What is Acrylamide?
Acrylamide is a chemical compound that occurs naturally in many plant-based foods when cooked at high temperatures. It's not added to food but is a result of the Maillard reaction, which gives food its brown color and flavor. This reaction happens between amino acids, like asparagine, and reducing sugars at temperatures above 120°C. Common dietary sources of acrylamide include potatoes, grains, and coffee. The discovery of acrylamide in food in 2002 led to significant research.
Acrylamide and Tea Processing
The presence of acrylamide in tea depends on the processing methods used. Certain methods involve heat that can cause acrylamide formation.
How Acrylamide Forms in Tea
During the processing of some teas, especially roasted or baked varieties, high heat triggers the Maillard reaction, leading to acrylamide formation. The concentration depends on the temperature and duration of heating. For example, Houjicha, a roasted green tea, is processed at 170–200°C, resulting in relatively high acrylamide levels. Teas that are not heat-treated, like some green, white, and yellow teas, have very low or undetectable acrylamide. Asparagine and reducing sugars in the tea leaves are precursors to acrylamide.
Factors Influencing Acrylamide Levels
Several factors affect acrylamide concentration in tea:
- Processing Method: Heat treatment is the most important factor. Roasting and baking increase acrylamide levels, while steaming or low-temperature drying does not.
- Roasting Temperature and Time: Higher temperatures and longer roasting times increase acrylamide, as seen with Houjicha.
- Tea Variety and Precursors: The amounts of asparagine and sugars vary by tea variety, influencing acrylamide formation.
- Tea Infusion vs. Product: The amount of acrylamide that transfers from the tea product to the brewed tea is much lower.
- Brewing Time: Longer steeping times can increase acrylamide transfer. Shorter brewing times are recommended to minimize transfer.
Acrylamide Content in Various Tea Types
Different teas have varying levels of acrylamide based on their processing:
- Roasted Green Tea (Houjicha): This tea has the highest acrylamide content due to roasting.
- Black Tea: Generally has low levels of acrylamide (<100 µg/kg), though levels can vary depending on drying.
- Oolong Tea: Levels are usually low, though some may have slightly higher concentrations depending on roasting.
- Green, White, and Yellow Tea: These teas, which are not roasted, usually have very low or undetectable levels of acrylamide.
- Pu-erh Tea: The formation pathway is complex due to fermentation. Raw Pu-erh has low acrylamide, while ripened (wet-piled) Pu-erh shows varying levels during fermentation, ultimately decreasing over time.
Tea vs. Coffee: A Comparison
| Feature | Tea (Unroasted) | Tea (Roasted) | Coffee (Roasted) |
|---|---|---|---|
| Processing Temperature | Low-temperature drying | High-temperature roasting (>120°C) | High-temperature roasting (>200°C) |
| Acrylamide Levels in Product | Very low to non-detectable | Ranges from ~250-1880 µg/kg | Ranges from ~152-682 µg/kg |
| Acrylamide Levels in Infusion | Non-detectable to very low | Very low (e.g., <5 µg/L) | Present, but generally higher than tea infusions |
| Precursors | Natural asparagine and sugars | Natural asparagine and sugars | Natural asparagine and sugars |
| Formation Mechanism | Limited/prevented by low heat | Maillard reaction activated by high heat | Maillard reaction activated by high heat |
How to Reduce Acrylamide Exposure from Tea
Consumers can take several steps to reduce acrylamide exposure from tea:
- Choose Wisely: Select unroasted teas like green, white, or standard black tea over roasted types like Houjicha.
- Limit Steeping Time: Shorter steeping times result in less acrylamide in the cup.
- Avoid Over-boiling: Prolonged contact with high heat can increase the amount of acrylamide extracted from tea leaves.
- Maintain a Varied Diet: Following dietary guidelines and eating a variety of foods helps minimize risk from any single food source.
Health Risks: What the Science Says
Acrylamide is a human health concern based on animal studies, showing it causes cancer at high doses. However, the relevance to human dietary exposure is unclear. Large-scale human studies on acrylamide and cancer risk have produced inconsistent results. While acrylamide levels are measurable in some teas, they are generally low compared to other sources. Public health agencies recommend minimizing exposure where possible, but it is not recommended to stop consuming commonly enjoyed heat-processed foods. Drinking tea can be part of a healthy diet, and concerns about acrylamide should be kept in perspective.
Conclusion
While some teas contain acrylamide, levels depend on processing, especially roasting. Unroasted teas have little to no detectable acrylamide, while roasted varieties have higher levels. The amount in the brewed cup is lower than in the dry product. Choosing less processed teas and limiting steeping time can reduce exposure. For a comprehensive overview, see the European Food Information Council's resource on the subject.
