Advances in the use of white light on broccoli and kale postharvest shelf life

Brassicaceae is one of the most reputed families, mainly because its species constitute valuable sources of phytochemicals with nutraceutical properties (Di Gioia et al., 2020; Šamec, Urlić, & Salopek-Sondi, 2019). Broccoli, cauliflower, cabbage, brussels sprouts, and rocket are some of the most widespread products. The anciently cultivated kale leaves have also started to gain popularity in recent years for their unique thick green or purple leaves which can be used either raw or processed. Nonetheless, like broccoli, kale is highly perishable and senesces very rapidly upon harvest. Cold storage can improve postharvest life, but even under proper refrigeration, extensive chlorophyll catabolism, sugar degradation, and antioxidant losses would still occur within a few days (Sripong, Janjob, Uthairatanakij, & Jitareerat, 2017). The increasing concern of many consumers on the chemical substances used in the food chain has expanded the interest in physical clean postharvest techniques which can prolong the shelf-life of harvested commodities while reducing the use of synthetic additives.

Proper visible light application along the postharvest chain has been proposed as a simple tool that can offer some benefits in terms of quality maintenance in some commodities (Ilić & Fallik, 2017). The use of Light Emitting Diodes (LED) particularly boosted this possibility, due to their improved energy efficiency, reduced heat production, and longer lifespan compared to traditional incandescent sources (Khan & Abas, 2011). Some studies have provided evidence of the utility of lighting treatments to extend the shelf-life of green vegetables such as broccoli and spinach held at room temperature (Ilić & Fallik, 2017; Jin, Yao, Xu, Wang, & Zheng, 2015). Bárcena, Martínez, and Costa (2019) showed that illumination with fluorescent red, and white light delayed the deterioration of red kale leaves stored at 25 °C and 50% RH. Whether or not these treatments are still effective under cold storage must be determined, if considered an accurate light treatment as a supplementary strategy to proper temperature management.

White, blue, green and red light were found to improve chlorophyll content and to delay senescence during the postharvest of vegetables (Perera, Navaratne, & Wickramasinghe, 2022). Taking this into account, the use of white light is feasible since in its broad spectrum it contains the aforementioned wavelengths and that applied together can improve the performance of postharvest treatment. On the other hand, the white light source in general is easier to obtain and does not have a negative visual impact on the illuminated vegetables as monochromatic lighting could have.

The outcome of light treatments to delay senescence has shown large variations depending on both the type of vegetable and the radiation conditions applied. In a previous work (Pintos, Hasperué, Vicente, & Rodoni, 2020) we showed that the radiation intensity is one of the main factors determining the efficacy of white illumination to delay senescence in minimally processed broccoli. To the best of our knowledge, the proper intensity required to delay the senescence of most green commodities including whole broccoli inflorescences and kale leaves under refrigerated storage has not been determined yet. Therefore, the present work aims to explore how white LED radiation intensity influences senescence and quality maintenance of fresh broccoli heads and kale leaves.

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