Path analysis of the effect of 1-MCP on the flesh softening and browning in Lingwuchangzao jujube during storage

Abstract: 【Objective】Lingwuchangzao jujube is an excellent and characteristics table jujube variety in Ningxia. It is rich in vitamin C, amino acids, minerals and other nutrients. However, it is prone to dehy- dration, softening, browning and alcoholization as well as nutrition loss at room temperature after har- vest, which results in the loss of edible value and commercial value. It is of great significance to clarify the mechanisms of softening and browning of Lingwuchangzao jujube fruit for developing appropriate preservation technology to maintain fruit quality during storage and transportation. 1-MCP can effec- tively maintain the storage quality of jujube fruit, but there is no clear conclusion about the regulation of 1-MCP on the key metabolites involved in the softening and browning process of Lingwuchangzao jujube fruit. In order to clarify the physiological mechanism of postharvest browning and softening of Lingwuchangzao jujube and find out proper storage technology, the effects of 1-MCP and different stor- age temperatures on fruit softening and browning in this cultivar were studied.【Methods】Lingwuchang-zao jujube was fumigated with 1-MCP, and then stored at room temperature and cold temperature. Four treatment groups were included in this study including room temperature control group (RT-CK), room temperature 1-MCP treated group (RT-MCP), cold temperature control group (CT-CK) and cold temper-ature 1-MCP treated group (RT-MCP). Changes in flesh firmness, browning degree, and the contents of cell wall pectin, soluble sugar components, chlorophylls, total phenols and other relatedcomponents during storage were determined. The effects of 1-MCP treatment and temperature on the quality indexes of Lingwuchangzao jujube were analyzed. The key substances affecting flesh softening and browning and the direct and indirect effects on Lingwuchangzao jujube were investigated by correlation analysis,stepwise regression and path analysis.【Results】The storage life of Lingwuchangzao jujube at room temperature was significantly shorter than that at cold temperature. The fruit in the room temperature groups rotted and deteriorated on the 10th day, while the storage life of Lingwuchangzao jujube was 56 days at cold temperature, and the 1-MCP treatment extended the storage period to 71 days. During the whole storage at cold temperature, the firmness of Lingwuchangzao jujube treated with 1-MCP was higher than that of the control group, which indicated that 1-MCP could delay the softening of Ling- wuchangzao jujube. The absorbance of 420 nm (A420) gradually increased as the browning degree of the fruit increased with the extension of storage. The A420 values of jujube fruit treated with 1-MCP were lower than those of CK group, which indicated that 1-MCP could effectively inhibit the occur-rence of browning. The CSP content in fruit treated with 1-MCP in cold temperature group was lower than that of the control group after 15 days of storage and the increase in WSP content was delayed by 15-29 days, indicating that 1-MCP could inhibit the pectin degradation in Lingwuchangzao jujube under cold temperature condition and thus delay fruit softening. The sucrose content in 1-MCP treated jujube fruit was higher than that of control group (p ＜ 0.05) in 15-29 days and on 56 th days of cold tempera-ture storage, and the treatment delayed the increase of glucose and fructose contents after 45 days, indi-cating that 1-MCP could inhibit the sucrose hydrolysis. Under room temperature, the contents of chloro- phyll a, chlorophyll b and total chlorophylls decreased significantly. 1-MCP significantly inhibited the decreases in chlorophyll a, chlorophyll b and total chlorophyll contents on 22 th days at cold temperature.The total phenol content and DPPH scavenging power slightly increased in the early stage of storage and then decreased continuously. On the 56 th day of storage, the total phenol content in fruit treated with 1-MCP was significantly higher than that of the control group, and the DPPH scavenging capacity in 1- MCP treatment group was significantly higher than that of the control group after 15 days of storage (p ＜ 0.05), indicating that 1-MCP could effectively delay the decrease in antioxidant component under cold temperature. By calculating and comparing the decision coefficients, it was found that the main de-cision variables affecting flesh firmness were total phenol, sucrose, fructose and chlorophyll b in CT-CK, CT-MCP, RT-CK and RT-MCP, respectively. The main decision factors affecting flesh browning de- gree of these 4 groups were glucose, glucose, fructose and SSP, respectively. The contents of sucrose,glucose, fructose and chlorophyll b all entered the multiple regression models of fruit firmness and browning degree as dependent variables, which had positive or negative effects. Soluble sugar content showed different positive or negative effects on firmness and browning degree, respectively, directly or indirectly.【Conclusion】The contents of sucrose and glucose were the important physiochemical param- eters affecting the flesh firmness and browning degree of Lingwuchangzao jujube treated by 1-MCP and stored at cold temperature. 1-MCP combined with cold temperature could maintain the soluble sug-ar contents in Lingwuchangzao jujube, delay softening and browning, and prolong the storage time.