Abstract
Adult (ADS) and larva stages of palm weevil Rhynchophorus phoenicis were analyzed for their nutritional potentials using proximate and mineral contents as indices. The early larva stage (ELS) contains the highest moisture content of 11.94% while ADS has the least value of 4.79%. The late larva stage (LLS) has the highest protein content of 10.51% while ADS contains 8.43%. Ash content is highest in ELS with a value of 2.37% and lowest in ADS with a value of 1.43%. ELS and LLS have the highest (22.14%) and lowest (17.22%) fibre contents respectively. The values of potassium, magnesium and iron in ELS were (455.00±21.21), (60.69±2.57) and (6.50±3.40) mg/kg while LLS recorded (457.50±10.61), (43.52±1.37) and (6.00±1.10) mg/kg and ADS recorded (372.50±24.75), (53.31±1.88) and (22.90±3.70) mg/kg. Chromium, phosphorus, nickel, calcium, lead, manganese and zinc were also detected. Copper was not detected in any of the samples. In all the developmental stages the protein solubilities were pH dependent with the minimum protein solubilities occurring at acidic pH while the maximum protein solubilities occurred at alkaline pH.
Keywords: Rhynchophorus phoenicis, Proximate composition, Mineral analysis, Solubility, Early larva, Late larva
INTRODUCTION
Members of the class insecta are important sources of food to many animal species including man (DeFoliart, 1992; Adedire and Aiyesanmi, 1999). Edible insects are important sources of high protein to rural dwellers and many city dwellers in Nigeria (Fasoranti and Ajiboye, 1993). Among the most important orders of insects consumed in Nigeria are Coleoptera, Hymenoptera, Isoptera, Lepidoptera, Odonata, Orthoptera and they are highly priced (Fasoranti and Ajiboye, 1993). Notable examples of these are the palm weevil, Rhynchophorus phoenicis, termites, Macrotermes nigeriense (queen, king and reproductives), Cirina forda, and variegated grasshopper, Zonocerus variegatus (Ashiru, 1988; Mercer, 1994; Adedire and Aiyesanmi, 1999). Rhynchophorus spp. are major pests of date palms, coconut palms, oil palms and sugarcane (Vidyasagar et al., 2000; Aldryhim and Al-Bukiri, 2003). Though they are very destructive, their nutritional potentials have endeared them to man. Another larval species which is highly cherished is the palm weevil, Rhynchophorus phoenicis which inhabits oil palms and coconut. Rhynchophorus phoenicis is a large insect, which usually measures over 25 mm in length and is found in wide geographical areas spanning many different climates such as Africa, Southern Asia, and Southern America (Kalshoven and Laan, 1981). The weevil is attracted to dying or damaged parts of palms, cut or split palm trunks and can also attack undamaged palms as well as decaying sugarcane.
This study determines the proximate composition, mineral potentials and the solubility potentials of the proteins of the palm weevil, R. phoenicis. The possibility of using R. phoenicis for domestic and industrial purposes is also discussed.
MATERIALS AND METHODS
Insect collection
Live larvae and adults (ADS) of palm weevil, R. phoenicis were purchased from the main jetty terminal market at Igbokoda, Ondo State, Nigeria. The larvae were classified into early and late larvae stages (ELS and LLS) based on head capsule measurement, weight, body length, body width and circumference (Table 1). The larvae and adults were killed, by asphyxiating them in a deep freezer for 48 h. The samples were dried separately in a Gallenkamp oven at 60 °C to a constant weight according to the procedures described by Adedire and Aiyesanmi (1999). The oil extracted during drying was put in a bottle and kept in the laboratory until required for analysis. The dried samples were pulverized with laboratory pestle and mortal and stored inside containers until required.
Table 1.
Dimensions of the larval and adult stages (ELS, LLS and ADS) of R. phoenicis used
| Sample | Weight (g) | Body length (cm) | Body width (cm) | Head region (cm) | Circumference (cm) |
| ELS | 2.59±0.14 | 2.54±0.04 | 0.77±0.04 | 0.65±0.04 | 3.07±0.06 |
| LLS | 8.14±0.14 | 4.61±0.06 | 2.05±0.04 | 1.10±0.01 | 5.47±0.08 |
| ADS | 6.98±0.13 | 5.70±0.04 | 1.59±0.02 | 2.88±0.05 | 4.49±0.04 |
Note: Each value is a mean±standard error
Proximate composition
The moisture content, ash and crude fat of the larvae and adults were determined by the methods of AOAC (1990). Crude protein was estimated by Kjeldahl method as described by Pearson (1976). Crude fibre was assayed by the method reported by Joslyn (1970). The nitrogen-free extract (i.e. the soluble carbohydrate) was calculated by difference. Each of these parameters was determined in triplicates.
