Effects of hypertonic CO2 preservation bags combined with 1-MCP slow-release agent and chitosan on postharvest softening of Akizuki pear

【Objective】Akizuki pear (Pyrus pyrifolia Nakai), a late- maturing sand pear cultivar, is prized for its superior organoleptic quality and extended harvest window. However, this variety exhibits significant postharvest challenges, particularly rapid flesh softening and skin cracking during storage, which substantially diminishes its marketability and commercial value. In previous studies, we have demonstrated that these physiological changes are closely associated with increased ethylene production and respiratory activity during fruit ripening. Consequently, developing an efficient, low-cost, and user-friendly postharvest preservation technique to mitigate quality deterioration in Akizuki pears is of paramount importance for the fruit industry. Ripening represents the terminal phase of fruit maturation, characterized by a climacteric rise in respiration and a concomitant surge in ethylene biosynthesis.These metabolic shifts accelerate the ripening process, leading to reduced shelf life and economic losses. The application of 1-methylcyclopropene (1-MCP), a potent ethylene action inhibitor, has proven effective in extending the storage potential of Akizuki pears, enabling long- distance transportation and prolonged marketability. Similarly, chitosan-based edible coatings have emerged as a promising alternative to modified atmosphere packaging (MAP), as they modulate fruit respiration and delay senescence. Despite these advancements, the underlying mechanisms of flesh softening in Akizuki pears under ambient storage conditions (20±1) ℃ remain insufficiently explored. In this study, the synergistic effects of hypertonic CO2 preservation bags in conjunction with 1-MCP and chitosan treatments were investigated on postharvest fruit quality maintenance. By systematically analyzing the changes in fruit texture, softening- related enzyme activities, and oxidative stress markers, this research aimed to elucidate the biochemical basis of fruit softening and establish an optimized protocol for ambient-conditions (20±1) ℃ storage and transportation of Akizuki pears.【Methods】Four treatments were established under ambient logistics conditions at (20±1) ℃: The control group (CK), treatment with a hypertonic CO2 film bag, treatment with a hypertonic CO2 film bag (MAP) combined with a 1-MCP slow-release agent (MAP+1- MCP), and treatment with a hypertonic CO2 film bag combined with chitosan (MAP+chitosan). After sealing the three types of MAP treatment packaging bags for 3 days (72 hours), the bags were opened to remove 1-MCP slow-release agent, and then the pears were stored under shelf conditions until 19 days (sealing for 3 days and open for 16 days) with open packaging. During storage, the following indexes were measured, such as quality of Akizuki pear, texture profile analysis (TPA) of the flesh including cohesiveness, springiness, gumminess, and chewiness, respiration rate, ethylene production rate, starch content and amylase activity (AMS), and the relevant softening and senescence- related indices.【Results】Compared with CK, both the treatment with single hypertonic CO2 film bags and the treatment combining hypertonic CO2 film bags with 1-MCP slow-release agent can delay the decline of firmness, cohesiveness, elasticity, adhesiveness, and chewiness of Akizuki pears after harvest, and inhibit enzyme activity, the respiration rate and ethylene release of the fruits. The results showed after 15 days of storage, the hardness of the hypertonic CO2 film bags treatment and the hypertonic CO2 film bags with 1- MCP slow- release agent treatment decreased to 4.06 kg · cm- 2 and 5.00 kg · cm- 2 , respectively, and the stem freshness indices were 21 and 73, respectively, and delay the increase in the activity of AMS, CL, and pectin PME, inhibiting the increase of MDA within the fruits. The peak of respiration was delayed for 4 days and 6 days and the peak values increased by 18.2% and 15.9% respectively. The hypertonic CO2 film bags with 1-MCP slow-release agent treatment delayed ethylene rate for 2 days and the peak values increased by 30.4%. However, as the storage time extended, the softening of the fruits treated with single hypertonic CO2 film bags became manifest, while the treatment combining hypertonic CO2 film bags with 1-MCP slow- release agent can still maintain the good fruit quality until the end of the storage period. After 19 days of storage the treatment combining hypertonic CO2 film bags with 1-MCP slow- release agent can hold cohesion cohesiveness of 0.26, springiness of 1.79 mm, gumminess of 16.72 N, chewiness of 24.3 mJ, 4.49 kg· cm-2 of hardness, and a stem freshness of 46.67. The treatment with hypertonic CO2 film bags combined with chitosan accelerated the softening process of the fruits during storage. The peak of respiration brought forward 4 days compared with the combining hypertonic CO2 film bags with 1-MCP slow- release agent treatment and the peak values increased by 38.6%. The ethylene release rate increased to 358.75 nL·kg-1 ·h-1 . The treatment with hypertonic CO2 film bags combined with chitosan also promoted enzyme activity of the fruits.【Conclusion】Both the hypertonic CO2 film bags treatment and the hypertonic CO2 film bags combined with 1-MCP treatment can delaythe softening of Akizuki pears and maintain good fruit quality during room-temperature storage. However, the hypertonic CO2 film bags combined with 1-MCP slow- release agent treatment exhibits a better storage effect. The treatment of Akizuki pears with hypertonic CO2 film bags combined with chitosan coating not only increases production costs but also fails to achieve satisfactory preservation efficacy, and is therefore not recommended for commercial application.