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Abstract ［Objectives］ The effects of bag types on the appearance and internal quality of red Massh grapefruit were studied.
［Methods］Outer-yellow inner-black double-layer pomelo special paper bags, white single-layer paper bags, yellow plastic film bags, and red plastic film bags were used to cover the fruit of red Massh grapefruit. With the fruit free of bagging as a control, the effects of fruit bags with different materials were compared.
［Results］ The four kinds of fruit bag treatments effectively reduced pests and diseases, and increased the good fruit rate, and the effects of paper bag treatments were better than those of film bags. The outer-yellow inner-black double-layer pomelo special paper bags had good air permeability and were easy to operate. The bagged fruit had a smooth and beautiful surface and showed a unique uniform pink color after removing the bags. The fruit had moderate sour and sweet flavor and good overall benefits. It is worthy of popularization and application.
［Conclusions］Fruit bagging has good economic benefits, and it is recommended to use the outer-yellow inner-black double-layer pomelo special paper bags.
Key words Red Massh grapefruit; Bagging type; Fruit appearance; Quality
Received: December 23, 2020 Accepted: February 17, 2021
Supported by 2015 Guangxi Higher Institutions Scientific Research Project (KY2015YB428); Professional (Academic) Leaders and Young and Middle-aged Backbone Teachers (GNZY［2016］33).
Jie YANG (1977-), female, associate professor, master, devoted to research about fruit tree cultivation.
*Corresponding author. Haiyan GAN, E-mail: haiyan68098@163.com.
Red Massh grapefruit is a branch variation of Thompson grapefruit, which was introduced into Nanning, Guangxi in 2005［1］. This variety adapts to the climate of Nanning, Guangxi, and has excellent performance. It was approved by the Guangxi Crop Variety Approval Committee in August 2016 and named "red Massh grapefruit" (Guishenguo 2016016). It has broad market promotion prospects.
The flesh of red Massh grapefruit is pink, soft, moderately sweet and bitter, unique in flavor and rich in nutrition. In Nanning, Guangxi, the fruit development period of red Massh grapefruit is in the season of high temperature and high humidity. There are many diseases such as Phyllocoptruta oleivora and canker on the peel, and the diseases and insect pests are more serious, which reduces the fruit quality and restricts the improvement of fruit farmers economic benefits, so appropriate technical measures should be taken to protect the fruit in production. Bagging plays an important role in protecting fruit skin, improving fruit appearance quality, reducing fruit pesticide residues, and improving economic benefits［1-3］, and has been widely used in fruit tree production［4-6］. In recent years, after small-scale introduction of fruit bagging technique, it has been found that different fruit bag types have affected the color of red Massh grapefruit. In order to explore the types and techniques of fruit bags suitable for red Massh grapefruit, this study was conducted, aiming to provide a theory for the high-quality and high-yield cultivation technology of red Massh grapefruit. Materials and Methods
Materials and agents
Red Massh grapefruit (using sour grapefruit as rootstocks) of 12 years old planted in Yingquan Agricultural Grapefruit Plantation, Dongjiang Village, Fucheng Town, Wuming District, Nanning City, Guangxi, was selected.
The bagging materials were commercially available double-layer waterproof pomelo bags with a black inner layer and a yellow outer layer (the specification of which was 17 cm×19 cm), commercially available white single-layer paper bags (the specification of which 20 cm×30 cm), and commercially available yellow and red plastic film bags (both of which the specification was 30 cm×35 cm).
The agents were carbendazim wettable powder produced by DuPont of the United States and Abamectin EC produced by Chengdu Lvjin Biotechnology Co., Ltd.
