Effects of LED light on the ripening regulation of green mature banana during storage and transportation

Abstract: The purpose of this research was to clarify the effects of monochromatic lights with different fixed bands on the post-ripeness regulation in typical respiration fruits. Specifically, a systematic investigation was made on the effects of red, orange, yellow, green, blue, and purple LED lights on delaying and accelerating low maturity bananas ripening during simulated storage and transportation at room temperature (20±0.7 ℃). The low maturity of bananas ripening and quality changes were observed under different colors of LED lighting treatment. The results showed that the >440-505 nm blue and 400-440 nm violet LED light greatly contributed to inhibiting the intensity respiratory of banana and release quantity of ethylene. Two colors of LED light were utilized to effectively delay the shelf storage time of banana for 2 days, while decreasing the color turn and decomposition of cellulose and starch. Subsequently, the final firmness of bananas under the blue and purple lighting treatment after 8 days was 2.5 and 0.1 N higher than the CK group. In addition, the total sugars content of bananas in the blue lighting group was 51.71% of CK. Hence, better preservation was achieved under the blue and purple LED lighting treatment, where the bananas post-ripening was inhibited to prolong the freshness preservation period. The >640-700 nm red and >605-640 nm orange LED lighting treatments were utilized to effectively promote 2 days earlier on bananas respiration and ethylene peak. In addition, the red light was used to increase the respiratory peak by 24.20% and the ethylene release peak by 23.97%, compared with the CK group. More importantly, the peel color of bananas turned more outstandingly under red and orange light, and the total color difference (ΔE) reached 94.70 and 83.25 at full ripeness. The red-orange light was also employed to stimulate the decomposition of starch and cellulose, thus speeding up the accumulation of bananas soluble sugar and softening. Therefore, it was found that both red and orange LED lights were selected to effectively accelerate the ripening of bananas. Among them, the orange light was used as an accurate of ripening, due to its intensity less than the red light. Additionally, the bananas exposed to yellow and green LED lighting showed premature rotting and post-ripening disorder. Moreover, the banana peels rotted seriously after 4 days, but the color differences (ΔE) of peels were 40.35 and 46.23 less than those of the CK group. Particularly, the>565-605 nm yellow and >505-565 nm green light also prevented the rapid decline of banana firmness, but accelerated the cellulose decomposition, compared with the CK group. At the same time, the pectin contents in the yellow and green light group were lower than those in CK. The changes of cellulose, pectin, and hardness varied in the groups. A comprehensive analysis was performed on the texture, sugar content, and respiration of bananas. It was found that the six LED light colors treatments were used to delay ripening, promote ripening and disturb ripening. Correspondingly, the red light was selected to promote banana ripening faster, the orange light to promote banana ripening slower, the blue light to inhibit post-ripening and delayed senescence better than purple light, the yellow and green light to disrupt the normal post-ripening of banana. In conclusion, monochromatic LED lighting can be widely expected to serve as physical preservation to delay or accelerate ripeness in the process of storage and transportation of bananas. This finding can provide a theoretical basis for the ripening regulation on more respiration fruits and vegetables.