Oils of insects and larvae consumed in Africa: potential sources of polyunsaturated fatty acids

1 Université de Dschang, Faculté des Sciences, Département de Biochimie, BP 67 Dschang, Cameroun <womeni@yahoo.fr> 2 ENSAIA-INPL, Laboratoire de Science et Génie Alimentaires, 2 avenue de la forêt de Haye, 54500, Vandoeuvre-les-Nancy cedex, France 3 CIRAD, UMR IATE, Laboratoire de Lipotechnie, TA 40/16, 73 rue JF Breton, 34398 Montpellier cedex 5, France Abstract: The objective of this paper is to present the beneficial aspects of some insects consumed in sub-Saharan Africa, based on examples of insects consumed in Cameroon, to present their potential as sources of lipids and essential fatty acids. In Africa, termites, larvae of raphia weevil, caterpillars, crickets, bees, maggots, butterflies, weevil, etc. are significant sources of food. These insects belong mainly to the orders of: Isoptera, Orthoptera, Dictyoptera, Coleoptera, Hymenoptera, Lepidoptera and Diptera. Depending on the species, insects are rich in proteins, minerals (K, Ca, Mg, Zn, P, Fe) and/or vitamins (thiamine/B1, riboflavine/B2, pyridoxine/B6, acid pantothenic, niacin). The composition of oils extracted from the following six insects consumed in Cameroon was investigated: larvaes of raphia weevil (Rhynchophorus phoenicis), crickets (Homorocoryphus nitidulus), grasshopper (Zonocerus variegates), termites (Macrotermes sp.), a variety of caterpillars (Imbrasia sp.) and an unidentified caterpillar from the forest (UI carterpillar). The extraction yields of oil were 53.75%, 67.25%, 9.12%, 49.35%, 24.44% and 20.17% respectively for raphia weevil larvae, crickets, devastating crickets, termites, Imbrasia and UI caterpillar. The oil from raphia weevil mainly contains 37.60% of palmitoleic acid and 45.46% of linoleic acid. The oil from crickets is principally made up of palmitoleic acid (27.59%), linoleic acid (45.63%) and α-linolenic acid (16.19%). The oil from grasshoppers is composed of palmitoleic acid (23.83%), oleic acid (10.71%), linoleic acid (21.07%), α-linolenic acid (14.76%) and γ-linolenic acid (22.54%). The main components of termite oil are: palmitic acid (30.47%), oleic acid (47.52%) and linoleic acid (8.79%). Palmitic acid (36.08%) and linolenic acid (38.01%) are the two dominant fatty acids of Imbrasia oil. As Imbrasia oil, UI caterpillar oil is composed of palmitic acid (30.80%) and linolenic acid (41.79%). Stearic acid (7.04%), oleic acid (8.56%) and linoleic acid (6.59%) are also present. These results show that these insects are considerable sources of fat. Their oils are rich in polyunsaturated fatty acids, of which essential fatty acids are linoleic and linolenic acids. The ratio PUFA/SFA, in the majority of cases is higher than 0.8, associated with desirable levels of cholesterol.


