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A molecular dynamics simulation of mixtures of 26-mer amylose with three different egg yolk lipids, namely, cholesterol, triglyceride and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), demonstrated the formation of a stable complex. The 26-mer amylose fluctuated between a coiled and an extended helical conformation. The complex was a V-type amylose complex, with the hydrophobic tail of the lipids being inside the hydrophobic helical cavity of the amylose. The number of glucose units per turn was six for the two helical regions of the amylose-POPC complex and the palmitoyl tail region of the amylose-triglyceride complex. This value was eight for the cholesterol and the two-tail helical region in the amylose-triglyceride complex. Two tails of the POPC were in two different hydrophobic helical regions of the 26-mer amylose, whereas the palmitoyl tail of the triglyceride lay in one hydrophobic helical region and the linoleoyl and oleoyl tails both lay in another helical region, and the cross-sectional area of the latter was larger than the former to accommodate the two tails. The radii of the gyration of the complex were lower for all three cases compared to that of one single amylose. In addition, the stability of the complexes was ranked in the following order: POPC &lt, cholesterol &lt, triglyceride, with their average binding energy being −97.83, −134.09, and −198.35 kJ/mol, respectively.

This study characterized, the surface properties of plasticized and crosslinked zein films. We showed that the distribution of the surface energy into dispersive and polar components of the amphiphilic zein protein was strongly affected by the surface zein is cast on when zein was cast on polystyrene, polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE, Teflon™). Plasticized zein films had higher fractions of dispersive Lifshitz-Van der Waals (γ LW ) components than the Lewis acid base (γ AB ) polar components overall when the surface energy was analyzed and deconvoluted using the Van Oss method. When cast on PDMS the polar component increased, water contact angles were the lowest and the total surface free energy increased as a result. Oleic acid and glutaraldehyde concentration, were also varied during fabrication of the films in addition to contact surfaces. Film composition did not have an equally significant effect on the surface energy of films but as expected affected mechanical properties.

Hen egg is commonly used in bakery products, such as cakes, bread, and cookies, which are all abound with starch. Egg yolk lipids (EYL) with different polarity can affect the structure and properties of starch, as well as steamed bread-making performance. EYL were mainly divided into neutral lipids, cholesterol and phospholipids with increasing polarity by thin layer chromatography. Results from Rapid Visco Analyzer showed that both cholesterol and phosphatidylcholine (PC) promoted gelatinization of wheat starch, but neutral lipids did not. Texture analysis indicated that hardness of wheat starch gels significantly decreased only with PC, caused by an increasing in the spacing between double helical cross-links as characterized by differential scanning calorimetry. Furthermore, a single helix structure of amylose-PC complex was confirmed by molecular simulation and X-ray diffraction. Finally, yolk can be used to soften the firmness of starch-based food such steamed bread.

Antimicrobial peptides are one of the most promising alternatives to antibiotics for targeting pathogens without developing resistance. In this study, pore formation in 1,2-Dimyristoyl-snglycero-3-phosphocholine (DMPC) / cholesterol liposome induced by native melittin, its two mutant variants (G1I and I17 K), and cecropin P1 was investigated by monitoring the dynamics of fluorescence dye leakage. A critical peptide concentration was required for dye leakage with the rate of leakage being dependent on peptide concentration above a critical value. A lag time was required for dye leakage for low peptide concentrations that are above the critical value, which decreased at higher peptide concentrations eventually approaching zero. Lag time was found to be in the order I17 K mutant with lower hydrophobicity and higher net charge > G1I with higher hydrophobicity > melittin > cecropin P1. Cecropin P1 exhibited the highest rate of dye leakage followed by melittin, G1I, and I17 K. Size distribution and transmission electron microscopy (TEM) of liposomes exposed to peptides of different concentrations indicated pore formation with accompanied stretching of liposomes at low peptide concentrations for both melittin and cecropin P1. At much higher concentrations, however, size distribution indicated three peaks for both peptides. In both cases, TEM images show that the middle and small peaks are shown to be due to stretched liposome and broken stretched liposome respectively. For melittin, the large peak is due to peptide aggregates as well as aggregates of liposome. For cecropin P1, however, the large peak indicates cecropin P1 aggregates with solubilized lipids thus suggesting carpet mechanism.

Ultrasound technology employs cavitation to generate high-pressure soundwaves to disrupt bacterial cells. This study reveals the effectiveness of a single frequency ultrasound device for bacterial cell inactivation. A low-cost ultrasound device having a single frequency, i.e. 22 kHz for lab-scale application, was developed first, and the prototype was mechanically designed and analyzed using the finite-element method to assure the targeted natural frequency could be achieved. The prototype was then tested inactivating bacterial cells, Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis), in a simple medium and a food system, and the results were then compared to a commercial system. A treatment time of up to 15 minutes was able to reduce E. coli and B. subtilis cells by 3.3 log and 2.8 log, respectively, and these results were similar to those of the commercial system. The effectiveness of bacterial cell inactivation using the developed single-frequency ultrasound device is then discussed. The findings are useful for designing low-cost ultrasound devices for application in the food industry.

