Judul: Process engineering of langsat fruit peel (Lansium domesticum var. langsat) extraction as antibacterial and antioxidant
Abstrak: Langsat, a fruit plant in the family of Meliaceae, has long been used in traditional medicine to treat fever, diarrhea, malaria, and tumor. This study aims to obtain the optimum extraction condition and method of langsat fruit peel with the best antibacterial and antioxidant activities. The methods used to determine activities were agar diffusion method, dillution method for MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration) for antibacterial and DPPH (1,1-diphenyl-1-picrilhydrazyl) for antioxidant activity. Solvents used in the maceration extraction were hexane (non polar), ethyl acetate (semi-polar) and ethanol (polar). Solvent that gave the best antibacterial and antioxidant activity was further used for the microwave extraction. Conventional extraction methods namely reflux and maceration were then compared to microwave extraction. The microwave power and extraction time was determined based on the highest total phenol extract of langsat fruit peel. The best extraction method was used to optimize the extraction process with response surface method to determine the optimal conditions for the extraction of langsat fruit peel. The results showed that ethanol extracts have the highest antibacterial and antioxidant activity compared to other extracts. The MIC and MBC values of ethanol extracts were 62.5 and 125 ppm for bacteria S. aureus, while the bacteria E. coli with value of 500 and 1000 ppm, respectively. The antioxidant activity of ethanol extract DPPH method has IC50 value of 77.60 ppm. Microwave with power of 400 watt for 3 minutes, produced the highest total phenol extract. Extraction with microwave produced phenol with a total of 13.92% and 22.64%, higher than extraction with reflux and maceration. The optimum extraction of langsat fruit peel was obtained at the microwave power of 336.56 watts and for extraction time of 3.24 minutes, which resulted in a total phenolic extract of the langsat fruit peel 44.07 mg TAE/g. The validation results experimentally showed the value of total phenols 0.66% smaller than predicted. Validation results showed an increase in antibacterial and antioxidant activity than before the optimization, the MIC and MBC values for S. aureus were 31.25 and 62.5 ppm, whereas E. coli with value of 125 and 250 ppm. The antioxidant activity of the validation result has IC50 value of 47.44 ppm.
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Judul: Potensi Kulit Buah Langsat (Lansium domesticum) sebagai Antibakteri
Abstrak: The fruit peels of langsat (Lansium domesticum) have antibacterial activities. However, the active compounds responsible for the activities have not been studied. Therefore, this research was aimed to determine the metabolite compounds with antibacterial activity in the fruit peel of langsat. Some samples was macerated using ethanol 70% and further fractionated using column chromatography with gradient elution from non-polar to polar solvent. Antibacterial activity was tested to Staphylococcus aureus using dilution method. Antibacterial test results showed that the most active extracts was ethanol 70% extract with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 1.00 mg/mL. Fractionation using hexane:ethyl acetate gave 12 fractions and 9 fractions for ethyl acetate:methanol. The most active fraction was F29 with MIC and MBC of 0.5 mg/mL and 2.00 mg/mL, respectively. Based on identification using Fourier transform infrared spectrophotometers, the predicted active compound was flavonoids.
Keyword: fruit peels langsat, fraction, flavonoid, antibacterial

Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf