Kinetics of release from kafirin films

Two separate studies were performed. The first studied release of two different preservatives (lactic acid and calcium propionate) from a biopolymer film to a model food with a water activity of a_w=0.95. The second investigated the release of four sugars (fructose, maltose, raffinose and stachyose) with different molecular weights from a biopolymer film to a model food with water activities ranging from 0.85 to 0.95. In both studies, the biopolymer films containing the release components were made from kafirin and placed on the model food, consisting of a gel made of gelatine, sucrose and water with well defined water activity. The amount of preservatives and sugars released from the film to the gel were monitored over time using HPLC at different depths in the model food.The release of preservatives was rapid in both cases, and a gradient of released substances had already formed after 2 h in the model food. The gradients levelled out with time. Calcium propionate had a somewhat faster release than lactic acid.The water activity of the model food had a large impact on the release of sugars. A slow release was observed in the model food with a_w=0.85, while a much more rapid release occurred in the model food with a_w=0.95. There was a limited diffusion depth in the model food with a_w=0.85, probably owing to a limited trial time, while the sugars in the model food with a_w=0.95 diffused deeper into the model food until the film was depleted of available sugars.     

Rheological studies on specific ion forms of ι-carrageenate gels

Measurements have been made of the shear modulus for calcium, potassium and sodium ι-carrageenate gels as a function of biopolymer concentration and temperature. The results are discussed in terms of the application of rubber elasticity theory. Calcium ι-carrageenate gels appear to possess a random glass-like structure whereas both sodium and potassium ι-carrageenate gels form a pseudocrystalline structure. These differences are tentatively attributed to differences in the solubility of the salt forms which, through controlling the gelation temperature, moderate the kinetics of the gelation process.     

Water release kinetics from soy protein gels and meat analogues as studied with confined compression

In this paper, we report on the use of confined compression to study the water release properties from food gels and model meat analogues. Confined compression is a novel method in food science that provides information on the dynamics of water release under mechanical load. Confined compression measurements are compared with numerical simulations based on Flory-Rehner theory. Simulation results for soy protein gels are in reasonable agreement with experiments, while they underestimate the water release from model meat analogues. Time-domain nuclear magnetic resonance (TD-NMR) revealed the presence of internal water-filled cavities in the meat analogues. These cavities could provide a path of low resistance for the water to travel through. However, they are not captured by our current model, which explains the higher fluxes observed experimentally. Our results indicate a relation between the water release properties of meat analogues and pore structure. Control of the pore structure might, therefore, provide new opportunities to improve meat analogue juiciness.     

Reducing salt level in food: Part 2. Modelling salt diffusion in model cheese systems with regards to their composition

In the first part of the paper (Floury, J., Camier, B. Rousseau, F., Lopez, C., Tissier, J. P., & Famelart, M. H. (2009) Reducing salt level in food: Part 1. controlled manufacture of model cheese systems and their structure-texture relationships. LWT – Food Science and Technology 49(10), 1611–1620), a model cheese matrix presenting different textural properties was developed in order to further study the factors implied in the salt release in mouth during food chewing. The present work consists in physical and modelling approaches to better understand the mass transfer phenomena occurring in the product during its consumption in the mouth. Concentration profiles of several ionic species were measured during the release of salt from the different model matrices into artificial saliva. Apparent diffusion coefficients of the sodium chloride were determined by fitting the experimental data to the second Fick's law. Apparent diffusion coefficients were included between 2.81 and 3.43 × 10⁻¹⁰ m² s⁻¹ at 15 °C and 75% HR. D-value decreased strongly when the dry matter content decreased. Microstructure of the matrices with the lower protein concentration was coarser and fluffier, facilitating the diffusion of the solutes. The D-value increased with the pH at renneting, probably because of the chemical changes of the structure of the casein micelles and significant differences in textural characteristics of cheeses. The diffusion coefficient also significantly decreased with the initial salt concentration, due to the tightening of the matrix microstructure.     

