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Colloidal Phenomena in Food and Bioprocessing

Investigators
Narsimhan, Ganesan
Institutions
Purdue University
Start date
2011
End date
2016
Objective

1. Investigation of pore formation and rupture of cell membranes by antimicrobial peptides.

2. Investigation of combined effect of low frequency ultrasound and antimicrobial peptides on pore formation in cell membranes

3. Investigation of conformational changes of peptides on surfaces.

4. Soy protein as an anti-oxidative encapsulant for delivery of bioactive lipids in aqueous medium

5. Investigation of kinetics of swelling and pasting behavior of starch.

6. Characterization of controlled release properties of starch based dendrimers.

More information

NON-TECHNICAL SUMMARY:
It is important to devise effective methods of prevention of food contamination by pathogens. In order to design synthetic antimicrobial peptides that are more effective in deactivation of pathogens with improved selectivity, it is necessary to quantify their role in pore formation of cell membranes. The effectiveness of synthetic peptides in pore formation is governed by the conformation of molecule when interacting with cell membrane. Computer simulation will be employed to determine this for different amino acid sequence of peptides to help in their design. Pore formation will be quantified by monitoring leakage of a flourscent dye from the cell. Mathematical models will be developed to (i) elucidate the mechanism of pore formation and (ii) the relationship between the peptide structure and nucleation rate of pores in cell membranes. Sonication is generally employed to kill microorganism. Experiments will be performed to quantify synergistic effects of low energy sonication with antimicrobial action. Soyprotein hydrolysate will be investigated as an agent to prevent rancidity in food emulsion systems containing bioactive lipids such as omega 3 fatty acids, phytosterol etc. while providing physical stability. Hydrolysate will be prepared by enzymatic or acid hydrolysis. The rancidity of the emulsion will be quantified by peroxide value. Starch is commonly used in many types of food. Upon heating, starch granules tend to swell that results in thickening of the suspension. The extent of swelling and subsequent thickening influences the texture and mouthfeel of the product. Starch will be crosslinked using phosphoryl chloride. Experiments will be conducted to understand the relationship between the extent of cross linking of starch and its swelling and pasting characteristics. Mathematical models will be developed to connect the pasting behavior to the structure of starch. Starch based Dendrimer, phytoglycogen, is well suited for controlled release of antimicrobial peptide and flavor components. Mathematical model will be developed to describe the rate of release of peptides from phytoglycogen.

APPROACH:
Laboratory experimental techniques will be employed to characterize the conformation, interfacial properties of adsorbed proteins/polypeptides and particle size distribution of food dispersions. Flourescence spectroscopy and confocal microscopy will be employed to monitor pore formation in lipid bilayers. Circular dichroism, infrared spectroscopy, surface enhanced raman spectroscopy and ultracentrifugation will be employed to characterize the interfacial adsorbed layer of proteins and polypeptides. Molecular Dynamics will be employed to characterize the secondary and tertiary conformations of polypeptides interacting with surfaces and lipid bilayers. Dynamic light scattering will be employed to characterize the particle size of liposomes and emulsion droplets. Osmometry, static light scattering, intrinsic viscosity, microscopy and Rapid Visco Analyser will be used to characterize the starch granule. Principles of colloid and interfacial phenomena, statistical thermodynamics and transport phenomena are to be applied to describe the behavior of thin films and proteins/polypeptides at interfaces at the nanoscale. This information will be useful in understanding the role of food formulation on the texture and shelf life of food products and also in understanding the mechanism of deactivation of microorganisms using ultrasonication and pulsed electric field.

PROGRESS: 2011/10 TO 2012/09

OUTPUTS:
The conformation of Cecropin P1 in the presence of mixture of 2,2,2-triflouroethanol (TFE)/water of different composition as well as upon immobilization onto silica nanoparticles surface were characterized using molecular dynamics (MD) simulation and circular dichroism (CD). Explicit solvent MD simulation for TFE/water mixture indicated an increase in helical content with increasing TFE concentration from 12.90% (buffer) to 30.30% (15% TFE) consistent with experimental values (13.44% for buffer to 32.55% for 15%TFE) obtained from CD as a result of more intermolecular H-bond formation in nonpolar environment. Adsorption of CP1 onto silica was found to result in a decrease in ? helical content with increasing silica concentration (e.g. 32.55% in 15% TFE/water mixture to 30.02% and 28.83% in the same solution in the presence of 2.3% and 6.5% silica nanoparticles, respectively) with this effect being more pronounced for lower TFE concentrations. Flourescence intensity of dyes of different molecular weights vs time for small liposome (SL) and large liposome (LL) for different mellitin liposome ratio Q indicate a lagtime which was higher for lower Q. Above a critical Q, no lag time was observed. Lag time decreases with Q and is smaller for smaller size as well as for SL compared to LL at the same Q. In addition, the rate of increase of flourescence after the lag time is found to be smaller for lower Q for FD4 and FD20. Confocal images of very large liposomes containing calcein were captured at different times which show decay of flourescence intensity with time thus indicating dye leakage as a result of pore formation. Comparison of CD spectra for mellitin with that for mellitin + LL mixture (without dye) show a decrease in random coil. Similar results were observed for SL. The baby formula formulation without any protein (7S or SP) was unstable as indicated by a dramatic increase in emulsion drop size after day 1. The addition of either 7S or soyprotein (SP) was critical to the physical stability of the product. For 7S hydrolysate (7SH) stabilized baby formula product, the physical and oxidative stability were superior for an optimum degree of hydrolysis of 0.08 (Trypsin/7S ratio). As expected, drop size for was lower for 7S concentration of 0.5%. Eventhough the emulsion drop size of the product stabilized by SP and SPH increased with the degree of hydrolysis, degree of hydrolysis of 0.08 (Trypsin/SP ratio) was found to be optimum for oxidative stability.Fortified tomato soup with fish oil was made by reconstituting tomato soup (2% brix) and adding 2% fish oil and either 7S or 7SH. This mixture was then homogenized as described above. The product without any 7S or 7SH was unstable. The physical and oxidative stability were optimum for degree of hydrolysis of 0.08 (Trypsin/7S ratio). Orange oil (11% v/v) emulsion with 2% fish oil was made by homogenization either in the presence or absence of 7S or SP. The addition of 7S or SP was essential for physical stability of the product. The addition of 7S or SP (0.25% concentration) resulted in better oxidative stability with the former being slightly superior to the latter. PARTICIPANTS: Dr. Xiaoyu Wu worked on all the projects. Dr. Lu Zhou worked on the pore formation in liposome by melittin. Hector Chang worked on molecular dynamics simulation of Cecropin P1 in mixture of TFE and water to determine the secondary conformation and comparison with experiments. Xi Wu worked on the characterization of oxidative stability of fish oil emulsion with soy protein hydrolysate in food systems. Dr. Ramanathan Nagarajan, Natick Soldier Center: Collaborator in Cecropin P1 molecular dynamics simulation. Natick Soldier Center: Funding organization for the project on molecular dynamics of Cecropin P1 C. Indiana Soyboard Alliance: Funding organization for the project on oxidative stability of fish oil emulsions in food. TARGET AUDIENCES: Food scientists. PROJECT MODIFICATIONS: Not relevant to this project.