Mineral content determination
The mineral components of R. phoenicis were determined using the method described by Oshodi (1992). The insects were ashed at 550 °C in a muffle furnace for hours. The ash content was dissolved in 10% HCl and made up with distilled water to 100 ml mark in a standard flask. Some of the minerals present such as magnesium, iron, manganese, potassium, calcium, zinc, chromium, copper, lead and nickel were analyzed by alpha 4 atomic absorption spectrophotometer. Sodium and potassium were estimated by Corning 405 flame photometer (AOAC, 1990). Phosphorus was analyzed by employing vanadomolybate method and absorption was read on CECIL CE 3041 colorimeter (AOAC, 1990). Three determinations were made for each treatment.
Determination of protein solubility
The methods described by Ige et al.(1984) and Oshodi and Ekperigin (1989) were used to determine the protein solubility of the samples. Two hundred milligrammes of each of the samples was dissolved in distilled water and the pH was adjusted to the desired value with 0.1 mol/L HCl/NaOH. The tubes containing the mixture were then centrifuged at 4 000 r/min and the protein content of the supernatant was determined using Biuret method. Determinations were done in triplicates.
Statistical analysis
All the experiments were conducted in triplicate. Data were subjected to Turkey test. Significance of mean differences was accepted at P≥0.05.
RESULTS AND DISCUSSION
Proximate analysis
The dimensions of the larvae and adult palm weevils used for this study are presented in Table 1. The proximate composition of the weevil is given in Table 2. The moisture content of the weevil ranged from 4.79% in ADS to 11.94% in ELS. The ELS contained more ash content (2.37%) than any other developmental stage while the adult had the least value of 1.43%. The crude fiber content was highest in ELS and lowest in LLS stage. The highest protein content of 10.51% occurred in LLS while ADS had the lowest value of 8.43%. The protein contents of ELS and LLS stages were significantly different (P≥0.05) from that of ADS. Fat is the major food component of R. phoenicis. The highest value of 62.13% occurred in LLS while ELS and ADS contained 61.45% and 52.40% respectively. The ELS stage had the lowest carbohydrate value of 4.93% while the highest value of 15.97% was obtained in ADS stage. The moisture contents of all the stages were lower than the values reported by Adedire and Aiyesanmi (1999) for Zonozerus variegatus [(35.07%±0.85%)~(53.26%±4.61%)] and Acheta domesticus (73%) by Pennino et al.(1991). However, the values observed in ELS and LLS stages were higher than the values reported for Anaphe venata (6.61%) by Ashiru (1988). Low moisture content is a desirable quality in food processing industries since low moisture contents reduces food spoilage. The ash content of the weevil indicated that the larval stages contain more minerals than the adult. The ash contents of the weevil are comparable with the values reported by Pennino et al.(1991) for Tenebrio molitor (2.5%) and Ashiru (1988) for A. venata (3.21%). The minerals in the samples can be particularly useful to pregnant and lactating women. The trend of fibre from ELS to ADS probably is an indication that fibre is converted to energy-rich substances during eclosion. The protein contents of all the developmental stages are higher than the value reported by Mercer (1994) for R. ferrugineus (6.10%), but compare favourably with the values reported for Acheta domesticus (10.3%) by Pennino et al.(1991). However, the value reported for Euxoa auxiliaries (24.40%) by White and Kendall (1993) is higher than the values reported for palm weevils. The highest values of insect protein have been reported for first instar stage (53.10%) and fourth instar stage of grasshoppers (52.50%) (Adedire and Aiyesanmi, 1999). The fat content of ADS stage compares with the value obtained in Gallena mellonella (56%) by Pennino et al.(1991). Fat is essential in the diets because it increases the palatability of foods by absorbing and retaining their flavours (Aiyesanmi and Oguntokun, 1996). Fat is also vital in the structural and biological functioning of cells. The carbohydrate contents of the weevil are lower than the value reported by Ajakaiye and Bawo (1990) for termites, Trinervitermes germinatus (19.47%~53.62%). The value of 4.93%±0.02% obtained for early larva compares favourably with the value reported for Colorado pandora (4.30%) by Fowler and Walter (1985).
Table 2.
