Influence of Drying Methods on Volatile Aroma Compounds and Sensory Properties of Olive Leaf Herbal Tea

Olive leaves, a by-product of the olive oil industry, represent an interesting underutilized raw material for the preparation of herbal teas. However, processing conditions, particularly drying methods, may strongly influence their chemical and sensory quality. This study aimed to evaluate the effect of air drying (AD) and microwave drying (MWD) on the phenolic content, antioxidant capacity, volatile aroma compounds, sensory profile, and consumers' acceptability of olive leaf herbal teas. Olive leaves were subjected to AD (50 °C, 3 h) and MWD (400 W, 4 min), and infusions were prepared. Total phenolic content (TPC) and antioxidant capacity (AC) were evaluated spectrophotometrically, volatile compounds were analyzed by HS-SPME-GC-MS, and sensory characteristics were assessed through descriptive sensory analysis and consumers' acceptability test. MWD significantly increased TPC compared to AD; however, this increase was not proportionally reflected in AC. The drying methods influenced the volatile profile of herbal teas, with AD showing a higher amount of alcohols, esters, and terpenes associated with green and floral notes, whereas MWD showed a major content of aldehydes and ketones linked to fruity notes. Sensory analysis confirmed these differences; moreover, MWD herbal teas were more bitter and astringent, and consumer tests showed a clear preference for herbal teas produced from AD leaves. Overall, the results highlight the key role of drying methods in shaping the chemical and sensory attributes of olive leaf herbal tea, suggesting air drying to be the most suitable process for producing a sensorially acceptable product.