Quantitative analysis of the network structure that underlines the transitioning in mechanical responses of pea protein gels
Munialo, C.D. ; Linden, E. van der; Ako, K. ; Jongh, H.H.J. de - \ 2015
Food Hydrocolloids 49 (2015). - ISSN 0268-005X - p. 104 - 117.
whey-protein - rheological properties - gelation properties - large-deformation - particulate gels - ionic-strength - isolate gels - mixed gels - set - ph
The objective of this study was to analyze quantitatively the network structure that underlines the transitioning in the mechanical responses of heat-induced pea protein gels. To achieve this, gels were prepared from pea proteins at varying pHs from 3.0 to 4.2 at a fixed 100 mg/mL protein concentration. Gels were also prepared by varying the protein concentration from 100 to 150 mg/mL at a fixed pH 3.0. Mechanical deformation properties of the gels were determined. An increase in protein concentration at a fixed pH resulted in an increase in fracture stress and Young's modulus. Variation of the pH at a fixed protein concentration resulted in transitioning in mechanical responses such as fracture stress, fracture strain, and the recoverable energy. The network structures were visualized by the use of confocal laser scanning and scanning electron microscopy, and the characteristic length scales of these structures were quantitatively analyzed in terms of the pair correlation function. Variation of the protein concentration at a fixed pH did not significantly alter the microstructure of the gels, whereas variation of the pH at a fixed protein concentration resulted in significant changes in the gel structure. Structural transitioning was shown to occur around pH 3.7. The findings from this study show transitioning in rheological responses of pea protein gels occur as a result of structural changes. The results from this study offer opportunities to broaden the application of pea proteins in food products, as products with desirable rheological (textural) and structural properties can be designed from pea proteins.
Preparation, structure and stability of sodium caseinate and gelatin micro-particles
Ince, A.E. ; Saglam, D. ; Venema, P. ; Linden, E. van der; Scholten, E. - \ 2015
Food Hydrocolloids 45 (2015). - ISSN 0268-005X - p. 291 - 300.
glucono-delta-lactone - whey-protein particles - light-scattering - physical-properties - beta-lactoglobulin - swelling behavior - phase-separation - ionic-strength - high-pressure - mixed gels
Protein particles are promising candidates for texturing food products and can be produced in several ways. Here, we produced protein particles using a two-step emulsification method. This method is suitable to change the size of the particles and to control the protein concentration inside the particles. In this study, we prepared protein particles from two different protein sources, sodium caseinate (NaCas) and gelatin, that are gelled by acidification and cooling, respectively. The size and the internal protein concentration of the particles, their stability against heating and pH changes were studied. Although similar emulsification conditions were used to prepare the particles, NaCas particles were found to be 10 times smaller (average diameter 400 nm) than the gelatin particles (average diameter 4 µm). The internal protein concentration of the NaCas particles (16.8% w/w) is approximately twice as high compared to that of gelatin particles (7.6% w/w) (using an initial protein concentration of the solution of 10% (w/w)). The NaCas particle dispersions were found to be stable between pH 3 and pH 4. The particles disintegrated at pH values further away from the iso-electric point. Upon heating the dispersions at 90 °C, the NaCas particles were shown to be heat stable. Dispersions of gelatin particles were stable against aggregation at all pH values studied, except at pH 6, while the particles melted above 40 °C. Swelling of both particles was observed for both acidic and alkaline pH values. We conclude that emulsification method is robust for different protein sources used.
Modification of Ovalbumin with Fructooligosaccharides: Consequences for Network Morphology and Mechanical Deformation Responses
Munialo, C.D. ; Ortega, R.G. ; Linden, E. van der; Jongh, H.H.J. de - \ 2014
Langmuir 30 (2014)46. - ISSN 0743-7463 - p. 14062 - 14072.
protein gels - rheological properties - beta-lactoglobulin - maillard reaction - pea protein - neutral ph - mixed gels - gelation - aggregation - perception
The Maillardation of proteins has been used as a natural alternative to improve its functionality by covalent coupling of proteins with saccharides. However, the impact of Maillard reaction on the structural aspects of protein networks and, as a consequence, the mechanical breakdown properties of the gel networks has not been reported. The objective of this study was to evaluate how the attachment of linear oligo-sugar moieties onto ovalbumin affects its aggregation, network morphology, and consequently the mechanical deformation properties including the ability of the networks to elastically store energy in this material. To potentially alter the morphology of the network structure, ovalbumin was modified by conjugating some of its amino groups with fructooligosaccharide (FOS) moieties via the Maillard reaction. It was demonstrated that the attachment of FOS to ovalbumin does not affect the integrity of the secondary and tertiary structure as characterized using circular dichroism and tryptophan fluorescence. Differences in the network morphology were observed by scanning electron microscopy for FOS-modified ovalbumin variants. Upon increased modification, the microstructure of the gels had more and larger pores and had thinner strands than nonmodified variants. Evaluation of the large deformation properties of the gels demonstrated that FOS-modified gels were less strong and less brittle and showed lower stiffness than nonmodified variants. The recoverable energy (elastically stored energy) of gels reduced with an increase in the degree of modification. The results show that the attachment of FOS to ovalbumin alters the structural and mechanical (large) breakdown properties of the protein gels. The consequences of the alteration of the network structure and large deformation properties of FOS-modified ovalbumin offer opportunities to efficiently design food materials with desirable techno-functional applications
The ability to store energy in pea protein gels is set by network dimensions smaller than 50 nm
Munialo, C.D. ; Linden, E. van der; Jongh, H.H.J. de - \ 2014
Food Research International 64 (2014). - ISSN 0963-9969 - p. 482 - 491.
