Biochemical characterization of the flavedo of heat-treated Valencia orange during postharvest cold storage

Abstract

Heat treatment is a powerful and eco-friendly method to prevent Penicillium infection in citrus fruit dur-ing the postharvest. Several studies have been dedicated to investigate the general chemical changes thatjustify the immediate reaction responsible for the induced tolerance; but just how primary metabolismand enzymology are affected by heat treatment and along a prolonged cold storage is still unclear. Inthis work, the main enzymes of carbon metabolism of Valencia orange flavedo were analyzed during thepostharvest period after a heat treatment (HT) of 48 h at 37◦C. Enzymatic activity measurements indi-cated that the NADPH producing enzymes glucose 6-phosphate dehydrogenase and non-phosphorylatingglyceraldehyde 3-phosphate dehydrogenase have lower levels in HT fruit. In parallel, a higher synthe-sis of sucrose from organic acids was observed in HT epicarp. Sucrose-phosphate synthase would havean important role in sucrose accumulation. The pathway of carbon through glycolysis was affected bycold storage, independently of HT, in a way that it favors the ATP-dependent phosphofructokinase overthe PPi-dependent homologous enzyme and the use of phosphoenolpyruvate (PEP) by PEP carboxy-lase instead of pyruvate kinase. Similarly, phenylpropanoid compounds did not show major changes inresponse to HT, although some of them showed a marked descent along the cold storage. Proteomic stud-ies revealed alterations in the abundance of ascorbate peroxidase, two germin-like proteins and smallHSPs, completing the description of the main metabolic changes in this tissue.