Scoparone and Scopoletin Accumulation and Ultraviolet-C Induced Resistance to Postharvest Decay in Oranges as Influenced by Harvest Date

Abstract

<jats:p>`Washington Navel', `Biondo Comune', `Tarocco', and `Valencia Late' orange [<jats:italic>Citrus sinensis</jats:italic> (L.) Obsek] fruit, harvested at various periods of time, were subjected to ultraviolet-C (UV-C) irradiation at 0.5, 1.5, or 3.0 kJ·m<jats:sup>-2</jats:sup> doses and then stored at 7 °C and 90% to 95% relative humidity (RH) for 4 weeks plus one additional week at 20 °C and 80% RH. Following UV-C treatment, there was varying amounts of rind browning and necrotic peel damage, depending on cultivar, treatment dose, and harvest date. `Tarocco' fruit were damaged more easily by UV-C treatment than the other cultivars. `Valencia L.' were the most resistant to UV-C irradiation, showing no adverse effects at the lowest dosage and having the lowest percentages of damaged fruit at higher dosages. `Washington Navel' and `Biondo Comune' oranges showed an intermediate susceptibility to UV-C treatment, with negligible differences between these cultivars. The percentage of damaged fruit after irradiation at the higher UV-C dosages decreased in most fruit samples as the season progressed. UV-C irradiation at 0.5 kJ·m<jats:sup>-2</jats:sup> effectively reduced decay development compared with nontreated fruit. Irradiation with 1.5 kJ·m<jats:sup>-2</jats:sup> was more effective compared with 0.5 kJ·m<jats:sup>-2</jats:sup> only in early harvested fruit. In `Washington Navel' and `Biondo Comune' oranges in the later harvests, treatment with 3.0 kJ·m<jats:sup>-2</jats:sup> improved decay control further, compared with 0.5 kJ·m<jats:sup>-2</jats:sup>. Following UV-C treatments the phytoalexins, scoparone and scopoletin, accumulated in flavedo tissue depending on the cultivar, fruit age, and UV-C treatment. Both phytoalexins displayed a similar accumulation pattern, however, the levels of scopoletin were very low compared with scoparone. Concentrations of phytoalexins rose as the irradiation dose increased. No scoparone and scopoletin could be detected in nontreated fruit. The highest concentration of phytoalexins among cultivars was recorded in `Valencia Late' oranges, the lowest in `Tarocco', with similar intermediate accumulations in `Washington Navel' and `Biondo Comune'. In `Washington Navel', `Biondo Comune', and `Tarocco' oranges, the rate of scoparone accumulation was significantly higher in fruit harvested earlier in the season while `Valencia late' oranges exhibited an opposite trend.</jats:p>

Use of UV‐C Treatments to Maintain Quality and Extend the Shelf Life of Green Fresh‐cut Bell Pepper (Capsicum annuum L.)

“…Applying a potentially harmful agent such as UV‐C radiation, at appropriate intensities and doses, has been reported to induce some beneficial physiological responses (Shama and Alderson 2005). Accumulation of the phytoalexins scopoletin and scoparone has been found in UV‐C‐treated citrus fruit (D’Hallewin and others 1999). Increases in the activity of enzymes associated with the metabolism of phenolic compounds, such as phenylalanine ammonia‐lyase (PAL) and polyphenol oxidase (POD), may also contribute to reduce the susceptibility against pathogens in irradiated fruits (Pombo and others 2011).…”

Pulsed Light Treatments for Food Preservation. A Review

“…In treated plant tissues, chemical species with beneficial effects on human health can be induced (LagunasSolar et al 2006;Shama 2007;. These substances include phytoalexins such as scoparone in oranges (Dhallewin et al 1999), 6-methoxymellein in carrots (Mercier et al 2000), and resveratrol in grapes, with a number of cardioprotective properties (Cantos et al 2002). Enzymes such as chitinases and glucanases in peaches (El Ghaouth et al 2003) and tomatoes are also induced (Barka 2001).…”

Use of UV‐C irradiation to prevent decay and maintain postharvest quality of ripe ‘Tommy Atkins’ mangoes

“…Inducible resistance, especially with radiation at 254 nm, was related to the biosynthesis of substances (mainly phenols) toxic to the pathogens, induced by an increase in the activity of biosynthetic enzymes such as phenylalanine ammonia‐lyase (Frietzenheimer & Kindl, 1981). D’hallewin et al . (1999) found that the increases of scoparone and scopoletin in citrus fruit by UV‐C irradiation may be related with the resistance induced against pathogens.…”