Effect of instantaneous controlled pressure drop process on the hydration capacity of scleroglucan: optimisation of operating conditions by response surface methodology

Abstract

Response surface methodology was used to evaluate the effect of the processing parameters in the instantaneous controlled pressure drop process (DIC, “Détente Instantanée Contrôlée”) on the hydration capacity of scleroglucan. This process involves applying steam pressure of between 1 and 6 bar to scleroglucan for a short period of time and then dropping the pressure instantaneously to a vacuum at 15 mbar. Hydration was determined by measuring the increase in viscosity with rapid stirring. Responses were the initial dissolution rate and the maximum viscometer torque produced during hydration of the dried product. The optimum processing conditions selected for the maximum torque obtained from response surface analysis were as follows: pressure level: 1 bar; moisture content: 0.38 g H 2O/g of dry scleroglucan; processing time: 15.5 s. For the initial dissolution the optimum rate was attained at 1 bar for the processing pressure, 0.33 g H 2O/g of dry scleroglucan and a processing time of 12 s. Under these conditions, the experimental yields of the maximum torque and the initial dissolution rate were close to the predicted values (0.771 mN m and 0.417 μN m/s, respectively) calculated from the polynomial response surface model equation. Compared with a sample dried using a standard industrial method, the product treated by instantaneous controlled pressure drop had the same initial dissolution rate but the maximum torque produced (0.758 mN m) was twice that produced by the control sample dried in a rotary vacuum dryer (0.444 mN m). Preliminary measures performed using high resolution solid-state 13C CP/MAS NMR revealed a greater separation of the C-5 from the C-2 line, suggesting that the polysaccharide chain of the sample treated by instantaneous controlled pressure drop undergoes conformational changes.