乳清分离蛋白凝胶蔗糖释放过程的动力学分析

以蔗糖为食品风味成分,封装于乳清分离蛋白凝胶内,探讨pH值、温度、载药量、释放液离子浓度对乳清分离蛋白凝胶释放蔗糖的动力学机制。结果表明：蔗糖在乳清分离蛋白凝胶中的释放过程符合Korsmeyer-Peppas模型,且拟合相关系数R2在0.95～0.99之间,扩散常数n均小于0.45,符合Fick扩散机理。动力学常数K随pH值、温度、以及释放液离子浓度（0.05～0.10 mol/L）的增加而增大,随载药量的增加而减小。乳清分离蛋白凝胶具有环境应答性,以其为载体的物质释放过程受环境温度、pH值、载药量、释放液离子浓度等因素影响。通过调节释放体系的pH值、温度、载药量、释放液离子浓度可以达到控制载物释放的目的。     

Texture-taste interactions: Enhancement of taste intensity by structural modifications of the food matrix

The reduction of salt and sugar in food products remains a challenge due to the importance of those ingredients in providing a highly desired taste quality, enhancing flavor, determining the behavior of structuring ingredients, and ensuring microbiological safety. Several technologies have been used to reduce salt and sugar content in foods such as replacement of sugar by sweeteners, replacement of sodium salts by blends of other salts, taste enhancement by aromas and taste boosters or gradual reduction of sugar and salt in small steps over time. In this study we present two alternative approaches to enhance taste perception. First, the use of an inhomogeneous spatial distribution of sugar in food gels is introduced as a way to enhance sweetness perception [1]. The translation of the concept of taste contrast to bread applications is discussed which allows to reduce salt content in bread by 25% without loss of saltiness intensity and without addition of taste enhancers, aromas or salt replacers [2]. Secondly, it is demonstrated how the serum release under compression of mixed polysaccharide/protein gels can be engineered to enhance sweetness perception. An increase of serum release by 5x allowed to reduce sugar content of gels by 30% while maintaining sweet taste intensity [3]. The translation of this concept to low salt sausages is discussed. Sausages were engineered to exhibit enhanced juiciness which lead to a boost of saltiness allowing for up to 40% salt reduction [4]. These approaches can be used to further optimize the development of products with reduced salt and sugar content while maintaining taste intensity.     

Mathematical modeling of swelling in high moisture whey protein gels

Gels prepared from whey proteins can be used for controlled release of nutrients or active ingredients in food systems. The objective of this study was to characterize the water uptake by these hydrophilic gels to aid in the design of release systems. Whey protein isolate (WPI) gels (17% w/w protein) of different aspect ratios were submersed in aqueous solution at pH 7.0. Modeling of mass uptake is presented in terms of Case I (Fickian diffusion) and Case II (kinetic) models. Due to the extent of swelling, the Fickian diffusion with moving boundaries provided the most realistic reflection of the physics. An optimization routine provided the best fit values for the diffusivity. The average diffusivity for the smaller gels (with an initial radius of 6.7 mm) was 1.40 × 10⁻¹⁰ m²/s. The average diffusivity of the larger gels (with an initial radius of 8.5 mm) was 0.79 × 10⁻¹⁰ m²/s. The average diffusivities differed due to the slight variation in the composition of the gels. The model also yielded instantaneous values of the radius and sample length. The functionality of moisture uptake and total surface area was linear. The Fickian diffusion with moving boundary model can be extended to evaluate different geometries for controlled release systems.     

Texture design for products using food hydrocolloids

Some in vivo measurements have been carried out using polysaccharide gels of different physical properties (i.e., elastic and plastic) and degrees of hardness. In vivo measurements tested included electromyography (EMG) and acoustic analysis of the swallowing sound to investigate the dynamic changes of food texture during oral processing. As a model of foods for dysphagia patients, the gels were soft enough to be eaten by compression between the tongue and the hard palate without biting by the teeth. From EMG, no significant differences were found between elastic gels and plastic gels in the duration of oral processing and the EMG activity of the suprahyoid musculature when compared at equivalent hardness. The EMG activity of the suprahyoid musculature correlated well with the compression load of gels at 95% strain. From the acoustic analysis, the plastic gels required shorter time to transfer through the pharynx and were scored higher in sensory cohesiveness than the elastic gels. Results indicate that oral processing of soft gels requires equivalent EMG activity of the suprahyoid musculature when the gel hardness is the same. Also, the plastic gels flow through the pharynx as one coherent bolus with smaller variation of the flow speed. Texture of foods for dysphagia patients should be optimized in terms of viscoelasticity so that they can easily transform to swallowable bolus during oral processing.     

