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Nickel analysis of coffee substitutes by high resolution continuum
source graphite furnace atomic absorption spectrometry
C. Alves 1 , F. Dias 1 , S. Morais 2 , S. Casal 1 , C. Delerue-Matos 2 and M.B.P.P. Oliveira 1
1 REQUIMTE, Serviço de Bromatologia, Faculdade de Farmácia, Universidade do Porto, Rua Aníbal
Cunha 164, 4099-030 Porto, Portugal.
2 REQUIMTE, Instituto Superior de Engenharia do Porto, Rua Dr. António Bernardino de Almeida 431,
4200-072 Porto, Portugal.
Coffee is considered one of the world’s most popular drinks, being appreciated for its flavour
and stimulating effect. Its complex chemical composition makes the consumers exposed to
several components, which have been the subject of numerous studies over the years [1].
Despite some information showing potential benefits with moderated coffee consumption,
namely in Alzheimer disease, various adverse health effects could be considered in some
individuals, taking advantage of using coffee substitutes. The instant coffee substitutes are
mainly composed by roasted cereals. Besides contributing to a large portion of our daily
calories supply, cereal products are also nutritionally important due to their content in dietary
fibbers, a wide range of micronutrients and in bioactive components including minerals,
vitamins, antioxidants, as well as other bioactive compounds [2].
Nickel is a naturally occurring element, being present in soil, water, air and in the biosphere
itself. Nickel is present in several foods and is the most common skin allergy-inducing metal.
Nickel dietary ingestion is reported to be within 25 to 35 μg/day but its biochemical roles and
functions are not yet defined [3] taking the European Food Safety Authority to consider that it
has no known beneficial biological function in humans.
In this study, the nickel amount present in instant coffee substitutes (with and without blended
coffee; n=50) was determined by high resolution continuum source graphite furnace atomic
absorption spectrometry (HR-CS AAS). All measurements were carried out using an
AnalytikJena ContrAA 700 spectrometer equipped with a xenon short-arc lamp operating in
hot-spot mode (XBO 301, 300 W, GLE, Berlin, Germany). The beverages were prepared by
dissolution in hot water, as recommended by the manufacturer, and no other pre-treatment of
samples was performed except acidification with suprapure nitric acid (65%, v/v). The
performance characteristics of this recent technique, namely accuracy, repeatability and
reproducibility were evaluated. The values obtained for the coffee substitutes are discussed.
References:
[1] Lundsberg, S.L. (1998), Caffeine Consumption, CRC Press, LLC.
[2] Kamal-Eldin, A. (2008), Micronutrients in Cereal Products: Their Bioactivities and Effects on
Health, Taylor & Francis Group, LLC.
[3] World Health Organization (WHO), (1996), Trace elements in human nutrition and health, Geneva
(Switzerland).
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