globular protein - beta-lactoglobulin - large-deformation - particulate gels - heat-treatment - whey-protein - mixed gels - gelation - ph - dissociation
The objective of this study was to identify which length scales set the ability to elastically store energy in pea protein network structures. Various network structures were obtained frompea proteins by varying the pH and salt conditions during gel formation. The coarseness of the network structure was visualized by the use of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) and ranked from least coarse to most coarse networks. Least coarse networks were formed at a pH away from the isoelectric point (IEP) of pea proteins, and at a low ionic strength, whereas more coarse networks were formed at pH values close to the IEP and at a high ionic strength during gel formation. Mechanical deformation properties of the gels such as elastically stored (recoverable) energy, Young's moduli (stiffness of gels), fracture stress (gel strength), and fracture strain (brittleness of the gels) were measured by the use of a texture analyzer and correlated to the coarseness of the networks structure. The influence of coarseness on the ability of the networks to elastically store energy was observed for length scales below 50 nm. The findings show that elastically stored energy of pea protein gels can be modulated via the creation of different network structures below 50 nm length scales. The results from this study contribute to a better understanding of the dimensions that set the ability to elastically storage in pea protein gels. If the ability of pea proteins to store energy can be understood, products can be better tailored for consumers.
Whey protein particles modulate mechanical properties of gels at high protein concentrations
Saglam, D. ; Venema, P. ; Vries, R.J. de; Berg, L. van den; Linden, E. van der - \ 2014
Food Hydrocolloids 38 (2014). - ISSN 0268-005X - p. 163 - 171.
stabilized emulsion gels - beta-lactoglobulin - viscoelastic properties - rheological properties - isolate gels - mixed gels - microstructure - behavior - gelation - ph
We have studied the influence of dense whey protein particles on the mechanical properties of whey protein isolate (WPI) gels at high protein concentrations (16–22% (w/w)). Incorporation of dense whey protein particles in the gel, while keeping the total protein concentration constant, leads to a considerably lower storage modulus. By adding protein particles, the total protein concentration of the WPI gels could be increased by 25–55% (w/w), without increasing the storage modulus of the gel. The large deformation properties of the WPI gels were also influenced by the presence of dense protein particles. Gels containing protein particles fractured at a lower strain than pure WPI gels at the same protein concentration. We conclude that protein particles can be used to modulate mechanical properties of WPI gels and are promising candidates for the development of high protein foods with improved textural properties.
Serum release boosts sweetness intensity in gels
Sala, G. ; Stieger, M.A. ; Velde, F. van de - \ 2010
Food Hydrocolloids 24 (2010)5. - ISSN 0268-005X - p. 494 - 501.
mixed gels - sensory perception - microstructure - sugar - fat - preferences - rheology - quality - texture - impact
This paper describes the effect of serum release on sweetness intensity in mixed whey protein isolate/gellan gum gels. The impact of gellan gum and sugar concentration on microstructure, permeability, serum release and large deformation properties of the gels was determined. With increasing gellan gum concentration the size of the pores present in the protein network, the permeability and the serum release increased, as well as the Young's modulus, the fracture stress and the fracture strain. Increasing the sugar concentration induced an increase of the pore size, but resulted in a decrease of permeability and serum release. The addition of sugar resulted in gels with a higher Young's modulus and a lower fracture strain. This effect was more evident at higher gellan gum concentrations. By changing the protein concentration of the gels, a set of samples was prepared exhibiting constant large deformation properties but varying in serum release and sugar concentration. Serum release significantly boosted sweetness intensity. For example, the sweetness scores for gels with 12% serum release were the same as for gels with 2% serum release but 30% higher sugar concentration. The results indicate that serum release is a tool to compensate for the loss taste intensity related to the reduction of sugar and salt in gelled foods.