PROGRESS: 2010/10/01 TO 2011/09/30

OUTPUTS:
Molecular dynamics simulation was carried out for the antimicrobial peptide Cecropin P1 C (CP1) in solution, CP1 adsorbed onto silica surface as well as for CP1 tethered to silica surface with a polyethylene oxide (PEO) linker of two different lengths for explicit solvent. Low energy structure for CP1 in solution consists of two regions of high helix probability (residues AKKLEN and EGI) with a sharp bend. Water density profile in the vicinity of silica surface in the presence of adsorbed CP1 showed two peaks at distances of around 2.96 A and 5.03 A. H2 bond density profile in the vicinity of silica surface exhibited a single peak in the presence of CP1 (at 2.97 A). The ? helix probability for different residues of adsorbed CP1 is not significantly different from that of CP1 in solution at low ionic strength of 0.02 M whereas there is a decrease in the probability only in the second region of residues ISEGI at higher ionic strength of 0.12 M. The conformation of CP1 tethered to silica surface with either (PEO)6 or (PEO)3 linker exhibited only one region of high ? helix probability (residues SKTAKKL for (PEO)3 and TAKKLEN for (PEO)6 )). The conformation of CP1 in solution is closer to that of former than latter as a result of less surface interaction of tethered polypeptide with a longer linker. The conformation of SKKKKKKKKS in the vicinity of a titania surface was determined by molecular dynamics simulation using explicit solvent for three different crystal forms (rutile, brookite and anatase). Its conformation after interaction with the rutile surface exhibited a higher ?-helix content. The anatase surface induced much more turns in the conformation of the polypeptides compared to other two surfaces. The water density peak was at smaller distance from the surface for rutile, whereas the peak was at the largest distance for anatase. The conformation of SKKKKKKKKS in the vicinity of center, edge or corner of anatase showed insignificant differences. The conformation of SKKKKSSKKKKS and SSKKKKKKKK in the vicinity of anatase crystal indicated that the presence of a serine at the two ends of the polypeptide resulted in a bend whereas two serines in one end leads to a structure without a bend and with increased ? helix in aqueous medium. When SKKKKSSKKKKS from the solution was placed at the center of the anatase surface, the total helix did not decrease. However, there was a decrease in the total helix for SSKKKKKKKK. The effect of limited hydrolysis of soy ?-conglycinin (7S) on the oxidative stability of 7S hydrolysate (7SH)-stabilized emulsions was investigated. Two different methods of hydrolysis were carried out, namely trypsinization and acid hydrolysis. Oxidation of Menhaden oil-in-water emulsions was accelerated at 55oC in the dark over 7 days, and monitored by the ferric thiocyananate peroxide value assay. Enzyme hydrolysis of 7S provided superior oxidative stability compared to acid hydrolyzed 7S. In addition, oxidative stability of emulsion stabilized by enzyme hydrolyzed 7S at pH 12.5 was the highest followed by that at pH 9 and at pH 7.

PARTICIPANTS: Ganesan Narsimhan is the PI on all the three projects (i) Conformation of Cecropin P1 C immobilized on silica surface using Molecular Dynamics (ii) Effect of Interaction of Model Polypeptides with Titania on their Confromation and (iii) Soy protein as an anti-oxidative encapsulant for delivery of bioactive lipids in an aquoues medium. Xiaoyu Wu worked on both projects (i) and (ii) and was responsible for all the calculations for conformations of peptides using molecular dynamics. Hector Chang worked on project (i) and was responsible for the characterization of peptide-peptide interactions on conformation. Pui Yeu Phoon worked on project (iii) and was responsible for experiments to characterize the effect of hydrolysis of 7S on oxidative stability of emulsions. Fernanda San-Martin Gonzalez is a co-Pi for project (iii) and participated in the development of experimental strategies. Army Natick Lab sponsored both projects (i) and (ii) Ramanathan Nagarajan and Charlene Mello of Natick lab participated as collaborators in project (i). Shaun Filocamo and Robert Stote participated as collaborators in project (ii). TARGET AUDIENCES: Food scientists. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

