Effect of Temperature and Concentrationon Rheological Behavior of Xanthan-CarobMixed Gels

Sundaram Gunasekaran,Won B. Yoon 한국생물공학회 2007 Biotechnology and Bioprocess Engineering Vol.12 No.3

The gelation and melting behavior of 1:1, 1:3 xanthan-carob mixed gels were evaluated at isothermal and non-isothermal states, as a function of total polymer concentrations of 0.1, 0.5, and 1%. A thermal hysteresis was observed between gelation and melting. The higher the polymer concentration, the higher the melting temperature. The gelation points were determined by three criteria. Depending on the criterion used the gelation temperature was different (52 to 70℃). Pseudo-equilibrium modulus and elastic active network chain (EANC) concentration were calculated from the plateau modulus in the frequency spectrum. Temperature dependence of the monomeric friction coefficient was estimated from the relaxation time and EANC. Time-temperature superposition theory was not applicable due to dramatic phase transitions occurring during the gelation of X/C mixture.

Comparison of Concentration Dependence of Mechanical Modulus in Two Biopolymer Gel Systems using Scaling Analysis

김학정,김병용,Sundaram Gunasekaran,박재원,윤원병 한국식품과학회 2013 Food Science and Biotechnology Vol.22 No.6

Concentration dependence of mechanicalmodulus of two biopolymer systems, i.e., xanthan-locustbean (X/L) mixture and fish muscle protein (surimi) wasevaluated and compared at a wide range of polymerconcentrations. A small amplitude oscillatory shear testwas performed to measure changes in storage (G') modulusduring gelation and after gelation. Critical concentration(Cc) of the X/L mixture and surimi gel was determined tobe 0.15 g/100 mL of solvent and 2.04 g/100 g of solvent,respectively. Reduced concentration (CR=CL/Cc) was usedto compare the power-law dependence of modulus of thetwo systems. The elasticity exponent of the X/L mixtureand surimi gel was determined to be 2.4 and 1.97,respectively. The concentration dependence of twobiopolymer gel systems such as physical gels (X/L) andchemicals gels (fish muscle protein) theoreticallydemonstrated that the difference of flexibility of junctionsin the networks might distinguish the elasticity of each gel.

Determination of Frequency Independent Critical Concentration of Xathan and Carob Mixed Gels

Won Byong Yoon,Sundaram Gunasekaran 한국식품과학회 2007 Food Science and Biotechnology Vol.16 No.6

The frequency independent critical concentration (Cc) of xanthan and carob (X/C) mixed gel was determined based on the Winter-Chambon’s theory. X/C mixed (X/C=1:1 ratio) gels were prepared from 0.1 to 1% of concentration. The linear viscoelastic properties, i.e., storage and loss modulus, of X/C mixed gel at 20oC were measured by frequency sweep tests. The frequency independence of tangent function of phase angle (tan δ) of X/C mixed gels was graphically determined from the intersection of the plot of phase angle against concentration at varied frequencies. The intersection (C=0.43%) was considered to be Cc of X/C mixed gel.

Investigation of Linear Viscoelastic Properties of Xanthan-Carob Mixture in Sol and Gel States

Won Byong Yoon,Sundaram Gunasekaran 한국식품과학회 2009 Food Science and Biotechnology Vol.18 No.3

Synergistic interactions between xanthan (X) and carob (C) were investigated by studying the linear viscoelastic behavior of X, C, and X/C mixtures at sol and gel states. At the solution state, storage modulus (G’) dominates the linear viscoelastic properties of X/C mixtures. The gelation temperature (52 to 57℃) was weakly dependent on the xanthan fraction (φX) in the mixture. The φX also had a strong effect on G’ until φX=0.5. The elastic active network concentration (EANC) of X/C gels was estimated from the pseudo-equilibrium modulus. The EANC for systems with φX=0.25, 0.5, 0.75, and 1 at 1% total concentration was 2.3, 4.4, 4.1, and 0.32 (×10?³ ㏖/㎥), respectively. The maximum synergistic effect was observed at about φX=0.5. The G’ at the transition state of X/C mixed gel was proportional to ω<SUP>3/2</SUP> at ω>ωtr (the onset transition frequency) compared to the theoretical limit of ω<SUP>1/2</SUP>.