Introduction
Insects are known to constitute more than 76% of the animal kingdom [1]. There exist in Africa, more than 500 species of insects used as food by the indigenous population and play a significant role in the history of the nutrition. Several species are often considered as devastators of harvests (grasshoppers, weevil), whereas others (winged termites, raphia weevil larvae, caterpillars, crickets, bees, maggots, butter-flies…) are significant sources of food [2]. In many tropical countries, insects captured without control in nature, are consumed by the local populations or are used for other tools. The "palm weevil", various caterpillars, termites and many other insects serve as food of choice for man in several countries. Maggots are sometimes given to fowls or pigs in village breeding houses. In industrialized countries, besides the fact that insect chitin can significantly reduce serum cholesterol level, non-food uses of certain carnivore larvae of Diptera play an importance role in surgery [3]. Cultural practice of entomophagy dates centuries backward [4]. In developing countries, entomophagy is encouraged by the fact that animal proteins are expensive for the underprivileged populations and also due to the hypercholesterolemic effect of certain foodstuffs. Insects are valuable sources of proteins in certain regions of Zambia, where wild animals are rare [5]. A 10% increase worldwide of the protein mass via the entomophagy, would eliminate the problem of malnutrition and decrease the pressure exerted on the other sources of proteins [6]. In Nigeria, studies have showed that entomophagy contributed significantly to a reduction of protein deficiency [7][8][9]. Zambia and Nigeria, as well as other developing countries face nutritional problems due to the insufficiency of protein sources, carbohydrates, fatty acids and minerals salts. Moreover, the nutritional diseases such as; cardiovascular diseases, diabetes and obesity, related to the consumption of fat are become recurring in our countries. The fight against these plagues can be done by, assuring food safety (via the new sources of food) and by education of the population on the food products which they consume. It was proven in certain American and European countries that proteins and fats from insects have an effect on the reduction of cardiovascular and digestive diseases. This beneficial effect on health was associated to the hypocholesterolemic effect of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) contained in certain edible insects [10]. Unfortunately, these insects are not very often consumed for their beneficial effects. In Africa, insects are one of the immediate sources of fatty acids and proteins used to satisfy the elementary need. As a result, edible insects must be looked upon as alternative sources for the food problems faced in Africa. The objective of this paper is to give highlights on the nutritional aspects of insects consumed in sub-Saharan Africa, based on some examples of insects consumed in Cameroon, and to show their potential as a valuable source of lipids and essential fatty acids.
Insects consumed in sub-Saharan Africa and their place in the food safety Since time immemorial, insects have contributed significantly as food to many populations and cultures. Edible insects are very popular with the Indians of North America, in Mexico, as well as in many Asian and African cultures [4]. They are particularly important in Amazon, Congo basin and in South Africa, where they are regarded as a priceless source for the role they play in their tradition, medicine and diet [11]. Nowadays, insects are consumed like a daily supplement, an occasional dish or a substitute product during food shortages. The most consumed groups of insects are: Coleoptera (half being Cerambycidae and Scarabaeidae) [12], Lepidoptera (especially in the form of caterpillar or chrysalis) [12], Hymenoptera (majority being Meliponidae) [13], Orthoptera (especially Acrididae) [14][15][16][17] and some other groups which include termites (Isoptera), Hemiptera, etc. Certain species such as Edessa cordifera, Rhynchophorus phoenicis, Imbrasia ertli, Cirina forda, Anaphe sp., Gonimbrasia belina, Gynanisa maia, and the family of Notodomidae, Curculionidae, Saturniidae, etc., are besides largely preferred. Caterpillars and termites (winged adults) are the insects most consumed and marketed in Africa, but many other kinds or species are locally important, whether for economic reasons, ecological or nutritional. In South Africa, Pedis highly appreciate insect meals compared to other meals. During the harvest periods of caterpillars (Gonombrasia belina), beef sales experience a significant fall in demand [18]. An estimation in the 1960's indicated that more than 1600 tons of caterpillars of this species was collected each year, without taking into account the quantifies of caterpillars directly consumed by the caterpillar-collectors. Hundreds of tons, collected in South Africa and in Bostwana were marketed in Zambia and Zimbabwe. In Angola, Oliveira et