Mandarin postharvest LED irradiation can boost specific bioactive compounds

Citrus crops are among the most cultivated crops in the world. The total production of citrus crops surpasses 100 million metric tons annually [1] for its health-promoting properties [2]. The Phlegrean mandarin (Citrus reticulata Blanco) is specifically cultivated in the Phlegraean volcanic zone of Naples (Italy). The unique properties of Phlegrean soil and climate make this cultivar an excellent source of phytochemicals, such as polyphenols, vitamin C, and flavonoids, with most of them being actively used in pharmaceutical applications as potential anti-COVID-19 molecules [3,4]. The concentration of bioactive compounds in mandarins strongly influences the preference of consumers who look for health-promoting foods. Furthermore, fruits rich in phytochemicals may represent the raw material to produce functional foods, nutraceuticals, or natural additives (such as antioxidant or antimicrobial agents) [5]. It is well known that the major loss of fruit nutritional properties and phytochemical content occurs during postharvest storage due to the rapid senescence and deterioration of tissues induced by the increase of reactive oxygen species (ROS) production. ROS are the main cause of cellular oxidative stress. Therefore, counteracting ROS production through antioxidants represents an effective way to delay the senescence of fresh products during storage [6]. The traditional postharvest techniques used for preserving fruits and vegetables are based on cooling or the application of chemical additives. Alternative and novel methods involve the use of Light Emitting Diodes (LEDs) in the postharvest. It is well documented that LED technology may enhance plant growth and photosynthesis, regulate senescence, improve plant and fruit shelf-life, and modulate the bioactive compound synthesis by setting suitable light quality regimes during plant development [7,8,9,10,11]. However, it must also be considered that the light quality effects on plant secondary metabolites are species-specific; therefore, the benefits obtained for one species may not occur for another species under the same light regime. For example, blue light on pepper strongly increased the flavonoid content in the epidermis [12]; in broccoli, red light treatment preserved the vitamin C during postharvest, while blue LED treatment increased carotenoid content [13]; in lettuce, supplemental red light regime during the growing season enhanced phenols concentration compared to white light [14]. The application of blue (470 nm) and red (660 nm) LED light at 20 ?C for 6 days at a fluence rate of 50 W m?2 significantly increased some antioxidants in satsuma mandarin (Citrus unshiu Marc.) fruits, such as ?-cryptoxanthin [15]. Our previous research has revealed that Phlegrean mandarin is particularly rich in bioactive molecules compared to other commercial cultivars [16]. Furthermore, the peel and seeds of this specific cultivar are particularly rich in antioxidants [16]. The present study investigated the effects of the storage of Phlegrean mandarin fruits under two different light quality treatments: broad-spectrum white (W) and RB (red?blue), to assess if LED utilization in postharvest potentiates the content of phytochemicals also improving the conservation of fruits intended for marketing and human consumption. Regarding conservation, it is a priority to maintain the quality of fresh products after harvest and to make sure they are long-lasting. Traditional postharvest preservation methods rely on cooling and chemical techniques [17]. Besides the enrichment of fruit nutritive quality, the use of LED technology during postharvest represents an eco-friendly tool for improving food shelf-life, fruit ripening control, and reducing microbial and fungi contamination of fruits and vegetables [18,19,20]. AbstractPhlegrean mandarin fruits are already known for health-promoting properties due to the high concentration of phytochemicals in peel, pulp, and seed. Biotic and abiotic factors, including light, may modulate their biosynthesis, metabolism, and accumulation. In this context, light-emitting diodes (LED) have recently been applied to control nutritional traits, ripening process, senescence, fruit shelf-life, and pathogenic microbial spoilage of fruits. This study investigated the effect of the seven-day exposure of Phlegrean mandarin fruits to two LED regimes, white (W) and red?blue (RB), to test the possibility that the storage under specific light wavelengths may be used as green preservation technology that enhances fruit phytochemical properties. To pursue this aim, the antioxidant activity and polyphenolic profile of the pulp and peel of mandarins under W and RB light regimes were evaluated and compared with Control fruits not exposed to LED treatment. Our results indicated that storage under W and RB treatments modulates the antioxidant content in pulp and peel differently. Compared to W, the RB regime increases the ascorbic acid, flavonoid, anthocyanin, and carotenoid concentrations, while the polyphenol profile analysis reveals that the number of important phytochemicals, i.e., quercetin rutinoside, chlorogenic acid, sinensetin, and rutin, are higher under W. The overall data demonstrated that postharvest LED irradiation is a valid tool for modifying fruit phytochemical properties, which also boosts specific bioactive compounds. SourceModulation of Antioxidant Compounds in Fruits of Citrus reticulata Blanco Using Postharvest LED IrradiationGiulia Costanzo, Ermenegilda Vitale, Maria Rosaria Iesce, Michele Spinelli, Carolina Fontanarosa, Roberta Paradiso, Angela Amoresano & Carmen ArenaBiology 2023, 12(7), 1029https://doi.org/10.3390/biology12071029Picture shows the graphical abstract