Effect of pre-harvest 1-methylcyclopropene application on internal browning and storage quality of Bartlett pear

Abstract:【Objective】Storage life of European pear (Pyrus communis L.) fruits is restricted by loss of eating quality and occurrence of storage disorders. Eating quality of the pear fruits is mainly dependent on the development of ripening degree, sugar and acid content. Internal browning is a major storage dis-order influencing the postharvest management of Bartlett pears. The storage life is affected by cultiva-tion techniques such as irrigation, fertilizing, fruit maturity and harvest date. Labor shortages would lead to fruit over- maturity on trees, therefore, developing strategies to slow on- tree fruit maturation would be economically valuable for growers and industries by retaining high quality fruits for deliver-ing to the market. 1-Methylcyclopropene (1-MCP), an inhibitor of ethylene action, can reduce ethylene production and delay fruit ripening. The purpose of this study was to investigate the effects of pre-harvest 1-MCP application on the fruit maturation, internal browning, storage quality and ripening of Bartlett pear.【Methods】A proprietary formulation of 1- MCP for spraying of fruits (3.8% a.i.; HarvistaTM; AgroFresh Solution Inc., PA) was applied at 300 mg∙L^-1 using an application volume of 1350 L∙hm^-2 on July 29. All application was made with a sprayer to the point of runoff. The non-1-MCP treated Bartlett fruits were harvested on August 10 (Control), and the 1-MCP treated fruits were harvested on August 10  (the treatment labeled as“1-MCP”) and August 17 (the treatment labeled as“1-MCP & delayed harvest”), respectively. The non-damaged fruits were stored immediately after harvest at -1.1 ℃ and 90%- 95% relative humility. The internal browning was assessed visually on 1 d, 3 d, 5 d after transferring from cold storage to 20 ℃ condition. On 1, 3 and 5 days at 20 ℃ after 4 or 5 months of cold storage, the ethylene production rate was measured by gas chromatograph (GC-8A; Shimadzu, Kyoto, Japan), and the respiration rate was measured using a CO2 analyzer (Model 900161; Bridge Analyzers Inc., Alameda, CA). The peel chlorophyll content was determined on the opposite sides of the equator of each fruit using a DA meter (Sinteleia, Bologna, Italy). After removal of the peel, fruit firmness was measured on the opposite sides of the equator of each fruit with the fruit texture analyzer (Model GS-14, Guss Manufacturing Ltd., Strand, South Africa). The titratable acidity and soluble solid content were measured using a commercial titration system (Model DL15, Mettler- Toledo Inc., Columbus, OH, USA) and a digital refractometer (Atago, Tokyo, Japan), respectively. On the 5th day at 20 ℃,100 g of flesh tissue was grounded for 3 min using a juice extractor with uniform strip of milk filter and measured with 100 mL graduated cylinder. The extractable juice was measured in a 100 mL graduated cylinder. Meanwhile, the activity of polyphenol oxidase (PPO), the content of polyphenol and malondialdehyde (MDA) in the fruit flesh were determined.【Results】The internal browning in all fruit samples was not found in the end of 3 months of cold storage at -1.1 ℃. After 4 months of cold storage, the browning of the fruit cores of the control (harvest date 10th August) occurred, and the browning incidence was 33.33%. However, the browning symptoms in the fruits treated with 1-MCP (harvest date 10th or 17th August) was not found. After 5 months of cold storage, the browning of the core and flesh tissues of the control fruits were increased, and the browning incidence was 66.67% . The browning symptoms only occurred in the cores of fruits treated with 1-MCP & delayed harvest and the browning incidence was 21.74%, which was significantly lower than that of the control. The browning symptom of fruits treated with 1-MCP was not found. At harvest, the firmness of the fruits treated with 1-MCP (87.37 N) was significantly higher than that of the control (84.56 N) and the firmness of the fruits treated with 1-MCP & delayed harvest was 85.31 N, indicating that pre-harvest 1-MCP application could delay the fruit maturation on-tree. Compared with the control, the ethylene production rate and respiration rate were inhibited by pre-harvest 1-MCP application regardless of harvest date. The activity of polyphenol oxidase (PPO), the content of polyphenol and MDA were significantly inhibited, and the decrease of fruit firmness and peel chlorophyll content was retarded. The fruit firmness of the control was 32.55 N on the 5th day at 20 ℃ after 5 months of cold storage, indicating the fruits could not normally ripen. But the fruit firmness of 1-MCP and 1-MCP& delayed harvest was 23.33 N and 24.14 N, and the ex-tractable juice was 536 mL∙kg-1 and 585 mL∙kg-1 , respectively, indicating pre-harvest 1-MCP application did not affect the fruit ripening.【Conclusion】In conclusion, the pre- harvest 1- MCP treatment could delay the maturation on-tree, delay the onset of the internal browning for about 1 or 2 months and improve the storage quality of Bartlett fruits. Key words: