Judul: Total Fenolik, Total Flavonoid, dan Aktivitas Antioksidan Ekstrak Teh Hijau, Teh Hitam, dan Teh Putih Kombucha
Abstrak: Kombucha tea is a fermented drink made from tea containing sugar by kombucha culture or SCOBY (Symbiosis Culture of Bacteria and Yeast). Total phenolic, total flavonoid and antioxidant activity tests were carried out to analyze and compare the antioxidant ability of kombucha made from green, black, and white tea to ward off free radicals. Samples were made into four types of kombucha, consisting of control kombucha (without tea), as well as green tea, black tea, and white tea kombucha. The highest antioxidant activity carried out using the DPPH method was obtained by black tea kombucha with percent inhibition and IC50 values of 88,29 ± 2,20% and 30,84 ± 1,34 μL/ml, respectively. Black tea kombucha also had the highest total phenolics and total flavonoids of 921,28 ± 38,08 mg GAE/L kombucha and 421,82 ± 24,05 mg QE/L kombucha respectively. The correlation results showed total phenolics and total flavonoids are directly proportional to the percent inhibition and inversely proportional to the IC50 value in kombucha. The characteristics of kombucha include pH and density which decrease after fermentation., Teh kombucha merupakan minuman fermentasi dari cairan teh yang mengandung gula oleh kultur kombucha atau SCOBY (Symbiosis Culture of Bacteria and Yeast). Uji total fenolik, total flavonoid, dan aktivitas antioksidan dilakukan untuk menganalisis dan membandingkan kemampuan antioksidan pada kombucha yang berasal dari teh hijau, teh hitam, dan teh putih dalam menangkal radikal bebas. Sampel dibuat menjadi empat jenis kombucha, terdiri dari kombucha kontrol (tanpa teh), serta teh hijau, teh hitam, dan teh putih kombucha. Aktivitas antioksidan tertinggi yang dilakukan dengan metode DPPH didapatkan oleh teh hitam kombucha dengan persen inhibisi dan nilai IC50 masing-masing sebesar 88,29 ± 2,20% dan 30,84 ± 1,34 μL/ml. Teh hitam kombucha juga memiliki total fenolik dan total flavonoid tertinggi masing-masing sebesar 921,28 ± 38,08 mg GAE/L kombucha dan 421,82 ± 24,05 mg QE/L kombucha. Hasil korelasi menunjukkan total fenolik dan total fenolik berbanding lurus dengan persen inhibisi dan berbanding terbalik dengan nilai IC50 pada kombucha. Adapun karakteristik kombucha berupa pH dan massa jenis yang berkurang setelah fermentasi.
Keyword: Antioxidant, Black tea, Green tea, Kombucha, White tea

Judul: Aktivitas Antioksidan Kombucha Camellia sinensis (L.) Kuntze dengan Variasi Konsentrasi Sukrosa.
Abstrak: Kombucha merupakan minuman fungsional hasil fermentasi teh dengan kandungan antioksidan yang memiliki kemampuan dalam menghambat radikal bebas pemicu penyakit degeneratif. Penelitian ini bertujuan menentukan konsentrasi sukrosa terbaik untuk menghasilkan minuman kombucha dengan kandungan fenolik, flavonoid dan aktivitas antioksidan optimum. Kombucha pada penelitian ini dibuat menjadi 5 formula dengan konsentrasi sukrosa 0%;5%;7,5%;10%;12,5% dan 15% dengan waktu fermentasi 8 hari. Baby SCOBY hasil fermentasi kombucha memiliki kandungan air sebesar 81-95%. Kombucha F4 dengan konsentrasi sukrosa 10% memiliki kandungan total fenolik dan flavonoid paling optimum mencapai 1152,12 ± 7,93 mg GAE/100 mL dan 554,09 ± 8,70 mg QE/100 mL kombucha. Aktivitas antioksidan kombucha yang diuji melalui metode DPPH, AEAC dan Ferric Reducing Power (FRP) menunjukkan kombucha dengan konsentrasi sukrosa 10% juga memiliki aktivitas antioksidan optimum dengan nilai IC50 sebesar 22,01 ± 0,31 µL/mL, kapasitas antioksidan setara dengan 440,57 ± 4,63 mg asam askorbat, serta potensi daya reduksinya yang paling kuat diantara formula lainnya sebesar 2466,43 ± 36,89 mg AAE/100 mL. Hasil analisis menunjukkan adanya pengaruh konsentrasi sukrosa terhadap kadar air baby SCOBY, kandungan total fenolik, flavonoid dan aktivitas antioksidan kombucha (p<0,05)., Kombucha is a functional beverage resulting from fermented tea containing antioxidants which have the ability to inhibit free radicals that trigger degenerative diseases. This research aimed to determine the best sucrose concentration to produce kombucha drinks with optimum phenolic, flavonoid and antioxidant activity content. Kombucha in this study was made into 5 formulas with sucrose concentrations of 0%; 5%; 7,5%; 10%; 12,5% and 15% with a fermentation time of 8 days. Baby SCOBY fermented kombucha has a water content of 81-95%. Kombucha F4 with a sucrose concentration of 10% had the optimum total phenolic and flavonoid content reaching 1152,12 ± 7,93 mg GAE/100 mL and 554,09 ± 8,70 mg QE/100 mL kombucha. The antioxidant activity of kombucha tested using teh DPPH, AEAC and Ferric Reducing Power (FRP) methods showed that kombucha with a sucrose concentration of 10% also had optimum antioxidant activity with an IC50 value of 22,01 ± 0,31 µL/mL with an antioxidant capacity equivalent to 440,57 ± 4,63 mg of ascorbic acid, and the potential for the strongest reduction power among other formulas, amounting to 2466,43 ± 36,89 mg AA/100 mL). The results of the analysis showed that there was an influence of sucrose concentration on the water content of baby SCOBY, total phenolic content, flavonoids and antioxidant activity of kombucha (p<0,05).
Keyword: Antioxidant, green tea, kombucha, sucrose concentration

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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