Abstract
In this study, different drying methodologies (convective air, oven and microwave) of Myrtus communis L. (M. communis L.) leaves were conducted to investigate their effects on the levels of phenolic compounds, antioxidant capacity of ethanolic extracts (EEs) as well as the soybean oil oxidative stability. Drying methodology significantly influenced the extractability of phenolic compounds. Microwave drying led to an increase in the amounts of total phenols, flavonoids and proanthocyanidins followed by oven drying at 70 °C. Higher temperature of drying (100 and 120 °C) led to a significant reduction of their amounts (p < 0.05). An ultra-performance liquid chromatography method combined with high resolution mass spectroscopic detection was used to analyze the phenolic fraction of extracts. Higher amounts of the identified compounds were observed when leaves were heat treated. Furthermore, the evaluation of the antioxidant activity showed that the studied extracts possess in general high antioxidant capacities, significantly dependent on the employed drying methodology. The incorporation of the different extracts at 200 ppm in soybean oil showed that its oxidative stability was significantly improved. Extracts from leaves treated with microwave (EE_MW) and at 70 °C (EE_70) have better effect than BHT. The results of the present study suggest that microwave drying could be useful to enhance the extractability of phenolic compounds and the antioxidant capacity of M. communis L. leaf extract.
Highlights
Over the past few years, medicinal plants have attracted considerable attention as an efficient source of bioactive compounds, such as polyphenols endowed with antioxidant properties and could be used in the Snoussi et al BMC Chemistry (2021) 15:31 abovementioned sectors will need to pay more attention to the factors that could impact the quantity and quality of phenolic compounds [4, 5].Phenolic compounds extraction has several critical points like the choice of the plant phenological stage, the choice of solvent, the method of extraction and purification as well as the post-harvest technological processes mainly the drying process [6]
In the cases of air drying and ventilated oven treatments, dried myrtle leaves color turned to light brown with a green tinge
Eight phenolic compounds were identified in the different extracts including two phenolic acids: gallic and caffeic acids and six flavonoids: myricetin 3-O-rhamnoside, quercetin 3-O-glucoside, quercetin 3-O-rhamnoside, quercetin, myricetin and kaempferol (Fig. 2)
Summary
Over the past few years, medicinal plants have attracted considerable attention as an efficient source of bioactive compounds, such as polyphenols endowed with antioxidant properties and could be used in the Snoussi et al BMC Chemistry (2021) 15:31 abovementioned sectors will need to pay more attention to the factors that could impact the quantity and quality of phenolic compounds [4, 5].Phenolic compounds extraction has several critical points like the choice of the plant phenological stage, the choice of solvent, the method of extraction and purification as well as the post-harvest technological processes mainly the drying process [6]. Immediately after harvesting, fresh plants are usually dried in order to facilitate their transportation, storage and handling. The drying process is a key factor that enables to preserve the quality of medicinal plants and their bioactive extracts and compounds. Different methods are used to dry fresh plant tissues such as air drying, oven drying and microwave drying. Air and oven drying usually take a very long time which may lead to significant decrease of the quality of the dried product [9]. Microwave energy transfer causes a rapid evaporation of water from the plant tissue, treatment time is shorter, and quality is preserved [10, 11]
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