Citrus fruits have a tissue pH below 4 and are therefore heavily subjected to fungal attacks during the post-harvest phase. Penicillium italicum and P. digitatum represent the most common and serious causes of alteration during both storage and distribution.
Physiologists and chemists from the Pablo de Olavide University in Seville studied the effects of continuous and intermittent exposure (simulating a night-day cycle) to ozone-enriched atmosphere (between 1.6 and 60 mg/kg) at 5°C for 15 days and a subsequent 15-day shelf life at 20°C on six citrus varieties (two tangerines: Fortune and Ortanique and four oranges: Navelate, Lanelate, Salustiana and Valencia).
The in vitro and in vivo growth of Penicillium digitatum and Penicillium italicum was first assessed. Based on the results obtained, continuous exposure to 60 mg/kg of ozone and intermittent exposure to 1.6 mg/kg of ozone were chosen for industrial trials while decay and oleocellosis incidence, colour, firmness, weight loss and juice (soluble solid content, pH, titratable acidity and vitamin C) were analysed.
Results showed that ozone application did not damage the quality of the fruit and that P. italicum latency in exposed oranges was 3 times higher than that of fruit not subjected to ozone treatment.
"The study showed that continuous and intermittent ozone delayed decay as well as the incidence of oleocellosis, slowed down the colouring process and reduced loss of firmness and weight. For industrial applications, the advantage of using ozone for 12 hours/day, thus simulating the day-night cycle, is that workers would not be exposed to ozone in refrigerated units during the day-time shift," report researchers.
Source: García-Martín Juan Francisco, Olmo Manuel, García José María, 'Effect of ozone treatment on postharvest disease and quality of different citrus varieties at laboratory and at industrial facility', 2018, Postharvest Biology and Technology, Vol. 137, pag. 77-85.