Effect of high pressure processing on rheological and structural properties of milk–gelatin mixtures

There is an increasing demand to tailor the functional properties of mixed biopolymer systems that find application in dairy food products. The effect of static high pressure processing (HPP), up to 600 MPa for 15 min at room temperature, on milk–gelatin mixtures with different solid concentrations (5%, 10%, 15% and 20% w/w milk solid and 0.6% w/w gelatin) was investigated. The viscosity remarkably increased in mixtures prepared with high milk solid concentration (15% and 20% w/w) following HPP at 300 MPa, whereas HPP at 600 MPa caused a decline in viscosity. This was due to ruptured aggregates and phase separation as confirmed by confocal laser scanning microscopy. Molecular bonding of the milk–gelatin mixtures due to HPP was shown by Fourier-transform infrared spectra, particularly within the regions of 1610–1690 and 1480–1575 cm⁻¹, which reflect the vibrational bands of amide I and amide II, respectively.     

Effect of high pressure homogenization (HPH) on the rheological properties of tomato juice: Viscoelastic properties and the Cox–Merz rule

High pressure homogenization (HPH) is a non-thermal technology which has been widely studied as a partial or total substitute for the thermal processing of food. Although microbial inactivation has been widely studied, there are only a few papers in the literature reporting on physicochemical changes in fruit products due to HPH, especially regarding their rheological properties. The present work evaluated the effect of HPH (up to 150 MPa) on the viscoelastic properties of tomato juice. HPH increased the tomato juice storage (G′) and loss (G″) moduli. The parameters G′ and G″ were modelled as a power function of the oscillatory frequency (ω), and then evaluated as a function of homogenization pressure. It was observed that HPH processing improved tomato juice consistency more than it modified its nature/behaviour. The changes observed in the viscoelastic properties were attributed to disruption of the suspended particles during processing. Moreover, two modified Cox–Merz rules were used to correlate the products steady-state shear properties with viscoelasticity. The results obtained indicated that this process could be used to improve both product elastic and viscous behaviour, highlighting possible applications of the HPH process as a valuable tool to promote physical property changes in food products.     

Effect of heating–cooling on rheological properties of tapioca starch paste with and without xanthan gum

The effect of xanthan gum (Xan) on pasting and gelatinization behavior of tapioca starch (TS) was investigated. Rheological measurements of TS/Xan mixtures with 5% w/w total polysaccharide concentration at different mixing ratios (10/0, 9.5/0.5, 9/1 and 8.5/1.5) were performed to understand the pasting and gelatinization behavior of TS with and without Xan on heating–cooling cycle using a Rapid Visco Analyzer (RVA) and conventional rheometers. Xan increased storage modulus (G′) and loss modulus (G″) of TS dispersions during gelatinization process. Pastes of TS/Xan tended to be more solid-like, i.e., G′ larger than G″, with increasing Xan. The G′ of TS/Xan paste increased when kept at 10 °C indicating the network formation. Pasting temperatures, peak viscosity, final viscosity and breakdown values of TS increased with increasing Xan content but the opposite result was observed in setback value from RVA measurement. Temperature dependence of steady shear viscosity became less pronounced with increasing Xan content on both cooling and reheating indicating that Xan made the mixture more thermally stable. All the results suggest that the sample preparation and measuring conditions influence the rheological properties of TS/Xan mixtures, which should be taken into account in food application.     

Effects of protein interactions on properties and microstructure of zein–gliadin composite films

Zein and gliadin are both readily dissolved in aqueous ethanol and have good film-forming property. This article describes an attempt to improve the flexibility of zein films by the addition of gliadin to the zein film-forming solution. The properties of zein–gliadin composite films, i.e., color, transparency, moisture content, water solubility, water vapor permeability, dynamic contact angle which in turn affected the mechanical property, water resistance and glass transition temperature of films were investigated. The contents of second structure were characterized via Fourier transform infrared spectroscopy (FTIR), whereas morphology of films was examined by scanning electron microscopy (SEM). It was observed that the addition of gliadin enhanced the strain at break of zein–gliadin composite films as a result of the increase in the content of α-helix, β-turn structures and decrease in the level of β-sheet structure. The water resistance of films decreased with the content of gliadin increasing. Morphology of composite films showed that gliadin and zein organized a homogeneous material. This work opens a new perspective for zein in flexible food package.     

