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: 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.
Keyword: