Understanding the role of hydrocolloids viscosity and hydration in developing gluten-free bread. A study with hydroxypropylmethylcellulose

To understand the role of hydrocolloids' viscosity in developing gluten-free (GF) bread, a range of hydroxypropylmethylcellulose (HPMC) with similar backbone and percentage of methoxyl and hydroxypropoxyl residues was selected in order to vary the viscosity (100 mPa.s, 4000 mPa.s, 15,000 mPa.s) while keeping the main chemical structure. Viscosity of HPMC was used as quantitative independent factor in a multilevel factorial model along with HPMC level (1%, 2%, 3%) and hydration level (90%, 100%, 110%). The model results in 27 formulation based on rice flour. A Mixolab system was uses to analyse the rheological parameters of the GF batters during mixing, cooking and cooling stage. In addition, GF breads were characterised for their quality parameters. Analytical data were fitted to multiple regression equations in order to estimate the dependence of the collected parameters on the quantitative independent factors. Results confirmed the importance of hydration level in determining the viscoelastic behaviour of the GF batter and influencing the rheology characteristics of bread. Moreover, it was possible to underline the role of the HPMC viscosity along with the level of HPMC, both to control the batter consistency and some desirable textural features of GF bread such as crumb hardness, cohesiveness and resilience. Finally, some analytical parameters were used as quality indicators in desirability index calculation, which would represent a GF breads with optimum quality obtained by the inclusion of a 2.2% of HPMC 15000 cP with hydration level to 110%.