Chemical and biological evaluation of olive leaves as a waste by-product of olive oil industry

Background and objectives Finding new uses for by-products of cultivated plants is of great value economically and to the environment. Leaves represent about 10% of the total weight of olives yield. It is worth to obtain value-added products from this material. In this article, the leaves were evaluated chemically and biologically for phenolics and flavonoids as well as for microelements and macroelements and fatty acids. Also, antioxidant and antimicrobial activities were carried out. Materials and methods Air-dried powdered olive leaves were defatted with hexane and the marc was then soaked in 80% methanol and successively extracted with CH2Cl2, EtOAc, and n-BuOH. Total phenolic and flavonoid contents were determined as chlorogenic acid and rutin equivalents, respectively. Microelements and macroelements were detected in addition to fatty acids. The antioxidant effect was determined in vitro using 1,1-diphenyl-2-picrylhydrazyl and antimicrobial activity was carried out using in-vitro agar well diffusion method. Results and conclusion Total phenolics were found to be highest in the 80% methanolic extract and the lowest in water and ethyl acetate fractions. 1,1-diphenyl-2-picrylhydrazyl-free radical scavenging activity of olive leaf extracts were in this order: 80% methanolic extract, water extract, ethyl acetate fraction and butanol fraction. Also, the calcium : potassium value was 15: 1. Fatty acid profile revealed that linolenic acid was the major fatty acid in terms of percent (49.45%). Ethyl acetate fraction showed positive antibacterial activity and negative antifungal activity whereas water, 80% methanol, and butanol fractions have positive antifungal and negative antibacterial activity. Conclusion Olive leaves could be considered as a potential inexpensive source for food supplements for human health.