The espresso coffee machine. For many, this humble household appliance is limited to the brewing of that oh-so-important daily caffeine dose. For others, like Bianca Deans and Jeremy Just — both Organic Chemistry PhD candidates at the University of Tasmania, specialising in natural product isolation — the machine serves a rather unique purpose. Instead of using it to brew that daily dose of caffeinated goodness, they use a standard espresso machine to perform Pressurised Hot Water Extractions (PHWE) on a variety of other plant material.
This method essentially follows the same process as making a cup of coffee. However, rather than using coffee beans, Bianca and Jeremy use other plant material, such as endemic and native Tasmanian plant species. First, a sample of a plant, such as Banksia marginata or Acacia riceana, two endemic Tasmanian species Bianca has worked with during her PhD, is collected. The sample is then dried out in an oven, ground up in a spice grinder, and placed in the group head. Lastly, the “cappuccino” button is pressed, and hey presto — one organic plant material extract is ready to go.
“The coffee machine just happens to be a means to an end,” said Jeremy. “Instead of buying a very expensive accelerated solvent extractor, why not use a bench top coffee machine? That is what it does anyway – it extracts stuff out of plants, such as coffee — coffee is just a mix of chemicals out of a plant.”
Over the past three years (beginning in 2014) the Smith-Bissember group at the University of Tasmania — Bianca and Jeremy’s supervisors — developed the “Espresso Machine” Pressurised Hot Water Extraction (PHWE) procedure for the rapid extraction of plant material.
As the story goes, Jason Smith — the “Smith” half of “Smith-Bissember”, and Jeremy and Bianca’s primary supervisor — is an avid coffee drinker.
“He just thought, ‘I wonder if this could work?’” Jeremy said with a laugh. “Jason ran a few tests, and when it seemed promising, he passed it off to the only PhD student silly enough to take it on — me.”
“I basically did the initial method development,” continued Jeremy. “We had no idea how useful it would really be, but it turned out to be incredibly useful — we get results as good as, or better than, the commercial instruments designed specifically for this purpose.”
Traditionally, a variety of methods such as Soxhlet extraction, maceration (stirring plant material in a solvent for typically hours or even days), and steam distillation have been used to extract plant material. However, these methods have notable disadvantages.
“They are lengthy processes of extraction,” said Bianca. “They can also require large volumes of toxic solvent — such as methanol, or chlorinated solvents such as chloroform — which environmentally is hazardous.”
In comparison, the Espresso Machine Procedure is cheaper, faster, and more environmentally friendly. While specialised extraction equipment can cost tens of thousands of dollars, a commercial coffee machine is significantly less expensive.
“That’s the thing, you don’t have to spend anything to get started — you can just purchase a coffee machine,” said Jeremy. “The machines break down occasionally — as any piece of kitchenware would.
“But if we do break one, it doesn’t matter,” continued Jeremy. “$200 for a machine at a research level budget is nothing. We have probably destroyed five or six over the past four years but even then, that’s only $1500 bucks, which for that amount of time — and the number of extracts we run through it — is nothing.”
“Most of the coffee machines we have, Jason has either got second hand off Gumtree or online,” said Bianca. “So, it is fairly sustainable as well!”
The method is rapid, with the potential to go from a whole plant, and subsequent extraction via Pressured Hot Water Extraction, to a final pure chemical in a number of hours — an extremely challenging feat to achieve using traditional methods. Another unique feature is the size of the sample the machine can deal with.
“We can process approximately 10-15 grams of material,” said Bianca. “Often the accelerated solvent extraction instruments can’t deal with that much material in one go.”
“The extracts obtained from this method typically contain fewer or no plant pigments, such as chlorophylls, which is a common impurity within traditional extraction methods,” continued Bianca. “This is another advantage, as by avoiding these green or coloured molecules, we achieve a cleaner, easier to purify extract from the get go.”
The “Espresso Machine” method is significantly more environmentally friendly than traditional methods. The solvent used is primarily water, a “green solvent” as it is non-toxic, environmentally friendly, and can be easily disposed of. Often Bianca and Jeremy will add an organic modifier — up to 35% ethanol (% v/v) — to change the polarity of the solvent mixture. This too is a very green method.
“Ethanol is something you can just pour down the sink,” said Jeremy. “Getting rid of our waste is exactly the same as pouring a bottle of vodka — which is 35% ethanol — down the sink.”
So, is it likely organic chemists will be using industrialised, large-scale coffee machines for extraction in the future? Although it is a novel idea, Jeremy isn’t convinced.
“We were looking at trying to figure something like that out with a group in the United Kingdom,” he said. “But the point of this is that you don’t have to engineer anything, it is just there.”