Effect of γ-polyglutamate on the rheological properties and microstructure of tofu

The effects of γ-polyglutamates with different concentrations (0.1%, 0.15%, 0.2%) and molecular weights (high, medium, low) addition on the rheological properties, microstructure, and syneresis of tofu were studied. The addition of γ-polyglutamate increased the gelation time, and decreased the storage modulus (G′) and the loss modulus (G″) of tofu. The molecular weight and concentration of γ-polyglutamate effectively changed the rheological properties of tofu. The network of tofu without γ-polyglutamate addition was constructed by fine strands in a dense arrangement as seen by using scanning electron microscope. However, the addition of γ-polyglutamate reduced the thickness of the strands in tofu network. Tofu syneresis was also reduced by the addition of γ-polyglutamate. Increase the concentration of γ-polyglutamate significantly decreased the syneresis of tofu. This trend was more evident on the tofu with high molecular weight γ-polyglutamate.     

Effect of frozen storage and freeze–thaw cycles on the rheological and baking properties of frozen doughs

The effects of prolonged frozen storage and repeated partial freeze–thaw cycles on the rheological and baking properties of nine commercial wheat cultivars were evaluated. The gluten strength of the cultivars ranged from medium to high, whereas the starch swelling characteristics were similar for most cultivars, except Parshall, which exhibited exceptionally high swelling properties. The doughs were subjected to frozen storage for 4–12 weeks, with and without freeze–thaw cycles. The enthalpy of freezable water was significantly affected by initial freezing, whereas, the rheological properties of the doughs were more susceptible to freeze–thaw cycles. After baking, all cultivars produced bread of acceptable quality, although cv. Parshall exhibited the highest crumb softness, irrespective of the frozen treatment. Results indicate that flours with high starch swelling characteristics, along with moderately high gluten strength, may be most ideal for producing optimum quality frozen doughs, with good shelf life and baking properties.     

Sweetness–texture interactions in model dairy desserts: effect of sucrose concentration and the carrageenan type

Sweetness–texture interactions were investigated in model dairy desserts varying in both sucrose concentration and carrageenan composition (κ-, ι-, λ-carrageenans or an equal-weight mixture of the three). Nineteen panellists evaluated sweetness and five oral texture attributes while instrumental texture was characterised by penetrometry. For each carrageenan composition, sweetness significantly increased with sucrose. Rheological profiles or oral texture attributes allowed to distinguish four matrices. Sweetness–texture interactions were observed but no common rule was applied. On the one hand, firmness of κ-carrageenan desserts, springiness and firmness of ι-carrageenan desserts, unctuousness of λ-carrageenan desserts and brittleness and unctuousness of mix-carrageenan ones increased with sucrose concentration. These changes can be partly attributed to changes in the mechanical profiles. On the other hand, variation of carrageenan composition modified sweetness assessment at higher concentrations, λ-carrageenan desserts being the sweetest and ι-carrageenan desserts the least sweet. A model, which considered carrageenan composition, sucrose concentration and their interactions, was established to relate sweetness and composition of the desserts.     

Cookie making behavior of wheat–barley flour blends and effects on antioxidant properties

Refined wheat flour was replaced with whole barley flour at varying levels and the blends were evaluated for their cookie making behavior. The spread factor of cookies decreased as the proportion of barley flour increased while snap force and water activity increased significantly upto 114.7 N and 0.397 in only barley flour cookies. Increasing levels of barley flour lead to a significant decrease in L^∗ and b^∗ values of cookie dough. Peak viscosity (PV) and final viscosity (FV) increased significantly as the levels of barley flour increased. A significant increase in antioxidant activity (AOA), total phenolic content (TPC), metal chelating activity (MCA), reducing power (RP) and total flavonoid content (TFC) was observed as the proportion of barley flour increased. Baking lead to a significant decrease in TPC and TFC whereas AOA, MCA and RP increased. Baking lead to a significant increase in the non-enzymatic browning index of cookies.     