al. [19] mentioned some consumed species, amongst which one termite (Macrotermes subhyalinus), a larva of Curculionidae living in palm trees (Rhynchophorus phoenicis) and a caterpillar (Usta terpsichore) were present. In Malawi, many species of insects are consumed, sometimes in a seasonal way. The consumption of caterpillars of Gonimbrasia belina and Gynanisa maia in the park of Kasungu, is made in mid-October to December, which is the period of the year with lowest food reserves. Moreover, authorization from the persons in charge of the park to harvest the caterpillars, contributes to maintenance of biodiversity. There is also consumption of the adults of a Diptera Chaoborus edulis in this same region. In Uganda, the larvae of many species of the larger beetles are sought and eaten but are not as important as termites and grasshoppers in the diet. Chaoborus spp., adult lake fly, cakes are eaten and are possibly an important source of protein in Uganda [20]. In Nigeria, entomophagy is largely widespread, but more common in the rural zones than in the urban zones. As in other regions, the most educated social class readily gives up entomophagy, considering it to belong to the past. As in other African countries, the caterpillars Cirina forda are highly appreciated, sold relatively to their weight and twice more expensive than the meat of beef [21]. Termites (Macrotermes bellicossus) are eaten in several parts of western Nigeria. The winged adults are usually caught while on their nuptial flight or collected from the ground after they have shed their wings and then roasted for eating. The variegated grasshopper (Zonocerus variegates) which has a large dry season population in southwestern Nigeria is reported eaten in Akoko area of Ondo State [9]. The larvae and pupae of honeybees (Apis mellifera) have very high protein content. Edible insects constitute an important part of the daily diet of a large proportion of the population in southwestern Nigeria. These insect provide high quality of proteins and supplements (minerals and vitamins) even when dried [22]. In the Democratic Republic of Congo, more than 65 species belonging to at least 22 different families are consumed. A study in 1961 [23] estimated that insects represent 10% of the origin of animal proteins. This proportion strongly varies according to regions, because it can reach 64% in certain regions. Another study in 1980 [14] listed 35 different species of caterpillars in the south of the country. Knowing the ecological needs of certain species, the inhabitants search for young caterpillars to install them on particular trees near their residence, where they feed and grow on these trees. In the Yansi community, the consumption of caterpillars is regarded as a law and that of meat like an exception [24]. In Republic of Congo, the consumption of caterpillars around Brazzaville was estimated [25] to 30 grams per day per person. In the markets, Othoptera and the larvae of Rhynchophorus phoenicis are found particularly common and sold at very high prices. In Zambia, the consumption of caterpillars is done during the rainy season (from November to February) and constitutes one of the princi-pal sources of proteins (more than 30% of the dry weights of the caterpillars). Mbunda distinguished 31 species of caterpillars, of which 7 are highly commercialised. Mbunda, Nkangala, Lucazi, Luvale, Cokwe and Yauma estimated that termites (adults of Macrotermes sp.) constituted the best foods, were more delicious than meat or fish and only some species of caterpillars could be compared to them [26]. In Madagascar, certain ethnic groups (18 ethnic groups) consume larvae of several insects. The most appreciated larva is that of Polists hebraeus, one local wasp. These larvae are collected in group together with the nest. Some larvae of Coleoptera (longicornes), an indigenous species Megopis mutica, an acclimatized species Batocera rufomaculata and possibly a species of charançon Aphiocephalus limbatus [27] which consume wood in decomposition are collected one by one in their natural habitats, and are consumed fried with butter alone or together with garlic and parsley. In Cameroon, There are at least nine species of edible caterpillars in the south of Cameroon, and perhaps two species of larvae. In contrast to caterpillars, the larvae are consumed by all the populations in the south of Cameroon. There are two types of insect larvae on raphia trees, that is; the big type with dark caramel colour coming from the rotted trunks of raphia, and the small type with clearly brown colour coming from raphia trees growing in marshy areas. These larvae are usually called "phos" in Ewondo language. The caterpillars are fried and added to a sauce (tomato, cassava leaves, etc.), which is accompanied by cassava bread, boiled cassava, or "macabo". Otherwise, the larvae can also be eaten without accompaniment. There exists little specific literature to this subject, apart from the work of Dunias [28] on "white worms of palm tree", which underlines the fact that, although this resource is