Judul: Synthesis of Ulvan-based Hydrogel from Ulva lactuca Seaweed as Probiotic Immobilization Scaffold
Abstrak: Hidrogel berbasis polisakarida bersulfat ulvan terbuat dengan tambahan polimer pendukung yaitu matriks alginat. Sintesis hidrogel berbasis ulvan-alginat sebagai scaffold untuk imobilisasi probiotik belum pernah dilaporkan. Ulvan merupakan polisakarida bersulfat yang berasal dari rumput laut hijau Ulva. Ulvan diperoleh dari ekstraksi rumput laut Ulva lactuca yang umumnya dilakukan dengan suhu tinggi dan waktu yang lama sehingga diperlukan metode alternatif dalam proses ekstraksinya untuk menghasilkan ulvan dengan kualitas baik namun efisien dalam prosesnya. Alternatif proses ekstraksi yang bisa dilakukan yaitu penggunaan ultrasonikasi yang dapat mengurangi penggunaan pelarut organik dan energi yang tinggi. Penelitian bertujuan mengkarakterisasi Ulva lactuca, menentukan pengaruh Ultrasound-assisted Extraction (UAE) terhadap mutu ulvan, dan menentukan formulasi hidrogel terbaik berbasis ulvan untuk imobilisasi probiotik. Tahapan penelitian meliputi preparasi sampel, optimasi ekstraksi ulvan, dan sintesis hidrogel dengan variasi ulvan (0, 1, 2, 3, dan 4 %)) dan konsentrasi tetap alginat 4%. Ulvan terpilih berdasarkan kandungan sulfat terbesar yaitu 57,20 ± 0,11 % hasil ekstraksi dengan NaOH berbantu ultrasonikasi. Hidrogel ulvan-alginat menghasilkan fraksi gel dan rasio swelling terbaik sebesar 31,88 ± 3,80 % dan 57,18 ± 19,88 % dengan total bakteri probiotik sebesar 8,5 ± 4,9 × 106 log CFU/g. Ulvan dapat berperan sebagai bahan makanan pada hidrogel scaffold sehingga mampu mempertahankan keberadaan bakteri probiotik.
Keyword: imobilisasi probiotik, hidrogel, Ulva lactuca, ulvan

Judul: Synthesis and Characterization of Ulvan Alginate Hydrogel Beads with Encapsulated Probiotics.
Abstrak: Minuman probiotik memiliki berbagai keuntungan bagi saluran pencernaan. Namun, terdapat masalah pada kepastian kelangsungan hidup probiotik dan fungsionalitasnya selama melalui saluran pencernaan hingga mencapai usus besar, sehingga diperlukan metode alternatif untuk mempertahankan kelangsungan hidup probiotik yaitu enkapsulasi hydrogel beads dari biopolimer alami yaitu alginat dan ulvan. Hydrogel beads yang dikonstruksi dari alginat dan ulvan diprediksi akan sesuai dengan tantangan sebagai bioreaktor probiotik yang dapat menstimulasi kesehatan pencernaan manusia karena secara kimia dapat dikontrol porositas dan kapasitas retensinya. Pengaplikasian hydrogel beads dalam penelitian ini dilakukan pada minuman tisane sargassum. Penelitian bertujuan menentukan karakteristik konsentrasi ulvan terpilih, ketahanan bakteri probiotik terenkapsulasi dalam simulated gastric fluid (SGF) dan simulated intestinal fluid (SIF) serta karakteristik hydrogel beads di dalam minuman tisane sargassum. Tahapan penelitian terdiri dari karakterisasi hydrogel beads dengan konsentrasi ulvan (1%, 2%, 3%, dan 4%) dan alginat 2% serta pengaplikasian hydrogel beads pada tisane sargassum. Hydrogel beads ulvan alginat menghasilkan fraksi gel dan rasio swelling tertinggi sebesar 98,8% dan 19,7%. Hydrogel beads dapat mempertahankan tingkat kelangsungan hidup bakteri probiotik pada kedua kondisi yaitu SGF dan SIF sebesar 3,41×10^7 log CFU/g dan 0,14×10^7 log CFU/g. Hasil analisis sensori menghasilkan formulasi terpilih dengan perlakuan ukuran hydrogel beads R2 (sedang) dengan ukuran 9,05 ±0,92 mm, hal ini menunjukkan bahwa ukuran hydrogel beads memengaruhi tingkat kesukaan panelis., Probiotic beverages offer a range of advantages for the digestive system. However, issues arise concerning the viability and functionality of probiotics as they traverse the digestive tract to reach the large intestine. As a result, alternative methods are required to sustain probiotic viability, such as encapsulating them in hydrogel beads made from natural biopolymers like alginate and ulvan. The construction of hydrogel beads from alginate and ulvan is predicted to address challenges as a probiotic bioreactor that can promote human digestive health, primarily due to the controllable chemical properties of porosity and retention capacity. In this study, hydrogel beads were applied within the context of sargassum tisane, a beverage. The research aimed to determine the characteristics of the selected ulvan concentrations, the resilience of encapsulated probiotic bacteria within simulated gastric fluid (SGF) and simulated intestinal