Effect of drying method on oleuropein, total phenolic content, flavonoid content, and antioxidant activity of olive (Olea europaea ) leaf

Abstract

The purpose of this research was to study the effect of microwave drying (MD) on the major phenolic compound oleuropein, total phenolic and flavonoid contents, and antioxidant activity of the olive leaves. The results were compared to those obtained after using freeze drying (FD), vacuum drying (VD), oven drying (OD), and ambient air‐drying (AAD). Response surface methodology, using a central composite face‐centerd design, was used to optimize the effects of microwave irradiation power (300–500 W), solid mass (1.5–2.5 g), and drying time (4–6 min) on oleuropein and other olive leaves antioxidant compounds. The second‐order models were found highly adequate with very low root mean squared deviation (RMSD) and high coeffecient of determination (R2) values. The results of MD under optimum conditions (2.085 g sample at 459.257 W for 6 min of drying period) has demonstrated to be the best drying method followed by FD, VD, OD, and AAD. Practical applications Olive leaves are agricultural waste which contains significant amounts of valuable compounds such as oleuropein and phenolic compounds. Nowadays, application of these compounds has attracted considerable interest as food additives and/or nutraceuticals in both food and pharmaceutical industries. Several methods have been applied for the extraction of phenolic compounds from olive leaves and by‐products. However, to obtain higher extraction yield, it is important to reduce the water content of the samples before extraction. This study demonstrates the feasibility of using microwave drying as a promising technique compared to other methods (e.g., freeze‐, vacuum‐, oven‐, and ambient air‐drying) for drying of olive leaves with minimum changes in total phenolic, flavonoids, antioxidant activity, and oleuropein contents.

Physicochemical Characterization, Antioxidant Activity, and Phenolic Compounds of Hawthorn (Crataegus spp.) Fruits Species for Potential Use in Food Applications

“…In another study, the total content of polyphenols in fruits of C. pinnatifida was 96.9 ± 4.3 mg gallic acid equivalents/g weight [48]. The health and technological benefits associated with plant compounds in value-added food products had been attributed to the antioxidant and antimicrobial activity of phenols content [49,50]. Table 4 shows the TFC in fruits of hawthorn.…”

Effects of Ultrasound-Assisted Extraction and Solvent on the Phenolic Profile, Bacterial Growth, and Anti-Inflammatory/Antioxidant Activities of Mediterranean Olive and Fig Leaves Extracts

“…From ancient times, Mediterranean plants and trees have attracted the interest of human being due to their beneficial properties such as antiviral, anti-inflammatory, prevention of cardiovascular diseases, and improvement of lipid metabolism to reduce obesity [1]. Most of these health-related effects have been attributed to their high content in bioactive compounds, such as polyphenols and carotenoids [2][3][4]. Among the different Mediterranean fruits, olive and fig, especially their leaves, have attracted the consumer's attention because of their potential use as a source of traditional medicines, food additives, and preservatives.…”

Characterization of bioactive compounds in commercial olive leaf extracts, and olive leaves and their infusions

“…The pruning and olive harvesting for the production of olive oil and table olives generate a considerable volume of OL, used by some industries to obtain natural products rich in bioactive compounds for food additives, dietary supplements, cosmetic and nutraceutical purposes. [1][2][3] For many centuries, olive leaves and their extracts have been associated with preservation and health. Egyptians employed OL in the mummification process as a good preservative, 4 and they also have been used in folk medicine to combat fevers and other diseases, such as malaria.…”