Judul: The Development of Ice Cream Using Red Dragon Fruit Flesh and Skin on Antioxidant Activity and Organoleptic Quality
Abstrak: Es krim adalah produk olahan yang terbuat darisusu dan ditambahkan dengan komposisi bahan pembuat es krim, yang sering disebut bahan campuran es krim (ice cream mix), seperti krim, skim, stabilizer, emulsifier, sweetener, dan penambahan rasa (flavor) untuk menciptakan produk es krim yang lembut, enak dan rasa yang lezat. Tujuan penelitian ini adalah mendapatkan formula terbaik dari es krim dengan variasi rasio daging dan kulit buah naga merah sebagai cemilan tinggi antioksidan. Penelitian ini menggunakan Rancangan Acak Lengkap (RAL) dengan rasio daging dan kulit buah naga (%), yaitu F0 (100:0), F1 (70:30), F2 (60:40), dan F3 (50:50). Hasil organoleptik menunjukkan keempat formula dapat diterima oleh panelis dan formula yang paling disukai adalah F2, yaitu es krim dengan rasio daging buah naga 60% dan kulit buah naga 40%. Produk es krim buah naga memiliki kandungan (basis basah) untuk air sebesar 63,01-63,81%, abu 3,11-3,43%, lemak 11,82-12,33%, protein 12,60-13,14%, dan karbohidrat 7,28-9,36%. Kandungan antioksidan pada semua formula es krim lebih dari 200 ppm sehingga dikategorikan sangat lemah., Ice cream is a processed product made from milk and added to the composition of ingredients for making ice cream, which are often called ice cream mix ingredients, such as cream, skim, stabilizer, emulsifier, sweetener, and added flavors to create soft, tasty and delicious ice cream products. The purpose of this study was to obtain the best formula of ice cream with variations in the ratio of red dragon fruit flesh and skin as a snack high in antioxidants. This study used a completely randomized design with a ratio of dragon fruit flesh and skin (%), namely F0 (100:0), F1 (70:30), F2 (60:40), and F3 (50:50). The organoleptic results showed that the four formulas were acceptable to the panelists and the most preferred formula was F2, namely ice cream with a ratio of 60% dragon fruit flesh and 40% dragon fruit skin. Dragon fruit ice cream products contain (wet base) water 63.01-63.81%, ash 3.11-3.43%, fat 11.82-12.33%, protein 12.60-13.14%, and carbohydrates 7.28-9.36%. The antioxidant content in all formulas is more than 200 ppm so it is categorized as very weak.
Keyword: antioksidan, buah naga merah, es krim, kulit buah naga

Judul: The Substitution of Peel Puree to Dragon Fruit Ice Cream Improves Physical and Organoleptic Quality with Identical Calcium Bioavailability
Abstrak: Kalsium merupakan mineral makro yang memiliki peran penting dalam fungsionalitas tubuh. Kalsium yang diserap tubuh digambarkan oleh bioavailabilitas kalsium. Bioavailabilitas kalsium dapat dipengaruhi oleh zat anti-gizi yang dapat ditemukan dalam buah. Penelitian ini bertujuan mengkaji substitusi pure kulit buah naga dalam es krim buah naga merah. Desain penelitian ini adalah eksperimen dengan rancangan acak lengkap (RAL). Tahap penelitian terdiri dari formulasi, pembuatan produk, uji karakteristik fisik, organoleptik, proksimat, penentuan formula terpilih, analisis kandungan dan bioavailabilitas secara in vitro serta analisis kontribusi dan klaim gizi. Formula terpilih adalah F2 dengan rasio pure daging dan kulit buah naga merah 60:40. Es krim terpilih memiliki kadar air 63,6%; kadar abu 3,4%; lemak 12,0%; protein 13,0%; dan karbohidrat 8,1% dengan kontribusi energi 8,9% berdasarkan acuan label gizi (ALG). Kandungan kalsium es krim 264,90 mg/100 g dengan bioavailabilitas 70,55%. Kandungan dan bioavailabilitas es krim tidak berbeda antara es krim kontrol dan terpilih berdasarkan independent samples t-test (p>0,05). Es krim dapat diklaim sebagai makanan sumber kalsium dengan kontribusi sebesar 24,1%., Calcium is a macro mineral that has important roles in body functionality. Calcium absorbed by the body is described by the bioavailability of calcium. The bioavailability of calcium can be affected by anti-nutrients sometimes found in fruit. This study aims to examine dragon fruit peel puree substitution in red dragon fruit ice cream. The research design is an experiment with a completely randomized design (CRD). The research stages are formulation, product manufacture, physical characteristic, organoleptic, and proximate analysis, formula selection, analysis of calcium content and bioavailability in vitro as well as analysis of contribution and nutritional claims. The selected formula is F2 with a red dragon fruit pulp and peel puree ratio of 60:40. Ice cream has a moisture of 63.6%, ash 3.4%, fat 12.0%, protein 13.0%; and carbohydrates 8.1% with energy contribution 8.9% based on nutrition label reference. The calcium of ice cream is 264.90 mg/100 g with a bioavailability of 70.55%. The content and bioavailability of ice cream are identical between control and selected ice cream based on independent samples t-test (p>0.05). Ice cream can be claimed as a source of calcium with a contribution of 24.1%.
Keyword: calcium bioavailability, ice cream, red dragon fruit’s peel puree

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.
Keyword: