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The extraction process from leaves and twigs of gambier (Uncaria gambier Roxb)plant was conducted mechanically by using traditional hydraulic press, conventional screw press, and modified twin-screw press. The leaves and twigs of gambier plant was obtained from traditional farmer in Limapuluh Kota, West Sumatera, Indonesia. The water, ash and catechin contents of the gambier extracts were analyzed based on SNI 01-3391-2000 using spectrophotometry and thermogravimetry method. Antioxidant activity analysis of the extracts was also performed by 1,1-diphenyl-2-picrylhidrazyl (DPPH) method and compared tovitamin C as a standard antioxidant. The analysis results showed that the extracts contain no ash. Meanwhile, the catechin and water contents of the extracts were approximately 50 and 13% thus the extracts were classified as quality gambier 2. Other than that, analysis result of catechin and epicatechin contents of the extracts using HPLC and compared to the reference materials showed that catechins contents of the extracts using traditional hydraulic press, conventionalscrew press, and modified twin-screw press give catechin content in about 94.296-95.030%. However, epicatechin was detected in a trace amount. The antioxidant activity of the extracts were 2.5 times stronger than reference. The IC50 value of 4.37-4.52 µg/mL and was categorized as active antioxidant.

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Pada pembuatan yogurt terjadi konversi gula susu (laktosa) menjadi asam laktat melalui proses fermentasi oleh bakteri asam laktat (BAL). Konsentrasi stater dan waktu fermentasi yang digunakan akan mempengaruhi kecepatan perombakan laktosa menjadi asam laktat. Penelitian ini bertujuan untuk mengetahui pengaruh penambahan stater dengan variasi sebesar : 1, 5, 10, 15 dan 20% dan waktu fermentasi pada 24 jam dan 48 jam terhadap asam laktat. Parameter yang diuji diantaranya adalah pH, kadar laktosa, kadar protein, kadar asam lakat, dan aktivitas antioksidan. Parameter yang diuji dari hasil proses fermentasi adalah pH, laktosa, asam laktat, protein terlarut. Pengujian laktosa dan asam laktat dilakukan dengan menggunakan HPLC, pengujian konsentrasi protein terlarut dengan menggunakan metode Lowry. Asam laktosa dan asam laktat tertinggi diperoleh dari fermentasi dengan variasi konsentrasi BAL starter 15% dalam waktu fermentasi selama 24 jam. Hasil analisis % inhibisi pada yogurt konsentrasi stater 10% dan waktu fermentasi 48 jam tanpa penambahan dark coklat dan penambahan dark coklat menunjukkan % inhibisi antioksidan paling tinggi dibandingkan dengan yang lainnya sebesar 20,84 % dan 95,58%. Hasil penelitian Variasi starter konsentrasi BAL dan lamanya proses fermentasi tidak mempengaruhi pH dan kadar protein terlarut.