Effects of different drying processes on the quality changes in Arapgir purple basil (Ocimum basilicum L.) leaves and drying-induced changes in bioactive and volatile compounds and essential oils

The aim of this research is to examine the effects of drying purple basil leaves (Ocimum basilicum L.) under different drying conditions (freeze drying, sun-drying, and convective drying [CD] at 45, 50, and 55 degrees C and microwave drying at 350, 460, and 600 W) on color properties, total phenolic and anthocyanin content, antioxidant activities, and changes in the composition of volatile compounds and essential oils (EOs). Increasing the drying temperature and microwave power led to an improvement in the preservation of the total phenolic content of the samples by an average of 16.28% and 27.98%, respectively. Increasing the drying temperature resulted in lower anthocyanin content and antioxidant activity (AA); in contrast, increasing the microwave power resulted in higher anthocyanin content and AA when drying purple basil. The drying methods significantly changed the composition of volatiles and EOs, and microwave drying resulted in a different profile of volatiles and EO composition. The key volatile compounds in purple basil leaves were linalol (81.19-1176.09 mu g/g dw), 1,8-cineole (45.15-816.16 mu g/g dw), and methyl cinnamate (13.20-637.65 mu g/g dw). On the other hand, methyl cinnamate (11.68%-57.66%) and linalool (0.02%-20.39%) were the main volatile compounds of EOs in basil leaves. In conclusion, the following drying methods are suitable for the protection of phenolic and anthocyanin compounds and high performance of AA: freeze drying, sun-drying, and CD at 45 degrees C and microwave drying at 600 W.