fluid (SIF), and the attributes of hydrogel beads within sargassum tisane. The research phases encompassed the characterization of hydrogel beads with varying ulvan concentrations (1%, 2%, 3%, and 4%) and a constant 2% alginate concentration. Subsequently, the hydrogel beads were introduced into the sargassum tisane. The hydrogel beads composed of ulvan and alginate yielded the highest gel fraction and swelling ratio at 98.8% and 19.7%, respectively. These hydrogel beads effectively maintained the survival levels of probiotic bacteria under both SGF and SIF conditions, registering at 3.41×10^7 log CFU/g and 0.14×10^7 log CFU/g, respectively. Sensory analysis results identified a preferred formulation, indicating that the size of hydrogel beads, specifically the R2 (medium) size at 9.05 ± 0.92 mm, significantly influenced the panelists' preference levels. This underscores the impact of hydrogel bead size on palatability perception.
Keyword: alginate, bacterial probiotic, hydrogel beads, ulvan

Judul: Exchange Market Pressure and Central Bank Intervention for Three ASEAN Countries
Abstrak: Two of the exchange rate systems which are adopted by many countries are the floating and the fixed exchange rate system. Both the exchange rate systems have different characteristics. Countries that implement fixed exchange rates system tend to set their domestic currency exchange rate at a certain point. On the contrary, countries which implement floating exchange rate system tend to let their domestic currency exchange rate to move flexibly and thus their value will always change according to the demand and supply of the currency in the foreign exchange market. Countries which implement floating exchange rate system are facing the risk of fluctuation in the exchange rate of their domestic currency against foreign currencies. The currency exchange rate fluctuation may be caused by economic problems such as a financial crisis. A country can also be potentially affected by other countries’ earlier financial crisis. This effect could potentially happen if these countries are in the same region, such as ASEAN. The 1997 ASEAN economic crisis was an example of a country’s financial crisis could affect other countries. At that time, some countries such as Indonesia, Malaysia and Thailand had to change their currency exchange rate system from the fixed exchange rate system to the floating exchange rate system due to the high costs which has to be incurred if they were to enforce the fixed exchange rate system. During 2002 until 2012, the domestic exchange rate of Indonesia, Malaysia and Thailand against the U.S. dollar had tended to fluctuate. If the domestic currency exchange rate fluctuated excessively then the central bank would intervene to stabilize the exchange rate in the foreign exchange market. The pressure on domestic currency exchange rate pressures has forced the central bank to intervene. The amount of those pressures can be analyzed by calculating the Exchange Market Pressure (EMP) index. Apart from that, the time when interventions are done by the central bank can be known based on EMP by calculating the Exchange Market Intervention (EMI) index. The purposes of this study were to determine the level of international pressure on the currency exchange market and monetary authorities intervene in three ASEAN countries, as well as to determine the effect of the monetary authorities intervene on the exchange rate of the domestic currency against the U.S. dollar in those three ASEAN countries. Based on the EMP index calculation results which are obtained during 2002 to 2012 period, the exchange rate of Indonesia, Malaysia and Thailand’s domestic currency had always fluctuated and the results of the EMP index indicated that each country were under diverse level of currency exchange rate appreciation and depreciation pressures. Thailand was the country with the highest currency exchange rate pressure compared to Indonesia and Malaysia. The results on the intervention index calculation showed that Indonesia, Malaysia and Thailand have intervention index between zero and one and more than one. We can also see from the intervention index that Indonesia and Thailand implement the controlled floating currency exchange rate instead of the freely floating one. Based on the calculation of the currency exchange rate by comparing
Keyword: exchange rate, exchange market pressure, intervention