Judul: Changes of Chlorogenic Acid, Caffeine, and Microbial Load during Kombucha Green Arabica Coffee (Coffea arabica) Fermentation
Abstrak: Kombucha adalah produk fermentasi dari teh menggunakan symbiotic culture of bacteria and yeast. Beberapa penelitian terkini telah mengembangkan potensi penggunaan seduhan kopi sebagai media kombucha. Penelitian ini bertujuan menganalisis perubahan kadar asam klorogenat, kafein, dan jumlah mikroba selama fermentasi kombucha kopi arabika hijau. Penelitian dilakukan melalui dua tahapan, yaitu penelitian pendahuluan dan penelitian utama. Penelitian pendahuluan dilakukan untuk menentukan kadar sukrosa terbaik dalam pembuatan kombucha kopi arabika hijau. Penelitian utama dilakukan untuk menganalisis perubahan kadar asam klorogenat, kafein, dan jumlah mikroba selama fermentasi kombucha kopi arabika hijau. Hasil penelitian pendahuluan menunjukkan bahwa kadar sukrosa terbaik untuk pembuatan kombucha kopi hijau adalah 100 g/L. Hasil penelitian utama menunjukkan bahwa selama fermentasi 18 hari, kadar asam klorogenat cenderung stabil pada kombucha kopi Cibulao atau menurun dari kisaran 146,61 – 184,60 µg/mL pada hari hari ke-0 menjadi 138,94 – 143,67 µg/mL pada hari ke-18 pada kombucha kopi Gayo dan Kahayya, sementara kadar kafein menurun signifikan dari 62,29 – 89,35 µg/mL pada hari hari ke-0 menjadi 39,20 – 55,69 µg/mL pada hari ke-18 pada seluruh sampel akibat fermentasi menggunakan kultur kombucha. Penurunan asam klorogenat dan kafein sejalan dengan penurunan pH dari kisaran 2,98 – 3,05 menjadi 2,49 – 2,56 setelah 18 hari fermentasi. Penurunan pH sejalan dengan peningkatan jumlah mikroba hingga hari ke-6, kemudian menurun hingga hari ke-18. Kombucha kopi arabika hijau memiliki potensi sebagai pangan fungsional karena kandungan asam klorogenat pada kopi hijau relatif dapat dipertahankan selama fermentasi kombucha., Kombucha is a fermented sweetened tea using symbiotic culture of bacteria and yeast. Several recent studies have developed the potency of using brewed coffee as kombucha medium. The research was aimed to analyze the changes of chlorogenic acid, caffeine, and microbial load during the fermentation of kombucha green arabica coffee beans. The research was conducted in two main steps, which are preliminary and main research. The preliminary research was conducted to determine the suitable sucrose content to produce arabica green coffee kombucha. The main research was conducted to analyze the changes of chlorogenic acid, caffeine and, total microbial load during kombucha green coffee beans fermentation. The preliminary research showed that the suitable sucrose content to produce kombucha green coffee beans was 100 g/L. The main research showed that during 18 days of fermentation, the chlorogenic acid content tended to be stable for Cibulao green coffee kombucha or decreased from range 146,61 – 184,60 µg/mL in day 0 to 138,94 – 143,67 µg/mL in day 18 for Gayo and Kahayya green coffee kombucha, while the caffeine content decreased significantly from 62,29 – 89,35 µg/mL in day 0 to 39,20- 55,69 µg/mL in day 18 for all samples due to fermentation using kombucha culture. The decreased contents of chlorogenic acid and caffeine were in line with the reduction of pH values, ranging from 2,98 – 3,05 to 2,49 – 2,56 after 18 days of fermentation. The reduction of pH value was in line with the increased microbial load until day 6, then decreased until day 18. Kombucha green arabica coffee has a potential as a functional food because the chlorogenic acid content in green coffee can be likely
Keyword: caffeine, chlorogenic acid, green arabica coffee bean, kombucha, microbial load

Judul: Antioxidant Activity of Kombucha from Ganoderma lucidum and Camellia sinensis (L.) Kuntze Substrates with Various Fermentation Times
Abstrak: Kombucha merupakan produk minuman fungsional hasil fermentasi bakteri dan ragi. Penelitian ini bertujuan menentukan formula dan waktu fermentasi terbaik dari kombucha dengan substrat G. lucidum dan teh hijau berdasarkan kandungan fenolik, flavonoid, dan aktivitas antioksidan optimum. Sampel simplisia G. lucidum dan teh hijau dibuat menjadi 5 formula dengan perbandingan 1:0, 3:1, 1:1, 1:3, 0:1. Berdasarkan metode DPPH dan ferric reducing power (FRP), formula yang memiliki aktivitas antioksidan tertinggi didapatkan pada kombucha teh hijau (F5), dengan persen inhibisi dan IC50 DPPH paling optimum (rata-rata H-0 hingga H-17 sebesar 92,05% dan 22,302 µL/mL) serta potensi daya reduksi paling kuat di antara formula lainnya (absorbansi 0,523 pada 700 nm). Kandungan fenolik dan flavonoid pada F5 mencapai 479,729 mg GAE/L kombucha dan 95,766 mg QE/L kombucha. Sementara itu, kombucha G. lucidum (F1) menghasilkan fenolik dan flavonoid yang lebih rendah (nilai optimum 100,407 mg GAE/L kombucha dan 18,564 mg QE/L kombucha). F1 juga menunjukkan aktivitas antioksidan yang rendah, dengan rata-rata nilai inhibisi 32,45% dan IC50 DPPH 78,530 µL/mL serta potensi daya reduksi yang lebih lemah (absorbansi 0,150 pada 700 nm). Adapun variasi waktu fermentasi hampir tidak mempengaruhi aktivitas antioksidan DPPH kombucha., Kombucha is a functional beverage produced by bacterial-yeast fermentation. This study aimed to determine the best formula and fermentation time of kombucha with G. lucidum and green tea substrates for phenolic, flavonoid, and antioxidant content. Samples of G. lucidum and green tea simplisia were made into 5 formulas with ratios of 1:0, 3:1, 1:1, 1:3, 0:1. Based on the DPPH and ferric reducing power (FRP) methods, the formula with the highest antioxidant activity was found to be green tea kombucha (F5), with the most optimal percent inhibition and IC50 DPPH values (D-0 to D-17 average is 92.05% and 22.302 µL/mL) and the strongest reducing power potential among other formulas (absorbance 0.523 at 700 nm). The phenolic and flavonoid contents in F5 reached 479.729 mg GAE/L kombucha and 95.766 mg QE/L kombucha. Meanwhile, G. lucidum kombucha (F1) produced lower phenolics and flavonoids (optimum value of 100.407 mg GAE/L kombucha and 18.564 mg QE/L kombucha). F1 also showed lower antioxidant activity, with an average inhibition value of 32.45% and IC50 DPPH 78.530 µL/mL and weaker reducing potential (absorbance 0.150 at 700 nm). The variation of fermentation time barely affected the DPPH antioxidant activity of kombucha.
Keyword: antioxidant, Camellia sinensis, Ganoderma lucidum, kombucha

Judul: The Solution of Nonlinear Volterra Integral Equation using Linearization Method.
Abstrak: Many natural phenomena can be explained by mathematical models. One of those models is in the form of Volterra integral equation, which is usually nonlinear. Analitically, a nonlinear form is difficult to solve. Therefore, this research is aimed to discuss solution of Volterra integral equation using linearization method. Linearization is done to nonlinear integrand with Taylor series expansion. According to this linearization, a numerical solution of Volterra integral equation is obtained using MATLAB 7.0.1 software. Validity of this method is tested by comparing the approximate with the exact solution. The result of this research shows that the numerical solution agree with the exact solution quite well.
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