Preparing olives for the table takes for ever. Here is how to do it faster
DEBITTERING OLIVES is a messy process. In their natural state the fruit of the olive tree are loaded with compounds called phenols that make them unpalatable to people. If an olive is destined to be crushed for its oil, the phenols do not matter. Most will be retained in the pulp left over after pressing. Table olives, though, must be purged of their phenols before being eaten.
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At the moment, this is done by soaking them in water, or brine, or brine followed by a solution of sodium hydroxide known as lye. This liberates the phenols and draws them out by osmosis. For the osmotic process to be effective, though, the bathing liquid needs to be changed frequently. This is tedious, messy and generates phenol-rich waste that is toxic to plants and animals. A better way of cleaning olives would be welcome. And one is now on offer. Rebecca Johnson and Alyson Mitchell of the University of California, Davis, report in the Journal of Agricultural and Food Chemistry that they can do the job using tiny resin beads.
Ion-exchange resins are high-porosity forms of polystyrene tweaked with extra chemical groups that let them capture molecules of different sorts. Many varieties of ion-exchange resin are commercially available, often in the form of hollow beads. These beads have a large surface area relative to their volume, maximising the amount of polymer available for reaction. Beads are also easy to handle.
Dr Mitchell already knew, from previous work, that some ion-exchange beads are capable of collecting the phenols found in olives. She wondered whether adding these beads to the brine tanks in which olives are stored prior to processing with lye might make it possible to debitter olives without having to use lye at all.
To test this idea, she mixed samples of olive pulp with beads and left the mix for half an hour at room temperature. Of the four types of bead she tried, two proved good at removing phenolic compounds called oleuropein, ligstroside, oleacin and tyrosol from the pulp. One of these two, FPX66, is used for debittering citrus fruits and is therefore already certified by America’s Food and Drug Administration as safe for use in food preparation. Dr Mitchell therefore asked Ms Johnson to carry out a more extensive experiment using it.
This trial involved whole olives, which Ms Johnson put in flasks filled with commercial storage brine and FPX66 beads. She then left the olives to soak and sampled them from time to time until 273 days had passed, this being the normal period for which olives are stored in brine prior to processing with lye. The experiment worked. On the days of the first two samplings, the 6th and 26th of the experiment, Ms Johnson found that phenol levels had dropped to a point where the olives would be considered bitter but edible. By day 76 they were at a point where they would hardly be considered bitter at all.
If this discovery can be translated into commercial operation, the brine-soaking stage could be shortened by three-quarters and the lye step dropped altogether, with huge savings in time and materials—for the beads themselves can, after appropriate processing to remove and dispose of the phenols, be recycled. Ion-exchange beads thus have the potential to make processing olives cleaner, faster and cheaper.