Effects of ozone gas on the reduction of mancozeb residues and postharvest quality of ‘Jinda’ Chilies (Capsicum annuum L.) During Storage

Abstract

Mancozeb, a well-known carbamate fungicide, is widely used to combat fungal infections in various fruit and vegetable crops, particularly chili. Unfortunately, the presence of residual amounts of this fungicide in Thai chili poses a significant health risk, thereby necessitating a reduction of these toxic residues as a matter of urgency. Degreening of pericarp color plays a crucial role in mediating the deterioration and devaluing of 'Jinda' chili fruit after harvest. Reactive oxygen species (ROS) accumulation due to an imbalance between ROS generating and scavenging plays an important role in instigating chlorophyll degradation and programmed cell death (PCD) in activated deterioration in plant. However, the specific role of ROS in the degradation of chlorophyll and PCD during the senescence of chili fruit, as well as the extent to which ozone can detoxify mancozeb, remain unclear at present. This study aims to investigate the beneficial effects of ozone treatment in removing mancozeb contamination and the significant roles of ozone in preserving ‘Jinda’ chili fruit quality during storage. In the first study, the effect of ozone on removal mancozeb fungicide residual and fruit quality of ‘Jinda’ chili during storage was examined. Chilies were immersed in a mancozeb solution at a concentration of 10 mg L-1 for 2 min to simulate agricultural contamination before fumigation with ozone in concentrations of 15, 25 and 50 ppm for 30 or 60 min and stored at 251 °C with 75 % relative humidity for 12 d. Using ozone fumigation treatment at concentration of 0, 15, 25 and 50 ppm for 30 or 60 min then stored at 25 °C along with 12 days, the reduction of mancozeb fungicide residues and fruit quality of ‘Jinda’ chili was determined. From this study, all ozonation treatments also delayed postharvest loss, reduced disease index and maintained the quality of chili by higher the fruit firmness and lower color development by which the important parameter of chili marketing, indicated by delay the decreasing in hue angle values. The improving fruit color coincided with higher chlorophyll a and b contents than that of control. The maintaining fruit quality after ozone exposure resulted from the decrease in ethylene production and respiration rate. In addition, ozone fumigation between 25 to 50 ppm for 30 or 60 min showed the effective treatment to remove the mancozeb residues by 47 to 62 % according to GT-test Kit method and colorimetric analysis by spectrophotometer at absorbance 540 nm. The most effective treatment was found at concentration of 50 ppm for 30 min. These results suggest that ozone fumigation treatment at 50 ppm for 30 min could be a useful and effective method to reduced mancozeb fungicide residues and maintain postharvest quality of ‘Jinda’ chili during storage at 25 °C for 12 days. In the second study, the effect of ozone in maintaining fruit quality involved in ROS-mediated chlorophyll degradation and PCD and vital mechanisms involved in mancozeb degradation of ‘Jinda’ chili was then examined. Chilies were prepared as mentioned above before fumigation with ozone in concentrations of 50 ppm for 30 min. The dissipation of pericarp degreening and reddening of pericarp color were observed on day 3 of storage, which were associated with the significantly elevated levels of superoxide and hydrogen peroxide accumulations, as well as increased chlorophyll catabolic enzymes (chlorophyll peroxidase, chlorophyllase and pheophytinase activities). Moreover, both caspase-like enzymes and in situ DNA degradation, features of programmed cell death (PCD), became more obviously visible at the early period of deterioration. Fruit fumigated with ozone, enhanced the activity of antioxidant enzymes (ascorbate peroxidase, catalase and superoxide dismutase) and suppressed both chlorophyll degradation and the PCD process, which were compatible with lowering senescence in chili. Our findings showed that ozone fumigation increases antioxidant activity, which in turn helps to delay chlorophyll breakdown and cell death, hence slowing senescence in 'Jinda' chili. Furthermore, the toxicity of the degraded mancozeb solution was tested on brine shrimp. Ozone-promoted hydroxyl radical accumulation, accompanied by the reduction in mancozeb, as measured by GC-MS. The toxicity of ozone-treated mancozeb was reduced, as indicated by reduced brine-shrimp mortality and increased LD50. These results indicated that ozone fumigation is an effective treatment in mancozeb detoxification via oxidation process. Ozone fumigation enhanced antioxidant defense systems and retarded chlorophyll catabolic process, subsequently postponing PCD, thereby preserving chili fruit quality during storage.