Effects of γ-radiation on microbial load and antioxidant proprieties in black tea irradiated with different water activities

• Higher the Aw, lower is the radiation dose to archive microbiology safety.
• The doses up to 10.0 kGy had no effect on antioxidant capacity in all Aw used.
• The recommended dose to irradiated black tea is 5.0 kGy.

The aim of this paper is to study the effect of gamma radiation on black tea irradiated with different water activities. The black tea samples had their Aw adjusted to three values (0.92, 0.65, and 0.18) and were irradiated in 60Co source at doses of 0, 1.0, 1.5, 2.0, 2.5, 5.0, 7.5, and 10.0 kGy. The methods used were: microbiology, total phenolic compounds quantification, antioxidant activity by ORAC, and quantification of the main antioxidants. It was observed that the greater the amount of free water present in the samples, lower was the dose to achieve microbiological control. Regardless the water activity used, there was no difference in content of the phenolic compounds and at the mainly theaflavins, as well in the antioxidant activity at doses up to 5.0 kGy.