PROGRESS: 2009/10/01 TO 2010/09/30

OUTPUTS:
A model for creaming and formation of foam layer in an aerated system consisting of Newtonian liquid is proposed. The variation of air volume fraction in the dispersion layer is described by hindered creaming which is coupled to syneresis in the top foam layer that is described by flow of liquid through a network of Plateau borders due to gravitational and capillary forces. The analysis accounts for the compressibility of foam layer by coupling creaming analysis with syneresis in the foam layer. The behavior of the system is described by three parameters (a) characteristic time scale of creaming of an isolated bubble (b) hydrodynamic interaction factor and (c) capillary number, ratio of capillary and gravitational forces in the foam layer. System behavior is shown to be different for four different regions of initial air volume fraction for which the phase diagram as well as evolution of profile of air volume fraction for batch dispersion are presented. As a result of strong electrostatic interaction, the distance distribution between Asp9 and Arg16 exhibited a larger probability in the range of salt bridge for native Trp cage (TC5b) compared to mutant (TC5c in which Asp9 is replaced by Asn9). The probability of helix formation for residues 3-8 as well as for residues 11-14 were high for TC5b. Replica Exchange Molecular Dynamics (REMD) simulation at different temperatures in the range of 270 to 590 K indicated that the average distance between Asp9 and Arg16, end to end distance, root mean square deviation (RMSD) with respect to a reference NMR structure of TC5b did not change significantly with temperature below 370 K for TC5b and increased at higher temperatures. These values were higher for TC5c for the whole temperature range with their rate of increase with temperature being higher below 370 K. Molecular dynamics (MD) simulation of Cecropin P1 C show an equilibrium structure consisting of two helix regions with a sharp bend for Cecropin P1 C in solution consistent with the available structures of other antimicrobial peptides. At higher temperatures there was a loss of helical content resulting in unfolding of the hinge. The conformation of adsorbed Cecropin P1 C on silica surface indicated a ? helix content of around 10% as opposed to a value of around 30% in solution, with the end-to-end distance for the former being around 4 nm compared to a value of 1.5 to 2 nm for the latter. The equilibrium conformation of Cecropin P1 C tethered to silica surface with a PEO linker is found to have even lower helical content (4.5%) compared to the adsorbed polypeptide (7.8%) though the former was more compact (end to end distance of 2.0 nm) than the latter (end to end distance of 4.1 nm). Tethered Cecropin P1 C is found to have two helical regions (residues 2 to 8 and 24 to 28) as opposed to adsorbed Cecropin P1 C which is found to exhibit only one helical region (residues 17 to 25). PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Food Scientists. PROJECT MODIFICATIONS: Not relevant to this project.

PROGRESS: 2008/10/01 TO 2009/09/30

OUTPUTS:
The effect of different starch samples on the foamability and stability of foams formed with linear alkylbenzene sulfonate (LAS) were investigated. Foams were made in a continuous shear mixer at 1800 rpm for equal flow rates of air and liquid (4.8 ml/s) at room temperature. Foam volume fraction, bubble size, zeta potential, foam height, and apparent viscosity were measured to characterize the foam. Foam stability was also characterized by direct measurement of half life. The evolution of liquid holdup profile in a standing foam was measured for foams stabilized by LAS in 3;1 and 2:1 glycerine water mixture using magnetic resonance imaging. Adsorption isotherm as well as competitive adsorption of starch 1- LAS mixture at air-water interface was investigated using Langmuir minitrough. Interfacial dilatational elasticity and dilatational viscosity of starch1-LAS mixture at air-water interface were characterized for a frequency of 5 rpm using pulsating bubble surfactometer. The average bubble size increases with time as a result of bubble coalescence. The apparent viscosity is found to decrease with time since the foam becomes drier with time because of syneresis. Zeta potential became more negative at higher surfactant concentration due to adsorption of more surfactant at air-water interface. Half life of foam formed with a mixture of surfactant and starch (0.01 % of starch 5 or starch 6) increased noticeably with surfactant concentration. For uncharged hydrophobic as well as amphoteric samples, however, half life changed little with surfactant concentration. The half life was highest at the lowest surfactant concentration for cationic starch samples and decreased at higher concentrations. Highest positive charge provided greatest foam stability as a result of electrostatic complexation with anionic LAS, followed by highly charged amphoteric starch and starch of highest hydrophobicity. A coarse grain (CG) algorithm is developed for molecular dynamics (MD) simulation of proteins in which the polypeptide backbone as well as side chains were mapped into spherical interaction centers. The force field parameters for non bonded interaction between these centers (beads) were evaluated from the interaction of all atoms corresponding to these beads using pairwise additivity. The validity of CG algorithm was demonstrated by comparing potential energy, radius of gyration, end to end distance and root mean square deviation (RMSD) with those obtained by all-atom simulation (AA) for a small protein molecule Trp-cage as well as for lysozyme in solution. CG simulation for lysozyme in solution requires less than 1/50 CPU-time compared to that for AA method. Also, CG method converges to equilibrium potential energy much faster than AA simulation. CG simulation for lysozyme adsorbed on silica surface showed that the molecule is more unfolded with a less compact tertiary structure compared to that in the solution (with higher radius of gyration,end to end distance and projected area on silica surface), this effect being more pronounced at higher temperature. Higher ionic strength resulted in a more extended structure for lysozyme on silica surface. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.