Experimental methods
The experiment was set with four treatments using different types of fruit bags, i.e., the outer-yellow inner-black double-layer waterproof grapefruit paper bags, the white single-layer paper bags, the yellow plastic film bags, and the red plastic film bags, respectively, and the non-bagging treatment was set as a control. After the second physiological fruit drop was stable in June 2018, small fruits, diseased fruits, and deformed fruits were removed in 2-3 times. After thinning the fruits, 5 grapefruit trees with relatively uniform growth were selected, and 5 pieces of fruit with uniform sizes were selected in 5 directions in the south, east, north and north sides from each tree for bagging, respectively, that is to say 25 grapefruits were selected from each grapefruit tree for each bagging treatment. The fruit free of bagging was used as the control. One day before bagging, carbendazim and abamectin were sprayed on the tree body, branches, leaf surface, leaf back and fruit surface of the red Massh grapefruit trees thoroughly and evenly in the whole garden for pest control, and the bagging experiment was started immediately after the liquid was dried. Fruit was picked on November 3, and 100 pieces of fruit were randomly selected from each treatment to calculate the good fruit rate, and 10 ripe grapefruits fruit of uniform size were randomly selected for each treatment and were transported back to the laboratory in time. The appearance of fruit such as color and brightness was observed; the single-fruit weight, fruit longitudinal diameter, transverse diameter and peel thickness were determined; and for the internal quality indexes including the soluble solid content, edible rate, titratable acid content, total sugar content and vitamin C content and other fruits, each index was determined repeatedly for 3 times. Determination methods
The weight of the fruit was measured with an electronic balance; the thickness of the peel and the longitudinal and transverse diameters of the fruit were measured with a vernier caliper; the content of soluble solids was determined with a hand-held saccharimeter; the titratable acid content was determined in citric acid with sodium hydroxide titration method［7］; the reducing sugar and total sugar contents were determined by 3,5-dinitrosalicylic acid colorimetric method; the vitamin C content was determined by 2,6-dichlorophenol indophenol sodium titration method［8］; the edible rate was calculated according to Edible rate (%)=(Single fruit juice sac weight/Single fruit weigh)×100; and the good fruit rate was calculated according to Good fruit rate (%)=Normal fruit number/Total fruit number of corresponding treatment×100.
Results and Analysis
Effects of different bagging treatments on fruit diseases and pests
The four kinds of fruit bag treatments increased the good fruit rate of grapefruit, reduced the number of fruits suffered from diseases and pests, and achieved the expected control effect. Compared with the control, the fruit disease and insect rates of the outer-yellow inner-black double-layer paper bags, white single-layer plastic film bags, yellow plastic film bags and red plastic film bags were reduced by 30, 26, 21 and 21 percentage points, respectively, and the good fruit rates were 95%, 91%, 86% and 86%, respectively, indicating that various types of bagging treatments had good effects in protecting fruits and preventing diseases and pests. Among them, the outer-yellow inner-black double-layer paper bags showed the best control effect, followed by the white single-layer plastic film bags, while the yellow plastic film bags and red plastic film bags had poor control effects (Table 1). According to the investigation, the damaged parts of the bagged grapefruit fruit were the skin and outer flesh, while the damaged parts of the control fruit were as deep as the inner flesh and even rotten fruit and fruit dropping appeared. It can be seen that bagging during the development of grapefruit effectively reduced pests and diseases, and increased the rate of good fruit, and the effect of paper bag treatment was better than that of film bags.
Effects of different bagging treatments on fruit appearance quality
Compared with the control, all the four bag treatments improved the appearance quality of the fruit. Specifically, the fruit with yellow outer and inner black double-layer paper bags had pink peel when ripe, which was uniform in color, fine in oil vacuoles, and was smooth, bright, moist, and the effect was the best, reaching the color standard of superior fruit. The fruit treated with white single-layer paper bags was yellow-green when ripe, and the peel was rather uniform in color, fine in oil bubble, and was rather smooth, so the effect was rather good. For the fruit treated with yellow and red plastic film bags, the peel was yellow-green, not uniform in color, rough in oil vacuoles, dull, and had more P. oleivora and canker spots thereon, and there was no significant difference in fruit appearance between the two. From the perspective of the smoothness of the peel, the bagging treatments were better than the non-bagging control, and the paper bag treatment effect was better than film bags (Table 1). Compared with the control, after bagging, the single fruit weight, longitudinal diameter, transverse diameter and peel thickness of grapefruit all showed a downward trend. The fruit weight, longitudinal diameter and transverse diameter of the fruit did not decrease significantly in the outer-yellow and inner-black double-layer paper bag treatment, but the values of the fruit treated with white single-layer paper bags, red plastic film bags and yellow plastic film bags were particularly reduced, reaching a significant level. The two paper bag treatments were not significantly different in single fruit weight, but were significantly higher than other two film bag treatments. It can be seen that the effects of bagging on the individual fruit quality, fruit longitudinal diameter and fruit transverse diameter of grapefruit fruit had a decreasing trend. Bagging also had the effect of thinning the peel of red Massh grapefruit. The differences between film bag treatments from the control were significant, and the differences caused by the paper bag treatments did not reach a significant level (Table 1). The control showed the highest edible rate, followed by the treatments of the outer-yellow and inner-black double-layer paper bags, white single-layer paper bags, yellow plastic film bags, and red plastic film bags sequentially, but none of them reached a significant level (Table 2).
