Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2005
Publication Date: 5/12/2006
Citation: Chanjirakul, K., Wang, C.Y., Wang, S.Y., Siriphanich, J. 2006. Effect of natural volatile compounds on antioxidant capacity and antioxidant enzymes in raspberries. Postharvest Biology and Technology. 40:106-115. Interpretive Summary: Increasing evidence has shown that diets rich in fruits and vegetables may reduce the risk of some types of cancer and other chronic diseases. The main reason for the health benefits of fruits and vegetables is because they contain abundant chemicals known as antioxidants which may be involved in protecting against diseases. However, little information is available on the changes of antioxidant activities in fresh produce after harvest and how to maintain or increase these activities by using postharvest techniques. We treated raspberry fruit with some natural volatile compounds immediately after harvest and found that certain natural volatiles such as methyl jasmonate and essential oil of the tea tree are effective in promoting the antioxidant capacity and antioxidant enzyme activities in raspberries. In addition, these natural products also retarded decay of berry fruit during storage. Therefore, it is possible that the health benefits and the shelf-life of these berry fruit can be improved by postharvest exposure to certain natural volatile compounds. This information could be useful to the berry industry and beneficial to consumers by helping to devise postharvest treatments that maintain produce quality and extend self-life.
Technical Abstract: Changes in antioxidant capacity and antioxidant enzyme activities in raspberry (Rubus idaeus L.) treated with methyl jasmonate (MJ), allyl isothiocyanate (AITC), essential oil of Melaleuca alternifolia (tea tree oil or TTO), and ethanol (EtOH) were studied. All of the natural volatile compounds tested reduced the severity of decay during storage at 10 °C compared to the control. Most of these natural volatile treatments promoted the antioxidant capacity and antioxidant enzyme activities except AITC treatment. The MJ treatment had the highest antioxidant capacity expressed as oxygen radical absorbance capacity (ORAC) values after storage for 7 days (83.13 µmol TE/g fresh weight) or 14 days (81.71 µmol TE/g fresh weight). Raspberry extract from the MJ treatment also showed the highest activity in all antioxidant enzymes, including superoxide dismutase (SOD), guaiacol peroxidase (G-POD), ascorbate peroxidase (AsA-POD), glutathione peroxidese (GSH-POD), glutathione reductase (GR), monodehydroascorbate reductase (MDAR), and dehydroascorbate reductase (DHAR). Moreover, the MJ treatment showed the highest amount of ascorbate (AsA), dehydroascorbate (DHAsA), reduced glutathione (GSH), and oxidized glutathione (GSSG) compared to the other treatments. Even though AITC showed the best result for decay inhibition among all the treatments, it did not increase the antioxidant capacity or the antioxidant enzyme activities. These results indicate that MJ may increase the resistance of tissues to decay through enhancing their antioxidant system and their free radical scavenging capability, while AITC may retard the decay directly by its antimicrobial properties.