I wished I knew, before I brew- Coffee antioxidants
Similar to tea, Coffee is rich in phenolic compounds that have antioxidant activities. For more background on antioxidants, refer to the previous article on tea. Antioxidants are typically measured by antioxidant capacities using two methods: FRAP that measures the capacity of a sample to participate in one-electron redox reactions and ABTS that measures the extent of relative radical scavenging activity. Foods contain a number of antioxidants that has varying reactivity in the two methods. Thus, to verify the results, their values should be in agreement(1). Most studies used in this article were done in the laboratory using chemical reagents to measure the antioxidants in coffee samples without the actual involvement of the human body. Thus, it doesnt cover the bioavailability of coffee antioxidants in humans.
Preparation methods: Italian, espresso, filtered and freeze dried
How coffee is consumed is a matter of individual preference, availability, and socio-cultural habits. The study by Sanchez(2) used commercial columbian coffees in various roast and examined the effects of preparation methods: Italian, espresso, filtered and freeze fried to antioxidant capacity of coffee.
Lets have a look at each method:
Italian coffee: You have probably seen one of these. A metal coffee pot with an upper, middle, and bottom part. Coffee is in the middle part and water is in the lower part. As the water heats up, it flows to the middle part where the coffee is and the beverage is gathered at the top part. The extraction time takes only around 1 minute.
Filter or coffee maker method: In most coffee makers, there is a water tank filled with water, and coffee is
placed on a filter. When the machine is turned on, water is heated and flows up to the the filter and drips onto the cup or kettle below.
Espresso: Typical espresso machines have 3 parts: a boiler that generates hot water and steam for extraction of the coffee, an extraction port where the filter-holder is inserted, and the filter-holder, which is filled with ground
coffee. To extract coffee, the pressure of hot water should be hot enough to penetrate the coffee in the filter holder. It takes an average of 25 seconds to extract using this method.
Freeze-dried coffee- This is also known as instant coffee.
After roasting and grinding, coffee is dissolved in water and freeze-dried.
Roasting
The primary importance of roasting coffee beans is its influence on flavor and aroma. Interestlingly, this same paper found that roasting can affect antioxidant levels .
In general, their result show that dark-roast samples exhibited better antioxidant action than the medium roast samples.
Mechanism: When coffee beans are roasted, heat causes the inherent proteins and sugar to react with each other (this is called maillard reaction). One of the products of this reaction is an antioxidant called Melanoidins, which explains why dark-roasted coffee yields more antioxidants than its lighter counterpart.
The same table shows that in terms of the antioxidant capacities per SERVING, there is an agreement on results from 2 measurements (FRAP and ABTS). Highest antioxidant capacity was observed in filtered method (F1-5), followed by Espresso (Ex1-5), while Italian (IT) and Freeze Dried Methods (FD) are at the bottom.
Why did it appear that the filtered method resulted to higher antioxidants?
Ludwig (5) Explained that the longer time and turbulences in the extraction chamber of the filter coffeemaker allow the water to have immediate contact with the coffee to extract additional compounds. In other words, the longer extraction time in filtered method yielded more antioxidants due to longer contact of water to the coffee, compared to the espresso or italian method that used pressure that shortened the extraction time.
Addition of Milk
In this next study (2), the effect of adding milk in coffee was tested.
A variety of coffee bean samples were used and labeled accordingly:
They used a standard formulation of 7 g of coffee sample to prepare 50 ml of all coffee brews (using distilled water heated to 95–97 C), including instant and espresso. Macchiato (M) was prepared by adding 30 ml milk (with 2.6% milk fat), and 50 ml milk was added to prepare lattes (L).
As depicted in the figure, there is a substantial difference in antioxidants of Plain espresso (labeled E4) and espresso with 80 ml milk (macchiato) or
100 ml milk (Latte). It seems that adding milk reduces antioxidants by 50%. The same effect was observed in Italian and turkish brews but at lower extent. For filtered coffee, they didn't observe significant difference in antioxidant after adding milk. The same effect was observed in Sanchez's(1) study where adding 17 ml of milk significantly reduced antioxidant activity by 62% , and 100 ml of milk significantly reduced it by 95%. They noted that the reduction of antioxidants is proportional to the amount of added milk.
The mechanism behind this is that Chlorigenic acid, which is the main antioxidant compound in coffee interacts with milk proteins. This binding affinity increases with increasing molecular size of coffee. Also, similar to tea, polyphenols in coffee such as catechins can form insoluble complexes by interacting with the protein casein in milk(2).
Nestle Study
I thought discussion on cofffee would'nt be complete without a touch of food politics. A study funded by Nestle examined the effect of adding milk, sugar, and creamier to:
bioavailability (the levels absorbed in the body)
peak levels, and;
time to reach peak levels of antioxidants from coffee.
Their methods involve:
Nine participants
-fasted overnight
-provided with the treatment (drink) of either: plain coffee with water, coffee with milk, coffee with sugar and non dairy creamier
1 week washout period in between treatment
blood is drawn 24 hours later at intervals of 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 11, 12, and 24 hours (final blood)
lunch and dinner are provided
What they found out are rather predictable findings.
