Texture of emulsion-filled pea protein-potato starch gels: Effect of processing conditions and composition.

From a physicochemical perspective, foods like vegan cheese and meat analogues are complex multicomponent gels. The aim of this study was to investigate the effect of processing conditions and composition on the textural properties of multicomponent gels containing starch, pea protein isolate (PPI) and emulsion droplets. Mechanical properties were measured, and structural analysis was carried with CLSM and SEM. In the case of particle gels prepared with maize starch (MS), a higher shearing speed decreased Young's modulus, fracture stress and fracture strain due to break up of the starch granules. In polymer gels prepared with potato starch (PS), structure and mechanical properties were not much affected by processing conditions. The addition of emulsion droplets increased the Young's modulus of MS gels and decreased that of PS gels. In PS gels, the fracture stress decreased further for smaller oil droplets. The addition of emulsion droplets was also found to decrease adhesiveness, cohesiveness and chewiness, regardless of the matrix structure. With protein addition into PS gels, an increase in Young's modulus and a decrease in fracture strain were observed. These results show that processing conditions and composition can be used to modulate the physical properties of complex food systems.

Role of polysaccharide structure in the rheological, physical and sensory properties of low-fat ice cream.

Polysaccharides can be used as fat replacers in ice cream, as they contribute to an increase of viscosity. However, no research has clarified the exact role of viscosity from that of the structure of the polysaccharides on the properties of ice cream. In this study, the effect of polysaccharide structure on different properties of low-fat ice cream was investigated. The polysaccharides taken into consideration varied from flexible (locust bean gum and guar gum) to rigid (xanthan gum and iota carrageenan). Relationships between rheological properties of ice cream mixes and microstructural characteristics and sensory perception of the final ice cream were established. To separate the effect of the polysaccharide structure from that of viscosity, two series of ice cream were prepared: one in which the mix viscosity of the various samples was similar (approximately 68.3 mPa· s), and one in which the serum phase viscosity was similar (approximately 15563 mPa· s). Flexible polysaccharides showed a lower degree of shear-thinning and a more liquid-like viscoelastic behavior compared with rigid polysaccharides. In addition, flexible polysaccharides led to higher overrun (47-58%) than other samples (approximately 30%), which resulted in lower hardness of the ice cream (<3.2 MPa). Rigid polysaccharides caused gelation of the serum phase, which made the ice cream more difficult to scoop. Based on the results of the sensory evaluation, flexible polysaccharides could provide higher softness and creaminess-related properties, while rigid polysaccharides resulted in higher coldness and grittiness. Therefore, polysaccharides with a flexible structure are a better choice for improving the textural and sensory properties of low-fat ice cream.

Effect of plasmin on casein hydrolysis and textural properties of rennet-induced model cheeses.

Plasmin plays an important role in casein hydrolysis during cheese ripening, which may influence the properties of the casein network and the texture of the final product. In view of this, the relation between plasmin-induced casein hydrolysis and textural changes of cheese during ripening was investigated in this study. Four batches of model cheese with different concentrations of added plasmin (0, 0.4, 0.6 and 1.0 µL/g milk) were prepared, and were stored for 12 weeks at 16 °C. During this period, plasmin activity, casein hydrolysis, textural properties and other compositional characteristics (pH, dry matter) were determined. Our results show that the addition of plasmin had significant effect on both the degree and the pattern of proteolysis. As a result, cheeses with different plasmin content showed different textural properties. With increased plasmin concentration, Young's modulus, hardness, resilience and cohesion decreased, while brittleness increased. All textural properties showed linear relations with the degree of casein hydrolysis, and logarithmic relations with the percentage of intact casein fractions. At the beginning of ripening, only slight changes in textural properties were found, although a substantial part (40-60 %) of the casein fractions was already been broken down. When ripening progressed, ongoing proteolysis significantly weakened the protein network and consequently led to noticeable textural changes. Model cheeses became softer, more brittle and less elastic. The knowledge gained from this study provide new insights in the changes of different textural parameters of model cheese. This will help to optimize the existing products and create new ones.

Effect of different molecular characteristics on the lubrication behavior of polysaccharide solutions.

