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"ABSTRAKShape Memory Polyurethane (SMPU) telah disintesis dari penambahan polyethylene glycol (PEG-6000) sebagai segmen lunak dan 4,4'-Methylenebis (Cyclohexyl isocyanate) (HMDI) sebagai segmen keras serta 1,1,1-Trimethylol propane (TMP) sebagai chain extender. SMPU lalu ditambahkan nanopartikel Fe3O4 berukuran 20-50 nm untuk meningkatkan sifat kemagnetan. Untuk mengkonfimasi bentuk ikatan antarmuka komposit SMPU digunakan FTIR (Fourier Transform Infrared Spectroscopy). FE-SEM digunakan untuk mengetahui interface dari filler dan matriks SMPU. Konfirmasi nilai kemagnetan menggunakan VSM (vibrating sampel magnetometer) dan pengujian tarik menggunakan microtensile menunjukkan bahwa penambahan Fe3O4 dengan persentase 11 wt% menghasilkan nilai kemagnetan dan sifat mekanik tertinggi.

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ABSTRACTShape Memory Polyurethane (SMPU) has been synthesized by reacting polyethylene glycol (PEG-6000) as softsegment, 4,4'-Methylenebis (Cyclohexyl isocyanate) (HMDI) as hardsegment and 1,1,1-Trimethylol propane (TMP) as chain extender. SMPU was added by Fe3O4 as filler to provide magnetical property. Magnetite which had confirmed by Scanning Elctron Magnetic (SEM) have size 20-50 nm. Functional group was investigated by FTIR (Fourier Transform Infrared Spectroscopy). The magnetic behavior of the nanocomposites was observed by vibrating sample margnetometer (VSM). FE-SEM is used to acknowledge interface between filler and Shape Memory Polyurethane (SMPU) matrix. Mechanical properties tested by microtensile testing showed adding 11% Fe3O4 obtaining magnetic and nanocomposites SMPU resulted in improved materials with higher magnetical and mechanical properties."

"Debu terbang (fly ash) merupakan limbah padat sisa pembakaran batu bara yang dapat digunakan untuk adsorben dalam penyerapan senyawa fosfat dalam sistem akuatik. Jumlah senyawa fosfat yang berlebih dalam sistem akuatik dapat menyebabkan eutrofikasi, sehingga diperlukan penanganan untuk menguranginya. Dalam penelitian ini, debu terbang dimodifikasi dengan metode hidrotermal membentuk zeolite, selanjutnya zeolite debu terbang tersebut dicampurkan dengan partikel magnetite (Fe3O4) membentuk sebuah adsorben magnetik. Adsorben yang disintesis dari debu terbang dimanfaatkan untuk mengadsorpsi senyawa fosfat dari sistem akuatik. Adsorpsi fosfat oleh adsorben debu terbang diamati dalam beberapa variasi, meliputi jumlah adsorben, pH, waktu kontak, dan konsentrasi analit. Hasil yang diperoleh dalam penelitian ini menunjukkan bahwa adsorben debu terbang termodifikasi magnetite memiliki kapasitas dan efisiensi adsorpsi terbaik dibanding adsorben lainnya. Kapasitas adsorpsi maksimum fosfat yang diserap oleh adsorben debu terbang termodifikasimencapai 2,24 mg P-PO4/g dengan % efisiensi adsorpsi sebesar 90,42%. Sedangkan, debu terbang tanpa modifikasi memiliki kapasitas adsorpsi tertinggi pada 2,0107 mg P-PO4/g dengan % efisiensi adsorpsi sebesar 80,51% dan kapasitas adsorpsi tertinggi zeolite debu terbang adalah 2,1851 mg -PO4/g dengan % efisiensi adsorpsi 88,28%. Kondisi optimum penyerapan fosfat diperoleh pada pH asam, yaitu pH 3 untuk adsorben setelah modifikasi sedangkan pH basa, yaitu pH 11 untuk adsorben debu terbang tanpa modifikasi. Penambahan partikel magnetite memudahkan pemisahan adsorben dengan supernatan dengan bantuan medan magnet.

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Fly ash is residue from coal combustion that can be used as adsorbent for phosphate compound from aquatic system. The abundance of phosphate compounds in aquatic system can lead into eutrophication, so the handling of this problem is needed. In this study, fly ash is modified with hydrothermal method to form a fly ash zeolite. The zeolite is mixed with magnetite (Fe3O4) to form a magnetic adsorbent. The adsorbent from fly ash will be used to adsorp phosphate from aquatic system. Phosphate adsorption from fly ash adsorbents observed in various parameters, such as adsorbent amount, pH, contact time, and initial phosphate concentration. The result from this study showed that fly ash modified with magnetite has the highest adsorption capacity and efficiency. The maximum phosphate adsorption capacity for the adsorbent reach 2.24 mg P-PO4/gand 90,42% for the % adsorption efficiency. Meanwhile, the adsorption capacity of unmodified fly ash is 2,0107 mg P-PO4/g with 80,51 for the %adsorption efficiency and the maximum adsorption capacity of fly ash zeolite is 2,1851 mg P-PO4/g with 88,28% for its % adsorption efficiency. The optimum pH condition for fly ash adsorbent after modifications are on pH 3 (acid) and the unmodified fly ash adsorbent is on pH 11 (alkaline). Magnetite particle addition eased the separation of adsorbent and supernatant using magnetic field. "

"Magnetite nanoparticles (Fe3O4) are a type of magnetic particle with huge potential for application as a drug carrier due to their excellent superparamagnetic, biocompatible, and easily modified surface properties. One characteristic of nanoparticles is that they can be controlled by studying the evolution of crystal growth. The purpose of this research is to study the evolution of magnetite-crystal growth and determine the crystal growth kinetics using the Ostwald ripening model. Magnetite nanoparticles were synthesized from FeCl3, citrate, urea, and polyethylene glycol using the hydrothermal method at 220oC for times ranging from 1–12 hours. The characterizations using X-ray diffraction (XRD) indicated that the magnetite began to form after 3 hours synthesis. The crystallinity and crystal size of the magnetite increased with the reaction time. The diameter size of the magnetite crystals was in the range of 10–29 nm. The characterizations using a transmission electron microscope (TEM) showed that magnetite nanoparticles had a relatively uniform size and were not agglomerated. The core-shell nanoparticles were obtained after 3 hours synthesis and had a diameter of 60 nm, whereas the irregular-shaped nanoparticles were obtained in 12 hours and had a diameter of 50 nm. The characterizations using a vibrating sample magnetometer (VSM) revealed that magnetite nanoparticles have superparamagnetic properties. The magnetization saturation (Ms) value was proportional to the degree of crystallinity. The magnetite-crystal growth data can be fitted to an Ostwald ripening model with the growth controlled by the dissolution of the surface reaction (n?4)."

"Fly ash merupakan limbah padat hasil pembakaran batubara yang dapat digunakan sebagai adsorben untuk penyerapan senyawa fosfat dalam sistem perairan. Jumlah senyawa fosfat yang berlebihan dalam sistem perairan dapat menyebabkan eutrofikasi, sehingga diperlukan penanganan untuk menguranginya. Pada penelitian ini, debu lalat dimodifikasi dengan metode hidrotermal menjadi zeolit, kemudian zeolit ​​debu lalat tersebut dicampur dengan partikel magnetit (Fe3O4) untuk membentuk adsorben magnetik. Adsorben yang disintesis dari debu lalat digunakan untuk mengadsorbsi senyawa fosfat dari sistem perairan. Adsorpsi fosfat oleh adsorben debu lalat diamati dalam beberapa variasi, antara lain jumlah adsorben, pH, waktu kontak, dan konsentrasi analit. Hasil yang diperoleh pada penelitian ini menunjukkan bahwa adsorben debu lalat modifikasi magnetit memiliki kapasitas dan efisiensi adsorpsi yang paling baik dibandingkan dengan adsorben lainnya. Kapasitas adsorpsi maksimum fosfat yang diserap oleh adsorben debu lalat modifikasi mencapai 2,24 mg P-PO4/g dengan efisiensi adsorpsi 90,42%. Sedangkan debu terbang yang tidak dimodifikasi memiliki kapasitas adsorpsi tertinggi pada 2.0107 mg P-PO4/g dengan % efisiensi adsorpsi 80,51% dan kapasitas adsorpsi tertinggi debu terbang zeolit ​​adalah 2,1851 mg P-PO4/g dengan % efisiensi adsorpsi. 88,28%. Kondisi optimum penyerapan fosfat diperoleh pada pH asam yaitu pH 3 untuk adsorben setelah modifikasi, sedangkan pH basa yaitu pH 11 untuk adsorben debu lalat tanpa modifikasi. Penambahan partikel magnetit memudahkan pemisahan adsorben dari supernatan dengan bantuan medan magnet.Fly ash is a solid waste from coal combustion that can be used as an adsorbent for the absorption of phosphate compounds in aquatic systems. Excessive amounts of phosphate compounds in aquatic systems can cause eutrophication, so treatment is needed to reduce it. In this study, fly dust was modified by hydrothermal method into zeolite, then the fly dust zeolite was mixed with magnetite (Fe3O4) particles to form a magnetic adsorbent. The adsorbent synthesized from fly dust is used to adsorb phosphate compounds from the aquatic system. Phosphate adsorption by fly dust adsorbent was observed in several variations, including the amount of adsorbent, pH, contact time, and analyte concentration. The results obtained in this study indicate that the magnetite modified fly dust adsorbent has the best adsorption capacity and efficiency compared to other adsorbents. The maximum adsorption capacity of phosphate absorbed by the modified fly dust adsorbent was 2.24 mg P-PO4/g with an adsorption efficiency of 90.42%. Meanwhile, the unmodified fly dust had the highest adsorption capacity at 2.0107 mg P-PO4/g with % adsorption efficiency of 80.51% and the highest adsorption capacity of zeolite fly dust was 2.1851 mg P-PO4/g with % adsorption efficiency. 88.28%. The optimum condition for phosphate absorption was obtained at an acidic pH, namely pH 3 for the adsorbent after modification, while the alkaline pH was pH 11 for the fly dust adsorbent without modification. The addition of magnetite particles facilitates the separation of the adsorbent from the supernatant with the help of a magnetic field."

"Ceramic magnets with the chemical composition of barium hexaferrite (BaFe12O19) were obtained through the synthesis of magnetite powder from iron sand taken from the Southern Coast of Yogyakarta in Indonesia. The iron sand was dissolved and then synthesized to produce magnetite powder. Subsequently, the magnetite powder was oxidized at temperatures of 700, 900, and 1100°C for five hours to produce hematite. The un-oxidized magnetite and the magnetite which was oxidized at the different temperatures were each mixed with barium carbonate, respectively. The mixtures were then calcined at 1100°C for two hours. The calcined products were compacted and then sintered at 1100°C for one hour to produce sintered ceramic magnets. X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), a scanning electron microscope (SEM) with an energy dispersive X-ray spectroscope (EDS), and thermogravimetry analysis (TGA) were used to characterize the ceramic magnets. The results showed the magnetite that was directly calcined, compacted, and sintered had a BaFe12O19 phase and also had the presence of a Fe2O3 phase with a BH(max) of 0.26 MGOe, Hc of 1.27 kOe, and Ms of 31.421 emu/g. The sintered ceramic magnet which was initially oxidized at a temperature of 900°C had a BaFe12O19 phase with a BH(max) of 0.78 MGOe, Hc of 1.95 kOe, and Ms of 46.970 emu/g. These results indicate satisfactory results as a permanent magnet. Thus, the iron sand from the Southern Coast of Yogyakarta in Indonesia has potential for the production of ceramic permanent magnets."

"Penelitian ini memiliki tujuan untuk mengetahui pengaruh penambahan sodium sulfat Na2SO4 pada proses reduksi pasir besi titan. Sampel yang digunakan merupakan pasir besi yang berasal dari daerah Sukabumi, Jawa Barat, serta menggunakan batu bara sebagai reduktor dan aditif sodium sulfat Na2SO4 yang menjadi parameter pada penelitian ini. Dari hasil pengujian XRD dan data analisa perhitungan semi-kuantitatif diperoleh peningkatan kadar senyawa titano-magnetit Fe2TiO4-Fe3O4 yang lebih tinggi setelah proses reduksi menggunakan aditif sodium sulfat Na2SO4. Dari data hasil perhitungan semi-kuantitatif untuk variasi penambahan sodium sulfat Na2SO4 sebesar 5, 15, dan 25 didapatkan bahwa pembahan sodium sulfat Na2SO4 memiliki nilai optimum pada penambahan 15 dengan jumlah senyawa titano-magnetit Fe2TiO4-Fe3O4 yang terbentuk sebesar 46,9.

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This study aims to determine the effect of sodium sulfate Na2SO4 addition on the reduction proses of tiania iron sand. The sample that used in this research are the iron sand that taken from Sukabumi, West Java, coal as reductor, and sodium sulfate Na2SO4 as additive and primary parameter. From the result of XRD characterization and semi quantitative analysis the content of titano magnetite Fe2TiO4 Fe3O4 in the iron sand increase with addition of sodium sulfate Na2SO4. Meanwhile, from semi quantitative analysis result with the variation of sodium sulfate Na2SO4 in 5, 15, and 25 have an optimum point on the addition of 15 sodium sulfate Na2SO4 with 46,9 of titano magnetite Fe2TiO4 Fe3O4 content."

"Enzim kolesterol oksidase merupakan enzim yang dapat membantu mempercepat reaksi oksidasi kolesterol. Salah satu pemanfaatan enzim kolesterol oksidase adalah biosensor kolesterol. Metode enzimatis lebih unggul karena memiliki spesifitas tinggi dan tidak berbahaya. Namun metode enzimatis memiliki kelemahan yaitu enzim yang mudah terdegradasi sehingga perlu dilakukan imobilisasi. Penambahan material imobilisasi dapat menambah biaya karena material imobilisasi yang terbilang cukup mahal, sehingga studi aktivitas material imobilisasi perlu dilakukan. Imobilisasi enzim kolesterol oksidase dilakukan pada material kitosan-magnetit. Penelitian ini dimulai dengan memproduksi enzim kolesterol oksidase dari Streptomyces sp., yang hasilnya kemudian akan diimobilisasi dan digunakan dalam reaksi oksidasi kolesterol. Penelitian ini dilakukan dengan variabel bebas yaitu konsentrasi enzim (0,5;1;2 mg/mL), konsentrasi substrat (0,75;1,25;2,5 mg/mL), waktu oksidasi (5,30,60,120,180 menit), serta bentuk enzim (ekstrak kasar enzim kolesterol oksidase dan enzim kolesterol oksidase terimobilisasi). Hasil uji oksidasi dikuantifikasi dengan menggunakan HPLC. Material imobilisasi akan dicuci dengan menggunakan buffer agar dapat digunakan kembali dalam proses imobilisasi. Dari penelitian dihasilkan konsentrasi substrat yang optimum adalah 2,5 mg/mL, konsentrasi enzim yang paling efektif adalah 2 mg/mL. Reaksi oksidasi kolesterol dengan kondisi optimum dapat mereduksi kolesterol sampai 10%. Sedangkan uji penggunaan kembali material kitosan-magnetit dalam proses imobilisasi menghasilkan bahwa material dapat digunakan kembali saat digunakan sebanyak 2 kali penggunaan.

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Cholesterol oxidase enzyme is an enzyme which can be the catalyst for cholesterol oxidation reaction. One of the cholesterol oxidase utilizations is cholesterol biosensor. Enzymatic method has more advantages which highly substrate specific, and non-toxic. However, the enzymatic method has some weakness which are easily-degraded and loss its activity which makes enzyme immobilization needs to be done. Immobilization can add additional cost because the material is expensive in average, so the material repeatability study is important. In this research, cholesterol oxidase enzyme will be immobilized in Chitosan-Magnetite. Novelty of this research is the usage of Chitosan-Magnetite material for cholesterol oxidase immobilization, and material repeatability test. This research started with enzyme production from Streptomyces sp., The enzyme will be immobilized and used for the cholesterol oxidation reaction. The independent variables of this research are enzyme concentration (0.5; 1; 2 mg/mL), substrate concentration (0.75; 1.25; 2.5 mg/mL), oxidation time (5; 30; 60; 120; 180 mg/mL), and enzyme forms (crude cholesterol oxidase and immobilized cholesterol oxidase). The immobilization material was washed with buffer, so it can be used in repetition. The research resulted the optimum substrate concentration in cholesterol enzymatic oxidation was 2.5 mg/mL, and enzyme optimum concentration was 2 mg/mL. With the optimum condition of cholesterol oxidation reaction, immobilized cholesterol oxidase can reduce substrate up to 10%. The repeatability study of the chitosan-magnetite material with 2 times repeatability test resulted the material can be used to immobilize cholesterol oxidase enzyme without losing its ability for immobilization."

"The abundance of graphite waste can be processed into valuable materials; one alternative is by making it into an adsorbent. Graphite-based adsorbent modification can be accomplished by adding magnetite nanoparticles Fe3O4. The addition of magnetite nanoparticles has been reported to improve the adsorption ability of the graphite waste. In this study, we have developed a new carbon dioxide (CO2) adsorbent based on graphite waste modified with magnetite nanoparticle Fe3O4. The Fe3O4 were prepared using an impregnation technique. The graphite/Fe3O4 composites were characterized by scanning electron microscopy with an energy-dispersive X-ray system (SEM-EDX) and Brunauer, Emmett, and Teller (BET). The CO2 adsorption performance was evaluated using an isothermal adsorption method at various temperatures (30, 35, and 45oC) and pressures (3, 5, 8, 15, and 20 bar). This resulted in graphite with different magnetite modification levels, namely non-modified graphite (GNM), a graphite/Fe3O4 20% (w/w) composite (G/Fe3O4 20%), and a graphite/Fe3O4 35% (w/w) (G/Fe3O4 35%), which indicated that the largest adsorption capacity is 10.305 mmol.g-1 at 30oC and 20 bar pressure for the G/Fe3O4 20% composite. This finding further revealed that modifying graphite waste with magnetite nanoparticles Fe3O4 has been proved to increase the capacity for adsorbing CO2 gas."

"Penelitian ini berhasil mensintesis nanokomposit karbon aktif dari limbah teh yang dimodifikasi dengan magnetit-ZnO untuk degradasi fotokatalisis zat warna Congo red. Karbon aktif (KALT) disintesis dengan suhu kalsinasi optimum pada 800 ⁰C memiliki luas permukaan besar. Nanopartikel ZnO dan Fe₃O₄ disintesis dengan metode hidrotermal dan kopresipitasi, masing-masing memiliki energi band gap 3,15 eV dan 1,58 eV dengan ukuran partikel 29,59 nm dan 14,51 nm. Gabungan nanokomposit ZnO/Fe₃O₄ memiliki energi band gap sekitar 1,74 eV. Sedangkan nanokomposit KALT/ZnO/Fe₃O₄ diperoleh ukuran partikel 23,47 nm dan energi band gap 1,74 eV. Optimasi degradasi menggunakan response surface methodology (RSM) menunjukkan efisiensi degradasi 99% dengan kondisi dosis 25 mg, konsentrasi Congo red 34 ppm, pH 4, dan waktu reaksi 95 menit di bawah sinar tampak. Studi kinetika mengikuti pseudo orde kedua (R² = 0,9780) dan persamaan laju reaksi v=k[CR]^2 dengan kontanta laju reaksi 0,02336 g.(mg.min)⁻ˡ. Berdasarkan hasil penelitian ini, pengembangan nanokomposit berbasis karbon aktif dari limbah teh dengan magnetit-ZnO efektif sebagai fotokatalis untuk pengolahan limbah zat warna yang berpotensi untuk katalis yang ramah lingkungan.

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This study successfully synthesized activated carbon from tea waste modified with magnetite-ZnO for photocatalytic degradation of Congo red dye. Activated carbon (KALT) synthesized with optimal calcination temperature at 800 ⁰C has large surface area. ZnO and Fe₃O₄ nanoparticles were synthesized by hydrothermal and coprecipitation methods, respectively, having energy band gap of 3.15 eV and 1.58 eV with particle sizes of 29.59 nm and 14.51 nm. The combined ZnO/Fe₃O₄ nanoparticles have a band gap energy of about 1.86. While the KALT/ZnO/Fe₃O₄ nanocomposite obtained a particle size of 23.47 nm and a band gap energy of 1.74 eV. Degradation optimization using response surface methodology (RSM) showed 99% degradation efficiency under the condition of 25 mg catalyst dosage, 34 ppm Congo red concentration, pH 4, and 95 min reaction time under visible light. The kinetics study followed the pseudo second order (R² = 0.9780) and the reaction rate equation v=k[CR]^2 with a reaction rate constant of 0.02336 g.(mg.min)⁻ˡ. Based on the results of this study, the development of nanocomposites based on activated carbon from tea waste with magnetite-ZnO is effective as a photocatalyst for dye waste treatment which has the potential for environmentally friendly catalysts.

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"Penelitian ini mencakup rangkaian oksidasi kolesterol berupa studi oksidasi kolesterol, oksidasi dengan menggunakan substrat hewani, oksidasi dengan enzim terimobilisasi material magnetit silikon dioksida (M-SiO2)/magnetit kitosan (M-Chit) dan oksidasi dengan protein rekombinan Rhodococcus erythropolis BL21(DE3) (RhoChoA). Enzim kolesterol oksidase yang diproduksi dengan metode submerged fermentation dari Streptomyces sp memiliki nilai aktivitas sebesar 5,12 U/mL dan aktivitas RhoChoA sebesar 17,9 U/mL. Studi kinetika dilakukan dengan menggunakan orde satu dengan reaksi irreversible. Optimasi produksi enzim dilakukan dengan memperhatikan faktor suhu dan jenis substrat. Untuk meningkatkan karakteristik enzim, imobilisasi dilakukan pada enzim kolesterol oksidase Streptomyces sp. Material magnetit disintesis dengan metode sol-gel dengan modifikasi menggunakan magnetit silikon dioksida dan magnetit kitosan yang diberi kode M-SiO2 dan M-Chit secara berurutan. Enzim hasil produksi diimobilisasi dengan menggunakan teknik cross-linking. Hasil karakterisasi FTIR dari material magnetit menunjukkan gugus fungsi M-O di bilangan gelombang 559,88; 598,91 dan 680,1 cm-1 , gugus Si-O di bilangan gelombang 1615,78 dan 1761,65 cm-1.Uji oksidasi dilakukan dengan beberapa variabel bebas yaitu konsentrasi enzim (0,5; 1; 2 mg/mL), konsentrasi substrat (0,75; 1,25; 2,5 mg/mL), waktu oksidasi (5, 30, 60, 120, 180 menit), serta bentuk enzim (ekstrak kasar enzim kolesterol oksidase dan enzim kolesterol oksidase terimobilisasi). Hasil uji oksidasi dikuantifikasi dengan menggunakan HPLC untuk menganalisis konsentrasi substrat dan konsentrasi enzim yang optimum dalam oksidasi yang dijadikan sebagai referensi dalam penentuan uji biosensor kolesterol. Oksidasi kolesterol dengan menggunakan substrat hewani dilakukan dengan ekstraksi dengan pelarut lemak. Kuantifikasi kadar kolesterol dalam sampel menunjukkan susbtrat dari lemak hewani memiliki konsentrasi kolesterol tertinggi dari kuning telur dengan konsentrasi 1,94 mg/mL, hati ayam (0,93 mg/mL), daging sapi (0,25 mg/mL) dan daging ayam (0,23 mg/mL). Enzim kolesterol oksidase dengan konsentrasi 2 mg/mL dapat mengoksidasi ekstrak kasar kolesterol dari kuning telur, hati ayam dan daging ayam hingga teroksidasi 20%, sedangkan ekstrak kasar kolesterol dari daging sapi teroksidasi sebesar 10%. Hasil uji oksidasi dengan menggunakan HPLC diperoleh konsentrasi substrat secara optimal dioksidasi oleh enzim terimobilisasi M-SiO2 dengan konsentrasi 20 mg/mL serta konsentrasi kolesterol 1,94 mM sebesar 90%, sedangkan enzim kolesterol oksidase bebas mengoksidasi kolesterol sebesar 80%. Uji oksidasi kolesterol menggunakan enzim kolesterol oksidase terimobilisasi magnetit kitosan (M-Chit) ditemukan konsentrasi substrat yang optimum adalah 2,5 mg/mL dan konsentrasi enzim yang paling efektif adalah 2 mg/mL. Reaksi oksidasi kolesterol dengan kondisi optimum dan menggunakan enzim terimobilisasi M-Chit dapat mengoksidasi kolesterol sampai 10%. Uji penggunaan kembali material M-Chit dalam proses imobilisasi dapat digunakan sebanyak 2 kali.

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This research includes a series of cholesterol oxidation in the form of cholesterol oxidation studies, oxidation using animal substrates, oxidation with immobilized enzymes of magnetite silicon dioxide (M-SiO2) / magnetite chitosan (M-Chit) and oxidation with recombinant protein Rhodococcus erythropolis BL21 (DE3) ( RhoChoA). Cholesterol oxidase enzyme produced by the submerged fermentation method from Streptomyces sp has an activity value of 5.12 U / mL and a RhoChoA activity of 17.9 U / mL. The kinetic study was carried out using first order with an irreversible reaction. Optimization of enzyme production is carried out by controlling the temperatur and type of substrate. To improve the characteristics of the enzyme, immobilization was carried out on the cholesterol oxidase enzyme Streptomyces sp. The magnetite material was synthesized by the sol-gel method with modification using magnetite silicon dioxide and magnetite chitosan which were coded M-SiO2 and M-Chit, respectively. The immobilized enzymes are produced using a cross-linking technique. The FTIR characterization results of the magnetite material showed the M-O functional group at wave number 559.88; 598.91 and 680.1 cm-1, the Si-O group at wave numbers 1615.78 and 1761.65 cm-1.

The oxidation test was carried out with several independent variables, namely enzyme concentration (0.5; 1; 2 mg / mL), substrate concentration (0.75; 1.25; 2.5 mg / mL), oxidation time (5, 30, 60, 120, 180 minutes), as well as the form of the enzyme (crude extract of the cholesterol oxidase enzyme and the immobilized cholesterol oxidase enzyme). The results of the oxidation test were quantified using HPLC to analyze the optimum substrate concentration and enzyme concentration in oxidation which were used as references in determining the cholesterol biosensor test. Cholesterol oxidation using animal substrates was carried out by extraction with fat solvents. The quantification of cholesterol levels in the sample showed that the animal fat substrate had the highest cholesterol concentration from egg yolks with a concentration of 1.94 mg / mL, chicken liver (0.93 mg / mL), beef (0.25 mg / mL) and chicken meat. (0.23 mg / mL). Cholesterol oxidase enzyme with a concentration of 2 mg / mL can oxidize the crude extract of cholesterol from egg yolk, chicken liver and chicken meat up to 20%, while the crude extract of cholesterol from beef is oxidized only 10%. The results of the oxidation test using HPLC showed that the optimal substrate concentration was oxidized by the immobilized enzyme M-SiO2 with a concentration of 20 mg / mL and a cholesterol concentration of 1.94 mM of 90%, while the free cholesterol oxidase enzyme was 80% oxidized. Cholesterol oxidation test using immobilized cholesterol oxidase enzyme magnetite chitosan (M-Chit) found that the optimum substrate concentration was 2.5 mg / mL and the most effective enzyme concentration was 2 mg / mL. Cholesterol oxidation reaction under optimum conditions and using the immobilized enzyme M-Chit can oxidize cholesterol up to 10%. The M-Chit reuse test in the immobilization process can be used 2 times"