PROGRESS: 2007/10/01 TO 2008/09/30

OUTPUTS:
A continuous shearing apparatus was employed to make sodium caseinate stabilized foams which was characterized by bubble size, apparent viscosity, foam volume fraction and liquid holdup profile. The bubble size of the foam was smaller for higher rotational speed of the rotor, lower ionic strength, pH away from pI, higher xanthan gum concentration and room temperature and did not vary significantly with air-liquid ratio. Bubble size at different gum concentrations correlated well with dimensionless Weber number. The foam volume fraction was higher at higher values of rotational speed, air-liquid ratio, xanthan gum concentrations and at pH 7 and 9. The evolution of liquid holdup profile indicated faster syneresis at higher ionic strength, higher temperature and lower air-liquid ratio. Collapse of the foam caused by syneresis was more pronounced at higher ionic strengths and higher temperature. The foam produced at pH 6 was drier with liquid holdup less than 0.26. The foam exhibited shear thinning behavior with the apparent viscosity of foam increasing initially with time as a result of syneresis followed by a decrease at longer times due to coarsening of bubble size. The presence of emulsion droplets decreased foam stability. Changes in tertiary conformation of β lactoglobulin and lysozyme adsorbed on 90 nm silica nanoparticles with time were inferred using tryptophan fluorescence and Fourier Transform Infrared Spectroscopy (FTIR) for different surface concentrations, temperature, pH, ionic strength and 2,2,2-trifluoroethanol (TFE) and Dithiothreitol (DTT) concentrations. For lysozyme, rapid initial unfolding, followed by a much slower refolding and subsequent unfolding, were observed with the extent of unfolding being higher at lower surface concentration, higher ionic strengths, higher TFE and DTT concentrations and at pH 9. In contrast, β lactoglobulin unfolded slower and exhibited only an initial rapid and a subsequent slow unfolding phase. Circular Dichroism (CD) spectra showed that α helix content was lower for adsorbed lysozyme compared to bulk with a corresponding increase in β sheet and random coil. This decrease in α helix was found to be more pronounced at lower surface concentrations. For β lactoglobulin, however, altering the surface concentration by itself did not change the secondary structure on the surface. For lysozyme, DTT decreased α helix with a corresponding increase in random coil while TFE was found to have negligible effect on secondary structure. For β lactoglobulin, TFE was found to increase the α helix content at the expense of the fraction of β sheet, while β sheet was converted to unordered conformation in the presence of DTT. The results of the extent of change in tertiary conformation using FTIR as indicated by the change in the ratio of amide II'/amide I was consistent with those obtained by tryptophan fluorescence whereas the rates of conformational changes given by FTIR were found to be much faster. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.

