Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/30/2006
Publication Date: 4/19/2007
Citation: Chanjirakul, K., Wang, S.Y., Wang, C.Y., Siriphanich, J. 2007. Natural volatile treatments increase free radical scavenging capacity of strawberries and blackberries. Journal of the Science of Food and Agriculture. 87:1463-1472. 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 antioxidants. It is known that antioxidants may help protect cells against the oxidative damage caused by free radicals. Thus, plants have developed detoxifying mechanisms or free radical scavenging systems to keep low concentrations of free radicals. However, we do not know too much about the changes of scavenging capacities of antioxidants in fresh fruits and vegetables after harvest and how to maintain or increase these capacities by using postharvest techniques. We treated strawberry and blackberry fruits with some natural volatile compounds immediately after harvest and found that certain natural volatiles such as methyl jasmonate and essential oil of tea tree are effective in promoting the scavenging capacities of these berries on a variety of active free radicals. In addition, these natural products also retarded decay of berry fruits during storage. Therefore, it is possible that the health benefits and the shelf-life of these berry fruits can be improved by postharvest exposure to certain natural volatile compounds. This information could be useful to the berry industry and beneficial to the consumers.
Technical Abstract: Free radical scavenging capacities of strawberries and blackberries treated with methyl jasmonate (MJ), allyl isothiocyanate (AITC), essential oil of Melaleuca alternifolia (tea tree oil or TTO), and ethanol (EtOH) were investigated. All of these natural volatiles tested reduced the severity of decay in both strawberries and blackberries during storage at 10°C as compared to the control. Most of these compounds enhanced antioxidant capacity and free radical scavenging capacity, except the AITC treatment. The MJ treatment for strawberries and blackberries had the highest antioxidant capacity, expressed as oxygen radical absorbance capacity (ORAC) values, after 7 days of storage (40.77 and 67.70 µmol TE/g fresh weight, respectively). Moreover, the MJ treatment promoted the antioxidant capacity in strawberries and blackberries as measured by the radical 2, 2-di (4-tert-octylphenyl) -1-picrylhydrazyl (DPPH) and the radical cation 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS•+) scavenging activity in both 7 and 14 days after storage. The ED50 of the free radical DPPH scavenging capacity ranged from 31.79 to 36.94 mg after 7 days of storage and from 32.57 to 42.72 mg after 14 days of storage in strawberries, but only from 4.29 to 6.65 mg and from 5.10 to 7.73 mg in blackberries after 7 and 14 days of storage, respectively. Methyl jasmonate showed the highest percent inhibition for DPPH radicals among all the treatments in both strawberries and blackberries. The MJ treatment also increased scavenging capacities on the superoxide radical, hydrogen peroxide, hydroxyl radical, and singlet oxygen in strawberries and blackberries, with the exception of the superoxide radical scavenging capacity in blackberries stored for 14 days. Treatment with TTO or EtOH enhanced most of these free radical scavenging capacities, except for hydrogen peroxide in strawberries, and for superoxide radical and singlet oxygen in blackberries. These results indicated that all of the natural volatile compounds tested in this study, except AITC, promoted the antioxidant capacity and scavenging capacity of most major free radicals and, thus, help increase the resistance of these berry fruits to decay. While AITC was also very effective in reducing decay, its effect on free radical scavenging capacity was inconsistent, suggesting that additional mechanisms may be involved in its inhibition of fungal growth.