Can high hydrostatic pressures modify the technological properties of gluten-free raw materials?

Gluten-free (GF) baked goods contain a large amount of starch whose behavior during processing and storage greatly influences their quality and shelf-life. Even if high hydrostatic pressures (HHP) are generally used to inactivate microorganisms and enzymes, they were here employed as a non-conventional treatment to modify the technological aptitude of corn starch (CS), rice flour (RF) and waxy rice flour (WRF), raw materials commonly used in GF products. The samples were pre-conditioned up to 40% moisture content and then treated with HHP. The following parameters were considered: pressure (400MPa; 600MPa), pressure holding time (5min; 10min) and temperature (20°C; 40°C). The untreated and treated samples were evaluated for their viscoamylographic features, solvent retention capacity (SRC), thermal properties, X-ray diffractive and ultrastructural characteristics. According to the pressure applied, different pasting behaviours and SRC were evidenced. RF-starch was partially de-structurated at both the pressures applied, as highlighted by the lower peak values obtained (650 and 620BU, respectively) in comparison to that of the untreated sample (756BU). Few differences were found for WRF, indicating a lower susceptibility to pressure. CS treated at 600MPa presented diminished pasting properties in comparison to the untreated CS and to CS treated at 400MPa: even if the gelatinization temperature of all these samples was around 70°C, a clear shift of the 600MPa treated CS viscoamylographic curve was evidenced. Furthermore, both CS and RF treated at 600MPa showed a higher retention capacity of carbonate and lactic acid solvents, respectively related to starch and protein properties. HHP treatments thus seem to be able to change the technological behaviour of RF and CS, and this potential positive effect has been actually evidenced in preliminary breadmaking trials.