Reactive oxygen species scavenging capacities of oil palm trunk sap evaluated using the electron spin resonance spin trapping method

Abstract

Oil palm waste is a potential source of renewable energy and also of bioactive compounds. In the present study, we analysed oil palm trunk sap (OPTS) squeezed from different parts of the trunk stored for different times and measured the reactive oxygen species (ROS) scavenging capacity using the electron spin resonance (ESR) spin trapping method using 5-(2,2-dimethyl-1,3-propoxycyclophosphoryl)−5-methyl-1-pyrroline-N-oxide (CYPMPO) as the spin trapping reagent. The highest alkoxyl radical (RO•), hydroxyl radical (•OH) and singlet oxygen (1O2) scavenging capacities were found in OPTS squeezed from the middle and top parts of the oil palm trunk. OPTS from the bottom part exhibited a lower ROS scavenging capacity than the other parts. The highest scavenging capacity for RO• was found in OPTS from the middle part of the trunk (10.38 mM Trolox eq./mL), similar to that of green tea (12.42 mM Trolox eq./mL). The scavenging capacities for •OH of OPTS from the middle, top, and bottom parts of the trunk were 4779, 3729 and 1920 mM mannitol eq./mL, respectively, compared with 6594 mM mannitol eq./mL for blackberry. The highest 1O2 scavenging capacity of 228 mM GSH eq./mL was exhibited by OPTS from the top part of the trunk, which was higher than that of the green tea, blackberry, black tea, aloe and cucumber used as standards. The ROS scavenging capacity of OPTS measured by ESR was correlated with the corresponding values from the oxygen radical absorbance capacity (ORAC) assay. The antioxidant activity of OPTS decreased with storage time after the OPT was felled. The strong ROS scavenging capacity of OPTS makes it a potential source of bioactive compounds for use in pharmacological, cosmetic, chemical and functional food applications.