Optimization and characterization of bioactive compounds extracted from commiphora gileadensis barks and leaves using microwave-assisted and ultrasonic-assisted extraction methods / Aiman Awadh Saleh Bin Mokaizh

Faculty of Chemical and Process Engineering Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang – 2025

Includes bibliographical references

Most chronic diseases, such as diabetes and cardiovascular, have grown to be major global health concerns that cause cell damage and death. The use of synthetic medications has negative impacts on human systems; therefore, it is essential to source plant-based alternatives. Commiphora gileadensis (C. gileadensis) is one of the medicinal plants endowed with different biological activities. However, comprehensive research on the extraction and characterization of C. gileadensis's phenolic bioactive components is still lacking. Thus, the optimization of advance and eco-friendly microwave-assisted extraction (MAE), and ultrasonic-assisted extraction (UAE) factors in the recovery of phenolic compounds from C. gileadensis barks and leaves as compared to the Soxhlet extraction method (SE) had been investigated in this study. The characterizations and in-vitro antioxidant activities of the extracts at optimized conditions were also studied. The influence of MAE, and UAE factors, which include irradiation time, microwave power level, temperature, extraction time, ultrasonic frequency level, feed-to-solvent ratio, and ethanol concentration, on the extraction yields (% w/w); total phenolic contents, TPC (mg GAE/g d.w.), and total flavonoid contents, TFC (mg QE/g d.w.), were investigated using one-factor-at-a-time (OFAT) experimental approach. The significant extraction factors of MAE and UAE were identified and screened using a two-level factorial design. Then, four significant factors of MAE, and UAE namely irradiation time, microwave power, extraction time, ultrasonic frequency, feed-to-solvent ratio, and ethanol concentration were optimized via a face-centered central composite design (FCCCD) of response surface methodology (RSM). Similarly, OFAT was utilized to attain the ideal yields by SE, considering the ethanol concentration (20-100% v/v), feed/solvent ratio (1:20-1:50 g/mL), and extraction time (30-180 minutes) for both plant samples. Fourier transform infrared spectroscopy (FTIR), liquid chromatography-mass spectrometry quadrupole time of flight (LC-Q-TOF-MS), scanning electron microscopy (SEM), and inductively coupled plasma optical emission spectroscopy (ICP-OES), were used to characterize the extracts under the optimized conditions of MAE, UAE, and SE. The results demonstrated that 4 minutes of irradiation time (for both samples), a microwave power level of 380 W for barks and 283 W for leaves, a feed/solvent ratio of 1:13 for barks and 1:10 g/mL for leaves, and an ethanol concentration of 58% and 35% v/v were the optimum MAE conditions for C. gileadensis barks and leaves. The optimum recoveries of extraction yield, TPC and TFC were 44.12±0.85% and 34.54±0.57% w/w, 169.72±3.37 and 115.63±2.14 mg GAE/g d.w., 50.68±2.74 and 39.28±1.46 mg QE/g d.w., respectively for C. gileadensis barks and leaves. The kinetic studies also showed that the second-order kinetic model was more appropriate (significant) for this study where R2>0.96. The obtained outcomes reflected that MAE and UAE can recover higher yields of extracts from C. gileadensis barks and leaves as compared with SE, whereas the MAE recorded the highest. In addition, FTIR spectra indicate the presence of phenolic compounds. Furthermore, LC-Q-TOF-MS analysis confirmed that the phenolic and flavonoid compounds identified by optimized MAE were found to be the highest. Also, the ICP-OES study reported that the MAE recovered more mineral elements (sodium, silicon, and magnesium) from the plant material. More so, the obtained extract of both samples showed stronger antioxidant activities due to the availability of flavonoids and phenolics. Therefore, the extract of the barks and leaves of C. gileadensis via the MAE approach is considered a promising source of antioxidant medicine in the pharmaceutical and functional food industries. Future studies should consider studying the various biological activities of the extracts to ascertain their multiple functionalities.