Virgin coconut oil (VCO) merupakan minyak yang dihasilkan dari buah kelapa tua yang segar, diolah tanpa perlakuan panas tinggi dan tanpa pemurnian kimiawi, sehingga tidak mengakibatkan perubahan pada sifat alami minyak. Selama penyimpanan atau penjualannya sering terjadi kerusakan yang ditandai oleh timbulnya bau dan flavor tengik. Hidrolisis dan oksidasi merupakan reaksi utama penyebab kerusakan minyak. Akan tetapi, kerusakan lemak dan minyak lebih banyak terjadi akibat oksidasi dibanding hidrolisis. Reaksi tersebut diinisiasi oleh oksigen singlet atau dikenal sebagai fotooksidasi. Penelitian ini bertujuan untuk menghambat kerusakan VCO karena reaksi fotooksidasi melalui aplikasi mikroemulsi air dalam minyak (w/o) sebagai sistem pembawa asam askorbat yang merupakan antioksidan hidrofilik. Tujuan khusus dari penelitian ini adalah (1) Memastikan penyebab penurunan mutu VCO, (2) Mendapatkan formula dan cara pembuatan mikroemulsi w/o yang stabil, mengetahui kemampuan mikroemulsi w/o untuk membawa asam askorbat, serta mengetahui stabilitasnya terhadap fotooksidasi, (3) Mengetahui efektivitas mikroemulsi asam askorbat dalam menghambat kerusakan VCO karena fotooksidasi, dan (4) Mengetahui karakteristik fisik, kimiawi, dan sensoris produk VCO yang mengandung mikroemulsi asam askorbat. Penelitian ini dilakukan dengan tahap-tahap sebagai berikut: Pada tahap pertama yang dirancang untuk mengevaluasi penurunan mutu VCO, maka dilakukan analisis secara sensoris, fisik, dan kimiawi terhadap VCO komersial yang dijual di Yogyakarta dengan menggunakan VCO yang baru dibuat sebagai pembanding (R). Untuk mengetahui penyebab penurunan mutu VCO, maka dilakukan evaluasi tentang pengaruh fotooksidasi selama proses produksi dan penyimpanan serta pengaruh hidrolisis selama penyimpanan. Pengujian fotooksidasi selama proses produksi dilakukan dengan kondisi yang dipercepat menggunakan paparan cahaya dengan intensitas tinggi (4000 lux) pada suhu kamar (30 ± 1 ºC) selama 8 jam. Setiap jam dilakukan analisis angka peroksida (PV) dan kandungan klorofil. Untuk mengevaluasi pengaruh fotooksidasi selama penyimpanan, dua set sampel VCO disimpan secara terpisah, yaitu dalam kondisi gelap atau dalam ruangan dengan intensitas cahaya normal (380-400 lux) selama 4 bulan. Setiap satu minggu dilakukan analisis PV. Sedangkan untuk mengevaluasi pengaruh hidrolisis selama penyimpanan, disiapkan dua perlakuan, yaitu VCO yang baru dibuat sebagai kontrol dan VCO yang telah diserap kandungan airnya menggunakan Na2SO4 anhydrous. Semua sampel disimpan pada suhu kamar selama 4 bulan, dan setiap 2 minggu dilakukan analisis PV dan kadar asam lemak bebas (FFA). Tahap ke dua dilakukan untuk memperoleh mikroemulsi w/o yang stabil sebagai pembawa asam askorbat. Mikroemulsi w/o yang stabil diformulasikan menggunakan konsep hydrophilic lipophilic balance (HLB) dengan campuran surfaktan nonionik yang mempunyai nilai HLB tinggi, sedang, dan rendah. Terhadap mikroemulsi tersebut dilakukan uji stabilitas yang meliputi sentrifugasi, pemanasan, dan penyimpanan pada suhu kamar. Selanjutnya, mikroemulsi w/o yang