Optimisation of enzymatic pretreatment of soybean oil deodoriser distillate for concentration of tocopherols

Tocopherols have been purified from the deodoriser distillate produced in the final deodorisation step of vegetable oil refining by a process including molecular distillation. The deodoriser distillate contains mainly tocopherols, sterols and free fatty acids (FFAs); the presence of FFAs hinders tocopherol purification. In general, Candida rugosa lipase recognised FFAs as substrates but not tocopherols, and esterification of FFAs with methanol (MeOH) could be processed in an organic solvent-free system. Several factors affecting esterification of FFAs were investigated in detail and optimised by the Plackett–Burman and the central composite design. The optimal reaction conditions are as follows: water content 21.05%, lipase 115.45 U g^?1 mixture, temperature 28.95 °C and addition of methanol and FFA in a molar ratio of 4:1 in four steps, with degree of decrease of acid value (AV) above 93% in 18 h; this was a much efficient process. No significant tocopherol losses were observed during the process. In conclusion, enzymatic esterification of FFAs in soybean oil deodoriser distillate for concentration of tocopherols was shown to be a technically viable process.