PROGRESS: 2006/10/01 TO 2007/09/30

OUTPUTS:
Changes in tertiary conformation of beta lactoglobulin adsorbed on 90 nm silica nanoparticles with time was inferred using tryptophan fluorescence and Fourier Transform Infrared Spectroscopy (FTIR) for different surface concentrations, temperature, pH , ionic strength and 2,2,2-trifluoroethanol (TFE) and Dithiothreitol (DTT) concentrations. A rapid initial unfolding followed by a much slower rate at larger times was observed with the extent of unfolding being higher at lower surface concentrations, higher ionic strengths, higher temperature, higher TFE and DTT concentrations and at pI. The effect of temperature on unfolding of adsorbed protein on nanoparticle surface was similar to that in the bulk eventhough the extent of unfolding was higher for adsorbed protein molecules. The results of the extent of change in tertirary conformation using FTIR as indicated by the change in the ratio of amide II'/amide I were consistent with those obtained by tryptophan fluorescence whereas the rates of conformational changes given by FTIR were found to be much faster. Circular Dichroism (CD) spectra showed that altering the surface concentration by itself did not change the secondary structure of beta lactoglobulin on the surface. TFE was found to increase the alpha helix content at the expense of the fraction of beta sheet, while beta sheet was converted to unordered conformation in the presence of DTT. A continuous shearing apparatus was employed to make sodium caseinate stabilized foams which was characterized by bubble size, apparent viscosity, foam volume fraction and liquid holdup profile. The bubble size of the foam was smaller for higher rotational speed of the rotor, lower ionic strength, pH away from pI, higher xanthan gum concentration and room temperature and did not vary significantly with air-liquid ratio. Bubble size at different gum concentrations correlated well with dimensionless Weber number. The foam volume fraction was higher at higher values of rotational speed, air-liquid ratio, xanthan gum concentrations and at pH 7 and 9. The evolution of liquid holdup profile indicated faster syneresis at higher ionic strength, higher temperature and lower air-liquid ratio. Collapse of the foam caused by syneresis was more pronounced at higher ionic strengths and higher temperature. The foam produced at pH 6 was drier with liquid holdup less than 0.26. The foam exhibited shear thinning behavior with the apparent viscosity of foam increasing initially with time as a result of syneresis followed by a decrease at longer times due to coarsening of bubble size. The presence of emulsion droplets decreased foam stability. Waxy maize starch dispersions (2% w/w) were heated at 60, 65, 70, and 80 C for 80 minutes, and swelling ratio was determined as a function of time. Swelling kinetics was also measured at 80 C for waxy maize cross linked starch at two different levels of cross linking. Results indicated a rapid increase in water absorption of starch granules within 60 seconds, followed by a gradual increase to reach an equilibrium granule volume. Higher ionic strength led to less swelling. TARGET AUDIENCES: Scientists interested in biosensors and nanotechnology for food safety applications

PROGRESS: 2005/10/01 TO 2006/09/30

To investigate the dispersibility of wax coated particles in beverages, contact angle of wax surface at different pH, salt concentration, protein concentration, surfactant type and concintration was measured. Contact angle decreased with an increase in the emulsifier conecentration when the concentration was low, and reached a fairly constant value at higher concentrations. Whey protein was more efficient compared to other emulsifiers and decreased the contact angle from 100 degrees to 40 degrees at a concentration of 0.5 g/L or higher in water. Tween 20 was more efficient than other tween emulsifiers and it decreased the contact angle from 100 degrees to 67 degrees at a concentration of 1 g/L. Surface pressure area isotherm of wax particles at an air-water interface was obtained using Langmuir trough. Contact angle of the particles at the air-liquid interface, inferred from the critical surface pressure in the isotherm, agreed well with the contact angle of planar surface obtained using goniometer. Dispersibility of wax particles in aqueous solution was characterized by measuring the bulk particle concentration upon suspension. At pH 2.5, 5 g/L whey protein in the presence of 0.5 M NaCl in 50 g/L citrate buffer showed highest dispersibility. A generalized formalism for the rupture of an equilibrium foam film due to imposed random thermal and mechanical perturbations, modeled as a Gaussian white noise, is presented. The evolution of amplitude of perturbation is described by a stochastic differential equation. The average film rupture time is calculated by employing a first passage time analysis. The calculated values of rupture time agree well with the results of linear stability analysis for unstable film with immobile film interfaces. For stable films, the average rupture time was found to be higher for smaller amplitudes of imposed perturbations, larger surface potentials and smaller Hamaker constants. The mean rupture time for partially mobile gas-liquid interface, as characterized by two dimensionless groups, dimensionless surface viscosity and dimensionless Marangoni number, increased with the two dimensionless groups and approached the limiting value for immobile interfaces. The rupture time distribution was found to be broader for larger film thickness, smaller pressure amplitude, lower Hamaker constant and smaller surface potential. The evolution of fluorescence spectra of aromatic residues of adsorbed beta lactoglobulin molecules on surface of silica nanoparticle of 90 nm diameter when excited at 280 nm was measured for beta lactoglobulin to characterize the kinetics of unfolding. The rate as well as the extent of unfolding was more at lower surface concentrations, lower ionic strengths and near pI. The difference between unfolding at pH 7 and 5 was found to be more pronounced at lower surface concentrations. A phenomenological model for unfolding was proposed which accounted for adsorption of protein from the bulk followed by unfolding at the surface. The adsorbed protein molecule was visualized as being in native, intermediate, unfolded and dimer states. The model was shown to describe qualitatively the experimental behavior.

