Thomas W. M.
Crozier
a,
Angelique
Stalmach
a,
Michael E. J.
Lean
b and
Alan
Crozier
*a
aSchool of Medicine, College of Medical, Veterinary and Life Sciences, Joseph Black Building, University of Glasgow, Glasgow, G12 8QQ, UK. E-mail: alan.crozier@glasgow.ac.uk; Tel: +44 141 330 4613
bUniversity of Glasgow College of Medical, Veterinary and Life Sciences, Walton Building, Royal Infirmary, 84 Castle Street, Glasgow, G4 0SF, UK
First published on 30th November 2011
HPLC analysis of 20 commercial espresso coffees revealed 6-fold differences in caffeine levels, a 17-fold range of caffeoylquinic acid contents, and 4-fold differences in the caffeoylquinic acid:caffeine ratio. These variations reflect differences in batch-to-batch bean composition, possible blending of arabica with robusta beans, as well as roasting and grinding procedures, but the predominant factor is likely to be the amount of beans used in the coffee-making/barista processes. The most caffeine in a single espresso was 322 mg and a further three contained >200 mg, exceeding the 200 mg day−1 upper limit recommended during pregnancy by the UK Food Standards Agency. This snap-shot of high-street expresso coffees suggests the published assumption that a cup of strong coffee contains 50 mg caffeine may be misleading. Consumers at risk of toxicity, including pregnant women, children and those with liver disease, may unknowingly ingest excessive caffeine from a single cup of espresso coffee. As many coffee houses prepare larger volume coffees, such as Latte and Cappuccino, by dilution of a single or double shot of expresso, further study on these products is warranted. New data are needed to provide informative labelling, with attention to bean variety, preparation, and barista methods.
The value of coffee as a human beverage was initially recognised from the invigorating effect of wild coffee berries on goats in Abyssinia, sometime around 850 AD.2 This action, subsequently attributable to its caffeine content, has led to the extraordinary attraction of the beverage to many consumers who exhibit increased alertness and a capacity to remain awake for longer periods without sleep. Caffeine can, however, have unpleasant symptoms, and, in excess, can lead to a state of excitement and anxiety. Dose-responses vary. For some people even a single cup may be acutely unpleasant and cause sleeplessness with a racing mind. For others, through tolerance to increasing exposure, drinking ten times this amount may still be pleasant, partly reflecting genetic variation in susceptibility.3
The half-life of caffeine in adults is around 5 h, but can be up to 30 h, with extended retention in the body by women taking an oral contraceptive, pregnant women, the developing fetus, young children, and those with liver disease. These groups are thus more susceptible to the effects of caffeine toxicity.4 Current advice in the UK from the Food Standards Agency is for pregnant women to restrict caffeine to below 200 mg day−1, or four cups of strong coffee each with an assumed caffeine content of 50 mg.5 For the general public assessing caffeine intake is difficult. Current guideline figures suggest that an 8 oz (∼225 mL) cup of instant coffee contains 60–85 mg of caffeine, and a 1 oz (∼28 mL) espresso 30–50 mg.6 However, despite the increasing number of coffee shops on the high street and in airports, there appear to be no recent publications on the caffeine contents of the various types of commercially prepared coffees.
As well as caffeine, coffee contains substantial amounts of a family of conjugated hydroxycinnamates collectively referred to as chlorogenic acids. The main chlorogenic acids are 5-O-caffeoylquinic acid (5-CQA) and its isomers 3-O-caffeoylquinic acid (3-CQA) and 4-O-caffeoylquinic acid (4-CQA) (Fig. 1) and together these account for 80% of the total chlorogenic acids.7 Although the CQAs in coffee have antioxidant properties, and in vitro are able to scavenge free radicals, which in humans have been linked to conditions such as Parkinson's disease and cardiovascular disease, there is much speculation but only limited evidence of coffee consumption being linked to protective effects on human health.8 Epidemiological evidence and some intervention studies do, however, indicate that coffee consumption may reduce the risk of type 2 diabetes8 and one recent report provides evidence that coffee decreases the risk of depression among women with the effect being attributed to caffeine intake.9
Fig. 1 Structures of caffeine and the chlorogenic acids, 5-O-caffeoylquinic acid, 3-O-caffeoylquinic acid and 4-O-caffeoylquinic acid. |
It is against this background that HPLC analysis has revealed substantial variations in the caffeine and chlorogenic acid content of espresso coffees purchased from coffee shops in the west end of Glasgow near the University of Glasgow.
