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Agarose, a strongly gelling polysaccharide, is a common ingredient used to optimize the viscoelastic properties of a multitude of food products. Through aggregation of double helices via hydrogen bonds while cooling under quiescent conditions it forms firm and brittle gels. However, this behavior can be altered by manipulating the processing conditions viz shear. For example, gelation under shear leads to microgel particles with large surface area, which in turn leads to completely different rheological properties and texture. Such fluid gels are shown to play an important role in texture modification of foods and beverages for dysphagia patients. In this study, different concentration of agarose fluid gel (0.5 % wt, 1 % wt and 2 % wt) were considered. Rheological measurements of the microgel particles showed an increase of storage and loss modulus with increasing concentration. However, 1 % wt fluid gel exhibited the lowest viscosity in the low shear range and the shortest LVE range. Furthermore, the effect on the microstructure and size of gel particles were also investigated by using light microscopy and particle size analysis. It was observed that as the concentration of agarose increased the particle size and unordered chains present at the particle surface decreases. Based on our results, we propose specific models suggesting the impact of the particle size, the concentration and the “hairy” projections on the rheological and tribological properties that could help in understanding the differences in characteristics of fluid gels., Graphical abstract Image 1, Highlights • Formation of agarose fluid gels in dependence on concentration, temperature and shear rate. • Competing mechanism during gelation under shear of agarose fluid gels was studied. • The resulting gel particle structures, their size and shape vary with concentration. • Network structures, particle size and shape affect the rheological and tribological behavior. • Fluid gels provide unique properties of friction, viscosity and viscoelastic behavior.

Plant based meat surrogates attract increasing interest. Modern methods of biotechnology, food chemistry/technology, and process engineering allow for surrogates with high optical similarity. Nowadays, targeted molecular-sensory methods taste and smell to be largely approximated to the original products. Nevertheless, the products appear completely different on a molecular scale, which is clearly noticeable in texture, oral processing, friction, and bolus formation. A consequent physical consideration of the function and effects of the proteins of different origin reveals the strengths of the respective products and offers suggestions how sensory weak points can be understood better and avoided. This is illustrated here by means of exemplary examples and experiments joined with underpinned by molecular models. Meat sausages, vegetarian, and vegan surrogates are microscopically investigated by rheology, tribology, and tensile experiments. The interpretation of the results is illustrated and supported by simple models.

Colostrum puddings are widely popular in India as well as in some European countries. To prepare these desserts fresh colostrum from the first or second day of lactation is heated and flavoured by adding spices and sugar. Depending on the day of lactation the colostrum is mixed with normal milk in order to achieve a thinner consistency. However, no thickening agents like starch or different polysaccharides need to be added since, in contrast to drinking milk, the early milk of cows and other mammals, called colostrum, forms gels without adding gelling agents when heated. The aim of this study is to understand the mechanisms involved in colostrum gel formation. In order to learn about the fat distribution in colostrum and the melting of the fat, initially, differential scanning calorimetry (DSC) and optical microscopy were performed. Furthermore, the colostrum gel formation was investigated by carrying out rheological measurements. Temperature and time sweep were used to characterize the gel formation of colostrum under heating and an amplitude sweep was performed to understand the forces and molecular interactions involved in the formation of the gel network. Taking into account the different composition of milk and colostrum and comparing their distinct behavior under heating, conclusions could be drawn about which mechanisms cause the formation of a colostrum gel. The gel formation of colostrum is caused by its significantly higher concentration of different proteins, especially β-lactoglobulin. During the heat treatment these proteins denature and subsequently rearrange themselves. Consequently, soft elastic gels are formed by β-lactoglobulin in combination with other proteins, such as IGF-1 (insulin-like growth factor 1), IGF-2 (insulin-like growth factor 2), N-acetylgalactosaminyltransferase 1 (GALNT1) and lactoferrin.

Several studies have investigated xanthan-guar gum (XG-GG), xanthan-locust bean gum (XG-LBG), and xanthan-konjac glucomannan (XG-KGM) blends but little attention has been paid to the physical interactions between the hydrocolloids on a molecular basis. This requires a consistent sample preparation. Often, LBG is heated up to dissolve completely and then xanthan is added, whereas mixtures with guar gum are prepared at room temperature. To understand the synergy during gelation it is necessary to investigate the xanthan-hydrocolloid solutions in the non-heated state because it sets and controls the preferred initial conditions for the given interactions by chain stiffness, charge and polarity under different concentrations In this first part of the publication we focused on blends which are all prepared at room temperature and analysed the molecular interaction in these cold mixed systems. Regarding this, we used Rheology and AFM measurements to characterise the single molecules and the mixing behavior and synergism of the blends. We found, that the cold mixed systems are not stable at room temperature and show a phase separation after one and two days, according to the sample, but are stable when stored at 4 °C. Further, these mixing and demixing properties are highly corresponding to the synergism. Blends with xanthan-guar gum with the weakest mixing properties show the weakest synergism, whereas xanthan-konjac blends with a good mixing behavior exhibit the highest synergism. From the AFM micrographs it was observed that XG-KGM gave most homogeneous mixtures, whereas XG-LBG and XG-GG showed strong phase separation. Based on our experimental results and the characteristics of the molecules such as molecular size, shape and side chains we propose molecular models to explain the physical interactions in these systems which are supported by atomic force microscopy.