Polysaccharides strongly affect the sensorial properties of foods, which is partly related to the lubrication they provide. We investigated the lubrication performance of polysaccharides with different characteristics (i.e. molecular weight, conformation, stiffness, and charge density) to identify the most relevant structural features related to lubrication ability. The effect of viscosity was excluded using isoviscous systems. Conformation resulted to be a key factor in determining lubrication. Rigid rod-like polysaccharides (xanthan) showed higher lubricating capacity and better resistance to changes in pH and ionic strength compared to semi-flexible (pectin and carboxymethyl cellulose) and flexible polysaccharide (guar gum). The friction behavior of flexible polysaccharides was highly dependent on concentration and sliding speed, for which a model including parameters of friction, concentration, and speed was developed. The concentration-dependency of the lubrication was related to the shear-thinning behavior, and possible mechanisms to explain these differences in terms of molecular properties of the polysaccharides are proposed.

Effect of fat aggregate size and percentage on the melting properties of ice cream.

In this study, we investigated the effect of fat aggregate size and percentage on fat network formation and, ultimately, on the melting properties of ice cream. To control fat destabilization degree and fat network formation, we varied fat and emulsifier content, and blended coconut oil with milk fat, obtaining three different sample series varying in: 1) fat content, 2) fat aggregate size, and 3) fat aggregate percentage. The degree of fat destabilization in terms of aggregate size and the percentage was measured by light scattering techniques. The distribution of the fat around the air cells and in the unfrozen serum phase was calculated based on the measured overrun. Overall, a similar overrun was found in the three series of ice cream. The fat percentage in the remaining phase was measured to verify how much fat and what type of fat aggregates were present in the fat network. The results show that fat destabilization degree is relatively more important than fat content in determining the melting behavior of ice cream with low overrun. Clear relations between different fat destabilization parameters and ice cream melting behavior were established, indicating that the melting behavior of ice cream is related to specific properties of the fat network. Controlling fat destabilization in the unfrozen ice cream phase may be used to alter the properties of ice cream, and could contribute as a fat reduction strategy in ice cream.

Meat Analogues: Relating Structure to Texture and Sensory Perception.

The transition from animal to plant proteins is booming, and the development of meat analogues or alternatives quickly progressing. However, the acceptance of meat analogues by consumers is still limited, mainly due to disappointing organoleptic properties of these foods. The objective of this study was to investigate possible relationships among structure, textural characteristics, consumer acceptance, and sensory evaluation of commercially available meat analogues. The microstructure and texture of 13 chicken analogue pieces and 14 analogue burgers were evaluated with confocal laser scanning microscopy (CLSM) and texture profile analysis (TPA). The moisture of the samples was related to cooking losses and release of liquid upon compression after cooking. Meat products were included as references. A sensory panel (n = 71) evaluated both flavour and texture characteristics. For the chicken analogue pieces, samples with more added fibres had a harder and chewier texture but were less cohesive. No other relations between composition and structure/texture could be found. In the sensory evaluation, lower hardness and chewiness were only seen in products with more fat. A lower sensory hardness was found to be related to the presence of small air pockets. For analogue burgers, there was no clear relation between composition and structure/texture. However, instrumentally measured hardness, chewiness, and cohesiveness correlated well with the corresponding sensory attributes, even though they could not be clearly linked to a structural feature. Next to this, fat content showed a clear correlation to perceived fattiness. CLSM images of burgers with high perceived fattiness showed large areas of fat. Therefore, the release of large fat pools from the meat was most likely responsible for the perception of this attribute. However, perceived fattiness was not related to liking, which was the case also for chicken analogue pieces. For both pieces and burgers, even if some of the measured textural attributes could be linked to the sensory profile, the textural attributes in question could not explain the liking scores. Liking was related to other aspects, such as meaty flavour and juiciness, which were not directly linked to compositional or textural features. Juiciness was not directly related to the moisture loss of the products, indicating that this attribute is rather complex and probably involves a combination of characteristics. These results show that to increase the appreciation of meat analogues by consumers, improving simple texture attributes is not sufficient. Controlling sensory attributes with complex cross-modal perception is probably more important.

Effect of gelatinization and swelling degree on the lubrication behavior of starch suspensions.

