Red and blue LED weak light irradiation maintaining quality of cherry tomatoes during cold storage

Abstract: Tomatoes are rich in compounds including carotenoids, vitamin C (Vc), and flavonoids, which are believed to be beneficial to human health. The increasing growth in the consumption of fresh cherry tomato (Lycopersicon esculentum Mill.) has driven the demand for developing new green postharvest technology to maintain the quality during cherry tomato's storage period and shelf life. Blue and red lights among visible light regions may be still useful for the photosynthesis of some fresh products that are not fully mature during storage. Light-emitting diodes (LEDs) technologies could provide some opportunities to develop new equipment and method for controlling postharvest quality of cherry tomato treated by different light sources during storage and shelf life. Mature-green (breaker-stage) tomatoes were harvested and treated continuously with red and blue LED weak light at 4℃ for up to 20 d. Untreated tomatoes (the control) were kept in the dark for the same period. The effects of the treatments on the sensory quality (levels of appearance, color, odor and decay), Vc, reducing sugar, total soluble sugar, total soluble solids, titratable acid and lycopene were evaluated throughout the storage. The results showed that LED irradiation apparatus used in the experiment was stable and reliable. LED red and blue lamps could emit the designated light spectrum and not drift as the change of light intensity. The sensory quality was maintained at high level in all treatment during early storage period. After 10 d storage, the cherry tomatoes irradiated by LED red and blue light began to change color to yellow and red and had significantly better sensory quality than the control treatment (P<0.05), and LED red light had better effect than LED blue light. On the 20th day, the cherry tomatoes in the control showed inferior sensory quality involving flesh severe softening, apparent browning pitting on the peel and fungal decay spot, while the tomatoes irradiated by LED red and blue light kept good sensory quality (P<0.05). LED blue light irradiation could significantly inhibit the decrease of Vc content (P<0.05) in cherry tomato during storage compared with the control treatment, while the cherry tomatoes irradiated by LED red light showed lower Vc content than the control. LED red and blue light irradiation could lead to the accumulation of reducing sugar and total soluble sugar in cherry tomato during the early stage of storage, and reducing sugar and total soluble sugar content reached the highest on the 10th day. The contents of reducing sugar and total soluble sugar in cherry tomatoes decreased gradually between the 10th and the 20th day, while it was higher in the tomatoes irradiated by LED red and blue weak light than that in the control during the whole storage (P<0.05). Compared to the control, LED red and blue light irradiation could significantly delay the decrease of total soluble solids content and titratable acid content in cherry tomato (P<0.05), and LED red light had significantly higher effect than LED blue light (P<0.05). LED red light irradiation could lead to significantly higher lycopene content on the 20th day, while there was no significant difference between LED blue light and the control during storage. In comparison with the control treatment, LED red and blue weak light irradiation was beneficial for controlling the sensory and nutritional quality of cherry tomato at 4℃, completing the ripening process, and keeping the normal postharvest physiological metabolism. LED red weak light irradiation had the best effect among the treatments. In conclusion, LED red and blue weak light irradiation, as a simple and effective postharvest method, has the potential of application in the postharvest quality control of cherry tomato. The results provide the basis for sensory and nutritional quality control of fresh fruits and vegetables during cold storage.