Chapter 28 - Extraction of Oleuropein and Related Phenols from Olive Leaves and Branches

Abstract

Olive leaves and small branches are agricultural residues resulting from the beating of olive trees for fruit removal, and also from pruning. Spain produces a vast amount of olive leaves and small branches in mills prior to oil production. The interest in both raw materials as olive phenol (OP) sources may also promote their obtainment as industrial by-products from olive mills—in fact, they account for about 10% of the total weight of fruit processed. At present, however, most of these residues are simply disposed of by burning. The scientifically proven health properties of OPs, and their concentration levels in extracts from olive leaves and small branches, which have usually been studied jointly, are promoting the development of new, faster, more efficient automatic extraction methods for their industrial exploitation. The particular technique used to isolate OPs depends on the characteristics of the sample. The extraction of OPs from solid samples has aroused some industrial interest and been the subject of several patents concerned with the separation of phenols (particularly oleuropein) from olive leaves based on traditional solid–liquid extraction methodology. In the laboratory, OPs are usually isolated by using traditional methods involving maceration and Soxhlet extraction with various extractants such as methanol–water mixtures or hexane. It is important to avoid toxic extractants when the procedures are to be used on an industrial scale and the products targeted at human use. Also, it is desirable to shorten extraction times, which are most often in the region of 24–48 h. The extraction process can be expedited by using alternative procedures.