Advances in research on the chilling injury occurrence and control technologies of postharvest banana fruit

Abstract: Banana is one of the most popular fruits because of its rich nutrition and fragrant taste, as well as important economic value in the global market. Low temperature storage is the most widely used and effective strategy for fruit storage. Appropriate low temperature can delay the senescence pro-cess of post-harvest fruit, maintain the fruit quality and prolong the shelf life of commodities through slowing down the respiration rate and inhibiting reproduction of microorganisms. However, as a typical climacteric fruit, banana fruit is prone to suffering chilling damage when exposed to improper low tem-perature. Chilling injury in banana fruit caused huge economic losses to the banana industry and limited the application of low temperature storage on banana preservation in the past decades. The symptoms of chilling injury in banana fruit mainly include peel browning, pitting, increased fruit firmness, failure of normal ripening and flavor and aroma decline, resulting in reduced edible and commodity values. Ba-nana fruit under cold stress has inferior tolerance to disease and is more susceptible to spoilage. Pre-har-vest temperature, banana cultivar, maturity degree, storage temperature and duration of exposure to low temperature are main factors that influence the degree of banana fruit chilling injury. It is very crucial to control these factors for preventing the occurrence of chilling injury in banana fruit. Cell membrane damage has been considered to be the initial reaction of chilling injury. The changes of cell membrane are shown in membrane structure and composition. Membrane structure change exhibits the transition from the flexible liquid crystal state to the rigid gel state, resulting in low fluidity of membrane, and thus cell membrane permeability is observed to decrease in banana fruit under cold stress. The change of membrane composition in banana fruit exhibits the decrease of phosphatidylcholine, phosphatidyleth-anolamine and unsaturated fatty acids and the increase of phosphatidic acid and saturated fatty acid.The activities of phospholipase D and lipoxygenase involved in membrane lipid degradation are signifi-cantly enhanced when the banana fruit is subject to cold stress. In addition, due to the damage of cell membrane, the activity of enzyme attached to the membrane can be affected, resulting in the disorder of cell metabolism. Moreover, cold stress induces the outbreak of reactive oxygen species in banana fruit, accompanied with the decrease in antioxidant capacity. The balance between reactive oxygen species generation and antioxidant capacity is broken, resulting in causing oxidative stress to fruit cell. Mean- while, excessive reactive oxygen species can attack cell membrane, causing membrane lipid peroxida- tion. Low energy level is detected in banana fruit under cold stress, but more energy is needed to resist chilling injury. The shortage of cell energy supply accelerates chilling injury occurrence of banana fruit. In addition, osmotic substances including polyamine and proline are generated for resistance to chilling injury when the banana fruit encounters chilling injury. The abnormal ripeness of banana fruit caused by chilling injury was considered to be related to the decrease of ethylene binding ability. With the con-tinuous development of molecular biology technology, many genes that are associated with the occur-rence of banana fruit chilling injury have been identified, and the research on molecular regulation mechanism, in particular the transcriptional regulation mechanism of transcription factors in the process of chilling injury in banana fruits, has been paid more and more attention. It has been reported that tran-scription factors participated in cold stress response by binding to cis-acting elements of target genes or forming transcription complexes with other proteins, thereby regulating the expression of target genes.Taking into consideration of all the above-mentioned, the occurrence of banana fruit chilling injury is a complex process, which involves the changes of cellular level and molecular level. Investigations showed that a lot of control technologies have been developed to alleviate the symptoms of chilling inju-ry in postharvest banana fruit, including physical and chemical treatment methods. Physical treatment methods contain appropriate low temperature storage, heat treatment, cold shock treatment, poly ethyl-ene film packaging, and irradiation treatment. Physical treatment methods are preferred because non-chemical residues are considered to be safer than chemical treatment methods. Chemical treatment methods mainly include small molecule signaling substances, hormone and plant growth regulators, or-ganic acids, silk fibroin protein, and cold shock with electrolyzed functional water. Although these con-trol measures have been proven to be effective, they are rarely applied in industrial production process. Therefore, large-scale preservation measures suitable for industrial production process need to be devel-oped. The occurrence of banana fruit chilling injury is a complex process, which involves multi-level regulation. More studies from the perspective of molecular biology are needed to clarify the occurrence and development mechanism of banana fruit chilling injury in the future. Meanwhile, the research on the physiological and molecular mechanisms underlying chilling injury in banana fruit will provide new preservation technologies for preventing banana fruit from chilling injury. Taken together, this article aims to provide knowledge for further studying the occurrence mechanism of chilling injury in banana fruit, and references for developing new control technologies for preventing postharvest banana from chilling injury.