CONSTANT STRAIN RATE COMPRESSION OF BIOPOLYMER GELS

Usually, uniaxial compression of food materials is performed at constant speed, which causes an increase of the true strain rate during experiments. By using a method described previously (Jaros and Rohm 1994) highly elastic biopolymer gels were compressed at standard conditions and with decreasing crosshead speed in order to maintain constant strain rate conditions during test. In the case of gels showing failure at a Hencky deformation of > 0.5-0.6, significantly lower values for apparent fracture strain were found in constant strain rate compression. Differences in stress at apparent fracture showed good agreement with respect to this critical value. Implications and consequences on interrelation between sensory and instrumental measurements as well as on relationships between rheological and fracture properties are discussed.     

Monitoring Molecular Diffusion of Sucrose in Xanthan Solutions using Ultrasonic Velocity Measurements

Measurements of the velocity of ultrasound through a sample as a function of diffusion distance were used to study molecular diffusion of sugars through biopolymer solutions. A1 wt% xanthan solution was prepared which consisted of a lower layer containing no sucrose, and an upper layer containing sucrose (10, 20, 30, or 40 wt%). The velocity of ultrasound through the biopolymer solutions was measured as a function of sample height and time, and then converted into sucrose concentration-distance profiles using an empirical calibration curve. The translational diffusion coefficient of the sucrose in the upper and lower layers was determined by fitting the experimental data to a Fickian diffusion model. The measured diffusion coefficients were in reasonable agreement with published values for sucrose in aqueous solutions in the absence of xanthan, which suggests the biopolymer had little influence on molecular diffusion.     

NaCl diffusion kinetics in dry salting of goat cheese

With the aim of studying diffusion during the dry salting of goat cheese, the experimental profiles of salt and water concentrations were determined in terms of time and distance from the interface. The effective diffusion coefficient was determined using Fick’s Second Law for a semi-infinite model. NaCl was not present at distances greater than 2 cm from the interface after 24 h of salting. The moisture profiles were seen to decrease from the surface farthest from the interface to the zone in contact with the salt. In contrast, salt concentrations were highest at the interface and decreased with distance from this point. The value of the effective diffusion coefficient did not vary significantly with distance from the interface, but did decrease significantly with salting time. Essentially the same phenomenon of salt incorporation was found to occur in dry salting as in brining.     

Gelation and phase separation in maltodextrin-caseinate systems

A range of rheological techniques, including small deformation isothermal runs following quenching, controlled rate heating profiles, mechanical spectra, and large deformation strain sweeps and creep compliance testing, were employed in the investigation of maltodextrin—sodium caseinate aqueous dispersions. The concentration dependence, viscoelastic ratio and melting profiles of shear moduli for concentrated maltodextrin samples suggest a highly aggregated, enthalpically linked biopolymer gel. By contrast, the caScinate particles form a ‘pasty’ solid at low temperatures with a high viscous component, which upon moderate heating reverts readily into an entropically driven liquid body. Mixing of the polymers results in a composite system whose phase inversion from a maltodextrin continuous network with discontinuous protein inclusions to a caScinate dispersion suspending the polysaccharide particles is determined by the weight ratio of the two components in the blend. The overall strength of the composite has been related to the mechanical functions of the individual components, and the idea of kinetically trapped mixed gels has been put forward to rationalize the solvent partition between the two constituent phases. Results were used to advance the conclusions reached from work on other mixed biopolymer systems carried out in this laboratory.     