Source | Serving size (mL) | Caffeine (mg/serving) | Total CQA (mg/serving) | As a percentage of total CQA | ||
---|---|---|---|---|---|---|
3-CQA | 4-CQA | 5-CQA | ||||
Pattiserie Francoise | 52 | 322 | 422 | 23% | 26% | 51% |
University Cafe | 49 | 260 | 230 | 36% | 23% | 41% |
Café Cinnamon | 59 | 242 | 179 | 23% | 28% | 49% |
Paperino's | 50 | 205 | 207 | 31% | 26% | 43% |
S'mug | 32 | 173 | 294 | 21% | 27% | 52% |
Costa Coffee | 25 | 157 | 227 | 21% | 27% | 52% |
Heart Buchanan | 24 | 156 | 127 | 17% | 30% | 53% |
Jellyhill | 63 | 151 | 122 | 21% | 33% | 46% |
Baguette Express | 45 | 140 | 145 | 21% | 28% | 51% |
Chapter1 | 26 | 140 | 215 | 22% | 27% | 51% |
Peckham's | 70 | 140 | 199 | 13% | 29% | 58% |
Little Italy | 23 | 129 | 217 | 17% | 27% | 56% |
Coffee @ 291 | 49 | 98 | 108 | 21% | 29% | 50% |
Crepe á Croissant | 34 | 95 | 81 | 21% | 28% | 51% |
Kember & Jones | 43 | 90 | 175 | 21% | 26% | 53% |
Beanscene | 48 | 77 | 93 | 20% | 28% | 52% |
Tinderbox | 25 | 75 | 90 | 22% | 27% | 51% |
Morton's | 35 | 73 | 56 | 23% | 29% | 49% |
Antipasti | 36 | 72 | 44 | 18% | 34% | 48% |
Starbucks | 27 | 51 | 24 | 21% | 29% | 50% |
Median value | 43 | 140 | 145 | 21 | 28 | 51 |
Range | 23–100 | 51–322 | 24–422 | 13–36% | 23–34% | 43–58% |
Fig. 2 Variation in the total CQA:caffeine ratio of 20 espresso coffees purchased from outlets in the west end of Glasgow. |
It is evident from the data presented in Table 2 that the quoted figures for caffeine content of espresso coffee in the 2008 IFIC Review,6 which are widely cited in the popular press, do not provide a realistic picture. The levels of caffeine per serving varied more than 6-fold from 51 to 322 mg. At the low level, a pregnant woman and others with a need to restrict caffeine consumption, might safely drink 4 cups per day without significantly exceeding the recommended caffeine intake. In marked contrast, at the higher end of the scale, drinking even one cup of espresso will be well in excess of the advised limit of 200 mg day−1.
Coffee | Origin | Roasting temp. (°C) | Roasting time (s) | Roasting |
---|---|---|---|---|
a H-S: high temperature, short roast; L-L: low temperature, long roast. | ||||
Washed arabica | Colombia | — | — | — |
Colombia | 350 | 244 | H-S | |
Colombia | 270 | 595 | L-L | |
Unwashed arabica | Ethiopia | — | — | — |
Ethiopia | 350 | 247 | H-S | |
Ethiopia | 270 | 612 | L-L |
Responses to caffeine vary. Those habituated to the purine alkaloid suffer headaches when caffeine is withdrawn. At the other extreme, doctors not uncommonly see patients with a range of rather non-specific symptoms grouped as “caffeinism” which are resolved when caffeine is removed from the diet. These problems would only be suspected if caffeinated soft-drinks or coffee intake were high: our data show that one cup of high-caffeine coffee could cause as much difficulty to these susceptible consumers as six cups of coffee to another.
