Mucilage formation in food: a review on the example of okra

Analytical rheology as a tool for the structural investigation of citrus pectin

Rheological analysis of citrus pectin at pH 3 and 7 elucidates its structural dynamics, revealing distinct behaviors influenced by pH. At pH 3, pectin exhibits shear-thinning, with solvent-independent unified rheological profiles identifying three concentration regimes: 0.5%-1.5%, 2%-3%, and 3.5%-4%. These regimes, alongside Cox-Merz superpositions, outline the semi-dilute (c*) and concentrated (c**) transitions at 1.5%-2% and 3%-3.5%, respectively. Moreover, a Morris equation exponent of 0.65 indicates flexible, mobility-restricted macromolecules. Conversely, at pH 7, increased viscosities and Morris plot linearity for p = .1 suggest rigid chain behavior due to electrostatic repulsion among ionized acidic groups. This rigidity leads to concentration-dependent self-assembly structures that diverge from expected unified rheological profiles, a deviation amplified by heating-cooling cycles. This study clarifies the impact of pH on citrus pectin's rheology and emphasizes the intricate relationship between polymeric chain rigidity, self-assembly, and viscosity. By providing a refined understanding of these mechanisms, our findings contribute to the broader field of polysaccharide research, offering insights critical for developing and optimizing pectin-based applications in various industries.

Potential application of polysaccharide mucilages as a substitute for emulsifiers: A review

Mucilages are natural compounds consisting mainly of polysaccharides with complex chemical structures. Mucilages also contain uronic acids, proteins, lipids, and bioactive compounds. Because of their unique properties, mucilages are used in various industries, including food, cosmetics, and pharmaceuticals. Typically, commercial gums are composed only of polysaccharides, which increase their hydrophilicity and surface tension, reducing their emulsifying ability. As a result of the presence of proteins in combination with polysaccharides, mucilages possess unique emulsifying properties due to their ability to reduce surface tension. In recent years, various studies have been conducted on using mucilages as emulsifiers in classical and Pickering emulsions because of their unique emulsifying feature. Studies have shown that some mucilages, such as yellow mustard, mutamba, and flaxseed mucilages, have a higher emulsifying capacity than commercial gums. A synergistic effect has also been shown in some mucilages, such as Dioscorea opposita mucilage when combined with commercial gums. This review article investigates whether mucilages can be used as emulsifiers and what factors affect their emulsifying properties. A discussion of the challenges and prospects of using mucilages as emulsifiers is also presented in this review.

Clustering of instrumental methods to characterize the texture and the rheology of slimy okra (Abelmoschus esculentus) suspensions

Okra (Abelmoschus esculentus) is one of the ingredients widely used in African gastronomy because of the unique slimy texture it gives to sauces. However, processing and formulation can affect the textural and rheological properties of these sauces, leading to unacceptable quality for the African consumer. The aim of this study was to select the instrumental measurements best enabling (a) characterization of the rheology and texture of slimy sauces prepared from okra and (b) monitoring its evolution during the preservation process. Thirty-seven slimy suspensions (sauces and purées) were measured with 16 rheological and textural parameters. A principal component analysis revealed that flow consistency index K and flow behavior index n were well correlated with visco-elastic, adhesive, and shear thinning properties, and that stringiness was well correlated with elongational, cohesive, and ductile properties. These two sets of measurement methods are sufficient to characterize their rheological and textural properties, and necessary to discriminate them according to their process and formulation.

Emulsifiers from Partially Composted Olive Waste

Partial (one month) composting of solid olive processing waste is shown to produce extractable emulsifiers. Size exclusion chromatography (SEC) and Fourier-transform infra-red spectroscopy (FTIR) show that these consist of polysaccharides and proteins from the composted waste. Aqueous extraction at pH 5, pH 7, and pH 9 all yield extracts rich in oligosacchrides and oligopeptides which derive from the break-down of the macromolecules under composting, with the extract obtained at pH 5 being the richer in such components. Fourier-transform infra-red (FTIR) spectroscopy also confirms that these materials consist of proteinic and poly/oligosaccharidic populations. These materials can emulsify stable oil-in-water emulsions at pH 3 for a few days, while the same emulsions collapse in less than 24 h at pH 7. Confocal microscopy and droplet size distribution data suggest that Ostwald ripening, rather than coalescence, is the major course of emulsion instability. The above point to a short-process alternative to full composting in producing a high added value product from solid olive processing waste.

Extensional and shear rheology of okra polysaccharides in the presence of artificial saliva

Extensional and shear viscosities were studied for mixtures comprising artificial saliva and okra mucilage, the latter acting as a model thick-liquid food. These experiments aimed to obtain information on the flow-behavior information of the systems, underpinning the texture sensation of foods as perceived by dysphagic and xerostomic populations. Mixing okra mucilage with artificial saliva dramatically increases the shear viscosity of artificial saliva throughout the studied ranges of concentrations and deformation rates. Particle tracking does not suggest direct interactions between the components of artificial saliva and of okra mucilage. The rheology of the okra polymer (OP)–artificial saliva (AS) mixture is dominated by its extensional viscosity: Trouton ratios are in the order of tens to hundreds, while they decrease with increasing okra-mucilage concentration; this highlighs the dominance of the extensional rheology and the increasing importance of the shear mechanics with increasing okra content. The relaxation times and extensional moduli are also reported for the systems under study. Extensional and shear flows are of equal importance concerning the elastic behavior.

Artificial saliva is usually formulated to help people with dysphagia or xerostomia. Their mouth feels of food textures are largely dependent on the flow behaviors of the food–artificial saliva mixtures. Christos Ritzoulis and coworkers from Zhejiang Gongshang University now studied the rheological and structural properties of artificial saliva when mixed with okra mucilage. They found the shear viscosity and storage modulus of the artificial saliva were much higher in the presence of okra polysaccharide, suggesting the formation of a macromolecular-interacting network. Moreover, it was found the overall rheological behaviors of the mixtures were always dominated by the extensional viscosity, though the shear behavior became more and more obvious with the increasing amount of okra polymer. Together with the data obtained with real saliva, these on artificial saliva could guide the future formulation of artificial saliva.