Evaluation of Structure Development of Xanthan and Carob Bean Gum Mixture Using Non-Isothermal Kinetic Model

Won Byong Yoon,Sundaram Gunasekaran 한국식품과학회 2007 Food Science and Biotechnology Vol.16 No.6

Gelation mechanism of xanthan-carob mixture (X/C) was investigated based on thermorheological behavior. Three X/C ratios (1:3, 1:1, and 3:1) were studied. Small amplitude oscillatory shear tests were performed to measure linear viscoelastic behavior during gelation. Temperature sweep (-1℃/min) experiments were conducted. Using a non-isothermal kinetic model, activation energy (Ea) during gelation was calculated. At 1% total concentration, the Ea for xanthan fraction (φ_x)=0.25, 0.5, and 0.75 were 178, 159, and 123 kJ/mol, respectively. However, a discontinuity was observed in the activation energy plots. Based on this, two gelation mechanisms were presumed-association of xanthan and carob molecules and aggregation of polymer strands. The association process is the primary mechanism to form 3-D networks in the initial stage of gelation and the aggregation of polymer strands played a major role in the later stage.

Effect of Temperature and Concentration on Rheological Behavior of Xanthan-Carob Mixed Gels

Yoon, Won-B.,Gunasekaran, Sundaram Korean Society for Biotechnology and Bioengineerin 2007 Biotechnology and Bioprocess Engineering Vol.12 No.3

The gelation and melting behavior of 1:1, 1:3 xanthan-carob mixed gels were evaluated at isothermal and non-isothermal states, as a function of total polymer concentrations of 0.1, 0.5, and 1%. A thermal hysteresis was observed between gelation and melting. The higher the polymer concentration, the higher the melting temperature. The gelation points were determined by three criteria. Depending on the criterion used the gelation temperature was different (52 to $70^[\circ}C$). Pseudo-equilibrium modulus and elastic active network chain (EANC) concentration were calculated from the plateau modulus in the frequency spectrum. Temperature dependence of the monomeric friction coefficient was estimated from the relaxation time and EANC. Time-temperature superposition theory was not applicable due to dramatic phase transitions occurring during the gelation of X/C mixture.

A Switchable Linker-Based Immunoassay for Ultrasensitive Visible Detection of Salmonella in Tomatoes : A switchable linker-based immunoassay…

Hahn, Jungwoo,Kim, Eunghee,You, Young Sang,Gunasekaran, Sundaram,Lim, Seokwon,Choi, Young Jin Wiley Blackwell (Blackwell Publishing) 2017 Journal of food science Vol.82 No.10

Bifunctional linker-based immunosensing for rapid and visible detection of bacteria in real matrices

You, Youngsang,Lim, Seokwon,Hahn, Jungwoo,Choi, Young Jin,Gunasekaran, Sundaram Elsevier 2018 Biosensors & Bioelectronics Vol.100 No.-

<P><B>Abstract</B></P> <P>Detection of pathogens present in food and water is essential to help ensure food safety. Among the popular methods for pathogen detection are those based on culture and colony-counting and polymerase chain reaction (PCR). However, the time-consuming nature and/or the need for sophisticated instrumentation of those methods limit their on-site applications. We have developed a rapid and highly sensitive immunosensing method for visible detection of bacteria in real matrices based on the aggregation of AuNPs without requiring any readout device. We use biotinylated anti-bacteria antibodies as bifunctional linkers (BLs) to mediate the aggregation of streptavidin-functionalized gold nanoparticles (st-AuNPs) to produce visually recognizable color change, due to surface plasmon resonance (SPR), which occurs in about 30min of total assay time when the sample is mildly agitated or within three hours in quiescent conditions. The aggregation of st-AuNPs, which produces the indication signal, is achieved very differently than in visual detection methods reported previously and hence affords ultrahigh sensitivity. While BLs can both bind to the target and crosslink st-AuNPs, their latter function is essentially disabled when they bind to the target bacteria. By varying the amount of st-AuNPs used, we can tailor the assay effectiveness improving limit of detection (LOD) down to 10CFUmL<SUP>−1</SUP> of <I>E. coli</I> and <I>Salmonella</I>. Test results obtained with tap water, lake water and milk samples show that assay performance is unaffected by matrix effects. Further, in a mixture of live and autoclaved <I>E. coli</I> cells our assay could detect only live cells. Therefore, our BL-based immunosensor is suitable for highly sensitive, rapid, and on-site detection of bacteria in real matrices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An immunosensor was developed for the detection of bacterial targets. </LI> <LI> The indication signal is visual color change due to AuNPs aggregating away from target. </LI> <LI> The detection sensitivity is very high, down to 10CFU/mL. </LI> <LI> Total assay time is about 30min, without needing sample pretreatment or readout device. </LI> <LI> pH and constituents of real matrix has no effect of sensor effectiveness. </LI> <LI> The sensor can detect only live <I>E. coli</I> (ATCC 11775T) in a mixture of live and autoclaved cells. </LI> </UL> </P>