Judul: Proses pengolahan kopi bubuk (campuran arabika dan robusta) serta perubahan mutunya selama penyimpanan
Abstrak: Kopi merupakan bahan minuman yang tidak saja terkenal di Indonesia tapi juga terkenal di seluruh dunia. Hal ini disebabkan karena kopi, baik dalam bentuk bubuk maupun seduhannya memiliki aroma yang khas yang tidak dimiliki oleh bahan minuman lainnya. Di Indonesia, sebagian kopi bubuk yang dihasilkan adalah berasal dari biji kopi jenis robusta karena biji kopi jenis ini mendominasi perkebunan kopi di Indonesia hingga saat ini karena mempunyai sifat yang lebih unggul dan sangat cepat berkembang. Akan tetapi, kualitas buah dari kopi robusta lebih rendah daripada kopi arabika dengan rendemen kira-kira 22% serta memiliki kandungan kafein yang lebih tinggi dibandingkan dengan kopi arabika dengan rendemen kira-kira 18%. Kandungan kafein kopi robusta yang tinggi yang menyebabkan seduhan kopinya terasa lebih pahit, karena semakin kecil kandungan kafein dalam biji kopi maka akan semakin enak rasa kopi yang dihasilkan. Namun, kopi arabika memiliki rata-rata produksi sedang dengan harga yang relatif lebih tinggi dibandingkan dengan kopi robusta. Selain itu, perubahan sifat fisik dan kimia pada biji kopi juga terjadi pada saat penyangraian. Penggunaan media penyangraian yang berbeda seperti wajan stainless steel dan wajan tanah liat juga dapat mempengaruhi cita rasa dari kopi bubuk yang dihasilkan karena suhu pada saat penyangraian akan mempengaruhi keasaman dari seduhan kopi. Tujuan Penelitian ini adalah mendapatkan perbandingan blending kopi arabika dan robusta serta media penyangraian yang terbaik agar memperoleh aroma dan rasa yang maksimal yang disukai konsumen, mengetahui karakteristik kopi bubuk yang dihasilkan, serta mengetahui pengaruh kemasan yang digunakan, yaitu kertas kraft dan plastik Polypropilen (PP) selama penyimpanan kopi bubuk terbaik yang dihasilkan sebelumnya pada suhu 30oC, 35oC, dan 45oC terhadap perubahan mutunya serta melakukan pendugaan umur simpan dengan metode Arrhenius…
Keyword: Blending, Ground coffee, Stored, Shelf life, Bogor Agricultural University, Institut Pertanian Bogor, IPB

Judul: Processing Ground Coffee (Blending of Arabica and Robusta) and The Quality Changes During Storage
Abstrak: Coffee is beverage ingredient that not only popular in Indonesia but also around the world. Because either ground coffee or liquid coffee has a unique flavor which is not contained in other beverage ingredients. Some of ground coffee is derived from seed of Robusta coffee which is dominated plant in Indonesia. Seed of Robusta coffee has superior characteristic and very fast growing. However, seed quality of Robusta Coffee is poor compare with Arabica coffee that contain about 22% of yield and higher caffeine content with approximately 18% of yield. Caffeine content of Robusta Coffee causes taste of Robusta coffee is bitter, otherwise less content of caffeine will make the taste of coffee more delicious. However, the Arabica coffee has higher price due to the production capacity. In addition, changes of physical and chemical content of coffee seed also occur during roasting process. The use of different media such as stainless steel pan and clay pan also influence the taste of ground coffee because temperature during roasting period will affect acidity of steeping coffee. The purpose of this research were finding the best blending ratio between Arabica and Robusta coffee and also finding the media to obtain the maximum taste and flavor which is preferred by consumers, analyzing the characteristic and the quality change during storage temperature in level of 30°C, 35°C, and 45°C in different media packaging that are kraft paper and polypropilen (PP). This research also estimated shelf life of ground coffee through Arrhenius method. Based on organoleptic test, there were significant differences among each treatment. Analysis of moist content, VRS, coffee extract content, and pH also showed significant differences for each treatment. In the other hand, yield of ground coffee showed that there is no significant difference for every treatment. Based on result of hedonic test which is supported by result of moist content, yield, and VRS, there was selected blending ratio between 10% of Arabica coffee and 90% of Robusta coffee using clay roasting media. The best ground coffee was stored during one and a half month through observation in 10 points using kraft paper and polypropilen (PP) at several temperature levels, those are 30°C, 35°C, and 40°C. Some parameters which were measured such as: the change of moist content, (Volatile Reducing Substances), and the degree of acidity (pH). The quality of ground coffee decline during storage period. The result of the research showed that the moist content and pH vale were increasing, whereas VRS content was reducing. The packaging media that decrease quality of ground coffee was PP plastic at 30°C of temperature. Shelf life of ground coffee using PP were 13 months 27 days at 30°C of temperature, 10 months 27 days at 35°C of temperature, and 8 months 15 days at 45°C at temperature. Meanwhile, the shelf life of ground coffee using kraft paper were 3 months 27 days at 30°C of temperature, 2 months 6 days at 35°c of temperature, and 1 month 9 days at 45°C of temperature. Experiment by all parameters which are measured, it is concluded that the best ratio to blend
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Judul: Penentuan Nilai Eigen dan Vektor Eigen dari Matriks Tridiagonal 2-Toeplitz dengan Pendekatan Polinomial Chebyshev
Abstrak: The eigenvalues and eigenvectors of a matrix can be determined by finding its characteristic polynomials. The characteristic polynomials of a tridiagonal 2-Toeplitz matrix is shown to be closely connected to polynomials which satisfy the Chebyshev recurrence relationship. If the order of the matrix is odd, then the eigenvalues are found explicitly in terms of the Chebyshev zeros and the eigenvectors are found in terms of the polynomials satisfying the recurrence relationship. For even ordered matrices, the situation is more complicated. The problem in these cases is that although the Chebyshev recurrence formula is still applied, its initial values are not generating Chebyshev polynomials
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