Results of the Nestle Study
As depicted in the table, only the values marked with an asterisk are considered to be significantly different from plain coffee, indicating that the premixed coffee comprised of sugar and creamer affected peak blood levels of antioxidants, and the time to reach that peak. The catch is that despite those observed differences, the measured antioxidant levels from the blood (AUC) wasnt different from plain coffee. In other words, when milk, or sugar with creamier is added to coffee, the level of antioxidants absorbed in the body is unaffected. They concluded that adding milk, sugar or creamer as in 3 in 1 coffees will not affect the antioxidant levels in your body (bioavailability), but I dont totally agree coz there seems to be poor validity of this study in terms of:
sample size (only 9 participants)
clear bias- considering their products include non dairy creamier (coffeemate), milk, and premixed instant coffee
diet not completely controlled, and there is no measure of compliance for the instructed fasting.
Moreover, non-dairy creamers contain casein that binds with polyphenols and reduces the availability of these antioxidants.
Since company-funded research are directed toward marketing purpose, it is clear that these findings aim to promote the message that nestle milk and creamer will not affect antioxidant benefits obtained from drinking coffee.
Caffeinated or Decaffeinated?
The last part compared which among coffee brews, decaf coffee, and instant coffee has the highest antioxidant capacity. As depicted in this figure from Belscak's paper, Caffeinated coffee contains slightly higher antioxidants as compared to decaffeinated coffee.
Recently, Caffeine has aroused scientific interests because of its potentiality as an antioxidant compound. Tellone (6) and colleagues discussed on their paper the antioxidant properties of caffeine. It was observed to have strong scavenger activity against the dangerous free radicals and has an antioxidant activity toward the strong generators of those free radicals. This protective effect leads to reduction of disease incidences. Epidemiological studies show that coffee drinkers have lower risk of neurodegenerative diseases, type 2 diabetes, liver disease, and certain cancers.
A very interesting finding for decaf drinkers is that decaffeinated instant coffee (DI1) has the highest antioxidant, while espresso decaf (DE2) exhibited lowest levels. This is probably explained by the longer contact of coffee with water in instant coffee preparation, as compared to espresso which only took seconds to extract.
On the other hand, four instant cappuccino flavors were examined and labeled: Classic (IC1w), Chocolate (IC2w), Vanilla (IC3w), and Irish Cream (IC4w). Chocolate-flavored coffee mix (IC2w) has slightly higher antioxidants than classic and vanilla blend. Though the exact flavoring ingredient wasn’t mentioned in this paper, It is safe to say that chocolate enhanced the antioxidant capacity in chocolate flavored cappuccino (IC2w), while milk or creamer (containing casein) in Irish cream (IC4w) variety had probably binded with flavonoids and consequently reduced its antioxidant levels.
Take home message: The findings from these studies elucidate how antioxidant in coffee is dependent on preparation methods. However, this doesn’t give us the complete picture, since preparation is only a starting point. The actual utilization of antioxidants will take place after digestion and absorption sets in. A number of unbiased research is needed to determine the bioavailability of these compounds in the human body, but in the meantime, considering these points would be helpful to preserve antioxidants in preparation for anticipated loss in the body.
References:
1) Liang, N., & Kitts, D. D. (2014). Antioxidant property of coffee components: assessment of methods that define mechanisms of action. Molecules (Basel, Switzerland), 19(11), 19180–208. doi:10.3390/molecules191119180
2) Sánchez-González, I., Jiménez-Escrig, a., & Saura-Calixto, F. (2005). In vitro antioxidant activity of coffees brewed using different procedures (Italian, espresso and filter). Food Chemistry, 90(1-2), 133–139. doi:10.1016/j.foodchem.2004.03.037
3) Belscak, A., Horz, D., Budec, M., & Niseteo, T. (2012). Bioactive composition and antioxidant potential of different commonly consumed coffee brews affected by their preparation technique and milk addition, 134, 1870–1877.
4) Renouf, M., Marmet, C., Guy, P., Fraering, A., Longet, K., Moulin, J., … Williamson, G. (2010). Nondairy Creamer , but Not Milk , Delays the Appearance of Coffee Phenolic Acid Equivalents in Human Plasma 1 , 2, (14), 259–263. doi:10.3945/jn.109.113027.in
5) Ludwig, I. a., Sanchez, L., Caemmerer, B., Kroh, L. W., De Peña, M. P., & Cid, C. (2012). Extraction of coffee antioxidants: Impact of brewing time and method. Food Research International, 48(1), 57–64. doi:10.1016/j.foodres.2012.02.023
6)Tellone, E., Galtieri, A., Giardina, B., Russo, A., Bellocco, E., Barreca, D., & Ficarra, S. (2015). Antioxidant Activity of Caffeine : A Focus on Human Red Blood Cells and Correlations with, 835–842.
