[Fine Chemicals] Mechanism of thickeners and their application in food processing
Factors that affect gel formation by thickeners include the concentration of the gelling agent, the pH of the medium, molar mass, degree of polymerization, temperature, ion composition, and solutes. Beyond identifying these factors, it's also important to characterize the gels they form, usually through microstructure and rheological analysis, which helps when using thickeners as gelling agents. For example, the effect of adding sucrose and aspartame on the compressive strength of thickener gels—kappa-carrageenan, gellan gel, and kappa-carrageenan/locust bean gum—has been studied; adding sucrose increased the true fracture stress of all these gels. However, adding aspartame at low concentrations did not affect the texture compression parameters.
Also, the main factors determining gel sweetness are related to the gel's mechanical properties (gel strength, fracture stress, fracture strain, etc.), especially the deformation required to break the network and its resistance to deformation. In addition, co-solutes like sucrose, hydrocolloid concentration, shear rate, and temperature are important variables affecting the gel's rheological state.
2.1 Application in jelly production
In jelly production and processing, food thickeners often use two or more in synergy to achieve the best effect needed for jelly. Gellan gum is an extracellular linear polysaccharide synthesized and secreted by Pseudomonas bacteria during pure-culture fermentation of carbohydrates. Due to its good transparency and sufficient thermal stability, gellan gum is used in combination with xanthan gum to produce ready-to-eat dessert gels. Deacylated gellan gum is used to improve water retention, flavor release, and storage stability of puddings and to reduce syneresis.
Metal cations play a key role in gellan gum gel formation. Through site-specific binding, cations directly connect to carboxyl groups on the polysaccharide molecules, weakening the electrostatic repulsion between double helix chains, which is very favorable for forming "junction zones."
Carrageenan is a natural seaweed polysaccharide, a hydrophilic linear heterogeneous polysaccharide containing sulfate ester groups, composed of a basic backbone of 1,4-β-D-galactopyranose and 1,3-α-D-galactopyranose, extracted from red algae cell walls. When carrageenan is heated and then slowly cooled, its molecular shape gradually changes from a coiled form to a helical form, eventually from a single helix to a double helix, forming a three-dimensional network structure.
At lower concentrations, carrageenan can form thermoreversible gels; at this point, it has good transparency and can improve the appearance of jelly. Carrageenan is the most common thickener in jelly production, and its synergistic effects with other thickeners have been applied in food formulations. When carrageenan is combined with locust bean gum, gelatin, xanthan gum, and gum arabic, gel strength and elasticity can be significantly improved.
2.2 Application in yogurt
Thickeners can increase yogurt viscosity, stabilize its texture, prevent whey separation, and effectively improve the texture and mouthfeel of yogurt products. When propylene glycol alginate and modified starch are used together as thickeners, they show good synergy; the optimal addition levels are 0.15% (W/W) propylene glycol alginate and 1.20% modified starch.
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