Optimisation of the acidulation process of soapstock from the neutralisation of rice bran oil

Abstract

Soapstock from the neutralisation of rice bran oil was characterised through the most important parameters with direct influence on the acidulation process. A central composite rotational experimental design of two levels was used. The responses of the trials were γ -oryzanol concentration in the acid oil and process time necessary for total hydrolysis of the soaps present. The optimal process conditions were determined using the response surface methodology. Adjustments were made to second order mathematical models and validity was verified by analysis of variance using the STATISTICA program. The process variables studied were: molar ratio - sulphuric acid/soaps (0.55-0.95) and process temperature (70- 100 °C ). The results indicated that the process temperature does not significantly interfere in the concentration of γ -oryzanol of the acid oil, but it does affect process time. In the different concentrations of sulphuric acid added, represented by the molar ratio of sulphuric acid/soaps, the concentration of γ -oryzanol varied between 3.13 and 3.74 %. Through the superposition of the areas of the response surface contour curves the optimal process parameters were determined: process temperature of 95 °C and molar ratio of sulphuric acid/soaps of 0.74, resulting in a γ -oryzanol concentration of 3.64 % and a process time of 90 minutes.