Impact of postharvest processes on major phenolic constituents and antioxidant potentials of different Ocimum species

Tulsi (Ocimum sanctum Linn.) is one of the preferred herbs used as tea blended beverage in India. Ocimum is a rich source of antioxidants. The present study demonstrates the effect of post-harvest processes and blanching treatment on antioxidant potential of O. sanctum and seven other Ocimum species/cultivars. An optimized high performance liquid chromatographic method was applied to study the distribution of caffeic acid (CA) and rosmarinic acid (RA), and rutin (RU) in shed dried and blanched Ocimum leaves. Blanching treatments included thermal (Deep freeze- liq. N2, dry-hot air, and wet heat-boil H2O) and chemical methods (NaCl, NaHCO3, and CaOCl2). In general, blanching treatments have severely degraded the phenolic content of all Ocimum species. Only 77% increase in CA content of O. kilimandscharicum (OK) when treated with CaOCl2 was observed. Similarly, 14%, 18%, and 19% increase in RA content in the OK leaves were also observed when treated with boiling water, hot air, and CaOCl2, respectively. Shed drying process was found to be most appropriate to hold the antioxidant potential but compromised appearance. Blanching through a quick dip in wet-heat followed by indirect dry-heat drying reduced the loss of green colour. The present findings are useful to adopt the appropriate postharvest handling and pre-treatment of Ocimum for optimum retention of green colour appearance and their antioxidant potential.