In our previous investigation (Zhang et. al., J. Functional Foods 40 (2018) 700-706), we have proposed a method of complexation of alamethicin (ALM) with γ-cyclodextrin (γ-CD) to increase the solubility and demonstrated an enhancement in its antimicrobial activity against Listeria monocytogenes. In this study, transmission electron microscopy of L. monocytogenes treated with γ-CD/ALM complex indicated cell lysis due to pore formation. This was further corroborated by fluorescent dye leakage from DMPC/cholesterol liposomes when exposed to γ-CD/ALM complex for molar ratios of 1, 5 and 10. The extent of dye leakage increased with ALM-lipid ratio in the range of 0.00015 to 0.16. Dye leakage of γ-CD/ALM complex was found to be the highest for molar ratio of 5, consistent with our earlier results of antimicrobial activity of the complex against L. monocytogenes. All atom molecular dynamics (MD) simulation showed that γ-CD/ALM complex can effectively bind to the 3:1 POPE/POPG bilayer, a mimic of bacterial cell membrane. In addition, circular dichroism spectrum indicated that ALM in the complex has a helical conformation in solution as well as in the presence of liposome. Transmembrane MD simulation of six γ-CD/ALM complex aggregates in α helical conformation showed water channel with barrel stave like pore structure.

Rheological properties of starch are affected by swelling of the granules that is in turn controlled by the degree of crosslinking. A previously developed model for swelling of starch granules was extended to account for electrostatic interactions. Maize starch was crosslinked with sodium trimetaphosphate. Granule swelling of 8% suspension of crosslinked maize starch when subjected to heating to 70,75,80,85 and 90 °C was more pronounced at higher temperatures eventually approaching equilibrium with the swelling ratio decreasing with increase in extent of crosslink. The number of crosslinks in the starch network was inferred from equilibrium swelling and related to peak viscosity and zeta potential. Chemical potential profile as well as the temperature profile within the granule at different times were predicted which were then employed to evaluate the evolution of granule size. The proposed model is able to describe the effect of crosslinking on swelling behavior.

The evolution of 8% suspension of waxy maize starch granule size distribution when subjected to heating to 65, 70, 75, 80, 85 and 90 °C at a heating rate of 15 °C/min were measured. Granule swelling was more pronounced at higher temperatures with an increase in the average size from 13 μm to 25–28 μm, eventually approaching equilibrium. Cryo SEM images revealed porous structure of swollen granule. The proposed model for starch swelling accounts for entropy of mixing, enthalpy of water-starch interaction and elastic restoring force. The second virial coefficient of waxy maize in aqueous medium was characterized by static light scattering. Chemical potential profile as well as the temperature profile within the granule were predicted from the solution of unsteady state diffusion and heat conduction respectively. The granule size was then inferred from the chemical potential profile. The proposed model predicts the evolution of average granule size and granule size distribution accurately.

Foam is a high-volume fraction dispersion of gas into a liquid or a solid. It is important to understand the effect of formulation on shelf life and texture of food foams. The objective of this review is to elucidate mechanisms of formation and stability of foams and relate them to the formulations. Emulsifiers are important in foam formation, whereas proteins are generally preferred to provide long-term stability. Syneresis in foams is a precursor to their collapse in many instances. Intermolecular forces, conformation, and flexibility of proteins play an important role in foam stabilization. An adsorbed protein layer at air/water interfaces imparts interfacial rheology that is necessary to improve the shelf life of foam products. Wettability and spreading of food particles at the interface can stabilize or destabilize foams, depending on their properties. More studies are needed to fully understand the complex interplay of various mechanisms of destabilization in a real-food formulation.

Curcumin (CUR) is a natural food ingredient with known ability to target microbial cell membrane. In this study, the interactions of CUR with different types of model lipid bilayers (POPE, POPG, POPC, DOPC, and DPPE), mixtures of model lipid bilayers (POPE/POPG), and biological membrane mimics (Escherichia coli and yeast) were investigated by all-atom explicit solvent molecular dynamics (MD) simulation. CUR readily inserts into different types of model lipid bilayer systems in the liquid crystalline state, staying in the lipid tails region near the interface of lipid head and lipid tail. Parallel orientation to the membrane surface is found to be more probable than perpendicular for CUR, as indicated by the tilt angle distribution. This orientation preference is less significant as the fraction of POPE is increased in the system, likely due to the better water solvation of perpendicular orientation in the POPE bilayer. In E. coli and yeast bilayers, tilt angle distributions were similar to that for POPE/POPG mixed bilayer, with water hydration number around CUR for the former being higher. Insertion of CUR resulted in membrane thinning. The results from these simulations provide insights into the possible differences in membrane disrupting activity of CUR against different types of microorganisms.

