Have you ever opened a jar of olives and noticed the shimmering liquid floating on the surface? Believe it or not, that liquid is actually residual oil that is given off by the olives themselves. Since the oil is less dense than the aqueous solution that the olives are stored in (olive brine), it floats to the top of the jar. This may not seem like a big concern to the typical olive consumer, however, olive manufacturers believe that too much oil in a jar is something that negatively affects the final product. For this reason, olive companies are putting effort and resource into finding a way to quantify the amount of oil in their final product.
The solution to this problem is outlined in EPA method 1664B. This method allows you to quantify the amount of oil & grease you have in your water. More specifically, it allows you to separate and quantify the amount of n-hexane extractable material (HEM) you have in your water sample. Performing an oil and grease analysis on a jar of olives comes with two unique challenges. The first challenge is decanting off the olive brine to remove most of the large olive pieces from the sample. While the olives may contain additional oil, the sample is treated as though it is at equilibrium. For a consumer-ready jar of olives, the assumption is made that the maximum amount of oil has already been extracted out of the olives and into the water. Once decanted, the olive brine is measured out into a graduated cylinder to measure the volume of brine in each jar (this is necessary so that HEM values can be reported in units of mass per volume – typically mg/mL). Since this analysis is for quality control rather than regulatory compliance, the method serves as more of a guideline than something that the user must adhere to. This allows companies to report results in units that are most appropriate for their product – in this case it would be units of mg/jar. The company also creates their own acceptance criteria based around what they believe is too much oil for their product.
The second challenge in performing an oil and grease analysis on olive brine is dealing with a very complex sample matrix. Olive brine is an aqueous solution that has a very high salt content, a fair amount of suspended solids, and a large concentration of water-soluble plant matter, such as proteins. These matrix components can create application challenges, such as emulsions, particularly if you’re processing your samples using liquid liquid extraction (LLE). The emulsions are created due to the surfactant-like nature of some of the proteins, such as thaumatin, which contain a very hydrophobic, carbon-based core with very polar hydoxyl groups attached to the outermost ring structures. Once formed, these emulsions can be challenging to break up. Typically, large amounts of solvent and an experienced technician are required to complete an extraction once emulsions have formed. Along with the emulsions, some of the salt is also precipitated in the presence of the organic solvent, which can create data collection issues – did I mention that the final HEM concentration is measured gravimetrically?
Whenever I’m working with a method that could cause “challenging emulsions,” I instantly turn to solid phase extraction (SPE) to save myself the headache of having to deal with that hurdle. Not only does the use of SPE get rid of any emulsion problems I might have, but in this case, the disk actually catches the precipitated salt particles as well. Talk about killing two birds with one stone!