Freeze drying and spray drying for the retention of the active components, L‐theanine and caffeine, and antioxidant activity of tea‐based ingredients

Abstract

SummaryPreserving food products from oxidation improves their quality and stability. This study compares the effects of storage on L‐theanine, caffeine, moisture content and antioxidant activity of spray‐dried and freeze‐dried white tea infusions. The antioxidant activities of both dried infusions were restored over a 60‐day storage. On Day 60, the L‐theanine and caffeine levels of the freeze‐dried samples were respectively 1.45 ± 0.03 mg mL−1 and 2.23 ± 0.04 mg mL−1 compared with 1.16 ± 0.03 mg mL−1 and 1.97 ± 0.01 mg mL−1 on Day 0. In the spray‐dried samples, the L‐theanine was 0.32 ± 0.01 mg mL−1 on Day 60 and 0.36 ± 0.02 mg mL−1 on Day 0, while caffeine remained unchanged. Regarding undried/control samples, L‐theanine and caffeine declined from respectively 0.29 ± 0.0004 mg mL−1 and 0.33 ± 0.01 mg mL−1 on Day 0 to 0.2 ± 0.001 mg mL−1 and 0.26 ± 0.02 mg mL−1 on Day 60, associated with a decrease in DPPH activity from 75.87% (Day 0) to 15.34% (Day 60). Freeze‐drying and spray‐drying tea infusions yielded functional products with stable antioxidant activity and moisture. Both drying techniques are reliable for preserving tea preparations.