Alterations in total phenolic content and antioxidant capacity in response to low temperatures in olive (Olea Europaea L. "Gemlik")

Abstract

We investigated total phenolic contents and antioxidant capacities in olive cv. Gemlik leaves subjected to artificial low temperature tests (4°C, -10°C and -20°C) in cold-acclimated (CA, in January) and non-acclimated (NA, in July) stages. Total phenolic content was estimated using the Folin-Ciocalteu colorimetric method and antioxidant capacity was determined using DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity. In addition, three different extraction methods using water, methanol (80%) or acetone (80%; containing 0.2% formic acid) were compared in such analyses. Cold-acclimation induced accumulation of total phenolics which was positively correlated with antioxidant capacity. While higher phenolic content occurring especially after low temperature treatment resulted in a greater antioxidant capacity in CA stages, phenolic content and antioxidant activity were increased to some extent in NA stage by 4°C treatment but declined below control level following -10°C and -20°C treatments. Although low temperature treatments caused significant alterations in total phenolic content, changes in antioxidant capacity were less pronounced. Furthermore, methanol or acetone extraction method was more capable in determining total phenolic content than water extraction. Our results indicate that olive plant gains cold hardiness by secondary metabolite production and in parallel, by enhancement of antioxidant capacity, during cold-acclimation.