Heat stress reduces the accumulation of rosmarinic acid and the total antioxidant capacity in spearmint (<i>Mentha spicata</i> L)

Abstract

Abstract Selected high‐phenolic lines of spearmint were subjected to a constant 30 °C heat regimen for a period of 4 weeks to determine the effects of heat stress on soluble phenolics, phenols and rosmarinic acid biosynthesis and antioxidant capacity. Heat stress significantly reduced levels of total phenolic acids (71–87%) and soluble phenols (75–87%). This loss was concomitant with a loss of total antioxidant capacity of 21–60% after week 1 and up to 95% by week 4. High‐performance liquid chromatography profiling of heat‐stressed plants at 270 and 320 nm detected nearly a complete loss of rosmarinic acid in all seven chemotypes. High‐temperature drying of non‐heat‐stressed plants at 80 °C resulted in a similar loss of total antioxidant capacity and rosmarinic acid content an effect not observed in material that was subjected to low‐temperature drying first, followed by exposure to high temperature. This suggests that heat stress negatively regulates rosmarinic acid biosynthesis and causes a potential rapid biological breakdown of rosmarinic acid in tissues. 2,2‐Diphenyl‐1‐picrylhydrazyl radical assays of heat‐stressed and non‐stressed plants clearly show that rosmarinic acid is the major contributor to the antioxidant capacity in spearmint. Copyright © 2005 Society of Chemical Industry