Designing microstructure into xanthan gum-enriched acid milk gels

• Phase separation was investigated in competition with gel formation.
• Interaction between milk protein and xanthan gum was commented on.
• In-depth characterization of mixed acid milk gel microstructure was performed.
• Specific fibrous structures were created by understanding combined phase separation and gelation processes.
• A large design of fibrous structure with defined properties was achieved.

Designing various microstructures through the interplay between phase separation and acid-induced gelation processes was investigated. Acid skim milk/xanthan gum mixed gels were prepared at different xanthan gum and glucono-δ-lactone (GDL) concentrations in order to modulate the extent of phase separation and the gelation rate, respectively. A gradual change in acid milk gel microstructure was found by increasing xanthan gum concentration, from homogeneous protein network, to fibrous structures and finally to isolated protein-rich aggregates. Addition of xanthan gum in the milk led to an apparent depletion–flocculation with protein-rich domains dispersed in a continuous phase enriched in xanthan. The sedimenting denser protein-rich domains could be trapped by protein gelation, forming specific fibrous structures at 0.05 wt.% xanthan gum. Manipulating the microstructure through modification of the gelation rate resulted in a design of a broad range of fibrous morphologies varying from 20 to 400 μm long, which could be used to generate novel textures for food products.Industrial relevanceAs a response to industrial demand by the consumer for novel acid milk gels with superior structural properties, mouthfeel and potential health benefits, we present here a way to manipulate textures by designing specific fibrous microstructures. Protein–polysaccharide mixtures that are subject to phase separation and gelation are interesting not only for the creation of major differences in structure and rheological properties of mixed systems, but also because of resulting protein-enriched products (up to 4 times more concentrated than conventional yoghurt). This approach should make it possible to improve the nutritional benefits as well as formulate a wide range of acid milk gels with innovative structures and sensory properties.