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.