Alamethicin (ALM) inhibits the growth of bacteria by disrupting their cell membrane. ALM exhibits poor solubility in aqueous medium thus limiting its application. A method is proposed for encapsulation of ALM with γ-cyclodextrin (γ-CD) by forming a complex of higher solubility with thermal and pH stability as confirmed by FT-IR and DSC, thus greatly improving its application in food safety. Molecular dynamics simulation suggested a stable configuration of the complex when hydrophobic residues are inserted into the hydrophobic cavity of γ-CD. Aggregation of the complex was inhibited at higher γ-CD/ALM molar ratio. γ-CD/ALM complex exhibited significant antimicrobial activity against L. monocytogenes with the minimum inhibitory concentration being dependent on γ-CD/ALM molar ratio (>0.429 mg/mL for 1:1; >1.094 mg/mL for 5:1; >2.078 mg/mL for 10:1). Optimum γ-CD/ALM molar ratio for maximum antimicrobial activity is the result of competing effects of higher solubility and shielding of hydrophobic ALM groups by γ-CD.

This study performs Stokesian dynamics simulations of suspensions of rigid spheres to determine the conditions under which swollen starch granules can be considered rigid for rheology measurements. The first part of the study benchmarks the numerical simulations to experimental measurements of storage modulus (G′) for monodisperse polystyrene suspensions. The second part of the study compares the simulations to experimental measurements of G′ for waxy maize and normal rice starch suspensions swollen to volume fractions 0.4 0.5. These results indicate that granule deformability plays an important role when φ > 0.5, and indicates the range where one can apply theories of rigid suspension rheology.

Antimicrobial peptides (AMPs) have the ability to penetrate the cell membrane, form pores which eventually lead to cell death. Immobilization of AMP on nanoparticles can play a major role in antimicrobial materials, biosensors for pathogen detection and in food safety. The minimum inhibitory concentration (MIC) of free Cecropin P1 (CP1, sequence SWLSTAKKLENSAKKRLSEGIAIAIQGGPR) and adsorbed on silica nanoparticle against E. coli O157:H7 EDL933 were 0.78μg/ml. This was found to be consistent with preservation of α-helical secondary structure of CP1 upon adsorption as indicated by circular dichroism (CD). Cysteine-terminus modified Cecropin P1 (CP1C, sequence SWLSTAKKLENSAKKRLSEGIAIAIQGGPRC) was chemically immobilized onto silica nanoparticles with maleimide-PEG-NHS ester cross-linkers of different PEG chain lengths. The antimicrobial activity of CP1C in solution and adsorbed on silica nanoparticles against E. coli O157:H7 EDL933 were found to be the same as those for CP1. However, tethered CP1C exhibited much higher MIC of 24.38, 37.55 and 109.82μg/ml for (PEG)20, (PEG)6 and (PEG)2 linkers respectively. The antimicrobial activity of CP1C tethered to silica nanoparticles with (PEG)20 linker was found to be lower for lower surface coverage with MIC values being 86.06, 36.89, 24.38 and 17.84μg/ml for surface coverage of 12.3%, 24.4%, 52.8% and 83.8% respectively. All atom MD simulation of 1:3 DOPG/DOPC mixed membrane interacting with free and PEGlyated CP1C indicated that presence of PEG linker prevented CP1C from interacting with the bilayer which may explain the loss of antimicrobial activity of tethered CP1C.

Since antimicrobial peptides kill bacteria by pore formation in cell membranes, transient pores formed by low power ultrasonication should result in enhancement of antimicrobial activity. Because of its relatively gentle action, low intensity ultrasound is expected to have no adverse effect on food texture. Experiments were conducted for deactivation of pure culture of L. monocytogenes using a model system of naturally occurring antimicrobial peptide (AMP) melittin in the absence as well as in the presence of ultrasonication. In the absence of AMP melittin, ultrasonication has very small effect on cell density upto a power level of 40 W. However, at a higher power level of 60 W, a dramatic decrease in cell density was observed which implied cell lysis. At low AMP concentration, low power ultrasonication did not improve the antimicrobial activity. At high AMP concentrations, however, AMP was found to completely inactivate L. monocytogenes. The synergistic effect of AMP with ultrasonication was found to be the maximum at AMP concentration of 0.78 μg/ml of melittin. A dramatic decrease in 2 orders of magnitude in cell density was observed for ultrasonication in the presence of 0.78 μg/ml of melittin compared to either ultrasonication alone or AMP action alone.

