Mechanical properties of whey protein/Na alginate gel microparticles

•Mixed gel microparticles of WPI and Na alginate were produced by cold gelation with Ca and size reduction of the bulk gels.•A back extrusion test cell was designed to mechanically assess microparticles; results related well with those for bulk gels.•Microparticles exhibited an ample range of mechanical properties suitable for use as texture modifiers in liquids and purees.

A proportion of the fast-growing elderly population needs special foods which are soft to chew and easily swallowed. Gel microparticles, GMP, (e.g., less than 100 μm in size) are an alternative as texture-modifiers in liquid and pureed foods, and may be used as carriers of needed flavors and nutrients. GMP (sizes < 40 μm) were fabricated from whey protein isolate (WPI)/sodium alginate (NaAlg) mixtures by size reduction of bulk gels made by the cold-gelation method. A cell test based on back extrusion was designed to evaluate the mechanical properties of a GMP paste and image analysis techniques implemented to resolve the size of GMP. A good correlation (R2 = 0.89) was obtained between the stress (at 60% strain) of bulk gels and that of GMP. Compression stress at 30% strain depended on the concentrations of WPI and NaAlg and a maximum was observed at intermediate values. Through Principal Component Analysis gels with low and high sodium alginate contents were clearly explaining 93% of the variability. The ample range of mechanical properties of GMP suggest that they may be used to design or modify the texture of soft foods.