Lemon myrtle (Backhousia citriodora) is one of the most commercially grown native herbs in Australia. This study aimed to evaluate the effects of different drying methods on phenolic compounds and antioxidant properties of lemon myrtle leaves to identify the most suitable drying conditions. The drying methods include hot air drying, vacuum drying, microwave drying, sun drying, shade drying and freeze drying. The results showed that drying conditions significantly (p < 0.05) affected the retention of total phenolic content (TPC), total flavonoids (TFC), proanthocyanidins, gallic acid, hesperetin, and antioxidant properties of lemon myrtle leaves. The optimal conditions for hot air drying and vacuum drying are 90 °C for 75 min and 90 °C for 120 min, respectively; whereas optimal drying conditions for microwave drying are 960 W for 7 min, and the time required for sun drying and shade drying are 2 days and 12 days, respectively. The freeze dried leaves contained the highest level of TPC, TFC, proanthocyanidins, gallic acid and hesperetin (74.11 ± 2.87 mg GAE/g dw, 87.15 ± 2.70 mg CE/g dw, 123.49 ± 6.12 mg CE/g dw, 53.77 ± 0.22 mg/g dw and 38.99 ± 0.26 mg/g dw, respectively). The freeze dried leaves also contained higher antioxidant capacity as compared to other samples. No significant difference in phenolic compounds and antioxidant capacity was observed between tested other drying methods. Therefore, any of these methods can be selected for dehydration of lemon myrtle leaves for industrial purposes. However, microwave drying can be selected for drying of lemon myrtle leaves for an industrial scale as it was the most time and/or energy efficient technique.

Leptospermum petersonii is a native Australian medicinal and aromatic plant. This study was designed to evaluate the influence of solvents and ultrasound-assisted extraction (UAE) parameters including time, temperature, and sonication power on the yield of phenolic compounds and antioxidant capacity from lemon scented tea tree leaves. Extraction efficiency of the optimal UAE conditions were compared with that of shaking water bath technique. The results show that extraction solvents significantly affect extraction yield of phenolic compounds and antioxidant properties, and 50% acetone in water was found to be the most suitable solvent. The UAE optimal conditions were 60 min, 50 C and sonication power of 200 W. Under these optimal conditions the yields of total phenolics, flavonoids, proanthocyanidins were 98.91 AE 1.20 (mg GAE/g DW), 76.12 AE 0.79 (mg CE/g DW), 117.71 AE 2.18 (mg CE/g DW), respectively. Antioxidant properties from four assays including FRAP, CUPRAC,

Phenolic compounds are secondary metabolites of plants that function to protect the plant from adverse ecological and physiological situations such as pathogen and insect attack, UV radiation, and wounds (Kennedy & Wightman, 2011; Khoddami et al., 2013). These metabolites exhibit wide bioactivity; hence, they could have potential applications in food, pharmaceuticals, and cosmetic industries. Previous research has shown several properties of plant derived phenolic compounds including antimicrobial (Bhuyan et al., 2017;

Background: Lemon myrtle (Backhousia citriodora), is native to Australia and has a significant value as an aromatic herb and folk medicine. Recently it has shown potential applications in food, pharmaceutical, and cosmetic industries. Objective: This study was designed to identify the most suitable safe solvent for the extraction of phenolic compounds and antioxidant properties from lemon myrtle leaves, and then apply response surface methodology (RSM) to develop the optimal conditions (time, temperature, and sonication power) for extraction of phenolic compounds and antioxidant properties from lemon myrtle using ultrasonic-assisted extraction (UAE). Methods: Five different solvents viz water, acetone, ethanol, acetone: water (50:50), and ethanol: water (50:50) were tested for extraction efficiency of phenolic compounds and antioxidant properties from dried lemon myrtle leaves. A three-level three-factor Box–Behnken design was employed to elucidate the effect of sonication time, extraction temperature, and sonication power on the yields of total phenolics, antioxidant capacities, and major individual compounds (gallic acid and hesperetin). Results: The results showed that solvents have a significant impact on the extraction efficiency of bioactive compounds and antioxidant properties from lemon myrtle, and 50% acetone is the best solvent. Mathematical models were reliable for prediction of optimal extraction conditions and the optimal conditions for extraction of phenolic compounds and antioxidant capacity, as well as gallic acid and hesperetin are 50 min, 60 °C and sonication power of 250 W. Conclusion: These optimal conditions and 50% acetone in water (as solvent) are recommended to extract phenolic compounds and antioxidant capacity from lemon myrtle leaves for the application as a functional food ingredient.

The aromatic herb lemon myrtle is a good source of polyphenols, with high antioxidant and antimicrobial capacity. In this study, the green extraction technique microwave-assisted extraction (MAE) was applied and the extraction parameters were optimized using response surface methodology (RSM) to maximize the extraction yield of phenolic compound and antioxidant properties. Then, it was compared with other popular novel and conventional extraction techniques including ultrasound-assisted extraction (UAE) and shaking water bath (SWB) to identify the most effective technique for extraction of phenolic compounds from lemon myrtle. The results showed that the MAE parameters including radiation time, power, and sample to solvent ratio had a significant influence on the extraction yield of phenolic compounds and antioxidant capacity. The optimal MAE conditions were radiation time of 6 min, microwave power of 630 W, and sample to solvent ratio of 6 g/100 mL. Under optimal conditions, MAE dry extract had similar levels of total phenolic compounds (406.67 ± 8.57 mg GAE/g DW), flavonoids (384.57 ± 2.74 mg CE/g DW), proanthocyanidins (336.54 ± 7.09 mg CE/g DW), antioxidant properties, and antibacterial properties against (Staphylococcus lugdunensis and Bacillus cereus) with the other two methods. However, MAE is eight-times quicker and requires six-times less solvent volume as compared to UAE and SWB. Therefore, MAE is recommended for the extraction of polyphenols from lemon myrtle leaf.