any variations in the composition of these species based on the growing environment. Another limitation of the study is the lack of detailed protein analysis (amino acid profiles) to assess the quality of the proteins contained in these Coleoptera.

5. Conclusions

Chemical analyses carried out on adult O. monoceros and R. phoenicis show that adults, like the larvae, are highly nutritionally valuable. They are an important source of macronutrients (proteins, lipids) and minerals (calcium, magnesium, phosphorus, potassium, sodium, iron, manganese, copper, zinc). The lipids of these two species are rich in unsaturated fatty acids, especially essential fatty acids; however, R. phoenicis adults appear to be more nutritious than O. monoceros adults, containing more proteins, minerals, and unsaturated fatty acids. The species are free of heavy metals, despite being harvested from agricultural plantations. The quantity and quality of the nutrients in these edible Coleopteran species can help to improve the nutritional quality of the human diet. In view of these nutritional benefits, the promotion of this traditional food resource deserves particular attention from national governments and development cooperation programs. The high protein, high-quality lipid, mineral, and energy content of these weevils and beetles could help combat protein-energy malnutrition and micronutrient deficiency in developing countries. Given their high nutritional value and sustainability, as they can feed on waste products in oil palm and coconut plantations, O. monoceros and R. phoenicis could be promoted as novel food sources.