Granule size distribution of 8% w/w suspension of normal rice starch (NRS), waxy rice starch (WRS), modified potato starch (MPS), and normal potato starch (NPS) in water when subjected to heating at 60, 65, 70, 75, 80, and 85°C at different hold times (0–60 min) were characterized. The average starch granule diameter was larger at higher temperatures and hold times for NRS, WRS, and MPS indicating swelling, whereas for NPS it decreased indicating breakage. Swelling varied in the order: MPS > NRS > WRS. Earlier proposed pseudo first‐ and second‐order kinetic and Weibull models for swelling were evaluated. Swelling kinetics was also predicted using our previously developed mechanistic model (Desam et. al., 2018a Journal of Food Engineering 222:237–249) whose predictions agreed well with the experimental data of mean granule diameter and granule size distribution with time at different temperatures, and therefore can be employed to describe swelling at different processing conditions. PRACTICAL APPLICATIONS: Starches are incorporated in food products for a variety of reasons such as stabilizing, thickening, binding, and gelling. Starch occurs as discrete granules. Upon exposure to water, starch granules swell when heated. This results in thickening of starch suspension (known as pasting) due to an increase in volume fraction of swollen granules. Starch pasting results in an increase in its viscosity. Therefore, the texture of a variety of food products such as sauces, puddings, soups, batter mixes, and so forth are influenced by pasting. The rheology and texture of starch paste obtained by cooking of starch granules are governed by its swelling. It is, therefore, necessary to quantify swelling in order to predict the rheology of starch paste as well as to develop new food formulations. We developed a mechanistic model which predicts the swelling kinetics of rice and potato starch suspensions.

Equilibrium swelling of 8 wt % suspension of waxy (WMS) and normal (NMS) maize, waxy(WRS) and normal(NRS) rice when heated to 80 °C at different sucrose concentrations (0–30 wt %) were characterized. The swelling power reached maximum values of 10.5 and 14.5 at sucrose concentration of 5 wt % and 10 wt % for NMS and WRS respectively, increased with sucrose concentration for WMS from 11 to 15.5 and decreased for NRS from 11 to 8.2. The onset temperature of gelatinization increased with sucrose concentration for all starches whereas enthalpy of gelatinization increased for normal maize starches and did not vary significantly for waxy starches. The interaction parameters for three component system of starch, water and sucrose were inferred from static light scattering. The predicted equilibrium swelling for all starches at different sucrose concentrations using Flory-Huggins theory agreed well with experimental data.

We present a methodology to predict the storage modulus ( G ’ ) of starch paste due to granule swelling, given the physical properties of the starch granule and temperature history. This was tested on experimental measurements of granule size distribution and G ’ for 8% w/w suspensions of waxy maize, normal maize, waxy rice, normal rice, and cross linked normal maize – all heated to different temperatures (65–90 °C) with holding times between 2 and 60 min. Experimental data of storage modulus G ′ vs volume fraction φ fall onto a master curve when G ′ is normalized by a multiple of γ / R ‾ , where γ is the granule-solvent interfacial energy, and R ‾ is the average granule size. We show that one can combine this master curve with starch swelling theories to forecast the time-dependent rheology of starches. This work also demonstrates that granule-solvent interfacial energy is a key physical parameter in controlling starch rheology.

Antimicrobial peptides (AMPs) inactivate microbial cells through pore formation in cell membrane. Because of their different mode of action compared to antibiotics, AMPs can be effectively used to combat drug resistant bacteria in human health. AMPs can also be used to replace antibiotics in animal feed and immobilized on food packaging films. In this research, we developed a methodology based on mechanistic evaluation of peptide-lipid bilayer interaction to identify AMPs from soy protein. Production of AMPs from soy protein is an attractive, cost-saving alternative for commercial consideration, because soy protein is an abundant and common protein resource. This methodology is also applicable for identification of AMPs from any protein. Initial screening of peptide segments from soy glycinin (11S) and soy β-conglycinin (7S) subunits was based on their hydrophobicity, hydrophobic moment and net charge. Delicate balance between hydrophilic and hydrophobic interactions is necessary for pore formation. High hydrophobicity decreases the peptide solubility in aqueous phase whereas high hydrophilicity limits binding of the peptide to the bilayer. Out of several candidates chosen from the initial screening, two peptides satisfied the criteria for antimicrobial activity, viz. (i) lipid-peptide binding in surface state and (ii) pore formation in transmembrane state of the aggregate. This method of identification of antimicrobial activity via molecular dynamics simulation was shown to be robust in that it is insensitive to the number of peptides employed in the simulation, initial peptide structure and force field. Their antimicrobial activity against Listeria monocytogenes and Escherichia coli was further confirmed by spot-on-lawn test.

