Microwave-Assisted Extraction of Natural Antioxidants from the Exotic Gordonia axillaris Fruit: Optimization and Identification of Phenolic Compounds.

Our previous study reported that the fruit of Gordonia axillaris , an edible wild fruit, possessed strong antioxidant activity. In this study, a microwave-assisted extraction (MAE) method was established to extract antioxidants from the fruit of Gordonia axillaris . The influence of five parameters, including ethanol concentration, solvent/material ratio, extraction time, extraction temperature and microwave power, was investigated by single-factor experiments. Three factors, namely ethanol concentration, solvent/material ratio, extraction time, were found to exert a major influence on extraction efficacy, and were further studied by response surface methodology to investigate their interactions. Ethanol concentration of 36.89%, solvent/material ratio of 29.56 mL/g, extraction time of 71.04 min, temperature of 40 °C, and microwave power of 400 W were found to be the optimal condition. The TEAC value was 198.16 ± 5.47 µmol Trolox/g DW under the optimal conditions, which was in conformity to the predicted value (200.28 µmol Trolox/g DW). In addition, the MAE method was compared with two conventional methods (Soxhlet extraction and maceration extraction). Results showed that the antioxidant capacity of the extract obtained by MAE method was stronger than that obtained by maceration (168.67 ± 3.88 µmol Trolox/g DW) or Soxhlet extraction (114.09 ± 2.01 µmol Trolox/g DW). Finally, several phenolic compounds in the extract were identified and quantified by UPLC-MS/MS, which were rutin, gallic acid, protocatechuic acid, epicatechin, epicatechin gallate, 2-hydrocinnamic acid, p -coumaric acid, quercetin, chlorogenic acid and ferulic acid.

Ultrasound-Assisted Extraction and Identification of Natural Antioxidants from the Fruit of Melastoma sanguineum Sims.

The fruit of Melastoma sanguineum Sims is an edible and sweet wild fruit. In our previous study, the fruit was found to have a strong antioxidant property. In this study, an ultrasound-assisted extraction (UAE) method was developed to extract natural antioxidants from the fruit of Melastoma sanguineum Sims, and a response surface methodology was used to optimize the conditions of UAE to maximize the extraction efficiency. The influence of five independent extraction parameters (ethanol concentration, solvent/material ratio, extracting time, temperature, and ultrasound power) on the extraction efficiency were investigated using a single factor experiment, and then a central composite rotatable design was used to investigate the interaction of three key parameters. The results showed that the optimal extraction conditions were 42.98% ethanol, 28.29 mL/g solvent/material ratio, 34.29 min extracting time, 60 °C temperature, and 600 W ultrasound power. Under these conditions, the Trolox equivalent antioxidant capacity (TEAC) value of the extracts was 1074.61 ± 32.56 µmol Trolox/g dry weight (DW). Compared with conventional maceration (723.27 ± 11.61 µmol Trolox/g DW) and Soxhlet extraction methods (518.37 ± 23.23 µmol Trolox/g DW), the UAE method improved the extraction efficiency, in a shorter period of time. In addition, epicatechin gallate, epicatechin, rutin, epigallocatechin, protocatechuic acid, chlorogenic acid, and quercetin, were identified and quantified in the fruit extracts of Melastoma sanguineum Sims by UPLC-MS/MS.