Effects of carbon dioxide concentrations on the physiological indexes of ‘Hongxiangsu’pears during shelf-life after controlled atmosphere storage

Abstract:【Objective】‘Hongxiangsu’pear was bred by the Fruit Tree Research Institute of Zheng- zhou, Chinese Academy of Agricultural Sciences with‘Kuerlexiangli’pearבGoose’pear. When the fruit matures, the peel turns green yellow, 2/3 of the sunny fruit surface of the fruit is bright-red, the flesh is white, crisp, juicy and sweet with high quality. It is one of the main commercial pears on the fruit market. However, during the middle and later period of storage (after the Spring Festival) or the shelf life after storage, the peel of the pear is easy to turn from green to yellow and secrets sugar and greasy substabces. In some storage seasons, problems such as core browning or fruit decay occur, which greatly reduces the commodity value of the fruit and affects the pear industry development to a certain extent. Therefore, it is very important to solve the problem involved in‘Hongxiangsu’pear fruit storage. Under the conditions of fixed O2 volume fraction and different CO2 volume fractions, the‘Hong- xiangsu’pear fruits collected from a 10 years old orchard with first- class management level in Yuncheng Salt Lake area of Shanxi province were used as the samples. In order to reveal the effect of different CO2 volume fraction on the quality and physiological indexes of‘Hongxiangsu’pear fruits during storage and shelf life, the best CO2 volume fraction during controlled atmosphere storage and the sensitivity to CO2 were explored, which provided theoretical basis and technical support for delaying the yellowing of‘Hongxiangsu’pear peel during shelf life.【Methods】With N2, CO2 and air in the cyl- inder served as the gas source and 25 L wide mouth glass bottle (rubber plug seal) as the controlled at- mosphere container, three types of gases were mixed in designed proportions and sent into the glass bot- tle through the CA gas distribution system. The gas flow rate was set as 150 mL · min- 1, the O2 volume fraction was 3%, and CO2 volume fraction was set as 0%, 1%, 3%, 5% and 7%, totaling five treatments plus the control (CK, continuous flow of air). Fruits were stored in cold storage at (0±0.5) °C with 90% relative humidity for 130 d, 200 d and 270 d, and then stored on the shelf at 20 °C for 7 d. The changes including fruit external appearance and internal quality, taste and flavor, respiratory intensity and ethyl- ene release rate, ethanol and acetaldehyde content were compared.【Results】During the shelf life of fruits after cold storage, CK fruits always maintained a high respiration intensity and ethylene release rate. Compared with CK and other three controlled atmosphere treatments, CA-3-1 and CA-3-3 groups had a better inhibitive effect on fruit respiration intensity, as well as mass fraction of ethanol and acetal- dehyde. The higher the volume fraction of CO2, the lower the ethylene release rate. The fresh-keeping effect of each treatment mainly showed in the later stage of storage. When CK and CA-3-0 fruits were stored for 270 d + 20 °C shelf for 7 d, the negative value and b value of the peel color index were rela- tively high, h° was relatively low, L value decreased significantly, corresponding to the yellow or yel- low green peel, and some fruits appeared browning. It was preliminarily determined that the the fruit se- nescence caused the browning. CA-3-1, CA-3-3, CA-3-5 and CA-3-7 could delay the peel turning yel- low (the corresponding b value was relatively low), keep the green color (a value is low, h ° is high) and brightness of peel was improved (L value is high), thus delaying the decrease of fruit hardness and solu- ble solid content. The sensory evaluation results showed that there was no significant difference in the sensory scores among different treatments (including CK) after 130 days storage and 7 days shelf life, but the sensory scores of the other four modified atmosphere treatments were significantly higher than those of CK and CA-3-0 at 200 d + 7 d. CA-3-5 and CA-3-7 treatments were significantly higher those with 270 d + 7 d storage. Although the two modified atmosphere treatments could maintain the appear- ance color and fruit hardness better, but the flesh of some fruits had a little of peculiar smell. For sake of overall evaluation, the sensory scores of CA-3-1 and CA-3-3 were higher.【Conclusion】In the range from zero to 7% CO2, the‘Hongxiangsu’pear fruit was stored for 270 d without core browning and pulp damage caused by CO2, but only showed slightly peculiar smell with the fruits treated with 5% CO2 and 7% CO2. Comprehensive analysis showed that 3% O2 combined with 1% or 3% CO2 were the best parameters for long-term storage (≥200 d) for‘Hongxiangsu’fruit, which could not only keep good external appearance, internal quality and flavor, but also delay the fruit senescence.