A model for drainage of aqueous foam film with a partial coverage of particles accounts for an inner clean air-liquid film surrounded by a film stabilized by close packed particles at the outer periphery. The drainage of the inner film occurs due to capillary pressure gradient. The film thickness is found to decrease fastest at the center with the inner film being thinner than the outer film eventually leading to its rupture as a result of film thickness becoming zero at the center. The velocity of film drainage is found to be higher for lower particle concentration and higher surface tension. The lifetime (time of rupture) of the film is found to be larger for larger bubble size and liquid holdups (higher initial film thickness). For a film stabilized by close packed monolayer or multilayer of particles, the disjoining pressure is larger for larger particle number concentration and particle size, increases with surface tension only for film stabilized by single or two layers of particles and is a function of bubble size only for film stabilized by multilayers of particles. The maximum disjoining pressure decreases with contact angle approaching zero for a critical contact angle of 129° and increases linearly with surface tension. At mechanical equilibrium, the particle stabilized foam gets drier for larger bubble sizes, contact angles and particle number concentrations.

In this study we employed a layer-by-layer (LbL) deposition technique to produce fish oil in water emulsions encapsulated with a positively charged inner soy β-conglycinin (7S) layer by high shear mixing followed by deposition of a negatively charged outer high methoxyl pectin (HMP) layer using either high shear mixing or homogenization (500 or 3000 psi) and compared them with emulsions produced by 7S-HMP complex. The size, shape, morphology and wall structure of emulsion droplets were characterized by dynamic light scattering and microscopy. Emulsion produced by high shear mixing only were unstable with a droplet size of 7.48 μm. Stable emulsions were produced by high shear mixing followed by homogenization at 500 psi with significantly lower droplet size (3 μm) and uniform two layer shell thickness (80–170 nm) around the drops. The two layer shell thickness of emulsion drops produced by homogenization at 3000 psi was non uniform although it exhibited good long term storage stability. More diffuse distribution of 7S was observed in the adsorbed layer of emulsion droplets that were produced by 7S-HMP complex compared to LbL with a higher layer thickness and a lower ζ potential for the former thereby indicating a difference in morphology of adsorbed layers in the two cases. The results of this investigation seem to indicate that the mechanism of emulsion formation in the second homogenization step is closer to layer by layer deposition than stabilization by 7S-HMP complex and demonstrated a new method of LbL to utilize 7S as an emulsifier.

Lysozyme-silica interactions and the resulting complexation were investigated through adsorption isotherms, dynamic and electrophoretic light scattering, circular dichroism (CD), and isothermal titration calorimetry (ITC). A thermodynamic analysis of ITC data revealed the existence of two binding modes during protein-nanoparticle complexation. Both binding modes are driven by the cooperation of a favorable enthalpy in the presence of a dominating entropy gain. The first binding mode has a higher binding affinity, a lower equilibrium stoichiometry and is driven by a higher entropic contribution compared to the second type. The observed favorable enthalpy gain in both modes is attributed to non-covalent complexation whereas the entropy gain is associated with the re-organization of the silica surface including not only the solvent and counter ion release, but also the protein's conformational changes. Possible mechanisms are proposed to explain non-covalent complexations for each binding mode by relating the changes in the zeta potential and hydrodynamic radius to the obtained adsorption isotherms and calorimetry profile. Based on all these findings, it is proposed that lysozyme adsorption on nano-silica is the result of protein-nanoparticle and protein-protein interactions that further leads to spontaneous, non-directional and random complexation of silica through bridging flocculation.

Emulsions can be prepared from protein microgel particles as an alternative to traditional emulsifiers. Prior experiments have indicated that smaller and more deformable microgels would decrease both the physical destabilization of emulsions and the diffusion-based losses of entrapped volatile molecules. The microgels were prepared from β-lactoglobulin with an average diameter of 150 nm, 231 nm, or 266 nm, large microgels were cross-linked to decrease their deformability. Dilute emulsions of 15–50 μm diameter were prepared with microgels by high shear mixing. Light scattering and microscopy showed that the emulsions prepared with larger, untreated microgels possessed a larger initial droplet size, but were resistant to droplet growth during storage or after acidification, increased ionic strength, and exposure to surfactants. The emulsions prepared with cross-linked microgels emulsions were the least resistant to flocculation, creaming, and shrinkage. All emulsion droplets shrank as limonene was lost during storage, and the inability of microgels to desorb caused droplets to become non-spherical. The microgels were not displaced by Tween 20 but were displaced by excess sodium dodecyl sulfate. Hexanol diffusion and associated shrinkage of pendant droplets was not prevented by any of the microgels, yet the rate of shrinkage was reduced with the largest microgels.