Elastic networks of protein particles
Riemsdijk, L.E. van; Sprakel, J.H.B. ; Goot, A.J. van der; Hamer, R.J. - \ 2010
Food Biophysics 5 (2010)1. - ISSN 1557-1858 - p. 41 - 48.
rheological behavior - silica suspensions - phase-separation - concentrated suspensions - viscoelastic properties - biopolymer mixture - scaling behavior - flow behavior - mixed gels - microstructure
This paper describes the formation and properties of protein particle suspensions. The protein particles were prepared by a versatile method based on quenching a phase-separating protein–polysaccharide mixture. Two proteins were selected, gelatin and whey protein. Gelatin forms aggregates by means of reversible physical bonds, and whey protein forms aggregates that can be stabilized by chemical bonds. Rheology and microscopy show that protein particles aggregate into an elastic particle gel for both proteins. Properties similar to model systems of synthetic colloidal particles were obtained using protein particle suspensions. This suggests that the behaviour of the particle suspensions is mainly governed by the mesoscopic properties of the particle networks and to a lesser extent on the molecular properties of the particles
Microstructural features of composite whey protein/polysaccharide gels characterized at different length scales
Berg, L. van den; Rosenberg, Y. ; Boekel, M.A.J.S. van; Rosenberg, M. ; Velde, F. van de - \ 2009
Food Hydrocolloids 23 (2009)5. - ISSN 0268-005X - p. 1288 - 1298.
heat-induced gelation - protein isolate - beta-lactoglobulin - kappa-carrageenan - mixed gels - pressure - food - microscopy - model - ph
Mixed biopolymer gels are often used to model semi-solid food products. Understanding of their functional properties requires knowledge about structural elements composing these systems at various length scales. This study has been focused on investigating the structural features of mixed cold-set gels consisting of whey protein isolate and different polysaccharides at different length scales by using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Whey protein cold-set gels were prepared at different concentrations to emulate stiffness of various semi-solid foods. Mixed gels contained different concentrations of gellan gum, high methyl pectin or locust bean gum. Results obtained with CLSM, at the micrometer length scale, indicated the homogeneous nature of the investigated gels. Results obtained with SEM, at the sub-micron length scale, indicated the presence of spherical protein aggregates. During the gel preparation (acidification), the presence of polysaccharides in the whey protein gels led to on initially segragative phase separation into a gelled protein phase and a polysaccharide/serum phase at a micrometer length scale. At the final pH of the gels (pH 4.8, i.e. below the pI of whey proteins), the negatively charged polysaccharides interacted with the protein phase and their spatial distribution was effected by charge density. Polysaccharides with a higher charge density were more homogeneously distributed within the protein phase. Neutral polysaccharide, locust bean gum, did not interact with the protein aggregates but was present in the serum phase. Using SEM, a new type of microstructure formed in the whey protein/polysaccharide gels was characterized. It composed of a protein continuous, porous network at the length scale of 100 [mu]m, coexisting next to the pools of serum which contained spherical protein-rich domains. Heterogeneity of the structure strongly related to the macroscopic behavior of the gels under large deformation. Upon uniaxial compression these heterogeneous gels releases a large amount of serum. Combination of the results of two microscopic techniques, CLSM and SEM, appeared to offer unique possibilities to characterize the structural elements of whey protein/polysaccharide cold-set gels over a wide range of length scales.
Physical Properties Giving the Sensory Perception of Whey Proteins/Polysaccharide Gels
Berg, L. van den; Vliet, T. van; Linden, E. van der; Boekel, M.A.J.S. van; Velde, F. van de - \ 2008
Food Biophysics 3 (2008)2. - ISSN 1557-1858 - p. 198 - 206.
heat-induced gelation - beta-lactoglobulin - mixed gels - xanthan gum - microstructure - rheology - ph
Establishing relationships between physical and sensorial properties of semi-solid foods is essential to develop tailored products. Whey protein/polysaccharide mixed gels were used to model both natural and fabricated semi-solid foods. The presence of various polysaccharides modulated the microstructure and large deformation properties of the mixed gels. The gels exhibited a large spectrum of sensorial properties as evaluated by panellists in a quantitative descriptive analysis. Mouthfeel attributes that discriminated best between the gels were wateriness, crumbliness, and spreadability. Wateriness strongly correlated with the amount of exuded phase (serum) measured during uniaxial compression. Serum release may have a positive effect on, for instance, the juiciness of a product. Large deformation measurements showed that highly crumbly gels fracture readily via a free-running crack. Low serum release is a requirement for that. Low crumbly gels fracture slowly, often releasing a high amount of serum. Spreadability related to the occurrence of multiple microcracks during deformation as observed by confocal laser scanning microscopy, which resulted in a large number of pieces after oral processing