Judul: Optimization of Oxalate Content Decrease in Kathak Porang Bulbil (Amorphophallus sp.) Flour Through Immersion in Warm NaHCO3 Solution
Abstrak: Umbi porang (Amorphophallus sp.) merupakan komoditas yang diminati karena memiliki kandungan serat pangan yang tinggi. Porang dapat berkembang biak dari bulbil yang disebut kathak. Bulbil kathak porang dapat dipanen dalam jumlah yang produktif. Akan tetapi, terdapat keterbatasan lahan untuk mengembangbiakkannya. Maka dari itu, muncul kekhawatiran akan berlebihnya stok bulbil kathak porang di masa yang akan datang sehingga potensi penggunaannya sebagai bahan pangan perlu diteliti. Salah satu bahan pangan yang dapat diolah dari umbi-umbian adalah tepung, tetapi bulbil kathak mengandung oksalat yang kadarnya perlu diturunkan terlebih dahulu. Optimasi proses perendaman dalam larutan NaHCO3 hangat dapat menurunkan kadar oksalat pada umbi-umbian. Tepung yang telah melalui proses optimum akan dikarakterisasi proksimat, kadar glukomanan, warna, densitas kamba, dan profil gelatinisasi. Tepung dengan penurunan kadar oksalat optimum (62,70%) diperoleh dengan perlakuan perendaman dalam larutan NaHCO3 hangat konsentrasi 6% dengan durasi perendaman 60 menit. Tepung yang telah melewati proses optimum masih mengandung kadar air, abu, dan oksalat yang cukup tinggi serta derajat putih yang kurang baik sehingga diperlukan optimasi lebih lanjut. Berdasarkan profil gelatinisasinya, tepung bulbil kathak porang memiliki setback viscosity yang rendah sehingga cocok diaplikasikan sebagai pengental atau penstabil pada produk pangan., Porang tubers (Amorphophallus sp.) is a commodity with great demand due to its high content of dietary fiber. Porang can be cultivated from bulbil called kathak. Bulbil kathak porang can be harvested in productive quantity. However, the land to cultivate them is limited. Therefore, there’s a concern of excessive kathak porang bulbil stock in near future, so the study for its potential use as food is necessary. One of the foodstuffs that can be processed from tubers is flour, but kathak porang bulbil has oxalate content which needs to be decreased first. Optimization of the immersion process in warm NaHCO3 solution can decrease oxalate content in tubers. Flour that has gone through the optimum process will be characterized by proximate, glucomannan content, color, kamba density, and gelatinization profile. The flour with optimum decrease of oxalate content (62,70%) was obtained by immersion in warm 6% NaHCO3 solution for 60 minutes. The flour that has gone through the optimum process had high water, ash, and oxalate content, and also a less preferred whiteness degree, therefore it still needs further optimization. Based on the gelatinization profile, kathak porang bulbil flour had low setback viscosity thus suitable to be thickener or stabilizer in foodstuffs.
Keyword: bulbil kathak porang, NaHCO3, oksalat, tepung

Judul: Effect of Initial pH and Cultivation Time of Kimchi Bacteria on Oxalate Levels of Modified Porang Flour
Abstrak: Porang (Amorphophallus oncophyllus) merupakan umbi yang memiliki kadar glukomanan tinggi, namun permasalahan pada umbi porang yakni adanya kandungan oksalat. Oksalat pada umbi porang menyebabkan umbi tidak dapat dikonsumsi secara langsung karena dapat menyebabkan berbagai masalah kesehatan. Kadar oksalat pada umbi porang dapat diturunkan melalui proses kultivasi dan penambahan bakteri kimchi, namun faktor pH awal dan waktu kultivasi masih belum diketahui, Kultivasi umbi porang menggunakan 3 taraf pH awal (5, 6, dan 7) dan tiga taraf waktu kultivasi (1, 2, dan 3 hari). Karakteristik umbi porang 2 dan 3 musim panen tidak terdapat perbedaan yang signifikan. Hasil isolasi dan identifikasi bakteri kimchi menunjukkan adanya kemampuan tumbuh pada media yang ditambahkan oksalat. Berdasarkan hasil analisis waktu kultivasi berpengaruh signifikan terhadap penurunan asam oksalat tepung porang termodifikasi. Penurunan asam oksalat terbaik tepung porang termodifikasi yakni sebesar 65%, dengan penurunan kristal dan total oksalat sebesar 35,67% dan 48,16% apabila dibandingkan tanpa kultivasi., Porang (Amorphophallus oncophyllus) is a tuber with high glucomannan levels, but the problem with porang tuber is the presence of oxalate. Oxalate in porang tubers causes the tubers to not be consumed directly because it can cause various health problems. Oxalate levels in porang tubers can be reduced through the cultivation process and the addition of kimchi culture bacteria, but the initial pH factor and duration of cultivation are still unknown. Cultivation of porang tubers used 3 initial pH levels (5, 6, and 7) and three levels of cultivation time (1, 2, and 3 days). There were no significant differences in the characteristics of porang tubers 2 and 3 during the harvest season. The results of the isolation and identification of kimchi bacteria showed the ability to grow on media with oxalate added. Based on the analysis results, cultivation time had a significant effect on the reduction of oxalic acid in modified porang flour. The best reduction in oxalic acid in modified porang flour was 65%, with a decrease in crystals and total oxalate by 35.67% and 48.16% when compared without cultivation.
Keyword: fermentation, kimchi, oxalate, modified porang flour

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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