Increased phenolic content and antioxidant capacity of the heated leaves of yacon (Smallanthus sonchifolius).

We investigated the content of phenolic compounds and antioxidant capacity of two batches of non-heated and heated leaves of the yacon cultivar "Andes no yuki", grown in Japan. Lyophilized yacon leaves heated at 160°C for 20 min and 100°C for 60 min had a 1.96 to 9.69-times higher total phenolic content than that of the non-heated leaves. Heated leaves exhibited a 1.98 to 4.07-times higher antioxidant capacity than that of the non-heated leaves in three different free radical scavenging assays. Heated leaves were more efficient at attenuating the superoxide anion radical production in human granulocytic cells than the non-heated leaves. High-performance liquid chromatography analysis revealed that, in the heated leaves, the caffeic acid content was 2.13 to 3.64-times higher and the chlorogenic acid content was slightly lower than those in the non-heated leaves. Hence, heat processing may affect the active constituent contents in yacon leaves, potentiating its antioxidant capacity. Abbreviations: ABTS⁺: 2,2'-azinobis(2-ethylbenzothiazoline-6-sulfonic acid) cation; DPPH: 1,1-diphenyl-2-picrylhydrazyl, HPLC: high-performance liquid chromatography; NBT: nitroblue tetrazolium; O₂^-: superoxide anion; PMA: phorbol 12-myristate 13-acetate; PMS: phenazine methosulfate; TEAC: Trolox equivalent antioxidant capacity.