Green coffee: Mineral deposits by FAAS

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  • Published: Apr 15, 2015
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Green coffee: Mineral deposits by FAAS

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The content of Ca, Cu, Fe, Mg and Mn and antioxidant activity of green coffee brews

Unroasted, green, coffee beans have become a popular alternative to regular coffee because of purported health benefits so getting a clearer picture of what mineral ions and other components might be present in different infusions is important. Now, a fast and simple method for the analysis of infusions has been developed - high resolution-continuum source flame atomic absorption spectrometry - the technique can provide total concentrations of calcium, copper, iron, magnesium and manganese ions.

Many of us enjoy hot and even iced  infusions of the roasted seeds, or beans, of the Coffea canephora (robusta) or C. arabica plants, often in the form of elaborately prepared and flavoured drinks. But, prior to the luxury roast or the deli frothed mochachoccafrappacino with cinnamon and sprinkles was the unroasted, green, bean. The presence of minerals, antioxidants and other compounds of possible physiological activity has led to numerous claims to the health and weight loss benefits of green beans. Of course, as with many proposed panaceas, the supplement and diet industries are quick to exploit even scant evidence to promote products and books.

Healthy coffee

Now, Ewelina Stelmach, Pawel Pohl and Anna Szymczycha-Madeja of the Department of Analytical Chemistry, at Wroclaw University of Technology, in Wroclaw, Poland, explain that coffee beans do indeed have a complex matrix of many different substances some of which have antioxidant and stimulating effects on the human body. And, there is some evidence that conventional, roasted, coffee drinks may have benefits in reducing the risk of type II diabetes, Parkinson's and Alzheimer's disease and even liver cancer. Conversely, there are studies that show that too much coffee and excessive caffeine consumption in general may also have detrimental effects on health. As Paracelsus pointed out, the dose makes the poison.

Studies in mice have also shown that imbibing the green coffee extract may accelerate metabolic processes perhaps leading to weight loss and even reducing obesity. It could be that a single compound is responsible for this effect, acting as an inhibitor of fat absorption from the gut and suppressing fat metabolism in the liver. There is also evidence from studies in rats that green coffee may reduce blood pressure and that the effects can last for 24 hours after administration, according to the literature.

Others have determined the general constituents of green coffee beans as follows: carbohydrates (50% dry mass) - water soluble (galactomannan, arabinogallactan) and insoluble (cellulose) - phenols, including caffeine itself and chlorogenic acids, as well as other polysaccharides, proteins, polyphenols, melanoids, lipids and minerals. The team points out that much of the research into putative health benefits of green coffee have focused on the antioxidant activity of the chlorogenic acids but that health effects of foods usually derives from synergistic effects between such constituents and others, including metal ions. Moreover, ingestion of calcium, potassium and magnesium from food is also linked to blood pressure reduction.

Mineral deposits

Unfortunately, mineral extraction from green coffee beans is limited in preparation of an infusion, which usually involves pouring hot water over the beans and leaving to brew for mere minutes. The team hoped to provide definitive information on the mineral potential of green coffee, nevertheless, especially for macro-elements - calcium and magnesium, and micro-elements copper, iron and manganese. The research would also define origin of the most mineral-rich beans and those beans that were quickest to leach useful quantities of the metal ions into the drink.

The team has now carried out high resolution-continuum source flame atomic absorption spectrometry (HR-CS FAAS) with no pre-treatment using wet oxidative digestion being necessary. The technique allowed them to carry out a sequential multi-element analysis much more quickly than is possible with ICP OES (inductively coupled plasma optical emission spectrometry) and with sufficient analytical performance and accuracy, -1 to 2 percent). The team also carried out assays with Folin–Ciocalteu reagent (FCR) and free diphenylpicrylhydrazyl radical to allow them to correlate mineral content with antioxidant activity. Additionally, different brewing methods were tested: preparation in a mug, Turkish, filter dripper and coffee machine coffee preparation, and one tested with different brew times.

The team found that calcium and magnesium were leached from green coffee beans the most effectively, at 75% and 70%, respectively. The rate of extraction was lowest with a mug preparation and much improved with dripper or Turkish coffee preparation methods. Leaching was more effective with green beans than seen in the same tests carried out on roasted beans. The team also found that antioxidant activity of green coffee infusions did indeed correlate positively with the total content of phenolic compounds and the concentration of calcium in the brew. Copper, iron and manganese were found not to be present in concentrations greater than 0.15 micrograms per millilitre.

Related Links

Food Chem 2015, 182, 302-308: "The content of Ca, Cu, Fe, Mg and Mn and antioxidant activity of green coffee brews"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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