Effects of different drying methods on extractable phenolic compounds and antioxidant properties from lemon myrtle dried leaves

Abstract

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.

Effect of drying techniques and operating conditions on the retention of color, phenolics, and antioxidant properties in dried lemon scented tea tree ( Leptospermum petersonii ) leaves

“…It required only 0.096 kWh energy which is approximately 9, 4.5, and 1,700 times more energy efficient in comparison with hot air drying, vacuum drying, and freeze-drying, respectively. The results from this study is supported by previous studies, for instance,Nguyen et al (2018) andSaifullah et al (2019) found the microwave drying was the most energy efficient and suitable drying technique for drying S. spinescens leaves and stems, and lemon myrtle leaves, respectively. The microwave drying method was also reported as the most suitable method for drying banana peel to retain high bioactive compounds and antioxidant properties(Vu et al, 2017).…”

The Effect of Infrared Drying on Color, Projected Area, Drying Time, and Total Phenolic Content of Rose (Rose electron) Petals

“…The same trend was observed by Chang, Lin, Chang, and Liu [47] for tomatoes, Honarvar et al [48] for Rosa moschata, and Da Silva et al [49] for pineapple when they evaluated the content of phenolic compounds after drying; they also obtained higher values of TPC in the dried samples than in the fresh samples. Similar findings were also observed by Saifullah et al [50] during drying lemon myrtle with hot air at 50, 70, and 90 • C for 315, 105, and 75 min, respectively. They obtained the highest total phenolic content at 90 • C for 75 min and suggested that drying at higher temperatures requires shorter times in order to avoid phenolic and other phytochemical content degradation.…”

Application of immersion pre-treatments and drying temperatures to improve the comprehensive quality of pineapple (Ananas comosus) slices

“…The present study found that total flavonoids increased with increasing temperature in some cases, which is somewhat unstable with different treatments. These results can be explained by the shorter times required by higher drying temperatures; thus the pineapple slices had shorter exposure to heat, which resulted in a minor breakdown of TFC ( Saifullah et al., 2019 ). Our findings are quite consistent with the summary of Roshanak et al.…”

“…Drying has been considered as one of the most crucial preservation techniques, commonly applied for extending shelf-life of fruits and vegetables, and improving food stability by minimizing moisture content, chemical degradation, and microbial load ( Brasiello et al., 2017 ). Unfortunately, the drying process can provoke countless physicochemical alterations in tissue structures that result in poor reconstitution properties in rehydrated products ( Saifullah et al., 2019 ; Lewicki, 1998 ). This leads to physicochemical changes like chemical composition, color, texture, shrinkage, and nutritional variations, which have a high impact on its overall quality of dried products and, therefore, consumers' acceptability ( Sasongko et al., 2020 ; Hossain et al., 2021 ).…”