CHAPTER ONE
INTRODUCTION
1.1 Background to the study
Plant essential oils (EOs) have been widely used for many years due to their antimicrobial properties in foods and pharmaceutical products 1. Essential oils are natural products obtained from plants. It is estimated that the global number of plants is of the order of 300,000 and about 10% of these contains essential oils and could be used as a source for their production 2. A large number of essential oils extracted from different families have been shown to have high repellence against arthropod species. Among the essential oil producing plants, such as Cymbopogon spp., Eucalyptus spp. and Ocimum spp. have been widely studied. Cymbopogon plants have been traditionally used to repel mosquitoes in jungle regions such as the Bolivian Amazon 3. Cymbopogon produces the most used natural repellents in the world 4. Many extracts and essential oils isolated from these plants have been tested against different kinds of arthropods. Cymbopogonexcavatus gave 100% repellence for 2 h, when it was evaluated in the laboratory against Anopheles arabiensis and its repellence decreased to 59.3% after 4 h 5.
Mosquito-borne diseases cause significant morbidity, mortality and economic burden to humankind 6. The mosquito, Aedesaegypti is the major vector of yellow fever, dengue and dengue hemorrhagic fever (DHF). These mosquito-borne infections are found in tropical and sub-tropical regions around the world, predominantly in urban areas and semi-urban areas. The global incidence of dengue has grown dramatically around the world in recent decades and there are approximately 2.5 billion people at risk 7. One of the methods available for the control of mosquitoes is the use of insecticides. In last two decades, the use of chemical insecticides in mosquito control method has resulted in instability of the environment, mosquito resistance, mosquito resurgences and toxic to nontarget organisms including natural enemies in the agriculture ecosystem 8. Hence, it has now become important to find an alternative means of mosquito control method, which can eliminate the use of chemical pesticides 9.
Mosquitoes play an important role in the spread of vector-borne diseases like malaria, dengue, chikungunya, filariasis and Japanese encephalitis which cause thousands of deaths per year 1. Mosquitoes are the most important and abundant pest in urban, sub- urban and rural environment. Although, chemical control provides quick mortality, resistance of mosquito against the use of insecticides have been widely reported. Moreover, chemical mosquito repellents contain toxic synthetic pyrethroids as active ingredients whose exposure to food and water is hazardous to health. In the present study, an attempt has been made to develop an eco-friendly mosquito repellent sprayed with lemon grass oil. It is an established fact and practice is that the natural mosquito repellent is more effective and keeps environment pleasant and eco-friendly. Raw materials have been selected based on experience and practice by ancestors. The formulation is safe, eco-friendly, cheap, easy to use and has maximum repellence against mosquitoes. In addition this, the mosquito repellent is less harmful to our health than the ones available in the market 10.
World Health Organization (WHO) estimates globally, shows that about 25 million people harbouring microfilaria and 19 million cases of people suffering from filarial disease manifestations were recorded in India 11, 12. The use of chemical insecticides to control mosquito population is fast and easy to use but mosquitoes are becoming resistant with continuous use. Alternatively, natural pesticides (especially from plants) can be used as a very good substitute. Aromatic plants and their essential oils are best sources of many active compounds for multipurpose uses. Plant-based phytochemicals having mosquitocidal properties are now recognized as potent alternative insecticides to replace synthetic insecticides 13.
Apart from the hazards caused by the use of established pesticides and insecticides to man and livestock, they are also very expensive to purchase; therefore, they are no more within the reach of many Nigerians. Moreover, chemical control technology is subject to the predicament of unstable foreign exchange. In the light of these shortcomings, it becomes inevitable to research into local sources of insecticides that would be cheap and readily available to individuals. Moreover treatment using medicines of natural origin is gaining momentum nowadays on account of increasing concern about potentially harmful synthetic additives 14.
Cymbopogon citrates, commonly known as lemon grass and other Cymbopogon species is a tall, coarse grass with a strong lemon taste. Lemon grass is a perennial herb widely cultivated in the tropics and sub-tropics, and it designates two different species; East Indian Cymbopognflexuosus (DC.) and West Indian, Cymbopogoncitratus 15. It is a tropical plant, grown as an ornamental in many temperate areas with maximum a height of about 1.8m and its leaves 1.9cm wide covered with a whitish bloom 16. Biologically active compounds derived from selected plants species such as Cymbopogon citrates, Ocimumgratissiumum, hyptissauveolen, Acarcia Arabica, Azadirachtaindica and Eleusiveindica have been commonly used in the past to control insects in many tropical counties 14, 16. The essential oils obtained from the leaves and stems of this plant are used as remedy for several health problems like fever, throat inflammations, ears or eyes a typical example is the use of the leaves in the Eastern Nigeria to treat various heart disorders 1.
