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Abstrak :
Minuman kefir merupakan suatu produk fermentasi yang dapat dibuat secara mudah dan murah. Minuman kefir dikenal luas sebagai suatu minuman probiotik. Pembuatan kefir dapat dilakukan dengan menggunakan baik susu sapi maupun susu kambing. Penelitian ini bertujuan untuk menguji aktivitas antibakteri dari kefir susu sapi dan susu kambing, serta mengisolasi bakteri lactobacilli yang berperan. Aktivitas antibakteri dari kefir diuji berdasarkan perbedaan pada jenis susu yang digunakan dan lama waktu fermentasi. Isolasi dan karakterisasi isolat dilakukan berdasarkan Cowan and Steel’s Manual for the Identification of Medical Bacteria. Kefir dibuat dengan menginokulasikan 5% (w/v) granula kefir lokal ke dalam 50 mL susu sapi atau kambing yang telah dipasteurisasi. Fermentasi dilakukan selama 3, 4, dan 5 hari untuk kedua jenis susu. Uji antibakteri dari kefir dilakukan dengan metode difusi menggunakan silinder (cylinder diffusion method) terhadap 5 bakteri uji, yaitu Staphylococcus aureus NBRC 100910, Pseudomonas aeruginosa DRK 9.1, Eschericia coli NBRC 3301, Bacillus subtilis NBRC 13719 dan Kocuria rhizophila NBRC 12708. Pengukuran nilai pH kefir dilakukan dengan pH meter dan nilai total asam kefir dengan metode titrasi. Hasil uji aktivitas antibakteri dari kefir susu sapi maupun susu kambing menunjukkan adanya aktivitas antibakteri terhadap kelima bakteri uji. Secara umum kefir susu sapi menunjukkan aktivitas antibakteri yang lebih kecil dari kefir susu kambing, baik dari hasil fermentasi dengan lama waktu 3, 4, maupun 5 hari. Selanjutnya, aktivitas antibakteri yang paling optimal secara umum diperoleh pada kefir dengan lama fermentasi 4 hari baik untuk kefir susu sapi maupun susu kambing. Sebanyak 9 isolat bakteri berhasil diisolasi. Seluruhnya menunjukkan karakteristik bakteri yang berasal dari kelompok lactobacilli. ......Kefir is a fermented beverage that can be made easily and cheaply. Kefir is widely known as a probiotic beverage. The production of kefir can be done using either cow milk or goat milk. This study aims to examine the antibacterial activity of cow milk and goat milk kefir, as well as to isolate responsible lactobacilli bacteria. The antibacterial activity of kefir is examined based on differences in type of milk used and fermentation time. The isolation and characterization of isolates is done according to Cowan and Steel’s Manual for the Identification of Medical Bacteria. The kefirs are made by inoculating 5% (w/v) local kefir grains into 50 mL pasteurized cow milk or goat milk. Fermentation was carried out for 3, 4, and 5 days for both types of milk. The antibacterial test of kefirs was carried out using diffusion method utilizing cylinders (cylinder diffusion method) against 5 test bacteria, namely Staphylococcus aureus NBRC 100910, Pseudomonas aeruginosa DRK 9.1, Eschericia coli NBRC 3301, Bacillus subtilis NBRC 13719 and Kocuria rhizophila NBRC 12708. The measurement of kefir pH values was performed using pH meter and kefir total acidities by using titration method. Antibacterial activity test results from either cow milk or goat milk kefir showed the presence of antibacterial activity against five test bacteria. In general, cow milk kefir showed lower antibacterial activity than goat milk kefir in fermentation times of either 3, 4, or 5 days. Furthermore, the most optimal antibacterial activity was generally obtained in kefirs with a fermentation time of 4 days for both cow milk and goat milk kefir. A total of 9 bacterial isolates were successfully isolated. All of which shows the characteristics of bacteria from the lactobacilli group.

Abstrak :
Bakteri asam laktat merupakan kelompok bakteri yang sering ditemukan pada makanan fermentasi. Bakteri asam laktat seperti Lactobacillus diketahui memiliki aktivitas antibakteri terhadap bakteri pathogen dan dapat berperan sebagai agen probiotik. Penelitian yang telah dilakukan sebelumnya oleh Wang (2022) dan Andika (2022) menunjukan adanya aktivitas antibakteri dari filtrat tape ketan hitam dan kefir serta berhasil mengisolasi 13 isolat bakteri asam laktat. Tujuan penelitian ini adalah untuk melakukan penapisan aktivitas koagulasi susu serta aktivitas antibakteri dari masing-masing isolat bakteri asam laktat yang telah berhasil diisolasi dari tape ketan hitam dan kefir. Dari penapisan aktivitias antibakteri tersebut kemudian dipilih isolat terpilih yang kemudian dilakukan uji antibiosis. Sebanyak 13 isolat bakteri asam laktat telah berhasil dilakukan penapisan aktivitas kogulasi susu dan aktivitas antibakteri. Semua isolat bakteri asam laktat menunjukkan dapat mengkoagulasi susu. Kemudian berdasarkan penapisan aktivitas antibakteri didapatkan 3 isolat terpilih dengan kode isolat TM2, KNB2, dan KNB4 dengan nilai Indeks Aktivitas (IA) zona bening tertinggi disetiap perlakuan bakteri uji. Ketiga isolat terpilih tersebut kemudian dilakukan uji antibiosis. Hasil uji antibiosis dari filtrat fermentasi isolat terpilih (TM2, KNB2, dan KNB4) dengan menggunakan medium standar de Man Rogosa Sharpe Broth (MRSB) menunjukkan terdapat aktivitas antibiosis terhadap semua bakteri uji dan ketiga isolat tersebut berpotensi sebagai agen probiotik. ......Lactic acid bacteria are a group of bacteria that are often found in fermented foods. Lactic acid bacteria such as Lactobacillus are known to have antibacterial activity against pathogenic bacteria and can act as probiotic agents. Previous research by Wang (2022) and Andika (2022) showed that there was antibacterial activity from fermented black glutinous rice and kefir filtrate and succeeded in isolating 13 isolates of lactic acid bacteria. The purpose of this study was to screen the coagulation activity of milk and the antibacterial activity of each lactic acid bacteria isolated from fermented black glutinous rice and kefir. From the screening of antibacterial activity, selected isolates then subjected to an antibiosis test. A total of 13 isolates of lactic acid bacteria has been successfully screened for milk coagulation activity and antibacterial activity. All isolates of lactic acid bacteria showed the ability to coagulate milk. Then based on the antibacterial activity screening, 3 selected isolates were selected with the isolate codes TM2, KNB2, and KNB4 with the highest clear zone Activity Index (IA) value in each treatment of the test bacteria. The three selected isolates were then subjected to an antibiosis test. Antibiosis test results from the fermented filtrate of selected isolates (TM2, KNB2, and KNB4) using standard de Man Rogosa Sharpe Broth (MRSB) medium showed that there was antibiosis activity against all tested bacteria and the three isolates had the potential as probiotic agents.