A study on texture–taste–aroma interactions: Physico-chemical and cognitive mechanisms

Texture–taste, texture–aroma and aroma–taste interactions were examined in custard desserts varying in viscosity (at identical composition), sucrose level and aroma nature. All reciprocal interactions were investigated, with each binary interaction addressed through an independent sensory study. Rheological, in vivo aroma release and sucrose release measurements were run in parallel to control for a possible physico-chemical origin of these interactions. Observed interactions were found to be dependent upon the nature of the sensory modalities involved; physico-chemical mechanisms could only in some instances entirely explain these interactions. Taste and aroma did not impact texture perception and this was linked to the fact that rheological properties of the desserts were not modified. Texture affected the taste intensity but not the aroma intensity. Discrepancies between these sensory results and the physico-chemical results were observed. Aroma influenced taste perception and vice-versa, likely through cognitive mechanisms.     

Freezing–thawing effects on the properties of dialdehyde carboxymethyl cellulose crosslinked gelatin-MMT composite films

Freezing–thawing is used as a new method to disperse montmorillonite (MMT) in dialdehyde carboxymethyl cellulose (DCMC) crosslinked gelatin-based films. The effects of freezing–thawing on the structure and properties of gelatin-DCMC-MMT films were investigated. The data of XRD indicate that freezing–thawing plays an important role in dispersing MMT into gelatin matrix and reducing the nanoparticles aggregation. The optical properties studies show that gelatin-DCMC-MMT films are very transparent and have excellent barrier properties against UV light. Freezing–thawing process decreases the transparency of films at visible region due to the better dispersion of MMT. The resulting films exhibit similar total soluble matter (TSM) values. However, the films prepared by freezing–thawing method have higher moisture content (MC), may be resulting from the more void volume obtained during the freezing–thawing process. The water vapor permeability (WVP) measurements show that the addition of MMT decreases the WVP of the films. Moreover, the freezing–thawing method can further decrease the WVP of the films. In addition, the films prepared by freezing–thawing are observed with better mechanical properties and thermal stability. The results suggest that the freezing–thawing method is beneficial to dispersing MMT into the gelatin matrix and raising the properties of DCMC crosslinked gelatin-MMT films.     

Combined effects of wheat gluten and carboxymethylcellulose on dough rheological behaviours and gluten network of potato–wheat flour-based bread

Incorporating high level of potato flour into wheat flour enhances nutritional values of bread but induces a series of problems that lead to the decline of the bread quality. To overcome the barrier, wheat gluten and carboxymethylcellulose (CMC) were added into potato–wheat composite flour to improve dough machinability and bread quality. The rheological properties, thermo-mechanical properties and microstructures of dough were investigated. The results showed that the interaction between gluten and CMC mitigated the discontinuity of gluten matrix and gluten protein aggregation caused by the addition of potato flour, which yielded a more branched and compact gluten network. The compact three-dimensional viscoelastic structure induced improvements of gas retention capacity and dough stability, making it mimic the machinability properties of wheat flour dough. Bread qualities were apparently improved with the combined use of 4% gluten and 6% CMC, of which specific volume increased by 42.86%, and simultaneously, hardness reduced by 75.93%.     

Effects of starches on the textural,rheological, and color properties of surimi–beef gels with microbial tranglutaminase

In order to evaluate effects of starches (corn starch, potato starch, and tapioca starch) on the characteristics of surimi–beef gels with microbial transglutaminase, the cooking loss, gel strength, color and rheological properties of samples were investigated. Results demonstrated that starches gave negative effects on the cooking loss of surimi–beef gels. The gel with corn starch had the highest cooking loss while that with tapioca starch showed the lowest value. The gel with potato starch obtained the highest gel strength. During the sol–gel transitions, surimi–beef complexes with 3% corn starch exhibited the highest storage modulus value, while that with 3% tapioca starch had the lowest one. The addition of starch caused the increase of L* values of surimi–beef gels. Results showed that the excessive amount of starch resulted in the decrease in gel strength of surimi–beef gels.     