Some amyloid related proteins/peptides are involved in aggregation and pore formation in phospholipid membranes (cell membranes), which result in a variety of neurological disorders such as Alzheimer's disease, Parkinson's disease and Huntington disease. In this research, the mechanism of pore formation by β amyloid (Aβ) peptides was investigated using molecular dynamics simulation by simulating the interaction of the Aβ(11-42) peptide, with a lipid membrane and the potential of the mean force of interaction was evaluated. A 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane system with different cholesterol concentrations was used to simulate the neural cell membrane. The results indicated that Aβ(11-42) peptide oligomers with peptide numbers larger than two were more likely to lead to lipid deformation and water channels, and the free energy of penetration into the membrane decreased with the increasing number of peptides. Increasing the concentration of cholesterol leads to a higher energy barrier for the penetration of peptide into the lipid bilayer thereby protecting the membrane. The results of this research have potential application in the prevention of pore formation by Aβ aggregates on the lipid membrane.

In this review, the definition of interfacial dilatational and shear rheology is outlined and the basis of different experimental methods for their characterization is provided. The connection between interfacial rheology and structure of proteins and other macromolecules is highlighted through the application of polymer theories. Key experimental results on interfacial rheology of air–liquid interfaces stabilized by proteins and protein surfactant mixtures are then presented. This is followed by the analysis of the effect of interfacial rheology on stability of air–liquid interface.

A new approach to the theory of nucleation, formulated relatively recently by Ruckenstein, Narsimhan, and Nowakowski (see Refs. [7–16]) and developed further by Ruckenstein and other colleagues, is presented. In contrast to the classical nucleation theory, which is based on calculating the free energy of formation of a cluster of the new phase as a function of its size on the basis of macroscopic thermodynamics, the proposed theory uses the kinetic theory of fluids to calculate the condensation (W+) and dissociation (W−) rates on and from the surface of the cluster, respectively. The dissociation rate of a monomer from a cluster is evaluated from the average time spent by a surface monomer in the potential well as obtained from the solution of the Fokker–Planck equation in the phase space of position and momentum for liquid-to-solid transition and the phase space of energy for vapor-to-liquid transition. The condensation rates are calculated using traditional expressions. The knowledge of those two rates allows one to calculate the size of the critical cluster from the equality W+ = W− as well as the rate of nucleation. The developed microscopic approach allows one to avoid the controversial application of classical thermodynamics to the description of nuclei which contain a few molecules. The new theory was applied to a number of cases, such as the liquid-to-solid and vapor-to-liquid phase transitions, binary nucleation, heterogeneous nucleation, nucleation on soluble particles and protein folding. The theory predicts higher nucleation rates at high saturation ratios (small critical clusters) than the classical nucleation theory for both solid-to-liquid as well as vapor-to-liquid transitions. As expected, at low saturation ratios for which the size of the critical cluster is large, the results of the new theory are consistent with those of the classical one. The present approach was combined with the density functional theory to account for the density profile in the cluster. This approach was also applied to protein folding, viewed as the evolution of a cluster of native residues of spherical shape within a protein molecule, which could explain protein folding/unfolding and their dependence on temperature.

Allyl isothiocyanate (AITC) are natural essential oil components that have outstanding antimicrobial activities. However, low water solubility, high volatility, and easy degradation by heat, restricting their application in food packing industry. Development of the inclusion complex of β-cyclodextrin/AITC (β-CD/AITC) is a promising solution. Furthermore, the incorporation of β-CD/AITC complex into polylactic acid (PLA) films would be an attractive method to develop food antimicrobial materials. The aim of this study was to evaluate the enhancement in physicochemical properties, antimicrobial activities, and controlled release of β-CD/AITC from such films. The addition of β-CD/AITC significantly increased the flexibility and thermal stability of films. The Fourier transform infrared (FTIR) results revealed that the interactions between β-CD/AITC and PLA films occurred. The controlled release of AITC encapsulated in β-CD was significantly affected by relative humidity and temperature. The PLA films containing β-CD/AITC can be applied as an effective antimicrobial packing material for food and non-food applications.

Antimicrobial peptides (AMPs) inactivate microorganisms by forming transmembrane pores in a cell membrane through adsorption and aggregation. Energetics of addition of an AMP to a transmembrane pore is important for evaluation of its formation and growth. Such information is essential for the characterization of pore forming ability of peptides in cell membranes. This study quantifies the potential of mean force through molecular dynamics (MD) simulation for the addition of melittin, a naturally occurring AMP, into a DOPC/DOPG mixed bilayer, a mimic of bacterial membrane, for different extents of insertion into either a bilayer or a pore consisting of three to six transmembrane peptides. The energy barrier for insertion of a melittin molecule into the bilayer was highest in the absence of transmembrane peptides and decreased for the number of transmembrane peptides from three to six, eventually approaching zero. The decrease in free energy for complete insertion of peptide was found to be higher for larger pore size. Water channel formation occurred only for insertion into pores consisting of three or more transmembrane peptides with the radius of water channel being larger for a larger number of transmembrane peptides. The structure of the pore was found to be paraboloid. The estimated free energy barrier for insertion of melittin into an ideal paraboloid pore accounting for different intermolecular interactions was consistent with MD simulation results. The results reported in this manuscript will be useful for the development of a model for nucleation of pores and a rational methodology for selection of synthetic antimicrobial peptides.