This large variability in caffeine and CQA content could be due to a number of factors with the amount of coffee used to prepare a serving of espresso probably being substantially less for the low-caffeine coffees than for those at the upper end of the scale (Table 1). Other factors that could impact on the caffeine and CQA content, arguably to a lesser degree, are (i) batch-to-batch differences in the arabica beans, (ii) roasting procedures, (iii) grinding conditions and (iv) the coffee-making/barista process (temperature of water/steam in the extraction vessel, its duration, coffee:water/steam ratio etc.).
To investigate the possible impact of roasting techniques on the CQA and caffeine contents of coffee, infusions were prepared from two batches of espresso coffees. One was a washed Columbia coffee and the other unwashed beans from Ethiopia. Unroasted coffees were included along with samples which had been roasted (i) at a high temperature for a short time (H-S) and (ii) at a low temperature for a longer time (L-L) as outlined in Table 2. After grinding the beans, 100 mL of boiling water was added to 5 g of coffee and brewed for 5 min before filtering. The CQA and caffeine contents of the infusions prepared in this manner are presented in Table 3. The caffeine content of brews from both coffees declined by ∼80% with both the H-S and L-L roasts. There was a bigger loss of CQAs in the infusions with 11.0% and 13.3% recoveries after H-S and 8.0% and 6.8% following L-L roasting conditions. This was associated with reduced CQA:caffeine ratios of the coffees.
Coffee | Roast | As a percentage of total CQA | Total CQAs | Caffeine | Total CQA:caffeine ratio | ||
---|---|---|---|---|---|---|---|
3-CQA | 4-CQA | 5-CQA | |||||
a H-S - high temperature, short roast; L-L - low temperature, long roast (see Table 2). | |||||||
Washed arabica | — | 11% | 16% | 71% | 11.3 (100%) | 1.90 (100%) | 5.9 |
H-S | 22% | 27% | 51% | 1.45 (13.3%) | 0.39 (20.6%) | 3.7 | |
L-L | 23% | 27% | 50% | 0.92 (8.0%) | 0.37 (19.6%) | 2.5 | |
Unwashed arabica | — | 8% | 10% | 81% | 14.6 (100%) | 1.94 (100%) | 7.5 |
H-S | 22% | 25% | 51% | 1.59 (11.0%) | 0.37 (19.2%) | 4.3 | |
L-L | 24% | 26% | 50% | 1.06 (6.8%) | 0.35 (18.6%) | 3.0 |
During roasting, the chlorogenic acids are subjected to a complex series of reactions including acyl migration which results in 3-CQA and 4-CQA being destroyed more slowly than 5-CQA10 while caffeine is lost through sublimation.7,11 The data in Table 3, including the total CQA:caffeine ratios, indicate that CQAs are lost more rapidly than caffeine, especially during L-L roast conditions. This is in keeping with the long held use of the CQA:caffeine ratio as a rule of thumb index of the extent of roasting.12 The CQA:caffeine ratios in Table 3 are much higher than those obtained with the commercial espresso coffees (Fig. 2), probably because the beans used to prepare the various espresso coffees were roasted for longer periods of time resulting in enhanced breakdown of CQA compared to losses of caffeine. Robusta coffee beans contain almost twice as much caffeine as arabica13 so if any of the espressos were produced from an arabica–robusta blend, as opposed to being 100% arabica, this would also contribute to a lower the CQA:caffeine ratio. Batch to batch variation in coffee beans is also likely to have an impact on this ratio.
This journal is © The Royal Society of Chemistry 2012 |