Gelling properties of a κ/ι hybrid carrageenan: effect of concentration and steady shear

The gelling properties of κ/ι hybrid carrageenans extracted from Portuguese seaweeds have been studied for various concentrations and shear conditions. The gel equilibrium storage modulus in 0.05 m KCl shows a power law dependence with the biopolymer concentration. Data analysis with a fibril model indicates that the fractal dimension of networking fibrils differ from the one displayed by pure κ‐ or ι‐carrageenan fibrils. κ/ι hybrid carrageenan gels show thermal hysteresis reminiscent from κ‐carrageenan gels under similar salt conditions. Application of steady shear rate during the cooling of a hot κ/ι hybrid carrageenan solution impedes the gel formation. However, a shear‐rate‐dependent gel structural rebuilding is observed after shear cessation. Shear‐processed gels are softer and show a depressed melting temperature when compared with gels formed under quiescent conditions. These experimental results are compared with data obtained with pure κ‐carrageenan and pure ι‐carrageenan solutions under similar steady shear and salt conditions.     

Retention of ethyl butyrate by gellan gels in the presence of potassium ions

The air/biopolymer partition coefficient (K) and percentage of retention (R%) of ethyl butyrate (400 ppm) added to gellan gels were determined, using static headspace gas chromatography. Potassium chloride (40–120 mM) was used to induce gellan gelation. When 5 g of sample were left to equilibrate at 37 °C for 2 and 24 h, the coefficient values initially decreased with salt concentration to a certain value after which they raised again. The lower coefficient values, for the 24 h period, were observed at higher salt concentration than for the 2 h. Moreover, for both time periods, the lower coefficient values were found for the gellan gels with the greater strength and rigidity and were accompanied by positive percentages of retention. When 15 g of sample were used, after equilibration at 37 °C for 24 h, no significant changes in aroma release were observed. Moreover, negative percentages of retention values were calculated for all salt concentrations.     

A mathematical model to describe flavour release from gelatine gels

A theory of flavour release from gelatine-sucrose gels has been developed based on combined interfacial mass and heat transport. The driving force for flavour release is shown to depend on the bulk melting temperature of the gel, which depends on the gelatine and sucrose concentrations. For gels possessing melting points below the mouth temperature, the driving force for flavour release is the rate at which heat can diffuse into the gels matrix and initiate melting. For harder gels with melting points above mouth temperature the diffusion of sucrose from the surface of the gel into the adjacent saliva phase is the rate limiting step for flavour release, because this lowers the melting temperature of the surface layer. The theoretical model gives good agreement with in vitro release experiments using gelatine gels containing sucrose and dye.     

Understanding of the influence of composition,structure and texture on salty perception in model dairy products

The aim of this study was to better understand salt release and perception in model dairy products, having different composition, structure and/or texture. Sensory and instrumental methods were used to quantify and relate texture to salt mobility and perception. A high dry matter content (protein and fat jamming) and a gel structure with a protein network formation induced a decrease of diffusion coefficient of salt in matrices. Moreover, salty perception was higher for non-renneted products than for gelled ones. For gels, saltiness was enhanced in fat products. These results were discussed in regards with textural and physico-chemical food properties: the structural parameter tan δ was the most correlated with salty perception highlighting the impact of product structure on saltiness. Results also demonstrated that physiology and complex events (mastication, dilution and mixing with saliva, dynamic of bolus formation) occurring during food consumption must be considered to go further in understanding.     

Temporal Sodium Release Related to Gel Microstructural Properties—Implications for Sodium Reduction

The microstructure of food can be engineered to enhance sodium release during mastication, which may be used as a strategy to reduce sodium content in foods. This study aimed to relate sodium release to microstructural properties of solid lipoproteic colloid (SLC) foods. The SLC gels with 1.5% (w/w) NaCl were prepared by homogenization of whey protein isolate and anhydrous milk fat, followed by heat‐induced gelation. The gels varied in protein content (8% or 16%), fat content (0%, 11%, 22%, or 33%), and homogenization pressures (14 or 55 MPa). The maximum rate of sodium release during the initial gel compression increased with increasing gel porosity and pore size. This was due to more releasable serum in the gels with larger pore volume and larger pores. The maximum concentration of sodium at the end of sodium release increased with reduced size of the fat particles in the gels. The smaller fat particles were dispersed more uniformly and interrupted the protein network more, and facilitated the gel breakdown. The above findings suggested that, during the breakdown of the SLC gels, the major mechanisms of sodium release are via serum release followed by sodium diffusion, which are governed by the gel porosity and the particle size of fat, respectively. This study demonstrated the dependence of temporal sodium release properties on the microstructural properties of an SLC food system. The findings from this study could lay the foundation for further investigation of the dependence of saltiness perception on SLC microstructure, which can provide insight for sodium reduction in SLC products.     

