Effect of Boiling on the Phenolic Content and Antioxidant Activity of Tomato (Lycopersicon esculentum L.) fruits

This study was conducted in order to evaluate the effect of cooking (boiling) on the phenolic content and antioxidant activity of ripe tomato fruits. Fresh tomato fruits were divided into four groups amongst which three of them were respectively boiled at 98C for 10, 20 and 30 min. The last group was not processed and served as control. After processing, the fruits were dried, grounded and the natural antioxidants extracted with methanol. The dried extracts obtained were characterized by determining their total phenolic content and antioxidant activity [2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH-RSA), Ferric reducing Antioxidant power (FRAP) and Metal Chelation ability (MCA)]. Results showed that the total phenolic content of fresh tomato fruits significantly increase after boiling for 10 min (11.59-18.82 mg GAE/g) and that when boiled for more than 10 min, its concentration significantly decrease (18.82-9.36 mg GAE/g). The determination of the antioxidant activity of the extracts showed that processing time significantly reduce the DPPH-RSA, the FRAP and the MCA of ripe tomato fruits. No significant difference was registered between the radical scavenging activity of fresh tomato fruits and the sample boiled for 10 min at all concentrations. However, with the other tests, the activity of the sample boiled for 10 min was significantly lower (p<0.05) compared to that of the fresh sample. Practical Applications Ripe tomato fruits should be boiled for a maximum of 10 min this in order to better preserve the natural antioxidants present, as they can significantly contribute to the reduction of the damages caused by oxidative stress in the body.