Nitrous oxide (N2O) was tested as a potential fungicidal or fungistatic compound. Twelve postharvest fungi were exposed to 10 to 80 kPa with 20 kPa O2 in a static system at 20 °C. These fungi were divided into N2O high-, medium- and low-sensitive groups. Based on growth sensitivity, growth of high-sensitive fungi was completely inhibited, and that of medium-sensitive fungi up to 85%. With low-sensitive fungi, significant inhibition was achieved only when the fungi were exposed to N2O continuously for 6 days. Botrytis cinerea Pers.: Fr., Colletotrichum acutatum Simmonds, Monilinia fructicola (Winter) Honey, Penicillium expansum Link, Penicillium italicum Wehmer, Phytophthora citrophthora (R.E. Smith and E.H. Smith) Leonian and Rhizopus stolonifer (Ehrens.: Fr.) Vuillemin, were high-sensitive; Glomerella cingulata (Stoneman) Spaulding was medium-sensitive, and Alternaria alternata (Fr.) Keissler, Fusarium oxysporum Schlechtend1: Fr. f. sp. fragariae Winks and Williams, Fusarium oxysporum Schlechtend1: Fr. f. sp. lycopersici (Saccardo) Snyder and Hansen., and Geotrichum candidum Link., were low-sensitive fungi. Addition of up to 100 μL·L-l C2H4 did not reduce inhibition caused by N2O. The inhibitory effect of N2O was considered to be due to biophysical properties similar to CO2, the competitive inhibition on C2H4 action, or the biosynthesis of methionine. These results indicate the potential of N2O to control some postharvest decay fungi.
Effects of flavonoid pigments on chlorophyll (Chl) degradation by Chl peroxidase in the flavedo of Wase satsuma mandarin (Citrus unshiu Marc. var. praecox Tanaka) fruits were studied. Chl was degraded when hydrogen peroxide was added in a reaction mixture containing Chl and a phosphate buffer extract from the flavedo. Chlorophyllide, which was formed by the action of chlorophyllase in the extract, was also degraded. The flavonoid contents decreased with the Chl degradation in the reaction mixture. Analysis of the flavonoid with HPLC showed that hesperidin and narirutin were contained in the flavedo as a major flavonoid, and that the former decreased significantly and the latter showed almost no change with the Chl degradation in the reaction mixture. In the ethylene-treated fruits, the hesperidin content in the flavedo also decreased with the degreening of stored fruits, suggesting that the flavonoid oxidation by Chl peroxidase could be involved in the Chl degradation.