known (particularly in the Basin of Congo and in Cameroon), its exploitation is not sufficiently considered [11]. Malaisse [29] gives a good outline of the nutritional values of the caterpillars and confirms empirical knowledge of the local populations in a scientific way. To give an idea on their nutritional value, the average proportion of proteins, fats and average energy value of 24 species of fresh caterpillars were analyzed (table 1). The proximate composition of 14 species of edible insects collected in south western Nigeria [22], show that twelve species have protein contents of 20.0% and above. R. phoenicis has the highest value of ether extract (31.40%) and the least value is found in O boas (table 2). Compared with beef or fish, the insects have a high protein and fat proportion, and are thus extremely energetic (table 3). The proteins of the insects tend to be relatively low in particular amino acids like methionine and cysteine, and contain many of other types, particularly lysine and threonine [30]. Moreover, chitin not being digestible makes the insects a source of bad quality proteins compared to food coming from vertebrate animals [31]. According to species, the caterpillars are rich in various minerals (K, Ca, Mg, Zn, P, Fe) and/or vitamins (thiamine/B1, riboflavine/B2, pyridoxine/B6, pantothenic acid, niacin) (table 4). Studies show that 100 g of cooked insects provide more than 100 percent of the body needs in vitamins and minerals [30]. Malaisse [29] revealed that the daily consumption of 50 g of dried caterpillars satisfies the human requirements for riboflavin and pantothenic acid, as well as 30% of niacin requirement. Because of their strong nutritional values in certain areas, the caterpillars are mixed with flour in order to prepare a pap to fight against the malnutrition of children. The species which are particularly rich in proteins (Imbrasia epimethea, Imbrasia dione, Antheua insignata), calcium (Tagoropsis flavinata) or iron (Cinabra hyperbius) are given to feeble people and to pregnant women with their breakfast. Several other species play a significant role in traditional medicines, as in the Chinese culture [32]. However, certain insects can secrete toxic substances coming from plants on which they feed or which they produce themsel-ves [33]. Often, these species have colours which indicate or draw attention in another manner and hence are not collected. Generally, because of the high protein content of insects, they can replace meat and fish in the majority of the usual recipes. They are eaten rather salted than sweetened. There are multiple manners of preparing and of cooking the insects. Its recipes are inspired from the majority of methods of preparation used in African and Eastern traditional societies' haven consumed or which still consume these insects. The protein value varies according to insects between 10% and 86%, and is 99% assimilable by the human organism.

Material and methods
The composition of oils extracted from the following six insects consumed in Cameroon was investigated: Raphia weevil (Rhynchophorus phoennicis); Crickets (Homorocoryphus nitidulus); Grasshopper (Zonocerus variegates); Termites (Macrotermes sp.); a variety of caterpillars Imbrasia and an unidentified caterpillar from the forest (UI carterpillar). Larvae of raphia tree weevil and Grasshopper were purchased from Mvog-mbi market of Yaounde (Center Cameroon). Crickets and termites were collected in Dschang (West Cameroon). Carterpillars (Imbrasia and an unidentified one), were purchased from a market in Sangmelima town (South Cameroon). The life samples were transported to the laboratory for confirmation of identity at the Department of Biology, University of Dschang, Menoua, Cameroon. The insect larvae were killed by freezing [34,35]. The frozen samples were then allowed to thaw at room temperature and dried in an oven at 50°C for 72 hrs. The dried samples were ground into powder using a pestle and mortar and kept or stored in air-tight containers until required for subsequent analysis. The oil in the sample was extracted in Soxhlet using hexane as solvent and the lipid value (crude fat) was evaluated. The oil extracted after drying was put in a bottle and kept in the refrigerator until required for analysis. The extracted fat was hydrolysed and the fatty acids converted to their methyl ester derivatives (FAME) using the method of test tubes [36]; while the GLC used was equipped with one  FAME ionization detector (FID 260°C) and connected to a Hewlett Packard, model 5890A Hitachi Ltd, Tokyo, Japan, used to determine fatty acid constituents and their concentrations. The stationary phase comprised of 10% SP 2300 silanized chromosorb (Supelco inc Belle fonte, pa/USA) packed in an omega Wax 320, 30 mm ID, 0,25 μm film glass column of length 5ft. The carrier gas (Helium) flowed at 2,5 cm/sec set at 200°C while injection, oven and column temperature was 250°C 1 mL automatically in Split mode. The fatty acid peaks were identified with respect to reference co-chromatographed authentic fame standards.