Proximate composition of larval and adult stages of R. phoenicis
| Components | ELS (%) | LLS (%) | ADS (%) |
| Moisture | 11.94±0.20c | 8.40±0.10b | 4.79±0.26a |
| Ash | 2.37±0.15b | 2.33±0.23b | 1.43±0.40a |
| Crude fat | 61.45±0.41b | 62.13±1.80b | 52.40±0.96a |
| Crude fiber | 22.14±0.15b | 17.22±0.01a | 21.80±0.01b |
| Protein | 9.10±0.01b | 10.51±0.01c | 8.43±0.06a |
| Carbohydrate (by difference) | 4.93±0.02a | 7.82±0.01b | 15.97±0.03c |
Means followed by different letters in a row show significant difference P≥0.05 (Turkey’s test)
Mineral
Mineral analysis of the weevil showed that all the developmental stages have minerals such as chromium, manganese, magnesium, calcium, phosphorus, iron, zinc, nickel, sodium, potassium and lead (Table 3). Copper was not detected in any of the developmental stages. The ADS stage has the highest value of 22.90 mg/kg for iron. Phosphorus was highest in LLS (6.52 mg/kg) while nickel was highest in the ADS (0.70 mg/kg). The values of manganese in ELS and ADS compared favourably (0.49 mg/kg and 0.50 mg/kg respectively) while LLS recorded 0.30 mg/kg. All the developmental stages of palm weevil are very rich in minerals. The highest value of 457.50 mg/kg observed for potassium in LLS is lower than the values reported for all the instar stages of Z. variegatus which ranged between 637.86 mg/10 g and 1 117.67 mg/10 g (Adedire and Aiyesanmi, 1999). Magnesium and sodium recorded their highest values of 60.69 mg/kg and 17.00 mg/kg in ELS. The iron content of ADS is higher than the values reported for the third, fourth, fifth instar stages and the adult of Z. variegatus (Adedire and Aiyesanmi, 1999). The levels of minerals present in the samples indicate that they will be good sources of minerals for young, pregnant and lactating mothers. Daily requirements of essential minerals can be derived from the consumption of these weevils. Minerals are very essential for the normal development and functioning of the body systems of organisms.
Table 3.
Mineral composition (mg/kg) of larval and adult stages of R. phoenicis
| Elements | ELS | LLS | ADS |
| Na | 17.00±1.00 | 15.67±0.58 | 13.67±0.58 |
| K | 455.00±21.21 | 457.50±10.61 | 372.50±24.75 |
| Ca | 0.28±0.01 | 0.27±0.01 | 2.63±0.02 |
| Mg | 60.69±2.57 | 43.52±1.37 | 53.31±1.88 |
| Fe | 6.50±3.40 | 6.00±1.10 | 22.90±3.70 |
| P | 4.89±0.05 | 6.52±0.12 | 4.71±0.02 |
| Zn | 0.47±0.13 | 0.31±0.13 | 0.56±0.10 |
| Mn | 0.49±0.04 | 0.30±0.12 | 0.50±0.08 |
| Cr | 0.49±0.06 | 0.24±0.15 | 0.18±0.05 |
| Ni | 0.30±0.30 | 0.30±0.50 | 0.70±0.10 |
| Pb | 3.92±2.60 | 1.81±3.29 | 2.19±1.67 |
| Cu | ND | ND | ND |
Each value is a mean of three replicates±standard deviation; ND: Not detected
Solubility
The results of the effects of pH on protein solubility (Fig.1) showed that the highest solubility of ELS occurred at pH 11 while the least was observed at pH 3. In LLS the highest solubility was observed at pH 8 while the least value was observed at pH 2. In ADS the minimum and maximum protein solubility occurred at pH 2 and pH 10 respectively. In each of the developmental stages, there are three isoelectric points (ELS pH 3, 5, 7 and 10; LLS pH 2, 5 and 9; ADS pH 2, 5 and 8 respectively). The ELS has the highest solubility in alkaline media. As in the case of variegated grasshopper high solubility of ELS of R. phoenicis was recorded in this study (Olaofe et al., 1998). This same trend was observed in LLS and ADS stages. The isoelectric point values of LLS are pH 2, 5 and 9 while that of ADS are pH 2, 5 and 8. These isoelectric points are close to the values reported by Ige et al.(1984) for some Nigerian oil seeds (i.e. pH 6 and 8). The possession of 3 isoelectric points showed that each of the developmental stages of palm weevil has more than one major protein constituents.
Fig. 1.
Protein solubility curve of all the developmental stages of R. phoenicis
R. phoenicis is an essential source of different food components and nutrients. The knowledge of the protein solubility and the mineral content of this organism makes it an important food item which needs industrial application. The developmental stages of this weevil could be used in the preparation of animal feeds (e.g. poultry, goat, fish) and other feed formulations.
