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: 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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