PROGRESS: 2004/10/01 TO 2005/09/30

Surface tension response of a pulsating bubble with adsorbed layer of beta lactoglobulin was measured for different frequencies and protein concentrations using a pulsating bubble tensiometer. The adsorption rate constants were inferred from the surface pressure dynamics of protein adsorption using a Langmuir minitrough. A model was proposed to infer the interfacial dilatational viscosity and elasticity of adsorbed beta lactoglobulin layer at air-water interface from the experimental pulsating bubble data for protein concentrations in the range of 0.01 to 0.5 wt % at pH 7. The interfacial dilatational rheological properties were higher at higher protein concentrations, this effect being less pronounced for dilatational elasticity. The traditional approach for the inference of interfacial dilatational rheological properties is found to overpredict the interfacial dilatational elasticity whereas the viscosity values do not differ significantly from those obtained using the current analysis. Linear stability analysis for a film on a solid surface with a viscoelastic air-liquid interface is presented. The interfacial dilatational and shear viscoelastic properties were described by Maxwell models. Dilatational and shear interfacial elasticity and viscosity were shown to improve film stability. Calculated values of maximum growth coefficient for thin film stabilized by 0.5% beta lactoglobulin approached those of mobile films for thick (>2000 nm) and those for immobile films for thin (IMPACT: 2004/10/01 TO 2005/09/30The results from the first study will provide information on dilatational viscosity of adsorbed protein layer that is essential for the prediction of stability of food foams. The second and third studies characterize the effects of surface elasticity and external perturbations on thin film stability and therefore foam stability. The understanding of the effects of different parameters on formation and stability of protein stabilized foams is essential for the development of formulation for food foams with desirable texture and shelf life.

PROGRESS: 2003/10/01 TO 2004/09/30

Evolution of liquid holdup profile in a standing foam formed by whipping and stabilized by sodium caseinate in the presence of xanthan gum when subjected to 16g and 29g centrifugal force fields was measured using magnetic resonance imaging for different pH, ionic strength, protein and xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Foam drainage was slowest at pH 7, lower ionic strength, higher protein and gum concentrations. Foam was found to be most stable at pH 5.1 near the isoelectric point of protein, lower ionic strength and higher protein and xanthan gum concentrations. Predicted equilibrium liquid holdup profile based on a previous model agreed well with experimental values at sufficiently long times. Proposed model for velocity of drainage of a power law fluid in a Plateau border for two different simplified geometries was incorporated in a previously developed model for foam drainage to predict the evolution of liquid holdup profiles. The model predictions for simplified circular geometry of Plateau border compared well with the experimental data of liquid holdup profiles at small times. At longer times, however, the predicted liquid holdup profile was larger than the observed, this discrepancy being due to coarsening of bubble size and decrease in foam height not accounted for in the model. Newtonian model for foam drainage under predicted drainage rates and did not agree with the experimental data. Pasting and rheological behavior of pastes made from different characteristics of commercial soy proteins and starches were studied for the development of soy protein-based pudding system. Among different sources of commercial starch and soy protein, starch Novation (copyright) 2300 and soy protein concentrate Alpha (copyright) 5812 were found to exhibit the most desirable pasting properties. All tested pastes and commercial puddings exhibited pseudoplastic behavior with yield stress. The yield stress values of commercial puddings were in the range of 27.1-59.6 Pa, Consistency index (K) were in the range of 6.57-18.63 (Pa.Sn) and flow behavior index (n) were in the range of 0.4192-0.6558. The K, and n values for soy protein-based puddings were found to be comparable to those for the commercial puddings. During two weeks of refrigeration, both G prime and G double prime increased for all the puddings.

Funding Source
Nat'l. Inst. of Food and Agriculture
Project source
View this project
Project number
IND010657
Accession number
131798
Categories
Prevention and Control
Predictive Microbiology
Parasites
Natural Toxins
Viruses and Prions
Bacterial Pathogens
Chemical Contaminants
Commodities
Produce