Effect of reaction temperature on the yield of CG
The conversion, solubility of the PAs and the stability as well as the activity of the lipase are strongly related to the reaction temperature. The effect of reaction temperature on esterification of CA with glycerol in lipase-catalyzed reaction was investigated at different temperatures from 70 ℃ to 90 ℃. As shown in Fig. 6, the yields of CG increased with the rising of the temperature from 70 ℃ to 80 ℃ and reached 94.4 % at 80 ℃ after 10 h, which were mainly attributed to the decrease of the reaction system viscosity and fast mass transfer rate of caffeoyl to glycerol at a high temperature. However, the yields of CG decreased when the temperature was over 80 °C, which could due to be the thermal enzyme deactivation at high temperature. Similar phenomenon could also be found in other studies (Sun & Hu, 2017; Sun & Chen, 2015). Therefore, the optimal reaction temperature was chosen to be 80 °C.
Fig. 6. Effect of reaction temperature on the yield of CG. Reaction conditions: molar ratio of CA to glycerol 1:150, 25% of Lipozyme435 (relative to the weight of total substrates), 86.7 kpa.