Various herbal sources with mosquito repellent activities have been claimed in various traditional resources like Ayurveda 17. The stable fly Stomoxyscalcitrans L. and mosquitoes are among the most damaging arthropod pest of livestock worldwide, with a high economic impact on dairy and beef cattle production. Control of stable fly populations includes various methods, such as chemical control (pesticides and repellents), cultural control (sanitation), mechanical control (trapping devices), and biological control (parasitoids and entomopathogenic fungi) 17.
The rationale for carrying out this study was to contribute to the ever growing and increasing scientific database knowledge on traditional medicine and medicinal plants via the studying the mosquitocidal activities of Cymbopogon citrates, a traditional medicinal plant available worldwide.
1.2 Statement of the problem
A study conducted over a decade ago in 1996-97 estimated the demand for essential lemongrass and peanut oils for the year at 14,900 tons. The growth rates it estimated then was for domestic and export markets at 9 and 25% respectively. The demand and supply gap was then projected at 8,000 tons. It is difficult to guess the actual produce and supply.
What is perceived is that there is a good demand for essential oils.
This increasing demand of essential oil, mainly for commonly used essential oils such as lemongrass, peanut oil, have opened up wide opportunities for global repellent for mosquito disease. As mentioned earlier, essential oil is a volatile component. Therefore, it is vital to identify the best extraction technique, so that a higher yield of essential oil with good quality can be used as repellent of mosquito disease.
Using lemongrass and peanut oil as mosquito repellent is a more technique used to recover volatile components such as essential oils. In this method, plant material placed in a Clevenger apparatus is heated inside a microwave oven for a short period of time to extract the essential oil whereby heat is produced by microwave energy. The sample reaches its boiling point very rapidly, leading to a very short extraction or distillation time. With the microwave distillation technique, it is possible to achieve distillation with the indigenous water of the fresh plant material (Kürkçüoğlu and Baser, 2010). This method could support the current demand of essential oil and is believed to be able to close the gap between the current demand and production rate. Besides, it also found to be energy and cost saving “green” extraction method. It is advantageous over conventional method makes it to be an alternative extraction method in this field.
1.3 Objective of the study
The objective of the study is to investigate extraction of lemongrass and peanut oils to produce mosquito repellent. The specific objective are as follows:
1. To investigate the potential of for the extraction of essential oils from Lemongrass (Cymbopogoncitratus),
2. To compare chemical composition of the extracts with those of Lemongrass
3. To optimize the extraction of essential oils by applying Response Surface Methodology (RSMcitratu.
1.4 Significant of the study
The rationale of this proposed research project is to investigate the Extraction of lemongrass and peanut oils to produce mosquito repellent (Cymbopogoncitratus), and to compare the result with conventional hydrodistillation based on their extracted yield. The results of this research would be an advantageous technique over other extraction methods including for industrial applications.
There are various advantages of using Lemongrass and peanut oil method for this extraction purpose of mosquito repellent. Although the distillation was accomplished in a shorter time, an oil yield through this process is slightly higher compared to the conventional extraction method. This would go well to supply the ever increasing rate of demand for essential oil from lemongrass. This isshorter period of consumption for extraction leads to lower power consumption and this reduces the operating cost as well. Therefore, the essential oil extracted from this method is essentially pure and safe. These criteria are very important for essential oil such as lemongrass oil since they are mostly used for culinary and medicinal purposes.
1.5 Methodology
Procurement of Raw material: Cymbopogan citrates leaves would be harvested and collected freshly from a native farm in Ota, kaduna State, Nigeria. The leaves would be sorted to remove insects, variegated leaves and debris. They would then rinsed in water to remove dust particles after which they were allowed to air dry.
1.5.1 Material
All chemicals used are of analytical grade.
Sample preparations: The Lemon grass was separated from its stalks and air-dried at room temperature after which it was cut into smaller sizes in other to fit into the extraction chamber. Soxhlet extraction method was used for the extraction of essential oil from lemongrass; hexane and ethanol were conveniently used for this extraction process. Further analysis were done on the essential oil obtained using the GC-MS which was used to characterize the compositions and concentration of elements in the essential oil.
The extraction process: The already cut leaves were weighed and placed in the thimble. The thimble was inserted in the extraction chamber placed above a flask containing the solvent. A condensing unit is attached to this setup. As the solvent boils, vapour moves up into the condenser, condenses and flows into the thimble allowing for separation. The volatile compounds which have high affinity for the solvent get attached to it and it drops back into the flask below.
250 ml of each solvent was used throughout the course of the experiment. The mass of the leaf was varied for each of the solvent from 25 g to 30 g. At the end of the experiment, the extract was distilled. The evaporator embedded in this unit removes the solvent from the extract by evaporation leaving the essential oil.
