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

Response surface methodology was used to evaluate the effect of the process ing parameters in the instantaneous controlled pressure drop process (DIC, "Detente Instantanee Controlee") on the hydration capacity of scleroglucan. This process involves applying steam pressure of between 1 and 6 bar to sc leroglucan for a short period of time and then dropping the pressure instan taneously to a vacuum at 15 mbar. Hydration was determined by measuring the increase in viscosity with rapid stirring. Responses were the initial diss olution 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; mois ture content: 0.38 g H2O/g of dry scleroglucan; processing time: 15.5 s. Fo r the initial dissolution the optimum rate was attained at 1 bar for the pr ocessing pressure, 0.33 g H2O/g of dry scleroglucan and a processing time o f 12 s. Under these conditions, the experimental yields of the maximum torq ue and the initial dissolution rate were close to the predicted values (0.7 71 mN m and 0.417 mu N m/s, respectively) calculated from the polynomial re sponse surface model equation. Compared with a sample dried using a standar d industrial method, the product treated by instantaneous controlled pressu re drop had the same initial dissolution rate but the maximum torque produc ed (0.758 mN m) was twice that produced by the control sample dried in a ro tary vacuum dryer (0.444 mN m). Preliminary measures performed using high r esolution solid-state C-13 CP/MAS NMR revealed a greater separation of the C-5 from the C-2 line, suggesting that the polysaccharide chain of the samp le treated by instantaneous controlled pressure drop undergoes conformation al changes. (C) 2000 Elsevier Science Ltd. All rights reserved.