Water–water and water–macromolecule interactions in food dehydration and the effects of the pore structures of food on the energetics of the interactions

A molecular dynamics (MD) modeling and simulations approach has been rationally built and developed to study porous food systems constructed with amylose and dextran chains. The findings from our MD studies indicate that the presence of food macromolecules decreases the energetics of the water–water interactions for the nearby water molecules in the pore space, but provides additional water–macromolecule interactions that can significantly outweigh the partial loss of water–water interactions to make the adjacent water molecules strongly bound to the food macromolecules so that the water activity and water removal rate are decreased as dehydration proceeds and, thus, the dehydration energy requirement would be increased. The effects of pore structures are greater in systems with higher densities of food macromolecules, smaller in size pores, and stronger water–macromolecule interactions. Dehydration of food materials can thus be reasonably expected to start from the largest pores and from the middle of the pores, and to have non-uniform water removal rates and non-planar water–vapor interfaces inside individual pores as well as across sections of the food materials. The food porous structures are found to have good pore connectivity for water molecules. As dehydration proceeds, water content and the support from water–water and water–macromolecule interactions both decrease, causing the food porous structures to adopt more compact conformations and their main body to decrease in size. Dehydration in general also reduces pore sizes and the number of pore openings, increases the water–macromolecule interactions, and leads to the reduction of the overall thermal conductivity of the system, so that more energy (heat), longer times, and/or greater temperature gradients are needed in order to further dehydrate the porous materials. Our thermodynamic analysis also shows that the average minimum entropy requirement for food dehydration is greater when the water–macromolecule interactions are stronger and the food macromolecular density is higher. The importance of the physicochemical affinity of food molecules for water and of the compatibility of the resultant porous structures with water configurational structures in determining food properties and food processing through the water–macromolecule interactions, is clearly and fundamentally verified by the results and discussion presented in this work.     

Solutions properties and solute–solvent interactions in ternary sugar–salt–water solutions

Viscometric constants were used to provide information on solute–solvent interactions in ternary water–sugar–salt solutions. Comparison was made between pure water and aqueous salt solution as solvents affecting the behaviour of small carbohydrates. The determination of intrinsic viscosity was made more accurate by applying triple extrapolation of the three equations (Huggins, Kramer and Meffroy-Biget). Results obtained with this triple extrapolation method were compared to that obtained with the Jones–Dole equation usually used. The B coefficient of the Jones–Dole equation was interpreted in terms of its components (B_size) and (B_structure), respectively assigned to the hydrodynamic volume and the contribution to solvent structural change. The determination of the apparent molar volumes in pure water enabled calculation of the hydration numbers. The determined apparent molar volumes of the studied sugars in aqueous salt solutions suggested a dehydration of the sugars explained by sugar–salt interactions. The most important perturbations observed in LiCl solutions compared to those in NaCl solutions were explained by LiCl being surrounded with more water molecules.     

Sweet–bitter interactions and the solution properties of chlorinated sugars

Among chlorinated sugars, some are intensely sweet, some are bitter and others are tasteless. Although chlorination of sugars provokes an increase in lipophilicity, a certain hydrophilic/lipophilic balance is needed for sweeteners to be perceived. Two chlorinated sugars, sucralose (trichlorogalactosucrose) and methyldichlorogalactoside, respectively known for their enhanced sweetness (650×) and inhibitory effect on the sweetness of sucrose, are studied. Their sapid properties are interpreted on the basis of their physicochemical properties (intrinsic viscosity, apparent specific volume, surface tension, contact angle and vibrational spectra). It is particularly shown that the perturbation of the structure of water by these molecules, compared with that by simple sugars, helps in understanding their taste mechanism.     

FT–IR studies on polymorphism of fats: molecular structures and interactions

FT–IR analyses have been made on polymorphic structures of food fats, employing newly developed techniques such as attenuated total reflection (ATR), micro-probe polarized, oblique transmission, reflection absorption spectroscopy (RAS), etc. Two fat crystals, 1,2-dipalmitoyl-3-myristoyl-sn-glycerol (PPM) and 1,3-distearoyl-2-oleoyl-sn-glycerol (SOS) were focused on: PPM is a β′-stable fat and SOS is the major component of cocoa butter. The stearoyl chains in SOS were fully deuterated, so that the FT–IR spectra of the oleoyl and stearoyl chains were differentiated. As for β′₁ form of PPM, the conformations of three acyl chains with respect to the glycerol group and the inclination of the acyl chains against the O⊥ subcell axes and the lamellar plane were observed. In five polymorphs of SOS, it was found that the conformational ordering of stearoyl chains took place in a less stable form, γ form, whereas the ordering of oleoyl chains occurred in a more stable form, β form. These results indicate that the FT–IR spectroscopic analyses are sensitive to molecular-level structures of the polymorphic forms of fats.