Antimicrobial peptides (AMPs) kill microbial cells through insertion and damage/permeabilization of the cytoplasmic cell membranes and has applications in food safety and antibiotic replacement. Soy protein is an attractive, abundant natural source for commercial production of AMPs. In this research, explicit solvent molecular dynamics (MD) simulation was employed to investigate the effects of (i) number of total and net charges, (ii) hydrophobicity (iii) hydrophobic moment and (iv) helicity of peptides from soy protein on their ability to bind to lipid bilayer and their transmembrane aggregates to form pores. Interaction of possible AMP segments from soy protein with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPC/POPG) bilayers, a mimic of bacterial cell membrane, was investigated. Pore formation was insensitive to helicity and occurred for hydrophobicity threshold in the range of -0.3-0kcal/mol, hydrophobic moment threshold of 0.3kcal/mol, net charge threshold of 2. Though low hydrophobicity and high number of charges help in the formation of water channel for transmembrane aggregates, insertion of peptides with these properties requires overcome of energy barrier, as shown by potential of mean force calculations, thereby resulting in low antimicrobial activity. Experimental evaluation of antimicrobial activity of these peptides against Gram positive L. monocytogenes and Gram negative E. coli as obtained by spot-on-lawn assay was consistent with simulation results. These results should help in the development of guidelines for selection of peptides with antimicrobial activity based on their physicochemical properties.

A mechanistic model for baking of leavened aerated food is proposed. The model accounts for heat conduction, moisture diffusion, diffusion of CO2 that is produced by fermentation, and the resistance to bubble expansion by the viscoelasticity of the dough which is described by Oldroyd B constitutive equation. Unsteady state heat conduction and moisture diffusion equations are solved accounting for bubble expansion due to heating, evaporation of moisture as well as diffusion of CO2 that is produced by fermentation to obtain the evolution of temperature, moisture and air volume fraction profiles as well as dough rise. The bubble expansion due to CO2 diffusion is coupled to temperature and moisture profiles. The model predicts that the growth of bubble exhibits a lag time followed by an exponential growth phase consistent with experimental observations. Eventhough the surface region is more expanded initially, at longer times, it is found to be more dense. The calculated air volume fraction profiles at longer times indicated an expanded inner region of more or less uniform density and a denser surface crust region of decreasing air volume fraction (or increasing density). The thickness of the crust region is found to increase with baking time. The average air volume fraction is found to increase with time because of the combined effects of air expansion as well as CO2 diffusion. The model predictions of dough rise as well as force exerted by the rising dough compare well with the experimental data (Singh and Bhattacharya, 2005; Romano et al., 2007).

In this study, the effect of limited hydrolysis of soy β-conglycinin (7S) on the oxidative stability of 7S hydrolysate (7SH)-stabilized emulsions was investigated under different conditions of pH, ionic strength, degrees of hydrolysis (DH), and protein concentration in the continuous phase. The hydrolysis was performed using trypsinization and acid hydrolysis. Interfacial protein conformations were studied by thioflavin T fluorescence, scanning and transmission electron microscopy techniques, and Raman spectroscopy at oil-mimicking, functionalized silver surfaces. The antioxidant property was tested by the Trolox equivalent antioxidant capacity (TEAC) assay. At DH 0.7%, trypsinization improved emulsion oxidative stability at pH 7 under low ionic strength, as a result of an increase in protein antioxidant property and enhanced interfacial barrier property due to substantial increment of intermolecular β-sheets. The loose coil/helix to intermolecular β-sheet transition was deemed essential in the building of an effective interfacial barrier. At pH 3, however, the tryptic 7SH turned pro-oxidant, and interfacial coverage by the protein became uneven. As such, the emulsion oxidative stability was not better than that based on the native 7S at pH 7. The modification of the surface charge of the oil from non-polar to anionic led to increased formation of intermolecular β-sheet, but it did not improve the emulsion oxidative stability. Lastly, acid hydrolysis of 7S at a similar DH led to flocculation-induced destabilization of the emulsion at pH 3, which exacerbated the intrinsic oxidation of the encapsulated oil even further. Depletion flocculation and bridging were a result of fibril formation during acid hydrolysis.