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In this study the heat induced synergistic gelation of different hydrocolloid solutions, xanthan gum types (XG) in mixture with galactomannans like guar gum (GG), locust bean gum (LBG) and konjac glucomannan (KGM) is investigated. The physical mechanism of the synergy in thickening and gelling of blends depends on the monomer structure, the molecular weight, the charge, the polarity, and the chain stiffness of the hydrocolloids. Particularly the properties of the electrically neutral galacto- and glucomannans mixed in combination with xanthan gum strongly affect the synergistic effects. These are influenced by the number and distribution of mannan side chains and thus their flexibility. While the pure components do not show gelation on their own, they form viscoelastic solutions or even gels when mixed together and heated. In this study, rheological properties of the resulting composite gels of 0.5% (w/w) were examined under different physicochemical and thermal conditions. Focus was laid on thermally induced gels, as these gels showed higher synergistic effects compared to the non-heated ones. The gelation mechanisms were investigated by strain and temperature dependent oscillatory rheological measurements. Blends with XG-GG (20:80) showed the weakest synergism, followed by XG-LBG blends (20:80), whereas XG-KGM (60:40) blends showed the highest increase of the storage modulus. This can be explained by different local interactions in combinations with the flexibility of the various components. Furthermore, the impact of monovalent salt on the interactions was investigated. Addition of sodium chloride at 0.05% and 0.5% (w/w) concentrations influenced the gelling due to Coulomb screening of the negative charges of XG. Consequently, the synergism, in particular the storage modulus, is strongly affected by variation in salt concentration. We propose specific models based on the gel formation in case of XG-LBG and XG-KGM blends, whereas XG-GG shows an entropic phase separation due to flexibility of GG.

Hypothesis Oleosomes are stabilized by a complex outer phospholipid-protein-layer. To improve understanding of its structure and stabilization mechanism, this shell has to be studied in extracellular native conditions. This should be possible by SANS using contrast variation. Oleosomes are expected to be highly temperature stable, with molecular changes occurring first in the protein shell. Direct measurements of changes in the shell structure are also important for processing methods, e.g. encapsulation. Experiments Extracted soybean oleosomes were studied directly and after encapsulation with pectin by SANS using contrast variation. In order to determine structure and size, a shell model of oleosomes was developed. The method was tested against a simple phospholipid-stabilized emulsion. The oleosomes’ temperature stability was investigated by performing SANS at elevated temperatures. Findings Size (Rg = 1380 A) and shell thickness of native and encapsulated oleosomes have been determined. This is the first report measuring the shell thickness of oleosomes directly. For native oleosomes, a shell of 9 nm thickness surrounds the oil core, corresponding to a layer of phospholipids and proteins. Up to 90 °C, no structural change was observed, confirming the oleosomes’ high temperature stability. Successful coavervation of oleosomes was shown by an increase in shell thickness of 10 nm after electrostatic deposition of pectin.

The food industry has discovered that oleosomes are beneficial as carriers of bioactive ingredients. Oleosomes are subcellular oil droplets typically found in plant seeds. Within seeds, they exist as pre-emulsified oil high in unsaturated fatty acids, stabilised by a monolayer of phospholipids and proteins, called oleosins. Oleosins are anchored into the oil core with a hydrophobic domain, while the hydrophilic domains remain on the oleosome surface. To preserve the nutritional value of the oil and the function of oleosomes, microencapsulation by means of spray drying is a promising technique. For the microencapsulation of oleosomes, maltodextrin was used. To achieve a high oil encapsulation efficiency, optimal process parameters needed to be established. In order to better understand the mechanisms of drying behind powder formation and the associated powder properties, the findings obtained using different microscopic and spectroscopic measurements were correlated with each other. By doing this, it was found that spray drying of pure oleosome emulsions resulted in excessive component segregation and thus in a poor encapsulation efficiency. With the addition of maltodextrin, the oil encapsulation efficiency was significantly improved.