Pasting Behavior and Viscoelastic Properties of Fresh, Chilled, and Rehydrated Freeze-Dried Gel Beads from Blends of Tapioca Flour, Soy Flour, and Cane Sugar

An extreme vertices design for a mixture of three components was used to establish the proportions of tapioca flour (50% to 100% w/w), soy flour (0% to 50% w/w), and cane sugar (0% to 10% w/w) mass fractions in a food gel bead system. Thus, nine compositions were prepared and analyzed. The pasting profiles of the mixtures were studied using a Rapid Visco Analyzer. The texture profiles of fresh, chilled, and rehydrated freeze-dried gel beads were studied using a texture analyzer. Increasing the proportion of soy flour in the range of 11.25% to 50.00% w/w decreased the peak viscosity, breakdown, final viscosity, and setback of mixed flour. Tapioca flour in the proportion of 81.25% to 100.00% w/w recorded the lowest hardness of fresh gel beads (92.00 to 283.00 g). Soy flour in the proportion of 11.25% to 50.00% w/w exhibited lower texture profiles (hardness, chewiness, and gumminess) than tapioca flour in gel beads for both chilled and rehydrated freeze-dried gel beads. Significant relationships were found among pasting profiles of the flour mixtures and texture profiles of fresh, chilled, and rehydrated freeze-dried gel beads, implying a functional role for soy flour in food gel beads. In conclusion, soy flour can act as an anti-retrogradation agent for the gel beads both in chilled (stored at 4°C for 7 days) and freeze-dried conditions. A small amount of cane sugar does not affect the inhibition of starch retrogradation in the gel bead system. Keywords: Anti-retrogradation, Food gel bead, Pasting profile, Soy flour, Tapioca flour, Texture profiles

Uranium biosorption by immobilized active yeast cells entrapped in calcium-alginate-PVA- GO-crosslinked gel beads

A novel biosorbent, i. e. Saccharomyces cerevisiae entrapped in graphene oxide (GO), polyvinyl alcohol (PVA) and alginate and cross-linked in CaCl2- boric acid solution, was prepared, characterized and applied for U (VI) biosorption. The performance of U sorption and cations release (Na, K, Ca and Mg ions) was investigated under different contact time, initial uranium concentration and initial pH. Uranium sorption equilibrium basically achieved after 360 min. The kinetic data of U biosorption and Ca release were best described by the pseudo first-order equation. Both Langmuir and Freundlich models could fit the U sorption isotherm data. With increase of initial uranium (3.7 ~ 472.2 μmol/L) and sodium concentration (78.8 ~ 3911.7 μmol/L), the cations release ((Na + K)/2 + (Ca + Mg)) decreased from 116.9 to 30.1 μmol/g when the corresponding U sorption increased from 0.6 to 77.3 μmol/g. Initial solution pH at 3 was favorable for U sorption when pH ranged from 3 to 7. With increase of uranium concentration, ion exchange played a less role in U removal. The maximum U sorption capacity reached 142.1 μmol/g, calculated from the Langmuir model at initial pH 5. The O-containing functional group, such as carboxyl on the gel bead played an important role in U adsorption according to FTIR and XPS analysis. XPS analysis showed the existence of U (VI) and U (IV) on the surface of gel bead. Ion exchange, complexation and uranium reduction involved in uranium adsorption by the immobilized active dry yeast gel beads.

PEMBUATAN KITOSAN PERAK SEBAGAI ADSORBEN UNTUK MENURUNKAN KADAR LOGAM BESI (Fe) DAN ZINK (Zn) PADA AIR SUNGAI DESA KOPAS KECAMATAN SIMPANG EMPAT KABUPATEN ASAHAN

Penelitian pembuatan kitosan yang dimodifikasi dengan larutan AgNO3 menjadi kitosan perak sebagai adsorben untuk menurunkan kadar logam besi (Fe) dan zink (Zn) pada air sungai desa Kopas kecamatan simpang empat kabupaten asahan telah dilakukan. Pada penelitian ini, didahului dengan pembuatan kitosan perak dengan melarutkan kitosan komersial dan asam asetat 1% serta dicampurkan dengan larutan AgNO3 0,5 M dengan rasio 2:1 lalu diteteskan kedalam larutan NaOH 2 M yang kemudian membentuk gel (bead) berwarna hitam. Kitosan perak yang telah dikeringkan dimasukkan ke dalam kolom, lalu ditambahkan dengan 50 mL sampel yang telah didestruksi dan sudah diketahui kadar logam Fe dan Zn sebesar 1,5175 mg/L dan 0,7218 mg/L. Didiamkan berdasarkan variasi waktu kontak selama 30, 45, dan 60 menit. Penentuan penurunan kadar logam yang telah di adsorbsi oleh kitosan perak dilakukan dengan menggunakan Spektrofotometri Serapan Atom (SSA). Hasil penelitian menunjukkan bahwa pada proses adsorpsi diperoleh persentase penyerapan logam Fe 82,154% dan logam Zn 84,871 % pada waktu kontak optimum penyerapan yaitu 45 menit.