In order to study the effect of solvent type, two different solvents (n-hexane and petroleum ether) were independently used. Grounded larvae (5 g) were placed in a 250 cm³ laboratory Soxhlet apparatus made in a porous cellulose thimble (Figure 1). Oil was extracted by repeated percolation using the above two organic solvents as described by Adejumo et al. [23] .

Twelve extraction experiments were performed to evaluate the impact of extraction time and solvent volume on extraction yield. The parameters of extraction time and solvent volume were varied based on the experimental design presented in Table 1.

After the extraction, the flask containing the solvent and oil mixture was removed, and the solvent was evaporated. The extracted oil was then dried at 100˚C for 60 minutes in an oven to eliminate any remaining solvent residue. The mass

of the dried oil was measured, and the oil extraction yield was calculated using Equation (1).

Formula (1).

O y = W b − W a W b (1)

where:

O_y = oil yield %;

W_b = weight before extraction;

W_a = Weight after extraction.

Fatty acid profiles of WPL oil were performed in the Biochemistry Laboratory, Friedrich Alexander University of Erlangen-Nuremberg, Germany using gaz chromatography method according to the procedure of AOAC, (2000) as described by Jayanegara et al. [24] .

a) Acid Index

The acid index was measured by titration with potassium hydroxide (ASTM D-664) as described by Asmare and Gabbiye [25] . For acid index determination, the oil samples were titrated in triplicate using 0.5 g ± 0.1 g in a 125 ml Erlenmeyer. Then 10.0 mL of ethanol and ethyl ether (1:1 mixture (v/v) and phenolphthalein drops (0.1% in ethanol) as the indicator were added. The titration was performed with an aqueous solution of KOH (0.01 mol∙L⁻¹), properly standardized with a solution of potassium biphthalate. The volume 𝑉₀ of KOH used was noted at the end of the titration and the acid index was calculated using equation 2:

I a = V 1 − V 0 m × 56.1 × T (2)

b) Iodine Number

The Iodine Number (IN) was measured according to ASTM D664, NFT60-204 standard. For iodine number determination, approximately 0.5 g of WP larval oil was placed in a 250 ml conical flask. Cyclohexane: glacial acetic acid (1:1 V/V) (20 ml) and 10 ml of Wijs reagent solution were added into the flask. The entire solution was thoroughly mixed and kept in the dark for an hour. About 15 and 100 ml of 15% Potassium iodide (KI) and distilled water were added to the flask and the solution was titrated against 0.1 M sodium thiosulphate (Na₂S₂O₃) solution to a colorless end point using starch as an indicator. The IV was calculated using Equation (3.3).

Iodine Value g∙I₂∙g⁻¹⁰⁰ oil = B ∗ S ∗ M ∗ 126.9 ∗ 100 W g ∗ 1000 (3)

where B = volume 0.1 M sodium thiosulphate used in titrating the blank, S = volume of 0.1 M sodium thiosulphate used in titrating the sample, 126.9 = molar mass of iodine, M = Molarity of sodium thiosulphate, W = sample weight in gram.

c) Saponification Value

The saponification number was determined according to Ogbunuga et al., [26] . White palm larvae (WPL) oil weighing 5 g was placed in a flask and 50 ml of 1.0 M ethanolic potassium hydroxide (KOH) was added. The flask was connected to a reflux condenser and was refluxed for 1 h until the solution became clear. A blank sample containing only 50 ml ethanolic potassium hydroxide was similarly treated as the sample. The solution was then titrated to a faint pink color endpoint against 1.0 M hydrochloric acid (HCl) using a phenolphthalein indicator. The saponification value (SV) was calculated using Equation (3.5):

SV (mg∙KOH∙g⁻¹) oil = ( A − B ) ∗ N ∗ 56.02 W (4)

where A = Blank ethanolic HCl volume in ml, B = sample ethanolic HCl volume in ml, N = Normality of HCl, W = Weight of sample/oil in grams.

Physical characteristics of white palm larvae such as cetane number (CN) and calorific value (CV) were determined. The cetane number was determined by applying Equation (5), as proposed by Molla and Nigus [27] , which relies on an empirical formula incorporating the saponification value and the iodine number.

C N = 46.3 + ( 5458 ∗ S V ) − ( 0.225 ∗ I N ) (5)

where CN: Cetane number;

SV: Saponification number;

IN: iodine number.

Calorific Value (CV), which represents the quantity of heat released by the complete combustion of biofuel, was calculated from Equation (6) [28] .

C V = 49.43 − ( 0.04 ∗ S V ) − ( 0.015 ∗ I N ) (6)

where CV: calorific value (MJ/Kg);

SV: Saponification number;

IN: iodine number.

The solvent type had a significant impact on the acid value, as shown in Table 4 (p < 0.05). The highest acid value was observed in petroleum extracted oil, with a measurement of 4.90 mg KOH/g. The acid value of the HEO (Hexane Extracted Oil) used in this study was similar to the value of 4.37 mg KOH/g reported for R. phoenicis larvae oil [39] , but higher than the values of 0.4 mg KOH/g for Moringa stenopetala seed crude oil [31] and 0.53 mg KOH/g for jatropha oil [21] . However, the acid value in this study is lower than the value of 51.81 mg KOH/g reported by Atabani and colleagues [15] for WPL oil extract obtained with a mechanical press. This difference could be attributed to the fact that oil extracted with organic solvents tends to have a lower acid value compared to oil obtained through mechanical extraction [40] .

The influence of solvent type on the iodine value is evident from the data presented in Table 4. The iodine value was significantly affected by the choice of solvent (p < 0.05). Specifically, the use of hexane solvent resulted in the highest iodine value of 3.02 g/100 g, whereas petroleum ether yielded a lower value of 2.05 g/100 g. The iodine value is a measure of unsaturation and serves as an indicator of the amount of double bonds present in the oil, which is related to its susceptibility to oxidation. This finding is consistent with previous research conducted by Lesten and Kingsley [30] , who also reported a difference in iodine values between hexane-extracted oil and petroleum-extracted oil from pumpkin seeds. Furthermore, the iodine values obtained in this study were lower than those reported by Tangka et al. [14] , who extracted Rhynchophorus phoenicis oil using a mechanical press and obtained a value of 36.83 g/100 g. This difference can be attributed to the lower level of double bonding (polyunsaturated acid value of 8.85%) found in the fatty acid composition of the WPL oil in our study.

When R. phoenicis was extracted with hexane solvent instead of petroleum ether, the cetane number and colorific value increased (Table 4). The cetane number of WPL oil was higher than that of conventional diesel (50) and rapeseed vegetable (39) oil, [41] but lower than that of WPL mechanically extracted oil. This difference can be attributed to the high concentration of unsaturated fatty acids in the WPL oils obtained in this study. Oils with a higher content of saturated fatty acids have a higher cetane number and are more likely to self-ignite under compression [42] .