Effects of different fruit bags on the peel browning of Ruixue apple

Abstract: 【Objective】The study aimed to reveal the effects of different fruit bags on the browning and antioxidant substances of the peel of Ruixue apple (Malus × domestica Ruixue), in order to mitigate the browning of the peel and enhance the economic benefits and market competitiveness of Ruixue apple in the Longdong region.【Methods】Six-year-old Ruixue apple trees were used as experimental materials. The single-layer bags with green dot (G1), the single-layer bag with green polka dot and exposed white rim (G2), the white single-layer bags (G3) were used 84 days after blooming for bagging treatment. The ordinary double-layer bags (control) were used as control. The fruit peel browning rate and browning index were counted 189 days after blooming. Meanwhile, a temperature and humidity probe was used to measure the temperature inside the different fruit bags from 84 d to 189 d after flowering, and the antioxidant substances and antioxidant enzyme activities of the Ruixue fruit peel were measured.【Results】 Based on the statistics of peel browning rate and browning index of the fruits with different bags during the harvest period, it was observed that G1, G2, and G3 treatments resulted in a significant reduction of peel browning rate in Ruixue fruit in comparison with the control, the peel browning rate of Ruixue decreased from 78.6% to 7.0%, 6.0%, and 1.4%, respectively. The browning indices of the 1 to 4 degree browning of the control peel was the highest. Compared with control, G1 and G2 exhibited 1 and 2 de-gree peel browning, while G3 only exhibited 1 degree peel browning with a browning index of 1.4%. Compared with the control, G1 and G2 delayed the occurrence of browning by 11 days and G3 delayed by 13 days. The daily average temperature of the fruits inside the different fruit bags showed a downward trend, and the downward trend was consistent in all the fruits with different treatments. Among them, the differences in daily average low temperature and daily average temperature among the fruits with different fruit bags were not significant, while the effective accumulated temperature of the control was the lowest. Compared with the control, the effective accumulated temperature of G3 increased by 36.9 ℃. An illuminometer was used to measure the transmittance of different fruit bags. The Transmittance of the control was zero, and the transmittance of G1 and G3 were 36.6% and 51.2%, respectively, while the transmittance of G2 in the exposed area of the bags was 51.2%, and the transmittance of G2 in the other area of the bags was 32%. The Vitamin C content of G3 was significantly higher than those of the other treatments. Compared with the control, the total phenolic content of G1, G2, and G3 significantly increased by 38.9% , 42.4% , and 57.7% , respectively; The flavonoids of G3 was significantly higher than those of the other treatments, while the flavonoids of G2 was 34.0% higher that of the control; the flavonoids of G1 was 21.0% higher that of the control, while there was no significant difference in the total flavonoid content between G2 and G3. Compared with the control, G3 treatment significantly reduced the content of MDA in the peel, while G2 and G3 treatments significantly reduced the content of O2 in the peel. There were significant differences in antioxidant enzyme activity among the fruits with different fruit bags. The SOD activity of G3 was significantly higher than those of the other treatments. The POD activity of G3 was the highest, followed by G2, G1. The CAT activity of G1 and G3 was significantly higher than that of G1. The PPO activity of the control and G1 was significantly higher than those of the other treatments. The comprehensive evaluation indexes of the four fruit bags on the browning and antioxidant quality indicators of Ruixue apple peel were ranked as follows: G3＞ G2＞G1＞control, according to the above indicators and the comprehensive evaluation of the membership function.【Conclusion】The antioxidant content and antioxidant enzyme activity of Ruixue apple peel were strongly influenced by the type of fruit bags used during cultivation. G3 fruit bag was particularly effective in increasing the antioxidant content and antioxidant enzyme activity, and decreasing both the browning rate and the degree of peel browning of Ruixue apples. The use of G3 fruit bag would be a promising strategy to mitigate the peel browning and maintain the nutritional quality of Ruixue apples.