This research aimed to investigate the effect of starch gelatinization and swelling degree on the lubrication properties of starch aqueous suspensions. Three types of maize starch with different amylose content of 70% (HAS), 25% (NS), and <1% (WS) were used to vary the swelling capacities. The granule suspension of NS showed the highest swelling factor (SF) of 26.5, and gave the best lubrication capacity by decreasing friction by 78%. WS was only able to decrease friction by 50% due to a lower swelling capacity. The leached-out amylose increased friction of highly swollen granules (SF = 26.5) but decreased friction of stiff granules (SF = 2.5). Adding unstimulated human saliva to starch suspensions with native and limited swollen granules reduced friction and masked differences in friction coefficients among starch types. Both the salivary layer on the contact surfaces and the salivary proteins in the bulk phase played a role in determining lubrication properties.

Lubrication properties of model dairy beverages: Effect of the characteristics of protein dispersions and emulsions.

In this study we investigated the individual contribution of different ingredients to the lubrication properties of dairy-based model beverages containing whey protein (native or aggregated), micellar casein and emulsified oil in different combinations. In single-component systems, whey protein isolate (WPI) solutions showed the lowest friction coefficients of all protein samples. Whey protein aggregates (WPA, ∼247 nm, irregular morphology) led to higher friction coefficients than micellar casein isolate (MCI) with comparable size (∼207 nm, near spherical shape). When protein particles were combined, i.e. WPA and MCI, lubrication was not much affected. However, when WPI was added to either WPA or MCI, higher friction coefficients were observed compared to single-component systems. Emulsions (droplet size âˆ¼ 440 nm) provided better lubrication than the protein samples. Oil droplets stabilized by soy lecithin (SL) were more efficient at reducing friction than those stabilized by WPI. The friction coefficient of SE strongly increased in the presence of WPI. In comparison, lubrication of WE was less affected by the addition of WPI. These results show that different proteins affect the lubrication properties of emulsions stabilized with different emulsifiers in a different way. Our research also indicates that multicomponent systems are complex, and that control over the lubrication properties requires a better understanding of the contribution of individual components.

Rheological behaviour of attractive emulsions differing in droplet-droplet interaction strength.

HYPOTHESIS: We hypothesise that interaction strength between oil droplets determine the rheological properties of oil-in-water (O/W) emulsions by simultaneous formation and break-up of bonds between droplets. Using small (SAOS) and large (LAOS) amplitude oscillatory shear measurements, we aim to distinguish different classes of emulsions based on the specific microstructural evolution of the emulsions. EXPERIMENTS: Concentrated O/W emulsions differing in droplet-droplet interaction strength were obtained. Different interaction strength was obtained using different types of interactions; (a) electrostatic attraction, (b) salt bridging, or (c) crosslinking. FINDINGS: In line with our hypothesis, different rheological events in emulsions depend on the droplet-droplet interaction strength. Strong interactions lead to monotonous yielding, and droplets undergo jamming or densification to provide strain hardening and gel-like behaviour. Emulsions with weak interactions exhibit two-step yielding (SAOS) and continuous yielding in LAOS; indicating a soft-glassy material. In emulsions above maximum packing, and with weak interactions the rheology is controlled by cluster/cage breaking, and transient formation of new clusters. For medium-strength interactions, two-step yielding was reduced, and apparent stain-hardening occurred. The probability of two distinct time scales of yielding is hindered by stronger interactions and jamming. Overall, in concentrated emulsions, yielding is determined by network rupture and reformation, cluster rearrangement and -breaking, which in turn is influenced by interaction type and strength. We present a more differentiated categorisation of emulsions based on interaction strength.

Effect of particle size distribution on rheological properties of chocolate.

This study focused on the influence of the particle size distribution (PSD) of ingredients used for chocolate preparation (cocoa powder and sugar) on viscosity of model chocolates with different fat contents. Model chocolates with varying PSDs and two particle size ratios (cocoa particles : sugar of 1 : 4 and 1 : 6) were prepared by mixing highly defatted cocoa powder as a fine fraction and sugar as coarse fraction in several proportions. Samples containing spherical quartz beads were included as a reference to gain insight into the role of particle properties. Comparing chocolate samples with the same composition, but different particle size ratio, the largest difference in viscosity was found at a proportion of coarse fraction of 0.6. This shows that at this proportion of coarse particles, the highest maximum packing fraction was reached, which is in accordance with theoretical predictions. However, for the investigated chocolate samples, the lowest viscosity values were obtained at a proportion of the coarse fraction of 0.8 or 1. This could be attributed to parameters other than PSD, such as a decrease in surface area with an increasing amount of coarse particles. Also the morphology and surface properties were shown to influence viscosity. Compared to cocoa and sugar particles, spherical and smooth quartz beads led to an improved particle packing, and therefore a lower viscosity. The addition of lecithin led to a decrease in viscosity due to a decrease in particle-particle interactions, particularly for hydrophilic sugar particles. The knowledge obtained in this study provides possible approaches on how to reduce fat content of chocolates.

