The changes in total phenolics, hydroxycinammic acid derivatives, and antioxidant properties of spearmint after five
drying treatments (convection oven drying, freeze-drying, microwave drying, and air drying with the sun exposure
and without the sun exposure) were investigated. Phenolic composition of dried spearmint was analysed by spectrophotometric
assays, while DPPH radical scavenging activity and Ferric reducing/Antioxidant power (FRAP) assay was
used to measure the antioxidant properties. The results showed that freeze drying produced dried spearmint that
had the highest total phenolics (34.6 ± 1.9 mg/g) content and the most potent antioxidant capacity (126.2 ± 0.4 mg/g
for FRAP and 88.1 ± 5.9 mg/g for DPPH, respectively). On the other hand, spearmint that was dried by convection
oven and microwave drying presented the lowest amount of phenolic compounds (12.0 ± 0.5 mg/g) and antioxidant
potency (49.3 ± 0.7 mg/g for FRAP and 26.9 ± 1.6 mg/g for DPPH, respectively). This might be attributed to the fact
that heat-sensitive phenolics were degraded or biotransformed at high temperatures. The loss of phenolic compounds
and antioxidant activity reached up to 60% compared to freeze drying.