Iced tea

Green tea is drunk by many for the health benefits of the antioxidant catechins, which are thought to help fight heart disease and other conditions. The stability of these compounds is important for choosing the best storage conditions and determining an accurate shelf life. However, a study has revealed that they may not be as stable as was once thought.

In the study, published in the Journal of Agricultural and Food Chemistry,¹ spray-dried green tea extract powders were stored under various relative humidities and temperatures for up to 16 weeks. High performance liquid chromatography was then used to determine catechin contents. Those at the highest temperatures and humidities lost the most catechins, confirming that catechin degradation kinetics were affected by temperature, and to a lesser degree, humidity.

According to the study, it had been believed that the powders were stable below the glass transition temperature; the temperature at which an amorphous solid changes from a rigid, glassy state to a rubbery, viscous state where increased molecular mobility leads to significant chemical degradation. However the study found that green tea powder degrades at lower temperatures, even below the glass transition temperature.

The study concluded that it provided a powerful prediction approach for the shelf life of green tea powder and highlighted the importance of glass transition in solid state kinetics studies.

1. N. Li, L.S. Taylor and L. J. Mauer, J. Agric. Food Chem., 59(11), 6082–6090 (2011).

This story originally appeared in The Column. Click here to view that issue.