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

Preserving 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. This study showed that after 60 days, L-theanine, caffeine and DPPH activity of undried/liquid white tea infusions decreased. However, L-theanine, caffeine and DPPH activities of freeze-dried and spray-dried samples were more stable. Both drying techniques are reliable for preserving tea preparations, yielding functional products with stable antioxidant activity and moisture. image