Thermal stability and products chemical analysis of olive leaf extract after enzymolysis based on TG–FTIR and Py–GC–MS

Abstract

Olive leaf extract pretreated by enzymolysis was selected for studying the thermal stability at different heating rates by thermogravimetric coupled with infrared spectroscopy (TG–FTIR) and nonisothermal theoretical analysis, and products analysis by pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Results revealed that thermal decomposition of ethyl acetate extract from olive leaf extract pretreated by enzymolysis (EAEEH) consisted of two steps and had a lower thermal stability. The nonisothermal decomposition kinetics mechanism of EAEEH was D3 model (three-dimensional diffusion, Jander equation, the first step) and F3 model (chemical reaction, n = 3, the second step). TG–IR showed –CH3, –C=C–, –OH, –C–O were continuously accelerated to produce, and evolved gas were CO2, water, CO and CH4 at the end. In addition, it was found that there were mainly polyphenols with phenolic hydroxyl groups in the pyrolysis products by Py–GC–MS, and it was also explained for the thermal stability results. This will provide a theoretical guidance for thermal application of EAEEH in the safe natural food additives, cosmetic and medicine.