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United States Department of Agriculture

Agricultural Research Service

Research Project: SUSTAINABLE AND ORGANIC MANAGEMENT OF SELECTED FRUITS AND VEGETABLES Title: Recovery and stability of oleuropein and other phenolic compounds during extraction and processing of olive leaves (Olea europaeaL.)

item Malik, Nasir
item Bradford, Joe

Submitted to: Journal of Food Agriculture and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2008
Publication Date: April 1, 2008
Citation: Malik, N. and Bradford, J.M. 2008. Recovery and stability of oleuropein and other phenolic compounds during extration and processing of olives leaves (Oleau europaea L.). Journal of Food, Agriculture & Environment. 6(2):8-13.

Interpretive Summary: Lower incidences of coronary diseases and some forms of cancer in Mediterranean countries such as Greece, Italy, and Spain are generally attributed to high consumption of olive oil. It is also well known that a majority of health benefits credited to olive oil are in fact due to the presence of a variety of phenolic compounds. Oleuropein is the major component of olive polyphenols and is extensively studied for health benefits concerning a variety of ailments such as blood pressure, cancer, heart problems and an array of viral and bacterial diseases. Oleuropein is most abundant in developing fruits but its concentration sharply declines when fruits begin to mature. Thus, olive oil which is pressed from mature fruits contains very small amounts of oleuropein. On the other hand, oleuropein is the most abundant polyphenols in olive leaves and health benefits of leaf extracts are well documented. Thus to harness the benefits of olive polyphenols several preparations of olive leaves and their extracts are sold in the market at premium prices. However, there is a paucity of knowledge regarding stability of oleuropein and other polyphenols in leaves during processing and extraction of olive leaves for home consumers to benefit from valuable polyphenols at reasonable costs. A preliminary survey of commercial leaf products also showed inconsistencies between the claimed and actual levels of oleuropein in some products indicating problems in controlling stabilities or recoveries during extraction and processing procedures. These studies were therefore conducted to provide guidance regarding recovery and stability of oleuropein, and other polyphenols of olive leaves, during processing and extraction of olive leaves by researchers, home consumers, and by commercial entities.

Technical Abstract: Polyphenols in olive leaves, especially oleuropein, are of great interest to researchers, household consumers and commercial entities due to many health benefits of these compounds. Various processing and extraction methods were investigated to evaluate stability and recovery of oleuropein and other polyphenols from olive leaves. Brief thawing of frozen leaf samples (5 minutes) caused a sharp reduction in extractable oleuropein levels ( 57.7%), and 53.5% loss in oleuropein occurred when frozen leaf powder was thawed for only 2 minutes. Simple drying of fresh leaves at room temperature (25°C) fully preserved oleuropein and verbascoside levels while drying at an elevated temperature of 60°C resulted in losses, at various levels, of all polyphenols studied. While extraction in 80% methanol is the most effective method for olive leaf polyphenols for laboratory use, boiling dried leaves was also a very efficient method for extracting oleuropein and verbascoside that gave 96 and 94% recoveries of these compounds, respectively, when compared with the methanol extract. Oleuropein was quite stable in aqueous extracts for 7 days when stored at room temperatures but degraded after 17 days. Other polyphenols were less stable in aqueous extracts and started to show some degree of degradation after 7 days (little change occurred during the first 24 h storage at room temperature) and were completely degraded after 17 days. On the other hand, Oleuropein, and other polyphenols, in methanol extract were quite stable for 30 days when stored at room temperature, The studies provide important information for efficient and effective processing and extraction of olive leaf polyphenols for research, home, and commercial use.

Last Modified: 4/19/2014
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