Optimum conditions and verification
The optimum reaction variables for CG synthesis were as follows: load of Lipozyme 435 25 % (relative to the weight of total substrates), molar ratio of CA to glycerol 1:150, 80 oC and 10 h. Under the optimized conditions, CG yield was 95.0 ± 1.0 %, which was similar with the yield reported in the literature (Sun & Hu, 2017). However, CG was in the past synthesized by the transesterification of ethyl caffeate with glycerol, with the disadvantage of reducing the final reaction efficiency and increasing cost.
The above optimal reaction conditions were also used to synthesize FG and p -HCG via esterification of FA and p -HCA with glycerol, resulting in isolated yields of 82.1 % and 80.7 % respectively, validating the reaction model in the synthesis of PAGs.