Comparative Analysis of Essential Oils Extracted from Local Plants and their Repellent Properties

Interest in exploring the alternatives to commercial mosquito repellents such as DEBT and Permethrin have been increasing due to the side effects in respect of health and envinronment. Essential oil from plants serves as a promising alternative due to non-toxic, sustainability and natural. However, not much studies have reported the utilization of local plants for the development of mosquito repellent. Therefore, a selection of indigenous plants that have the potential as mosquito repellent, namely Plectranthus amboinicus. Coleus scutellariodes, Amomum curtisii, and Melaleuca cajupaii have been extracted and characterised. For physical characterisation, moisture content, density measurement and dielectric properties of the leaves were measured. The moisture content of the samples were measured using the wet and dried basis measurement and Plectranthus amboinicus showed the highest moisture content, whilst Melaleuca cajupati recorded the lowest moisture content. Density of the samples were measured using Archimedes principle; the highest density recorded is Melaleuca cajupatiy whilst Plectranthus amboinicus recorded the lowest density. The dielectric properties of fresh and dried sample conditions were characterized using Vector Network Analyzer (VNA); all samples showed frequency-dependent behaviour. The dielectric constant, e' of fresh samples depicted higher values than that of dry samples. For fresh samples, Plectranthus amboinicus recorded the highest dielectric constant, e’ 50, whilst for dried condition, Melaleuca cajupati recorded the highest dielectric constant, e’ ~ 3.0. The essential oils from all plant materials were extracted using conventional steam distillation, modified kitchen microwave and microwave-assisted extraction methods. In terms of yield, conventional steam distillation method produced more essential oils compared to the microwave-assisted extraction whilst, no pure essential oils were extracted using modified kitchen microwave method. The identification of repellent compounds have been carried out for all extracted essential oils using gas chromatography mass spectrometry (GC-MS) and the number of repellent compounds found in microwave-assisted extraction which are 12 is greater than that of 9 found at conventional steam distillation method of all. Melaleuca cajupati exhibits the highest number in repellent compound and this is proven in the repellency assessment that has been performed using arm-in cage test and the number of mosquito landings and bites were recorded over 5 min for each treatment. Melaleuca cajupati exhibited the highest percentage in repellent protection with only 20 landings of mosquitoes with 87.85% for SD method and 88.46% for MAE method whilst, Plectranthus amboinicus recorded the the lowest percentage of protection with 74.69% for SD and 82.59% for MAE .

Minat untuk meneroka altematif kepada bahan perosak nyamuk komersial seperti DEBT dan Permethrin telah meningkat disebabkan kesan sampingan terhadap kesihatan dan alam sekitar. Minyak pati dari tumbnhan berfimgsi sebagai alternatif yang menjanjikan kerana tidak beracun, kelestarian, dan semulajadi. Walau bagaimanapim, tidak banyak kajian telah melaporkan penggunaan tumbuhan tempatan untuk pembangunan perosak nyamuk. Oleh itu, satu pilihan tumbuhan asli yang berpotensi sebagai perosak nyamuk, iaitu Plectmnthus amboinicus, Coleus scutellariodes, Amomum curtisii, dsn Melaleuca cajupati telah diekstrak dan dicirikan. Untuk pencirian fizikal, kandungan kelembapan, pengukuran ketumpatan, dan sifat dielektrik daun diukur. Kandungan kelembapan sampel diukur menggunakan pengukuran dasar basah dan kering dan Plectranthus amboinicus menunjukkan kandungan kelembapan tertinggi, manakala Melaleuca cajupati mencatatkan kandungan kelembapan terendah. Ketumpatan sampel diukur menggunakan prinsip Archimedes; ketumpatan tertinggi direkodkan adalah Melaleuca cajupati, manakala Plectranthus amboinicus mencatatkan ketumpatan terendah. Sifat dielektrik keadaan sampel segar dan kering dicirikan menggunakan Analisis Rangkaian Vektor (VNA); semua sampel menunjukkan tingkah laku bergantung pada frekuensi. Pemalar dielektrik, e’ bagi sampel segar menunjukkan nilai yang lebih tinggi daripada sampel kering. Bagi sampel segar, Plectranthus amboinicus mencatatkan pemalar dielektrik tertinggi, e’ 50, manakala untuk keadaan kering, Melaleuca cajupati mencatatkan pemalar dielektrik tertinggi, e’ ~ 3.0. Minyak pati dari semua bahan tumbuhan diekstrak menggunakan penyulingan stim konvensional, mikro gelombang mikro dapur yang diubah suai, dan kaedah ekstraksi bantuan mikro gelombang. Dari segi basil, kaedah penyulingan stim konvensional menghasilkan lebih banyak minyak pati berbanding dengan ekstraksi bantuan mikro gelombang manakala, tiada minyak pati tulen diekstrak menggunakan kaedah mikro gelombang mikro yang diubah suai. Pengenalan sebatian perosak telah dilakukan untuk semua minyak pati yang diekstrak menggunakan kromatografi gas spektrometri jisim (GC-MS) dan jumlah sebatian perosak yang ditemui dalam ekstraksi bantuan mikro gelombang yang adalah 12 adalah lebih besar daripada 9 yang ditemui pada kaedah penyulingan stim konvensional. Di antara semua, Melaleuca cajupati menunjukkan jumlah tertinggi dalam sebatian perosak dan ini terbukti dalam penilaian penolakan yang telah dilakukan menggunakan ujian kandang tangan dan jumlah pendaratan dan gigitan nyamuk direkodkan selama 5 minit untuk setiap rawatan. Melaleuca cajupati menunjukkan perlindungan penolakan tertinggi dengan hanya 20 pendaratan nyamuk dengan 87.85% untuk kaedah SD dan 88.46% untuk kaedah MAE manakala. Plectranthus amboinicus mencatatkan peratus perlindungan terendah dengan 74.69% untuk SD dan 82.59% untuk MAE.