A mechanistic model for baking of unleavened aerated food is proposed. The aerated food was assumed to consist initially of uniformly distributed same sized bubbles. The liquid medium was assumed to be Newtonian. Bubble coalescence, nucleation of bubbles and formation of interconnected channels were neglected. Unsteady state heat conduction and moisture diffusion equations were solved to obtain the evolution of temperature, moisture and air volume fraction profiles as well as cake rise. Consistent with experimental observations reported in the literature, the height of aerated food was found to increase with time, reach a maximum and decreased at longer times. The cake rise was found to be faster and larger at higher oven temperatures and for aerated food of higher initial air fraction and larger sugar content. The model predictions of cake rise agreed fairly well with the experimental data of Pernell, Luck, Foegeding, & Daubert, 2002 for fitted initial air volume fractions with the agreement being better at longer times for decreasing air volume fractions. The calculated air volume fraction profiles indicated an expanded inner region of more or less uniform density and a denser surface crust region whose thickness increased with baking time.

A model for growth of bubbles during proofing of bread dough is presented for infinitely dilute as well as finite volume fraction gas dispersions. The model accounts for diffusion of CO2, produced by fermentation, along with the resistance to bubble expansion by the viscoelasticity of the dough as described by Oldroyd-B constitutive equation. The model predicts evolution of bubble size, bubble growth rate and the profiles of CO2 concentration and normal stresses in the vicinity of the gas bubble. The growth of bubbles exhibits a lag time followed by an exponential growth phase. The lag time is found to be smaller for larger dough relaxation time, larger surface tension, smaller dough viscosity, higher temperature, higher gas volume fraction and higher CO2 production rate. The bubble growth rate is larger for smaller bubbles resulting in crossover of bubble size at longer times.

A mutated variant of 20 amino acid miniprotein Trp-cage (TC5b), called TC5c (Asp9 replaced by Asn9), was designed to demonstrate the effect of a salt bridge. As a result of strong electrostatic interaction, the distance distribution between Asp9 and Arg16 exhibited a larger probability in the range of the salt bridge for TC5b compared to TC5c. The probability of α-helix formation for residues 3–8, as well as for residues 11–14, was high for TC5b. The salt bridge formation between Asp9 and Arg16 in TC5b was indicated by (a) a strong correlation of their distance of separation with the subtended angle with the centre and (b) a step decrease in the distance between Gly11O and Arg16H at 12 ns. Replica exchange molecular dynamics simulation at different temperatures in the range of 270–590 K indicated that the average distance between Asp9 and Arg16, end-to-end distance, root mean square deviation with respect to a reference NMR structure of TC5b did not change significantly with temperature below 370 K for TC...

A model for creaming and formation of a 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 present 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 fractions for which the phase diagram and evolution of the profile of air volume fraction for batch dispersion are presented.

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 centres. The force field parameters for non-bonded interaction between these centres (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 the potential energy, radius of gyration (RG), end-to-end distance and root-mean-square deviation with those obtained by all-atom (AA) simulation for a small protein molecule Trp-cage as well as for lysozyme in solution. The CG simulation for lysozyme in solution requires less than 1/50 CPU-time compared to that for the AA method. Also, the 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...

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.

A continuous system with a mechanical whipper was designed to make protein stabilized foams. Three different impellers (four-blade, six-blade-straight and six-blade-curve disc) were employed to make foams stabilized by sodium caseinate and whey protein. The inlet liquid flow rate of protein solution was varied in the range of 5–15 mL/s, the whipper speed in the range of 5000–15,000 rpm and temperature ranged from 21 to 80 °C. The effects of whipper speed, flow rate, type of protein, temperature and whipper geometry on foamability, foam stability, power input, apparent viscosity index and bubble size distribution of foams were investigated. Higher foaming capacity was observed at higher whipper speeds, lower liquid flow rates, and in the case of sodium caseinate stabilized foams. The power input was found to be highest for the lowest liquid flow rate. A six-blade curved impeller rotating along and opposite to the direction of the curvature of vanes produced the most foam and smallest bubble size, respectively. Higher temperatures resulted in better foam stability for foams formed with whey protein whereas it had detrimental effect on foam stability with sodium caseinate.

To investigate the dispersibility of lipid coated particles in food suspensions, contact angle of lipid surface at different pH, salt concentration, protein concentration, surfactant type and concentration 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° to 40° 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° to 67° at a concentration of 1 g/L. Surface pressure area isotherm of 150-80SV soybean oil coated 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 150-80SV soybean oil coated 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 mol/L NaCl in 50 g/L citrate buffer showed highest dispersibility.

Nanoparticles possess unique properties as a result of their large surface area per unit volume and therefore can be functionalized by the immobilization of enzymes for a variety of biosensing applications. Changes in the tertiary conformation of beta-lactoglobulin 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. Rapid initial unfolding followed by a much slower rate at longer 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 pI. The effect of temperature on the unfolding of adsorbed protein on the nanoparticle surface was similar to that in the bulk even though the extent of unfolding was higher for adsorbed protein molecules. 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 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 the beta sheet, whereas the beta sheet was converted to an unordered conformation in the presence of DTT.