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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.

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.

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.

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.

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.

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 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.

Low-field nuclear magnetic resonance (NMR) spin–spin relaxation (T2) measurements were used to study the denaturation and aggregation of β-lactoglobulin (β-LG) solutions of varying concentrations (1–80 g L−1) as they were heated at temperatures ranging from ambient up to 90 °C. For concentrations of 1–10 g L−1, the T2 of β-LG solutions did not change, even after heating to 90 °C. A decrease in T2 was only observed when solutions having higher concentrations (20–80 g L−1) were heated. Circular dichroism (CD) spectroscopy and fluorescence tests using the dye 1-anilino-8-naphthalene sulfonate (ANS) on 0.2 and 1 g L−1 solutions, respectively, indicated there were changes in the protein's secondary and tertiary conformations when the β-LG solutions reached 70 °C and above. In addition, dynamic light scattering (DLS) showed that protein aggregation occurred only at concentrations above 10 g L−1 and for heating at 70 °C and above. The hydrodynamic radius increased as T2 decreased. When excess 2-mercaptoethanol was added, the changes in both T2 and the hydrodynamic radius followed the same trend for all β-LG protein concentrations between 1 and 40 g L−1. These observations led to the conclusion that the changes in T2 were due to protein aggregation, not protein unfolding. Copyright © 2007 Society of Chemical Industry

In a wind tunnel experiment, the amount of seasoning retained by a fried tortilla chip when exposed to air at different flow rates (0.516 to 1.115 m/s) and angles of inclination (0° to 60°) was measured. The inferred adhesion force of seasoning particle and chip surface using boundary layer theory increased with seasoning particle size (32 to 300 μm), oil content of tortilla chip (24% to 32%), viscosity (55.9 to 72.2 cP), and surface tension (27.5 to 34.1 mN/m) of oil and was in the range of 1.6 x 10 - 9 to 3.3 x 10 - 7 N. The calculated values of adhesion force accounting for van der Waals, electrostatic, and capillary forces showed the same qualitative trend as the experimental data.

Pasting and rheological behavior of pastes made from different commercial soy proteins and starches were investigated for the development of soy protein-based pudding system. Commercial starch Novation ® 2300 and soy protein concentrate Alpha ® 5812 were found to exhibit the most desirable pasting properties. The yield stress values of commercial puddings were in the range of 27.1–59.6 Pa, Consistency index ( K ) values in the range of 6.57–18.63 (Pa s n ) and flow behavior index ( n ) values 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 2 weeks of refrigeration, both G ′ and G ″ increased for all the puddings. Neither water separation nor net syneresis were observed for soy protein-based puddings during 2 weeks of storage at 5 °C. Further adjustments of the formulation that was more comparable to the commercial pudding were achieved.

The effects of cooling rate, holding temperature, pH and polysaccharide concentration on gelation characteristics of gelatin and gelatin–polysaccharide mixtures were investigated using a mechanical rheometer which monitored the evolution of G ′ and G ″. At low holding temperatures of 0 and 4 °C, elastic gelatin gels were formed whereas a higher holding temperature of 10 °C produced less elastic gels. At slow cooling rates of 1 and 2 °C/min, gelling was observed during the cooling phase in which the temperature was decreased from room temperature to the holding temperature. On the other hand, at higher cooling rates of 4 and 8 °C/min, no gelation was observed during the cooling phase. Good gelling behavior similar to that of commercial Strawberry Jell-O ® Gelatin Dessert was observed for mixtures of 1.5 and 15 g sucrose in 100 ml 0.01 M citrate buffer containing 0.0029–0.0066 g low-acyl gellan. Also, these mixed gels were stronger than Strawberry Jell-O ® Gelatin Desserts as evidenced by higher G ′ and gel strength values. At a very low gellan content of 0.0029 g, increasing pH from 4.2 to 4.4 led to a decrease in the temperature at the onset of gelation, G ′ at the end of cooling, holding and melting as well as an increase in gel strength. The gelation time was found to decrease to about 40 min for gelatin/sucrose dispersions in the presence of 0.0029 g gellan at pH 4.2 whereas the corresponding time at pH 4.4 was higher (79 min). In general, the gelation time of gelatin/sucrose dispersions decreased by a factor of 2 to 3 in the presence of low-acyl gellan. The addition of low-acyl gellan resulted in an increase in the gelation rate constant from 157.4 to 291 Pa. There was an optimum low-acyl gellan content for minimum gelation time, this optimum being pH dependent. Addition of guar gum also led to a decrease in gelation time to 73 min with a corresponding increase in the gelation rate constant to 211 Pa/min though these values were not sensitive to guar gum content in the range of 0.008–0.05 g. The melting temperature of gelatin/sucrose/gellan as well as gelatin/sucrose/guar mixtures did not differ significantly from that of pure gelatin or Strawberry Jell-O ® Gelatin Desserts. At pH 4.2, the melting rate constant was highest at a low-acyl gellan content of 0.0029 g whereas the rate constant was insensitive to low-acyl gellan content at pH 4.4. Addition of guar did not seem to affect the melting temperature or the melting rate constant.

The effect of conformation of α-lactalbumin on the dynamics of adsorption as well as on the properties of adsorbed layer at air–water interface were investigated. The surface hydrophobicity of molten globule conformation of α-lactalbumin (prepared by lowering pH to 2) was found to increase by 15-fold compared to the protein in its native form (pH 7) with increased flexibility as evidenced by a much smaller hysteresis area of spread surface pressure isotherms. This higher surface hydrophobicity resulted in (i) higher surface activity of α-lactalbumin in its molten globule conformation compared to the native form inspite of a much higher electrical energy barrier due to much higher net charge and (ii) diffusion controlled adsorption for much longer times and surface pressures than the native form. The diffusion coefficient of α-lactalbumin in molten globule state was lower than that for native form (2.22×10−10 m2 s−1 vs 4.65×10−10 m2 s−1) and increased for the former at higher ionic strength. The area per molecule during the dynamics of adsorption was found to be the same at a fixed surface pressure for both the conformations and lower than the corresponding value for fully denatured protein thus indicating that α-lactalbumin does not fully unfold at the interface in both the conformations. Even though α-lactalbumin adsorbed much more in its molten globule conformation, it gave poor interfacial rheological properties compared to the native form. Ionic strength did not influence the relationship between the interfacial elasticity and surface concentration for both the conformations.

In this work, carbohydrate nanoparticles were created to prolong the efficacy of antimicrobial peptide against pathogens. Nisin and Listeria monocytogenes were used as the peptide and pathogen models, respectively, and phytoglycogen (PG)-based nanoparticles were developed as carriers of nisin. PG from su1 mutant maize was subjected to β-amylolysis as well as subsequent succinate or octenyl succinate substitutions. The goal was to minimize the loss of peptide during storage and meanwhile realize an effective release in the presence of bacteria. The capabilities of PG derivatives as carriers of nisin were evaluated using centrifugal ultrafiltration, zeta-potential, and the initial availability of nisin against L. monocytogenes. All methods indicated that nisin loading was favored by a high degree of substitution (DS), presence of hydrophobic octenyl moiety, and β-amylolysis of PG nanoparticles. To evaluate the prolonged nisin efficacy, preparations containing nisin and PG derivatives were loaded into a BHI-agar deep-well model (mimicking nisin depletion at the nutrient-containing surface). The residual inhibitory activities of preparations against L. monocytogenes were monitored during 21 days of storage at 4 °C. The results showed that all PG derivatives led to the prolonged retention of nisin activity and the longest retention was associated with high DS, β-amylolysis, and octenyl succinate. Evidently, both electrostatic and hydrophobic interactions are the driving forces of nisin adsorption, and the glucan structure at the nanoparticle surface also affects nisin loading and retention during storage.

Food samples of different compositions were formulated by extruding mixtures of starch and gluten of different compositions, whereas samples of varying pore structure were obtained through extrusion of durum semolina at 57 and 137°C. Experimental measurement of desorption isotherm of these samples at different temperatures in the range 25–40°C indicated that the water binding ability was fairly insensitive to the pore structure of food samples and was found to be lower for extruded and pregelatinized samples as well as for samples of higher gluten content. Experimental desorption isotherm data were represented by the Oswin equation in order to evaluate moisture binding energy as a function of moisture content and temperature by employing the Clausius-Clapeyron equation. Binding energy was found to be negligible at high moistures (above 0·2 d.b.), increasing at lower moisture contents, lower temperatures and higher starch contents. Effective diffusivity of moisture through the porous food at different moisture contents and temperatures was inferred from drying curves in the temperature range 60–105°C. Effective diffusivity (D eff ) was higher in pregelatinized samples and was found to be much higher through porous puffed pasta than regular pasta. The effect of composition on D eff was confounded by the effect of pore structure as a result of variations in pore size distribution in the extruded samples of different compositions. The decrease in D eff at lower moisture contents was postulated to be due to the decrease in the available free water for diffusion and was explained through a simple model which related the available free moisture to the binding energy.

A model for the unsteady state drainage of a standing foam has been proposed. This model accounted for (i) the liquid drainage from plateau borders due to gravity as well as the gradient of plateau border suction and (ii) the movement of the foam-liquid interface due to the accumulation of drained liquid, and assumed that the foam bed consisted of dodecahedral bubbles of the same size. The simplifying assumption of a negligible fraction of liquid in thin films, employed in the present model, was justified through the comparison of the timescales of film and plateau border drainage. Typical evolutions of a liquid holdup profile as well as a foam-liquid interface are reported for foam generated by bubbling inert gas through a liquid pool at a constant gas flow rate in the form of bubbles of the same size. The predicted equilibrium liquid holdup profile has been shown to depend only on the density difference, bubble size and surface tension but not on viscosity and surface viscosity, and compared well with experimental data. Asymptotic expression for the equilibrium disjoining pressure indicated that larger density difference, larger bubble sizes and smaller surface tensions would tend to make the standing foam less stable.