USDA Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Avenue, Parlier, CA 93648
Sunkist Growers 222 W. Lindmore Street, Lindsay, CA 93247
Biometrics Unit, USDA ARS, Western Regional Research Center, 600 Buchanan Street, Albany CA 94710-1100
Chlorine toxicity to Penicillium digitatum and Geotrichum citri-aurantii, causes of green mold and sour rot of citrus, respectively, was quantified. In 3% wt/vol NaHCO3 containing 200 µg free chlorine per ml at pH 8.3, 95% of P. digitatum spores died (LT95) by 180 s at 5°C, while only 32 s were required at 24°C. The LT95 of G. citri-aurantii arthrospores was 108 and 31 s at 5 and 24°C, respectively. Mortality slowed 2- to 4-fold for each unit of increase from pH 7 to 10. The LT95 of P. digitatum spores in 200 µg free chlorine per ml at 24°C at pH 7, 8, 9, and 10 was 13.2, 19.1, 29.4, and 88.4 s, respectively. The LT95 of G. citri-aurantii at pH 7, 8, 9, and 10 was 3.0, 12.6, 56.6, and 114 s, respectively. Models were prepared describing mortality. Brief immersion in 200 µg free chlorine per ml reduced viable spores of P. digitatum and G. citri-aurantii from 106 to 103 spores per lemon, and naturally occurring yeast and molds from 106 to 104 CFU. In fruit wound-inoculated and immersed 24 h later in water, 4,000 µg free chlorine per ml, or 3% wt/vol NaHCO3, green mold occurrence after storage was 98.5, 68.3 and 7.5%, respectively.