stabil diformulasikan sebagai pembawa asam askorbat dan dievaluasi kelarutan asam askorbat dalam mikroemulsi w/o dan stabilitas fotooksidatifnya. Tahap ke tiga dirancang untuk membandingkan efektivitas mikroemulsi asam askorbat dengan antioksidan sintetis serta mengetahui konstanta laju reaksi quenching-nya terhadap oksigen singlet. Untuk maksud tersebut, mikroemulsi asam askorbat didispersikan ke dalam VCO, sehingga konsentrasi asam askorbatnya adalah 50, 100, 150, 200, atau 250 ppm. Sebagai pembanding digunakan antioksidan lipofilik, yaitu askorbil palmitat, TBHQ, dan BHA yang dicampurkan ke dalam VCO pada konsentrasi yang sama. Semua sampel dipapar cahaya (4000 lux) selama 8 jam. Setiap jam dilakukan analisis PV, nilai panisidin, dan nilai TOTOX. Untuk mengetahui konstanta laju quenching-nya terhadap oksigen singlet digunakan persamaan kinetika steady-state dengan riboflavin sebagai sensitizer pada sistem asam linoleat dalam metanol. Tahap ke empat dilakukan untuk mengetahui karakteristik fisik, kimiawi, dan sensoris serta stabilitas fotooksidatif VCO yang mengandung mikroemulsi asam askorbat selama penyimpanan. Untuk maksud tersebut, VCO yang mengandung mikroemulsi asam askorbat dipapar cahaya (4000 lux) selama 3x5 jam, kemudian disimpan pada suhu kamar selama 2 bulan. Sebagai pembanding digunakan VCO tanpa mikroemulsi (kontrol) dan VCO yang mengandung mikroemulsi tanpa asam askorbat. Setelah penyimpanan 2 minggu dilakukan pengujian secara fisik, kimiawi, dan sensoris. Selanjutnya, pengujian secara fisik dan kimiawi dilakukan setiap 2 minggu. Hasil penelitian ini menunjukkan bahwa 10 dari 14 merk VCO komersial yang dijual di Yogyakarta telah mengalami kerusakan meskipun belum melewati tanggal kadaluwarsanya. Antioksidan alami yang terkandung dalam VCO tidak efektif menghambat fotooksidasi, sedangkan klorofil-a dalam VCO, meskipun hanya 0,098 ppm, efektif berperan sebagai sensitizer penyebab fotooksidasi yang menginisiasi kerusakan VCO. Penyimpanan VCO, pada intensitas cahaya relatif rendah (380-400 lux), menyebabkan kenaikan PV secara nyata setelah 10 minggu. Mikroemulsi w/o dapat diperoleh pada nilai HLB 7 dengan komposisi 16.6% Tween 20, 15.0% Span 20, and 68.4% Span 80. Mikroemulsi w/o hanya terbentuk pada rasio surfaktan terhadap air paling sedikit 4,5 dan rasio VCO terhadap air+surfaktan tidak lebih dari 3,5. Mikroemulsi tersebut tetap stabil selama disimpan pada suhu kamar. Kelarutan asam askorbat dalam mikroemulsi w/o maksimum 1%. Dibanding antioksidan lain (askorbil palmitat, TBHQ, dan BHA), mikroemulsi asam askorbat paling efektif menghambat fotooksidasi dengan laju quenching oksigen singlet 3,21x10 8 M -1 s -1 . VCO yang mengandung mikroemulsi asam askorbat mampunyai karakteristik fisik, kimiawi, dan sensoris yang tidak berbeda dibanding VCO kontrol. Hasil penelitian ini membuktikan bahwa mikroemulsi w/o efektif digunakan sebagai sistem pembawa antioksidan hidrofilik untuk menghambat penurunan mutu VCO, sehingga dapat diperoleh VCO dengan stabilitas oksidatif tinggi dan mempunyai karakteristik fisik, kimiawi, dan sensoris yang baik.