References
- 1.Adedire CO, Aiyesanmi AF. Proximate and mineral composition of the adult and immature forms of the variegated grasshopper, Zonocerus variegatus (L) (Acridoidea: Pygomorphidae) Bioscience Research Communications. 1999;11(2):121–126. [Google Scholar]
- 2.Aiyesanmi AF, Oguntokun MO. Nutrient composition of Dioclea reflexa seed—an underutilized edible legume. La Rivista Italiana Delle Sostanze Grasse. 1996;LXXIII:521–523. [Google Scholar]
- 3.Ajakaiye CO, Bawo A. Comparison of the chemical composition of Trinervitermes germinatus (Wasmann) with that of its feed. Nigerian Journal of Entomology. 1990;2:90–99. [Google Scholar]
- 4.Aldryhim Y, Al-Bukiri S. Effect of irrigation on within-grove distribution of red palm weevil Rhynchophorous ferrugineus . Sultan Qaboos University Journal for Scientific Research, Agricultural and Marine Sciences. 2003;8(1):47–49. [Google Scholar]
- 5.AOAC (Association of Official Analytical Chemists) Official Methods of Analysis. 15th Ed. Washington DC: Association of Official Analytical Chemists; 1990. [Google Scholar]
- 6.Ashiru MO. The food value of the larvae of Anaphe venata Butler. Ecol Food Nutrition. 1988;22:313–320. [Google Scholar]
- 7.DeFoliart GR. Insects as human food. Some nutritional and economic aspects. Crop Protection. 1992;11(5):395–399. doi: 10.1016/0261-2194(92)90020-6. [DOI] [Google Scholar]
- 8.Fasoranti JO, Ajiboye DO. Some edible insects of Kwara State, Nigeria. American Entomologist. 1993;39(2):113–116. [Google Scholar]
- 9.Fowler CS, Walter NP. Harvesting insects moth larvae with the Owens Valley Paiute. Journal California and Great Basin Anthropology. 1985;7(2):155–165. [Google Scholar]
- 10.Ige MM, Ogunsua AO, Oke OL. Functional properties of the proteins of some Nigerian oilseeds, conophor seeds and three varieties of melon seeds. Journal of Agricultural and Food Chemistry. 1984;32(4):822–825. doi: 10.1021/jf00124a031. [DOI] [Google Scholar]
- 11.Joslyn AM. Methods in Food Analysis. Physical, Chemical and Instrumental Methods of Analysis. 2nd Ed. San Francisco, New York: Academic Press; 1970. pp. 1–3. [Google Scholar]
- 12.Kalshoven LGE, Laan PAV. Pests of Crops in Indonesia. Jakarta: P.T. Ichtiar Van Hoeve; 1981. pp. 463–468. [Google Scholar]
- 13.Mercer CWL. Sago grub production in Labu swamp near Lae-Papua New Guinea. Klinkii Journal of Forestry Papua New Guinea. 1994;5(2):30–34. [Google Scholar]
- 14.Olaofe O, Arogundade LA, Adeyeye EI, Falusi OM. Composition and food properties of the variegated grasshopper, Zonocerus variegatus . Tropical Science. 1998;38:233–237. [Google Scholar]
- 15.Oshodi AA. Proximate composition, nutritionally valuable minerals and functional properties of Adenopus breviflorus benth seed flour and protein 9 concentrate. Food Chemistry. 1992;45(2):79–83. doi: 10.1016/0308-8146(92)90013-R. [DOI] [Google Scholar]
- 16.Oshodi AA, Ekperigin MN. Functional properties of pigeon pea (Cajanus cajan) flour. Food Chemistry. 1989;34(3):187–191. doi: 10.1016/0308-8146(89)90139-8. [DOI] [Google Scholar]
- 17.Pearson D. Chemical Analysis of Foods. 7th Ed. London: Churchill Livingstone; 1976. pp. 7–11. [Google Scholar]
- 18.Pennino M, Dierenfeld ES, Behler JL. Retinol, α-tocopheral and proximate nutrient composition of invertebrates used as feed. International Zoology Yearbook. 1991;30:143–149. [Google Scholar]
- 19.Vidyasagar PSPV, Hagi M, Abozuhairah RA, Al-Mohanna OE, Al-Saihati A. Impact of mass pheromone trapping on the red palm weevil: adult population and infested level in date palm Gardens of Saudi Arabia. The Planter. 2000;76:347–355. [Google Scholar]
- 20.White D, Kendall K. Grizzly bears and army cutworm moths in the alpine of Glacier National Park, Montana. International Bear News. 1993;2(3):2–3. [Google Scholar]