Abstract
Mature ‘Hamlin’ sweet oranges (Citrus sinensis (L.) Osbeck) were irradiated using light-emitting diodes (LEDs) and ultraviolet (UV) light for six days after harvest. Based on evaluation of the basic ripening parameters of fruits, the contents of soluble sugars, organic acids, and carotenoids were analyzed (in pulps) on the sixth day by high-performance liquid chromatography (HPLC). The results showed that LED and UV irradiation not only accelerated orange ripening but also caused significant changes in the soluble sugar, organic acid, and carotenoid content. Compared with fruit subjected to dark shade (DS) treatment, the total soluble sugar, fructose, and glucose contents increased significantly in UV-treated (UVA, UVB, and UVC) fruits, while the sucrose content increased remarkably in white light, UVB, and UVC-treated fruits (p < 0.05). UV treatment was associated with inducing the largest effect on the total soluble sugar content. Except for UVB, other types of light notably induced an accumulation of the total organic acid content, none but blue light and red light markedly induced citric acid accumulation (p < 0.05). Interestingly, only the red light and dark shade treatments had markedly positive effects in terms of inducing carotenoid accumulation, including the total carotenoid, isolutein, zeaxanthin, lutein, neoxanthin, all-trans-violaxanthin, phytofluene, cis-ζ-carotene, and β-carotene concentrations. Other light treatments had significantly negative effects on carotenoid accumulation (p < 0.05). Therefore, soluble sugar, organic acid, and carotenoid accumulation in sweet oranges vary depending on the levels of UV and LED irradiation. Appropriate light irradiation is a potentially effective way to maintain or improve postharvest fruit quality.
Highlights
Citrus is a staple type of crop worldwide; their fruits have a unique flavor and contain rich concentrations of health-promoting phytochemicals—such as phenolics, carotenoids, and vitamin C—that exhibit antioxidant, anti-inflammatory, antibacterial, and anticancer activities [1].Sweet oranges (Citrus sinensis (L.) Osbeck) account for approximately 60% of citrus production for both fresh fruit and processed juice consumption, its fruit and juice are important sources of human nutritional value [2]
When irradiated by lightemitting diodes (LEDs) and UV light for six days, there was a change in the total soluble solid (TSS) content of the fruit (Figure 1a)
Compared with the fruits subjected to dark shade treatment, TSS content was significantly enhanced in fruits treated with red light and UVA, while no significant change was observed in fruits treated with other types of light (p < 0.05)
Summary
Sweet oranges (Citrus sinensis (L.) Osbeck) account for approximately 60% of citrus production for both fresh fruit and processed juice consumption, its fruit and juice are important sources of human nutritional value [2]. Citrus quality will decline gradually after harvest, seriously reducing its edible and commodity value [3,4]. Many studies have investigated the role of postharvest exogenous chemical treatment on the maintenance of fruit quality. Light irradiation is more attractive than chemical methods because it is residue-free and safe. Some advances have been achieved in determining the influence of light on fruit quality and related metabolites [5,6].
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