Clustering of oil droplets in o/w emulsions: Controlling cluster size and interaction strength.

Clustering of oil droplets changes the rheological properties of oil-in-water (o/w) emulsions and can be used as a tool to structure foods. The aim of this study was to manipulate both oil droplet cluster size and cluster strength in liquid o/w emulsions, and to investigate the effect of these parameters on the rheological properties. Clustered emulsions were prepared using three different methods: (i) clustering by protein-proanthocyanidin interactions, (ii) clustering by hetero-aggregation of oppositely-charged emulsion droplets, and (iii) enzymatic clustering of protein-stabilised droplets using transglutaminase. Clustering by protein-proanthocyanidin interactions allowed to control oil droplet cluster size from 1 to 140 µm. Clusters decreased in size upon both an increase and decrease in pH, but were stable against changes in ionic strength. Hetero-aggregation of oppositely-charged oil droplets (gelatine/whey protein and gelatine/DATEM) allowed to control cluster size from 1 to 40 µm. Clusters showed a strong decrease in size in response to changes in pH and a small decrease in size with increasing ionic strength. Enzymatic clustering did not allow to control cluster size. Cluster strength of proanthocyanidin-stabilised clusters was found to be higher than that of hetero-aggregated clusters. Stabilisation of clusters was likely induced by different protein-proanthocyanidin interactions such as H-bridges, π-π stacking, and hydrophobic interactions, whereas hetero-aggregation is based on electrostatic interactions. Upon clustering, emulsion viscosity increased by up to three orders of magnitude. We conclude that protein-proanthocyanidin interactions and hetero-aggregation are effective methods to tune droplet cluster size and strength in o/w emulsions, and that cluster size and interaction strength control the rheological properties of o/w emulsions with clustered oil droplets.

Interfacial properties, thin film stability and foam stability of casein micelle dispersions.

Foam stability of casein micelle dispersions (CMDs) strongly depends on aggregate size. To elucidate the underlying mechanism, the role of interfacial and thin film properties was investigated. CMDs were prepared at 4°C and 20°C, designated as CMD4°C and CMD20°C. At equal protein concentrations, foam stability of CMD4°C (with casein micelle aggregates) was markedly higher than CMD20°C (without aggregates). Although the elastic modulus of CMD4°C was twice as that of CMD20°C at 0.005Hz, the protein adsorbed amount was slightly higher for CMD20°C than for CMD4°C, which indicated a slight difference in interfacial composition of the air/water interface. Non-linear surface dilatational rheology showed minor differences between mechanical properties of air/water interfaces stabilized by two CMDs. These differences in interfacial properties could not explain the large difference in foam stability between two CMDs. Thin film analysis showed that films made with CMD20°C drained to a more homogeneous film compared to films stabilized by CMD4°C. Large casein micelle aggregates trapped in the thin film of CMD4°C made the film more heterogeneous. The rupture time of thin films was significantly longer for CMD4°C (>1h) than for CMD20°C (<600s) at equal protein concentration. After homogenization, which broke down the aggregates, the thin films of CMD4°C became much more homogeneous, and both the rupture time of thin films and foam stability decreased significantly. In conclusion, the increased stability of foam prepared with CMD4°C appears to be the result of entrapment of casein micelle aggregates in the liquid films of the foam.

High-Pressure-High-Temperature Processing Reduces Maillard Reaction and Viscosity in Whey Protein-Sugar Solutions.

The aim of the study was to determine the influence of pressure in high-pressure-high-temperature (HPHT) processing on Maillard reactions and protein aggregation of whey protein-sugar solutions. Solutions of whey protein isolate containing either glucose or trehalose at pH 6, 7, and 9 were treated by HPHT processing or conventional high-temperature (HT) treatments. Browning was reduced, and early and advanced Maillard reactions were retarded under HPHT processing at all pH values compared to HT treatment. HPHT induced a larger pH drop than HT treatments, especially at pH 9, which was not associated with Maillard reactions. After HPHT processing at pH 7, protein aggregation and viscosity of whey protein isolate-glucose/trehalose solutions remained unchanged. It was concluded that HPHT processing can potentially improve the quality of protein-sugar-containing foods, for which browning and high viscosities are undesired, such as high-protein beverages.

Denaturation and in Vitro Gastric Digestion of Heat-Treated Quinoa Protein Isolates Obtained at Various Extraction pH.

The aim of this study was to determine the influence of heat processing on denaturation and digestibility properties of protein isolates obtained from sweet quinoa (Chenopodium quinoa Willd) at various extraction pH values (8, 9, 10 and 11). Pretreatment of suspensions of protein isolates at 60, 90 and 120 °C for 30 min led to protein denaturation and aggregation, which was enhanced at higher treatment temperatures. The in vitro gastric digestibility measured during 6 h was lower for protein extracts pre-treated at 90 and 120 °C compared to 60 °C. The digestibility decreased with increasing extraction pH, which could be ascribed to protein aggregation. Protein digestibility of the quinoa protein isolates was higher compared to wholemeal quinoa flour. We conclude that an interactive effect of processing temperature and extraction pH on in vitro gastric digestibility of quinoa protein isolates obtained at various extraction pH is observed. This gives a first indication of how the nutritional value of quinoa protein could be influenced by heat processing, protein extraction conditions and other grain components.

Effect of Temperature and Pressure on the Stability of Protein Microbubbles.

Protein microbubbles are air bubbles with a network of interacting proteins at the air-water interface. Protein microbubbles are commonly used in medical diagnostic and therapeutic research. They have also recently gained interest in the research area of food as they can be used as structural elements to control texture, allowing for the manufacture of healthier foods with increased consumer perception. For the application of microbubbles in the food industry, it is important to gain insights into their stability under food processing conditions. In this study, we tested the stability of protein microbubbles against heating and pressurization. Microbubbles could be heated to 50 °C for 2 min or pressurized to 100 kPa overpressure for 15 s without significantly affecting their stability. At higher pressures and temperatures, the microbubbles became unstable and buckled. Buckling was observed above a critical pressure and was influenced by the shell modulus. The addition of cross-linkers like glutaraldehyde and tannic acid resulted in microbubbles that were stable against all tested temperatures and overpressures, more specifically, up to 120 °C and 470 kPa, respectively. We found a relation between the storage temperatures of microbubble dispersions (4, 10, 15, and 21 °C) and a decrease in the number of microbubbles with the highest decrease at the highest storage temperature. The average rupture time of microbubbles stored at different storage temperatures followed an Arrhenius relation with an activation energy for rupture of the shell of approximately 27 kT. This strength ensures applicability of microbubbles in food processes only at moderate temperatures and storage for a moderate period of time. After the proteins in the shell are cross-linked, the microbubbles can withstand pressures and temperatures that are representative of food processes.

Disintegration of protein microbubbles in presence of acid and surfactants: a multi-step process.

The stability of protein microbubbles against addition of acid or surfactants was investigated. When these compounds were added, the microbubbles first released the encapsulated air. Subsequently, the protein shell completely disintegrated into nanometer-sized particles. The decrease in the number of intact microbubbles could be well described with the Weibull distribution. This distribution is based on two parameters, which suggests that two phenomena are responsible for the fracture of the microbubble shell. The microbubble shell is first weakened. Subsequently, the weakened protein shell fractures randomly. The probability of fracture turned out to be exponentially proportional to the concentration of acid and surfactant. A higher decay rate and a lower average breaking time were observed at higher acid or surfactant concentrations. For different surfactants, different decay rates were observed. The fact that the microbubble shell was ultimately disintegrated into nanometer-sized particles upon addition of acid or surfactants indicates that the interactions in the shell are non-covalent and most probably hydrophobic. After acid addition, the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay (release of air), while in the case of surfactant addition, there was a significant time gap between complete microbubble decay and complete shell disintegration.