| dc.description.abstract | The application of postharvest treatments to fruits and vegetables that improves their health-promoting properties, prior to their processing into value-added foods, is an emerging topic of research. Antioxidant phenolic compounds are bioactive secondary metabolites that can be increased by the application of postharvest treatments in horticultural crops. Chlorogenic acid is the main phenolic compound in carrots, and it possesses potent activity against the metabolic syndrome. Wounding stress has been reported as an effective postharvest treatment to increase chlorogenic acid content in carrots. Likewise, chitosan is another elicitor that induces the secondary metabolism of plants. However, the combined effect of wounding stress and chitosan treatment on the accumulation of phenolic compounds has not been previously reported. In the present study, the effect of postharvest wounding stress applied alone and combined with chitosan, over total and individual phenolic compounds in carrot was investigated. Carrots were wounded to obtain pie-cuts and shreds, and the tissue was further sprayed with a chitosan suspension (0.5% w/v). Whole carrots were used as control. After storage, wounding stress induced a significant increase in total phenolics by 278.9% and 1516.9% for carrot pie-cuts and shreds, respectively, as compared with the control before storage (further referred as CBS), whereas the whole tissue did not show an increase. When chitosan was applied in the tissue the wound-induced accumulation of phenolics was further enhanced, showing increases of 917.4% and 2332.7% for pie-cuts and shreds, respectively, as compared with CBS. Interestingly, after storage whole carrots treated with chitosan showed a significant increase (119.5%) in the total phenolic content as compared with CBS.
The major phenolic compounds identified in non-stressed carrot tissue (CBS) was chlorogenic acid (220.6 mg/kg), followed by p-coumaric acid derivative (112.9 mg/kg), p-coumaric acid (99.5 mg/kg), gallic acid (71.8 mg/kg) and protocateuic acid (39.3 mg/kg). After storage, the application of chitosan induced the accumulation of isocoumarin in whole carrots (27.9 mg/kg), which was not detected in CBS. An additional phenolic compound that showed accumulation due to chitosan application in whole carrots were chlorogenic acid, and protocatechuic acid, showing increases of 284.6% and 9.95%, respectively, as compared with CBS. As observed for total phenolics, the accumulation of certain individual phenolics increased with the wounding intensity applied. For carrot pies non-treated with chitosan, phenolics that showed increases in concentration after storage were the chlorogenic acid (670.0%), p-coumaric acid derivative (29.43%). Furthermore, biosynthesis of isocoumarin was also detected in carrot pies (45.9 mg/kg) due to wounding stress. Likewise, other compounds such as p-coumaric acid and protocatechuic acid did not show significant increase after storage of carrot pies, whereas the concentration of gallic acid decreased by 50.1%. On the other hand, shredded carrots non-treated with chitosan, showed higher accumulation of most individual phenolics as compared with carrot pies. In this context, shreds showed increases of chlorogenic acid (3,470.0%), p-coumaric acid derivative (200.8%), and p-coumaric acid (17.2%) as compared with CBS. Likewise, shredded carrots showed a high accumulation of isocoumarin after storage (377.5 mg/kg), which was 723.1% higher than isocumarin content in stored carrot pies.
When the two stresses were combined (wounding + chitosan) a synergistic effect on the accumulation of certain phenolic compounds were obtained. For instance, after storage chlorogenic acid increased by 1991.3% and 5069.1% in chitosan treated carrot pies and shreds, respectively; whereas p-coumaric acid derivative increased by 173.7% and 385.6% in chitosan treated carrot pies and shreds, respectively. Similarly, isocoumarin, which was not detected in CBS, showed a high accumulation after storage of chitosan treated carrot pies (413 mg/kg) and shreds (1074.8 mg/kg). Results presented herein demonstrated that the combination of wounding stress and chitosan can be used as an effective strategy to increase the content of antioxidant phenolic compounds in carrots. The stressed carrot tissue treated can be used as raw material to obtain value-added food products or for the extraction and purification of antioxidant phenolic compounds with application in the food and dietary supplement industries. | |
