Effects of storage temperature and harvest period on storage quality of Citrus reticulata Blanco‘W. Murcott’fruit

Abstract:【Objective】In this study, the suitable harvest time and storage temperature of W. Murcott was clarified, so as to extend the market supply time and relieve the pressure of sales, and provide reference for the harvest time and storage period of W. Murcott fruit in Guangxi.【Methods】W. Murcott fruit samples were collected at 4 harvest dates (November 29th, December 22nd, January 19th and March1st) and stored at 3 temperatures (2-4 ℃, 6-8 ℃ and room temperature). The changes in weight, color, soluble solids, titratable acid, vitamin C, reducing sugars, citric acid, methanol, ethanol and acetaldehyde in the fruit during storage were traced and shelf life were predicted.【Results】During storage, L*, a*, b* of W. Murcott fruit tended to level off after a rapid rise. They were highest in fruit stored at 6-8 ℃, followed by those in fruit stored at room temperature, and lowest in fruit stored at 2-4 ℃. On the 60th day of storage, the a* value of the fruit stored at 2-4 ℃, 6-8 ℃ and room temperature were12.94, 26.51 and 21.46, respectively. Low temperature storage significantly reduced the rate of weight loss and delayed the decrease in titratable acid and vitamin C contents, and the longer the storage time and the lower the temperature, the more significant the effect was. On the 90th day of storage, the weight loss rate of fruits stored at 2-4 ℃, 6-8 ℃ and room temperature were 1.73%, 2.12% and 3.37%, respectively. The content of titratable acid was 0.95%, 0.78% and 0.63%, respectively; and the contents of vitamin C were 16.00, 15.13 and 12.64 mg · 100 mL- 1 , respectively. The contents of reducing sugars increased first and then decreased, and the contents of reducing sugar sin fruit stored at low temperatures were higher than those stored at room temperature. The contents of ethanol and acetaldehyde rose in a fluctuating manner, with the highest at 2-4 ℃, the second at 6-8 ℃, and the lowest at room temperature. The contents of ethanol and acetaldehyde were lower within the first 60 days of storage at 2-4 ℃ and 6-8 ℃ and significantly higher at 2-4 ℃ than at 6-8 ℃ after 75 days at storage. L*, a* and b* of W. Murcott fruit gradually increased and reached the peak in phase Ⅲ with the delay of harvest date. During storage at 6-8 ℃, L* and a* increased continuously and then tended to level off. These color values in different phases followed a pattern of Phase Ⅲ and Phase Ⅳ ＞ Phase Ⅱ ＞ Phase Ⅰ, and the difference between phases was significant. The value of b* increased first and then decreased, and the later the harvest, the earlier the peak value of b* appeared during storage. Fruit weight loss was the fastest in phase Ⅳ and slowest in phase Ⅲ. The content of soluble solids increased with the delay of harvest, and was significantly higher in phase Ⅲ and phase Ⅳ than that in phase Ⅰ. The contents of titratable acids and vitamin C decreased with the delay of harvest, and were highest in phase Ⅰ and the lowest in phase Ⅳ. The content of reducing sugars first increased and then decreased with the delay of harvest, and was significantly higher in phase Ⅱ and phase Ⅲ than in phase Ⅰ and phase Ⅳ during storage. The content of citric acid decreased with the delay of harvest and fluctuated during storage, and the lowest content was found in fruit harvested in phase Ⅳ and stored at 6-8 ℃. The contents of ethanol and acetaldehyde increased with the delay of harvest time. During storage at 6-8 ℃, the rising rate of ethanol and acetaldehyde contents in the four phases followed a pattern of phaseⅠ ＜ phase Ⅱ, phase Ⅲ ＜ phase Ⅳ. At the 60th day of storage, the ethanol contents in fruit in phaseⅠ, phase Ⅱ, phase Ⅲ, and phase Ⅳ were 285.61, 894.79, 654.68 and 1 311.58 mg ·L- 1 , respectively. The contents of ethanol, acetaldehyde and methanol were significantly higher in the shelf-life than those in storage period. The ethanol content exceeded the threshold of 1500 mg · L- 1 in fruit harvested in phaseⅠ shifted to room temperature after stored for 120 days, and exceeded the threshold in fruit harvest in phase Ⅱ, phase Ⅲ and phase Ⅳ after 60 to 75 days of storage.【Conclusion】Compared with room temperature storage, low temperature storage could reduce the weight loss rate significantly, delay the decreasing rate of titratable acid and vitamin C contents, and increase the soluble sugar content in W. Murcott fruit. 6-8 ℃ fruit occurs when the green color of the fruit basically fades, the soluble solids reach 11%, and the titratable acid is greater than 0.8% (about late December to late January of the following year in Guilin area). 6-8 ℃ is suitable low temperature for storage the fruit of W. Murcott but storage time at this cold temperature range should not be longer than 90 d and should not be move out of storage at room temperature after 60 days of storage at low temperature.