Production of sugar fatty acid esters by enzymatic esterification in a stirred-tank membrane reactor: Optimization of parameters by response surface methodology

6-O-beta -D(+)-Glucose stearate serving as a model product of glucose fatty acid monoesters was synthesized using lipase B from Candida antarctica (Ch irazyme(R) L-2) in a mainly solid-phase system in a stirred-tank membrane r eactor. Esterification was performed in the presence of a small amount of e thyl methylketone (EMK), maintaining a catalytic liquid phase as well as fo rming an azeotrope with the reaction water. The azeotrope was evaporated an d broken by membrane vapor permeation, then the dried EMK was returned to t he reaction medium. The process was optimized by response surface methodolo gy based on five major reaction parameters (time (T-r), substrate ratio (ac yl donor to glucose, S-r), temperature (R-t), amount of solvent [solvent to substrates, [w/w], S-a), and enzyme load (E-l)] varied at three levels, re sulting in higher yields. Thus, under optimized conditions [T-r = 58 h; S-r = 2.7; E-l = 8.9% (w/w); R-t = 78 degreesC; S-a = 1.9], up to 93% yields o f glucose stearate were achieved.