Results and discussion Table 5 shows the lipid value of the six insects and larva. The result shows that three of those insects and the larva are good sources of fat because; these values are equal or higher than 50% (Raphia weevil, Crickets and Termites). These crude fat contents are more than 50% greater than the lipid range of 1.5 to 31.40%, previously reported for various forms of lepidopterous coleopterous and Orthopterous edible insects from south western Nigeria [22] and are similar or fall within the lipid range of 4.2-77.2% previously reported for seventy eight forms of edible insects from the State of Oaxaca, Mexico [37,38] The caterpillars (Imbrasia or unidentified one) have lipid contents of about 20%, which is similar to the range mentioned by literature. Grasshopper has the smallest quantity of lipids. Some insects or their larvae are potential sources of lipids. The difference in lipid values between these insects or larvae and those cited in literature could be attributed to their differences in com-position, especially the fat contents and other calorigenic components of the larvae. These lipid contents are higher than the amount found in most conventional foods like beef, chicken, egg, Herring, Mackerel and milk [39], and are seen to contribute to its highly acceptable flavour when roasted or fried. Malnutrition in developing countries is as much or more, a problem of caloric deficiency [30]. The fat level implies that a 100 g sample of the larva will meet the caloric needs in most developing countries [40]. Apart from oil from termites, these oils are rich in polyunsaturated fatty acids. This value when compared to oils from most conventional sources is quite high. These oil contents were more than 35.5% and 29.6% reported for poultry and fish respectively, near or more greater than 52.0% and 44.1% reported for beef and pork respectively [41]. Saturated fatty acids found in the larva included lauric acid, myristic acid, palmitic acid; palmitoleic acid and stearic acid. They contain a high amount of polyunsaturated fatty acids, linolenic acid and linoleic acid. Palmitic acid as well as myristic acid have been demonstrated to raise low density lipoprotein (LDL) cholesterol and are therefore considered atherogenic [42]. However, stearic acid which constitutes nearly 2.35% of the saturated fatty acid in the larva has been shown not to raise plasma LDL cholesterol [43]. Oleic acid, a monounsaturated fatty acid, has been shown to be hypocholesterole-

Conclusion
Edible insects contribute to the diet of various populations of the world. In Africa more than 500 species of insects are used as food and some do have a significantly high food value. Some contain proteins as meat and fish while others are rich in fat and contain significant minerals and vitamins. Animal proteins being expensive for the underprivileged class, the hypercholesterolemic effects of certain foods and the scarcity of savage animals have significantly encouraged entomophagy. The fatty substances of insects had an effect on the reduction of cardiovascular and digestive diseases. Edible insects must be regarded as a potential alternative to improve food security. These results show that these insects are considerable sources of fat. Their oils are rich in polyunsaturated fatty acids, of which essential fatty acids are linoleic and linolenic acids. The ratio PUFA/SFA, in the majority of cases are higher than 0.8, associated with desirable levels of cholesterol, suggest that the insects have the potential of being used in the dietary management of certain coronary heart diseases. The consumption of these insects would compensate the insufficiency of essential fatty acids brought mainly by tropical vegetable oils.
Due to the fact that: oils from insects are rich in polyunsaturated fatty acids, they are more likely to undergo oxidation and since these insects are not consumed fresh, heat treatments during cooking of the insects must be accorded a lot of attention. Also, particular attention must be given to the effect of culinary treatments and conservation on the lipid profiles and the quality of proteins of the insects ( figure 1 et 2).