Judul: Pendugaan Umur Simpan Kelopak Bunga Rosela (Hibiscus sabdariffa L.) Kering.
Abstrak: Roselle is a kind of plant from genus Hibiscus. Calyx of roselle flower from variety of sabdariffa has a lot of uses as a food material. Utilization of roselle (Hibiscus sabdariffa L.) has increased because many researches mentioned that roselle have chemical content which have many functions for human health, especially high content of vitamin C. Prediction of shelf life aims to know shelf life of dry calyx of roselle in certain condition. Determination shelf life product with ASS (Accelerated Storage Studies) method using environmental condition parameter enables to accelerate degradation process of quality of food product. The right packaging and storage is expected to increase shelf life and detain deterioration rate of dry calyx of roselle. The objectives of the research is to know quality changing, to determine shelf life, and to obtain better packaging to defend quality of dry calyx of roselle. The packaging materials which are used in this research were craft paper and plastic PP. Storage temperatures are held at 25°C, 35°C, and 45°C. Storage time in this research is 3 months. The analysis of dry calyx of roselle were water content, total of acid titration, total soluble solid, pH, vitamin C content, total mould, and sensory evaluation analysis. Based on this research, it is showed that dry calyx of roselle quality changed during 3 months of storage. Water content of dry calyx of roselle in craft paper packaging at storage temperature of 25°C increased by 0.12% per day and at temperature of 35oC and 45°C decreased by 0.03% and 0.04% per day respectively. In plastic PP packaging, water content of roselle at storage temperature of 25°C and 35°C increased by 0.06% and 0.04% per day respectively, while at 45°C it decreased by 0.03% per day. Total of acid titration of dry calyx of roselle in craft paper packaging at storage temperature of 25°C, 35°C, and 45°C decreased by 0.0007% per day, while in plastic PP at temperature of 25°C, 35°C, and 45°C decreased by 0.0008%, 0.0009%, and 0.0016% per day respectively. pH of dry calyx of roselle in craft paper packaging at storage temperature of 25°C, 35°C, and 45°C decreased by 0.0004% per day, while in plastic PP packaging at 25°C, 35°C, and 45°C, it decreased by 0.0003%, 0.0004%, and 0.0005% per day respectively. Vitamin C of dry calyx of roselle at storage temperature of 25°C, 35°C, and 45°C in craft paper packaging decreased by 0.0072%, 0.0136%, and 0.0142% per day respectively, while in plastic PP, it decreased by 0.0096%, 0.0161%, and 0.0166% per day respectively. Total soluble solid of dry calyx roselle in craft paper at 25°C, 35°C, and 45°C of storage temperatures increased by 0.0061%, 0.0067%, and 0.0077% per day respectively. In plastic PP, total soluble solid of dry calyx roselle at storage temperature of 25°C, 35°C, and 45°C increased by 0.0060%, 0.0071%, and 0.0076% per day respectively. During 3 months of storage, there was no mould found in dry calyx of roselle. There was no panelists refusal at assessment of common acceptance attribute of dry and extract calyx of roselle until 91 days of
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Judul: Nanoenkapsulasi Ekstrak Kelopak Bunga Rosella (Hibiscus sabdariffa) Hasil Ekstraksi Berbantu Gelombang Mikro Sebagai Bahan Antibakteri dan Antioksidan
Abstrak: Roselle has used as medicine because they contain bioactive medicine because they contain bioactive compound such as phenols. The present study was designed to develop Microwave Assisted Extraction (MAE) on phenolics extraction from roselle calyx which gave maximum yield, higher antioxidant and antibacterial activity, and maintain stability of roselle bioactive compounds through the application of nano-encapsulation technology. Scope of this research was divided in three stages of experimental activities. Firstly, investigated of solvent influence on characteristics of toxicity, antibacterial and antioxidant activities. Secondly, determined the optimum condition of Microwave Assisted Extraction and characterized the extract on optimum conditions, and thirdly, applied of nano-encapsulation technique to improved the stability roselle extract. The aims of the first research was to find solvent with the best extract characteristics of toxicity, antibacterial and antioxidant activity. Qualitative method was used to determine the phytochemical calyx content, Brine Shrimp Lethality for toxicity tests. Antibacterial tests were done against Staphylococcus aureus and Escherichia coli using disc diffusion method. Total antioxidant activity was determined by the ferric thiocyanate method. The results showed that bioactive compounds in Roselle calyx were flavonoid, phenolic compounds, tannin, alkaloid, and steroid. Ethanol 70% could extract the phenolics 19.45 + 0.32 mg/g compared with ethyl acetate and hexane, which only could extract the fenolik compound respectively 7.51 + 0.49 mg/g and 2.73 + 0.31 mg/g. It means that ethanol 70% is more effective than the other solvents. The ethanol 70% extract was found to be potential against brine shrimp with LC50 value below 1000 ppm, 510.613 ppm. On the other hand with ethyl acetate and hexane were respectively 1241.983, and 1718.446 ppm. Ethanol 70% and ethyl acetate extract had antibacterial activity, showed by inhibitory zone 7.7 + 2,01b mm and 7,53 + 2,19 bmm for S aureus and 13.28 + 3,30b mm, 12,35 + 3,13b mm against to E coli. There was no inhibitory zone for crude hexane extract. EC50 value for ethanol 70%, ethyl acetate and hexane were 4393.2; 5879,16 ;4813,92 ppm respectively. Roselle calyx was an excellent source of phenolic compounds. In this study, microwave-assisted extraction was employed to extract the phenols from Roselle calyx. The aims for the second stage were to determined the optimum condition of microwave assisted extraction, and characterized of the antibacterial and antioxidant activity extract from optimum condition. For the efficiency of extraction by using response surface methodology, the effects of microwave output power, ethanol concentration, and extraction time on total phenols yield were investigated and the optimal conditions were determined as follows: microwave output power 250 W, etanol concentration 78,36% and extraction time 4.91 min. The estimated values for total fenoliks yield, 24,61 mg/g was obtained at those conditions. A verification experiment at the optimum condition, consisting of 4 runs, was performed and the practical yield of 23.77 + 0.25 mg/g total fenoliks was higher than using conventional method 19.84 + 0.46 mg/g.. Compared with conventional method, total phenolics, antosianin, and vitamin C and yield of microwave assisted extraction were 23.77 + 0.25, 14.80 + 0.08, 10.74 + 0,14 mg/g and 22.09 + 3.3 % which are higher
Keyword: roselle, antibacterial, antioxidant, toxicity, phenolics

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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