• Journal of the Korean Applied Science and Technology
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• v.32 no.4
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• pp.758-766
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• 2015

Dextran is a generic term for a bacterial exopolysaccharide synthesized from sucrose and composed of chains of D-glucose units connected by ${\alpha}$-1,6-linkages by using dextransucrases. Dextran could be used as vicosifying, stabilizing, emulsifying, gelling, bulking, dietary fiber, prebiotics, and water holding agents. We isolated new strain capable of producing dextran from Korean traditional kimchi and identified as Leuconostoc sp. strain JYY4. Batch fermentation was conducted in bioreactor with a working volume of 3 L. The media was MMY and 15% (w/v) sucrose. Mineral medium consisted of $3.0g\;KH_2PO_4$, $0.01g\;FeSO_4$, $H_2O$, $0.01g\;MnSO_4$, $4H_2O$, $0.2g\;MgSO_4\;7H_2O$, 0.01 g NaCl, $0.05g\;CaCl_2$ per 1 liter deionized water. The pH of media was initially adjusted to 6.0. The inoculation rate was 1.0% (v/v) of the working volume. Temperature was maintained at $28^{\circ}C$. The agitation rate was 100 rpm. The production pattern of dextran was associated with the cell growth. After 24 hr dextran reached its highest concentration of 59.4 g/L. The sucrose was consumed completely after 40 hr. Growth reached stationery phase when sucrose became limiting, regardless of the presence of fructose or mannitol. When the specific growth rate was 0.54 hr-1, utilization averaged 5.8 g/L-hr. The yield and productivity of dextran were 80% and 2.0 g/L-hr, respectively. Dextrans produced by were separated to two different size by an alcohol fraction method. The size of high molecular weight dextran (45% alcohol, v/v), less soluble dextran, was between MW 500,000 and 2,000,000. Soluble dextran (55% alcohol, v/v) was between 70,000 and 150,000. The molecular weight average of total dextran (70% alcohol, v/v) was between 150,000 to 500,000. The enzymatic hydrolyzates of total dextran of ATCC 13146 showed branched dextrans by Penicillium dextranase contained of glucose, isomaltose, isomaltotriose, and isomaltooligosaccharides greater than DP4 (degree of polymerization) that had branch points. Compounds greater than DP4 were branched isomaltooligosaacharides. Hydrolysates by the Lipomyces dextranase produced the same composition of oligosaccharides as those by Penicillin dextranase.

• Korean journal of food and cookery science
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• v.18 no.1
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• pp.43-50
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• 2002

This study was carried out to evaluate the quality attributes of frozen soy yogurts prepared by freezine soy yogurts, which are made of different types of Bifidobacteria (B. bifidum, B.breve, B. infantis) and oligosaccharides (fructooligosaccharides, galactooligosaccharides, isomaltooligosaccharides) containing $\alpha$-chymotrypsin treated soy protein isolate were evaluated in terms of overrun, melt-down quality, changes in the total number of Bifidobacteria after freezing, and sensory evaluation. The quality attributes of soy yogurts were also evaluated in terms of changes in the number of viable cells of Bifidobacteria in soy yogurts after incubation at 37$\^{C}$, pH 3.0 for 90 min, water holding capacity, and viscosity. The overrun of frozen soy yogurts fermented by B. bifidum showed the hiehest value but those fermented by B. infantis showed the lowest, while the melt-down quality of soy yogurts were vice versa. The total numbers of Bifidobacteria after freezing for 30 min in ice cream maker showed more than 10$\^$9/ CFU/ml. In sensory evaluation, all $\alpha$-chymotrypsin treated frozen soy yogsurt showed little beany flavor. In sour, sweet, and bitter tastes and mouth feel, the frozen soy yogurts fermented by B. bifidum evaluated better but those fermented by B. infantis evaluated worse. Also in the overall quality, the frozen soy yogurts fermented by B. bifidum were evaluated desirable but those fermented by B. infantis were evaluated undesirable. The water holding capacity and viscosity of soy yogurts fermented by B. bifidum showed the highest values but those fermented by B. infantis showed the lowest values. The total numbers of Bifidobacteria of all soy yogurts decreased from 10$\^$9/ CFU/ml to 10$\^$8/ CFU/ml after incubation at 37$\^{C}$, pH 3.0 for 90 min.

• Korean Journal of Food Science and Technology
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• v.30 no.3
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• pp.630-637
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• 1998

Enzymatic properties of immobilized transglucosidase (TG) from Aspergillus niger was characterized and compared with soluble TG. Michaelis-Menten constant $(K_m)$ and maximum velocity $(V_{max})$ of immobilized TG were $122\;mM,\;3.9{\times}10^{-2}\;mM/min$ and in case of soluble TG, 21 mM, 0.4 mM/min. The optimum pH of immobilized TG was pH 5.0 like soluble TG but immobilized TG showed 16% and 45% higher activity than soluble TG at pH 5.0 and pH 6.0. Both of immobilized TG and soluble TG were stable from pH 2.0 to pH 9.0, and therefore their activities in these pH ranges were remained more than 90%. The temperature was optimal at $60{\sim}70^{\circ}C\;and\;70{\sim}80^{\circ}C$ for soluble TG and immobilized TG, respectively. The thermal stability of immobilized TG was significantly improved than that of soluble TG, and immobilized TG retained $32{\sim}40%$ higher activity than soluble TG. D-values from thermal inactivation of immobilized TG were 7690 sec at $65^{\circ}C$, 83 sec at $75^{\circ}C$, 7.2 sec at $80^{\circ}C$. Z-values of soluble and immobilized TG were $6.4^{\circ}C\;and\;5.3^{\circ}C$, respectively. The little difference of activation energies of soluble TG and immobilized TG supposed that there was little difference in mass transfer limitation during the reaction of soluble TG and immobilized TG.