Phytase treatment of a protein-enriched rice bran fraction improves heat-induced gelation properties at alkaline conditions

The effect of phytase treatment on the technological functionality of a protein-enriched rice bran fraction produced by air classification was studied. Protein solubility and surface hydrophobicity were analysed and heat-induced gels formed at pH 5, 6.7 and 8 were characterised using rheological measurements, confocal laser scanning microscopy (CLSM) and by measuring water retention capacity. Phytase treatment decreased phytic acid content from 22% to 1-3%, depending on the dispersion dry matter content, which led to improved protein solubility at acidic pH 2-4. Similarly, phytase treatment increased protein surface hydrophobicity; however, the difference between phytase-treated and control sample was diminished after heat treatment. During heat-induced gelation the non-phytase-treated fraction formed viscoelastic structures at pH 6.7 and 8 with final G' over 1000 Pa, while only weak gels were obtained at pH 5 (G' similar to 100 Pa). Phytase treatment improved gelling ability of the fraction at pH 8 reaching significantly higher final G' (11 340 Pa) and water holding capacity (77.8%) compared to the non-phytase-treated gel (1140 Pa and 54.6%, respectively). At pH 5 and 6.7 gel characteristics were not affected by phytase treatment. CLSM revealed a more evenly distributed protein and fibre network for phytase-treated protein-enriched rice bran gels formed at pH 8 compared to the other gels, which consisted of more void areas and densely packed protein aggregates. The results emphasise the advantage of using a phytase-treated protein-fibre ingredient from rice bran in gelled products both for techno-functional and nutritional quality improvement.