Microalgae biomass interaction in biopolymer gelled systems

Microalgae are an enormous biological resource, representing one of the most promising sources for the development of new food products and applications. Pea protein/κ-carrageenan/starch gels, interesting vegetarian alternatives to dairy desserts, served as model systems to study the addition of microalgal biomass, its effect, and subsequent rheological behaviour. Spirulina and Haematococcus gels presented a markedly different rheological behaviour compared to the control mixed biopolymer gelled system. The present goal is to clarify how these microalgae affect the gelation and interact with each biopolymer present in the complex mixed gel system. Hence, the aim of the present work is to study the effect of Spirulina and Haematococcus microalgal biomass addition on the rheological behaviour of pea protein, κ-carrageenan and starch simple gels, as well as in pea protein/κ-carrageenan and pea protein/starch systems. The gelation process was monitored in-situ through dynamic oscillatory measurements (temperature, time and frequency sweep tests) for a 24 h maturation period, and rheological results were supported with fluorescence optical microscopy observations. The addition of Spirulina and Haematococcus to biopolymer gelled systems induced significant changes in the gels’ rheological behaviour and microstructure. In general, it was observed that the gelling mechanism is ruled by the biopolymers, while microalgae seem to be embedded in the gel network acting as active particle fillers. The addition of Haematococcus resulted in more structured gels in comparison to the control and Spirulina systems. In the case of κ-carrageenan gels, both microalgae induced a large increase in the rheological parameters, which should be related to the high ionic content of microalgal biomass. Spirulina addition on starch systems promoted a decrease in the gels’ rheological parameters. This should be related to the starch gelatinization process, probably by competing for water binding zones during the granules’ hydration process.     

The effect of electrical processing on mass transfer in beetroot and model gels

The diffusion between solids and surrounding liquids has been studied under the influence of different electric field strengths varying between 0–1000 V m⁻¹, characteristic both of ohmic heating and Moderate Electric Field (MEF) processing. The rate of enhancement of mass transfer between slabs of beetroot and surrounding fluid has been studied at up to 60 °C, as a function of electric field strength and the orientation of the slab to the field. Enhancements in diffusion coefficient of up to a factor of 2 are seen, with decreased enhancement at higher temperature and when the electric field does not pass through the particle. Diffusion into gels has been studied and enhancement found only for alginate (an ionically set gel) and not for gelatin and egg albumin, that are thermally set gels.     

Compression of gellan gels. Part II: Effect of sugars

The effect of sucrose, glucose, fructose and their mixtures on the gelation of 0.5 wt% low acyl gellan in the presence of potassium chloride (100 mM) was investigated by large deformation compression experiments. The sugar concentration varied from 0 to 15 wt% whereas all their combinations at a final concentration of 15 wt% were also studied. Stress at failure and strain at failure along with Young's modulus were calculated from each compression curve. Samples prior to compression were refrigerated at 5 °C for 1, 2 and 24 h. Glucose showed no contribution to the gellan network strength but decreased the firmness of the gels. On the other hand, fructose and sucrose enhanced the strength of the network, with sucrose being slightly more effective, but had no effect on firmness. This behaviour depended solely on the presence of each sugar and not in their concentration. The elasticity of the gels was not significantly altered by the addition of sugars or their mixtures. Strength and firmness shared similar profiles when mixtures of sugars were used to promote gelation. Sugars, when in mixtures, showed no synergistic interactions whereas their type seems to affect the properties of the resulting gels.