Virgin coconut oil (VCO) is oil that is obtained from the fresh, mature kernel of coconut, without use thermal treatment, without undergoing chemical refining and which does not lead to the alteration of the nature of the oil. During prolong storage or display at retailers, VCO may undergo quality deterioration which was indicated with the presence of rancid flavor and odor. Hydrolysis and oxidation are the two main reactions which could result in the deterioration of oils. However, oxidation is mostly responsible for much more of the deterioration of fats and oils than hydrolysis. This reaction was initiated by singlet oxygen or known as photooxidation. The objective of this study was to inhibit the VCO deterioration due to photooxidation by using water in oil (w/o) microemulsion as delivery system of ascorbic acid which was hydrophilic antioxidant. The main objectives were (1) To ascertain the probable cause of VCO quality deterioration, (2) To obtain the stable w/o microemulsion, to determine the ability of w/o microemulsion as ascorbic acid delivery system, and its photooxidation stability, (3) To determine the effectiveness of ascorbic acid microemulsion in inhibiting the VCO deterioration due to photooxidation, and (4) To determine the physical, chemical, and sensory characteristics of VCO product containing ascorbic acid microemulsion. This study was designed as follows: In the first step which was designed to evaluate the quality deterioration of VCO, the sensory, physical, and chemical analyses were determined on the commercial VCO brands marketed in Yogyakarta with using a freshly prepared VCO as a reference (R). In order to observe the probable cause of VCO quality deterioration, the effect of photooxidation during VCO production and storage, and the effect of hydrolysis during storage were evaluated. Photooxidation test during VCO production was performed under accelerated condition using fluorescent lights (4,000 lux) for up to 8 hours at room temperature (30 ± 1 ºC). Peroxide value (PV) and chlorophyll contents of the samples were measured at 1 hour interval. To evaluate the effect of photooxidation during storage, two sets of VCO samples were separately stored either in the dark in a cupboard or in a normal room light intensity (380–400 lux) for a period of 4 months. PV of the samples was measured weekly. To evaluate the effect of hydrolysis during storage, 2 treatments were prepared, i.e. the freshly prepared VCO as control treatment and the VCO which has already filtered using filter paper in the presence of anhydrous Na2SO4 to obtain the dry VCO. All samples were stored at room temperature for up to 4 months, and the PV and free fatty acid (FFA) content were measured at 2 weeks interval. The second step of this study was designed to obtain the stable w/o microemulsion which was used to include the ascorbic acid. The stable w/o microemulsions were formulated based on the hydrophilic lipophilic balance (HLB) concept by using ternary nonionic surfactants mixture having high, medium, and low HLB value. These w/o microemulsions were subjected to stability test which include centrifugation, heating treatment, and storage at room temperature. The stable w/o microemulsion were subsequently formulated to include ascorbic acid. The solubility and the photooxidative stability of ascorbic acid in w/o microemulsion were evaluated. The third step of this study was designed to compare the effectiveness of ascorbic acid microemulsion with synthetic antioxidants and to determine their singlet oxygen quenching rate constants. For this purposes, the ascorbic acid microemulsion was dispersed into the VCO so that it contained of 50, 100, 150, 200, or 250 ppm of ascorbic acid. The same levels of lipophilic AP, TBHQ, and BHA were mixed into the VCO and used as comparison. All of these samples were subsequently subjected to photooxidation under fluorescent light exposure (4,000 lux) for up to 8 hours. The PV, p-anisidine values, and TOTOX values of photooxidized VCO samples were measured at 1 hour interval. To determine the singlet oxygen quenching rate constant of that antioxidants, the steady-state kinetic approximation was used in riboflavin-sensitized photooxidation of linoleic acid in methanol. The fourth step of this study was designed to determine the physical, chemical, and sensory characteristics of VCO product containing ascorbic acid microemulsion and the photooxidative stability of that VCO during storage. For this purposes, the VCO containing ascorbic acid microemulsion was exposed to fluorescent light (4,000 lux) for 3x5 hours and then stored at room temperature for 2 months. VCO without microemulsion (control) and VCO containing microemulsion without ascorbic acid were used as comparison. After 2 weeks storage, the physical, chemical, and sensory characteristics were analyzed. Then, the physical and chemical characteristics were determined at 2 weeks interval. This study indicated that within the period before the expiration date, 10 out of 14 commercial VCO brands marketed in Yogyakarta fell short of the quality standards. Naturally present antioxidants in the VCO were not effective for inhibiting photooxidation, while the presence of 0.098 ppm chlorophyll-a effectively act as sensitizer that caused photooxidation which could initiate VCO deterioration. The storage of VCO, at relatively low light intensity (380-400 lux), significantly increased PV after 10 weeks. The stable w/o microemulsion could be obtained at the HLB value of 7 which composed of 16.6% of Tween 20, 15.0% of Span 20, and 68.4% of Span 80. The w/o microemulsion was only produced at the ratio of surfactants to water should be more than 4.5 and the ratio of VCO to water+surfactants was no more than 3.5. These microemulsions remained stable during storage at room temperature. The maximum solubility of ascorbic acid in w/o microemulsion was 1%. This ascorbic acid microemulsion was the most effective for inhibiting photooxidation as compared with synthetic antioxidants (ascorbyl palmitate, TBHQ, and BHA) with the singlet oxygen quenching rate constant was 3.21x10 8 M -1 s -1 . There was no significant different on the physical, chemical, and sensory characteristics between VCO containing ascorbic acid microemulsion and the freshly prepared VCO. This study confirmed that the w/o microemulsion effectively used as hydrophilic antioxidant delivery system for inhibiting the VCO quality deterioration. Thus, it could be obtained the highly oxidative stability of VCO with good characteristics in physical, chemical, and sensory.

Kata Kunci : Virgin Coconut Oil