Judul: Immersion Treatment by Lime Solution in Making Mango (Mangifera indica L. var. Ariumanis) Peel Extract which was Added to Mango Puree
Abstrak: The arumanis mango (Mangifera indica L var. Arumanis) puree product with mango peel extract addition had the highest antioxidant activity compared to puree from flesh only or unpeeled mango. However, the addition of extracts to mango puree produced dark color, bitter taste and astringent flavor which was suspected to be caused by high tannin content in the skin, about 15%. The objective of this research was to study the improvement of sensory quality and antioxidant ability of arumanis mango peel extract by removing tannin using peel immersion in lime solution treatment before extraction. In addition, in this research also studied the optimum sensory results and antioxidant activity of the arumanis mango puree that had been added with the extract obtained. The making of the puree mango added to the extract was implemented using the method of previous studies by modifying part of sample preparation because there was a soaking treatment in lime solution before extraction. Formula optimization was performed using Response Surface Methodology (RSM) with the Design Expert 11 program. The immersion treatment of mango peel by lime solution before extraction could reduce tannin levels in mango peel extract significantly by 39%. The result of formula optimization of mango puree with peel extract addition 0.7% could reduce tannin levels significantly by 28% without decreasing their antioxidant activity. However, immersion treatment by lime solution was unable to improve sensory acceptance on either the color attribute, aroma, taste, or overall.
Keyword: Puree, Ekstrak Kulit Mangga, Tanin, Larutan Kapur, Response Surface Methodology

Judul: Optimization of Kepok Banana Peel Extract (Musa paradisiaca L.) as an Antioxidant Ingredient
Abstrak: Limbah kulit pisang kepok (Musa paradisiaca) yang berpotensi sebagai antioksidan belum dimanfaatkan secara optimum. Penelitian ini bertujuan menentukan kondisi optimum maserasi kulit pisang kepok berdasarkan nisbah sampel:pelarut, konsentrasi pelarut, dan waktu maserasi menggunakan metode permukaan respons desain Box-Behnken untuk menghasilkan bahan antioksidan terbaik. Waktu maserasi merupakan variabel yang paling memengaruhi kapasitas antioksidan, kandungan fenolik dan flavonoid total dengan nilai p terkecil (<0,05) berdasarkan uji statistik Anova. Sementara itu, konsentrasi etanol merupakan variabel yang paling memengaruhi rendemen. Kondisi optimum ekstrak kulit pisang kepok berdasarkan analisis metode permukaan respons ialah kombinasi variabel nisbah sampel:pelarut 1:8,1, konsentrasi pelarut 72,9%, dan waktu maserasi 28,7 jam, dengan nilai prediksi respon, yaitu rendemen 33,9%, kapasitas antioksidan 6,9 AAE/g ekstrak, kandungan fenolik total 13,5 mg GAE/g ekstrak, dan kandungan flavonoid total 20,1 mg QE/g ekstrak., Kepok banana peel waste (Musa paradisiaca), which has the potential to be an antioxidant has yet to be optimally utilized. Thus, this study aims to determine the optimum condition of maceration of banana peels based on the samples:solvent ratio, solvent concentration, and maceration time using the Box-Behnken design response surface method to produce the best antioxidant ingredients. The maceration time was the variable that most affects antioxidant capacity, phenolic content, and total flavonoids, with the lowest p-value (<0.05) based on Anova statistical tests. Meanwhile, ethanol concentration was the variable that most affects the yield. Therefore, the optimum condition of banana peel extract based on the analysis of the response surface method was a combination of variable sample:solvent ratio of 1: 8.1, solvent concentration 72.9%, and maceration time of 28.7 hours, with a predicted response value, namely yield of 33.9%, the antioxidant capacity of 6.9 AAE/g extract, total phenolic content of 13.5 mg GAE/g extract, and total flavonoid content of 20.1 mg QE/g extract.
Keyword: antioxidant, Box-Behnken, kepok banana peel, optimization, response surface model

Judul: Bifurkasi Hopf pada Model Siklus Bisnis Kaldor Kalecki tanpa dan dengan Waktu Tunda
Abstrak: Business cycle model is one of dynamical system models in economic. One of the business cycles model is Kaldor-Kalecki model. Kaldor-Kalecki business cycle model that is written in delayed defferential equations, is a business cycle model that involves gross product and capital stock of a company. In this paper Kaldor-Kalecki business cycle model is analyzed using both nondelay and delay in time of capital stock. By Taylor expansion for the time delayed model, an analysis of stability around the fixed points has been done. Furthermore, by using Hopf bifurcation theorem, it can be shown that there exists periodic orbits and limit cycle. In the nondelayed model, changing the parameter of goods market could lead to the occurrence of Hopf bifurcation and the existence of limit cycle. Similarly, for the delayed model, it has been shown that changing the time delay parameter may result in the occurrence of Hopf bifurcation and limit cycle.
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