Ozone fumigation effects on bacterial and anthracnose development on bell pepper (Capsicum annuum L.) and its effect on fruit quality

Bacterial contamination and anthracnose development on bell pepper pose a threat to food safety and food security. Bacteria contamination by pathogenic species can be a fatal outbreak and risking worldwide population. Meanwhile, anthracnose development on bell pepper can contribute to substantial product loses which will substantially affect world economy and food availability. Current postharvest treatment such as the use of chlorine and fungicide poses harmful effects on human and environment due to the production of carcinogenic by-products. This leads to urgency to develop a safe postharvest treatment which leads to the objective of this study to develop a new postharvest treatment; ozone fumigation which has high potential to reduce bacterial contamination and anthracnose development on bell pepper. Ozone fumigation treatment is safe to human and environment and very practical. This technology is promising hence, worth to study. This study investigated the effect of ozone fumigation on 1) growth of Escherichia coli O157, Salmonella enterica sv. Typhimurium and Listeria monocytogenes; selected pathogens that contributed to food poisoning in fruit 2) development of anthracnose disease on bell pepper caused by Colletotrichum capsici 3) activity of defense related enzymes 4) antioxidant capacity of bell pepper 5) physico chemical, physiology and sensory qualities of bell pepper. Antibacterial studies was conducted on fresh cut bell pepper with treatments of 0, 1, 3, 5, 7 and 9 ppm ozone for 0.5, 3, 6 and 24 h at 18 - 20 C, 95% RH. The results showed that ozone reduced growth of E. coli O157, Salmonella Typhimurium and L. monocytogenes populations where optimal dosage was 9 ppm ozone for 6 h. This ozone dosage resulted in 2.89, 2.56 and 3.06 log reduction of E. coli O157, Salmonella Typhimurium and L. monocytogenes populations, respectively. Scanning electron micrograph showed that the bacterial population was inactivated by disrupting the cell structure which leads to cell lysis. Ozone also reduced anthracnose development on bell pepper. Colletotrichum capsici, the causal agent of anthracnose on bell pepper was treated with 0, 1, 3, 5, 7 and 9 ppm ozone for 24, 72 and 120 h. The results showed that exposure to 7 ppm ozone for 72 h had the highest inhibition in disease incidence (34.8%) and disease severity (41.2%). This inhibition was non-significantly different to fruit exposed to 3, 5 and 9 ppm ozone for 72 h. The inhibition was due to effect of ozone on mycelia morphology where ozone inhibited mycelia development by inducing hyphae branching. Besides, the ozone dosage also significantly reduced spore production (31.6%) and spore germination (100%). Increasing ozone dosage by prolonging the exposure to 120 h induced fungal sporulation and had no significant effect on disease development. Reduction in anthracnose disease development was correlated with activity of plant defense enzymes. Increase in activity of plant defense enzymes such as phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) and β-1,3-glucanase was found to reduce variation in disease incidence on bell pepper. Optimal enzyme activity was observed from exposure to 3 ppm ozone for PAL, PPO and β-1,3-glucanase and 3 and 5 ppm ozone for POD. This showed that ozone inhibit disease incidence on fruit by stimulating the activity of plant defense enzymes as well as reducing mycelia elongation, spore germination and spore production. Analysis on antioxidant content and antioxidant capacity of bell pepper showed ozone dosage of 3 ppm ozone for 72 h was the most effective dose to induce fruit ascorbic acid (26.6%) and total phenol content (15.2%) which reflect antioxidant capacity (15.3%) of bell pepper. Further increase in ozone concentration reduced fruit antioxidant content and its capacity. Analysis on fruit β-carotene content showed negative correlation with fruit antioxidant capacity hence, suggested that β-carotene may not be the major antioxidant in the bell pepper under study. The increase in fruit antioxidants from exposure to 3 ppm ozone for 72 h reduced fruit oxidative status (malondialdehyde (MDA) content) and resulted in no oxidative damage. This maintained fruit ripening progress similar to control as indicated by fruit respiration, colour development, soluble solid concentration and titratable acidity. The ozone dosage also maintained fruit water content similar to control hence, maintaining its firmness during storage. Meanwhile, exposure to higher ozone dosage; 7 and 9 ppm ozone for 72 h; increased cell oxidative status which resulted in oxidative damage as observed in high MDA content and increase in membra ne permeability. This enhanced ripening progress as indicated by progressive colour development, increase in soluble solid concentration and reduction in titratable acidity and firmness. This quality deterioration negatively affected fruit flavour hence, not preferred by the panellist. Thus, under current observation, this study showed exposure to 3 ppm ozone for 72 h reduced populations of foodborne pathogen, decreased anthracnose development, increased plant defense enzyme as well as enhanced its antioxidant capacity. It can be used as an alternative to chlorine and fungicide and eliminate the risk of producing harmful by-products. Ozone treatment is also very practical where it can be installed in truck or shipping container which allows the treatment to be carried out during transport. This reduces fruit handling time and labour cost