Submitted to: Hortechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2003
Publication Date: 4/1/2003
Citation: Smilanick, J.L., Sorenson, D., Mansour, M., Aieyabei, J., Plaza, P. Impact of a brief postharvest hot water drench treatment on decay, fruit appearance, and microbe populations of California lemons and oranges. HortTechnology. 2003. v. 13. p. 333-338. Interpretive Summary: Citrus fruits are generally treated with fungicides to control fruit rot-causing fungi after harvest, but health-conscious consumers prefer fruit that are not treated with synthetic fungicides. An alternative, a brief hot water treatment of oranges or lemons for 30 seconds at 145F, controlled green mold, the major rot-causing disease, without injury to the fruit, but sour rot, another serious disease, was not controlled. Hot water treatment also greatly reduced natural microbe populations on the fruit, which can include microbes that contaminate juice and other citrus products made from the fruit. The brief hot water treatments controlled postharvest decay caused by the green mold pathogen without the use of synthetic fungicides and decreased populations of nuisance microorganisms on the fruit.
Technical Abstract: A brief (15s or 30s) high volume, low pressure, hot water (20, 49, 54, 60 or 63C) drench was applied over rotating brushes to lemons and oranges, and the impact of this treatment on populations of surface microbes, injury to the fruit, the incidence of green mold, or sour rot, caused by Penicillium digitatum or Geotrichum citri-aurantii, respectively, were determined. Microbe populations were determined immediately after treatment. Decay and injuries were assessed after 3 wk storage at 13C. The efficacy of the hot water treatments was compared to immersion of fruit in 3% wt/vol sodium carbonate at 35.0C for 30 s, a common commercial practice in California. Initial yeast and mold populations, initially log 10 6.0 per fruit, were reduced to log 10 3.3 on lemons and log 10 4.2 on oranges by 15 s treatment at 63C. Green mold control improved with increasing temperature and treatment duration. Green mold incidence was reduced from 97.9 and 98.0% on untreated lemons and oranges, respectively, to 14.5 and 9.4% by 30 s treatment with 63C water. However, immersion of lemons or oranges in 3% wt/vol sodium carbonate was superior and reduced green mold to 8.0 and 8.9%, respectively. Sour rot incidence on lemons averaged 84.3% after all water treatments, and was not significantly reduced, although arthrospores of G. citri-aurantii died at lower water temperatures than spores of P. digitatum in in-vitro tests. Sodium carbonate treatment for 30 s at 35C reduced sour rot to 36.7%. None of the treatments caused visible injuries to the fruit.