Impact of critical parameters influencing enzymatic production of structured lipids using response surface methodology with water activity control

Structured lipids with desired properties can be produced by enzymatic transesterification. This is a multistep reaction with many factors influencing both the product yield and quality. In this study, the single and combined effects of water activity, temperature and substrate ratio were studied on the reaction between high oleic sunflower oil and ethyl stearate producing 1,2-stearin-3-olein (SOS) using immobilized lipase from Rhizopus oryzae (Lipase DF “Amano” IM). Product quality was assessed as the ratio between SOS and the unwanted isomer SSO. Response surface methodology was used to create models at several time points, for increased understanding and showing the importance of the factors studied, for efficient production of structured lipids. To set the water activity, a control system based on dry/humid nitrogen gas sparging was developed. The models were found to adequately describe the effect of the factors on product yield and quality as well as being robust. For the yield, it was found that the factors influencing the enzymatic activity were highly important initially whereas factors affecting the thermodynamic equilibrium were dominating later. Increased temperature and water activity had initial positive influence that shifted to substrate ratio and a negative influence of water activity as equilibrium was approached. Product quality was mostly affected by temperature negatively, as an increased temperature promoted acyl migration.