Based on the above analysis, the outer-yellow inner-black double-layer paper bag treatment caused no significant differences in single fruit weight, fruit longitudinal diameter, transverse diameter, edible rate and other indicators, but better formed the unique pink appearance of red Massh grapefruit peel, improved glossiness, and showed the best peel appearance, followed by white paper bags, and film bags had the worst effect in improving appearance quality.
Effects of different bagging treatments on the internal quality of fruit
Compared with the control, the soluble solid and the total sugar contents in the flesh showed a downward trend after bagging. Specifically, the soluble solid contents of the red plastic film bags and the yellow plastic film bags were less than 10%, and the differences were significant. In particular, the treatments of the outer-yellow inner-black double-layer paper bags and white single-layer paper bags showed the soluble solid contents, respectively of 10.38% and 10.31%, which were both higher than 10%, and were very close to the value of the control at 10.57%. The differences in the total sugar content of the flesh between different bag types were similar to the soluble solid content (Table 2). It can be seen that the fruit maturity of the paper bag treatment was better, but the fruit maturity of the film bag treatments were poor. It can be seen that the fruit maturity of the paper bag treatments was better, but the fruit maturity of the film bag treatments was poor. Titratable acid is one of the important factors affecting fruit flavor quality. Compared with the control, the titratable acid content of the fruit after bagging showed an upward trend. Specifically, the titratable acid content of the fruit treated with the outer-yellow inner-black double-layer paper bags rose up to 0.94 g, followed by white single-layer paper bags, yellow plastic film bags, and red plastic film bags, but the differences in the titratable acid content of the fruit after the treatment with the 4 kinds of fruit bags did not reach a significant level. The ratio of soluble solids to acids is an important index to measure the flavor of the fruit. The ratios of soluble solids to acids of various treatments were close to 11, but the ratios of soluble solids to acids after bagging showed a downward trend. Among them, the values of paper bag treatments only decreased by 0.03%-0.08%, and were very close to the control (Table 2). It can be seen that bagging had little effect on the flavor of the fruit.
Vitamin C
Compared with the control, the vitamin C contents of the treatments of the outer-yellow inner-black double-layer paper bags, white single-layer paper bags, red plastic film bags and yellow plastic film bags decreased by 1.65, 2.67, 3.73 and 4.62 mg/100 g, respectively. Among them, the outer-yellow inner-black double-layer paper bag treatment had the least decrease, which did not reach a significant level, and the next was the white single-layer paper bag, red plastic film bag and yellow plastic film bag treatments, which all reached a significant level. It is consistent with the conclusion that the vitamin C content of fruit decreases after bagging［10-11］.
Conclusions and Discussion
Bagging affects fruit growth and fruit quality by changing the microenvironments of the fruit growth such as light, temperature and humidity［11］. Paper bags of different colors, materials and thicknesses will affect the quality of bagged fruit［12-13］. In the process of fruit development, the double-layer pomelo special waterproof paper bags with a yellow outer layer and a black inner layer selected were not easy to be washed out by rain or bitten by pests, and could be used for a long time with a more secure effect. Meanwhile, the inner-black outer-yellow double-layer paper bags had a certain shading effect, which prevented the synthesis of chlorophyll on the fruit surface, made the fruit surface turn color faster, and could avoid sunburn during high temperature and drought in summer and autumn. When the fruit was mature, the surface of the fruit had a high gloss and presented a unique pink skin color, and the appearance quality was good. The white single-layer paper bags were not as effective as the inner-black outer-yellow double-layer paper bags, and especially when the fruit was ripe, the peel was yellow-green, which might be due to the good light transmission performance of the white paper bags and the normal synthesis of chlorophyll on the fruit surface. The red single-layer film bags and yellow single-layer film bags were not as effective as the inner-black outer-yellow double-layer paper bags and single-layer paper bags, which might be related to environmental factors such as the quality, thickness, and airtightness of the film bags. According to observation, the red and yellow film bags faded due to the sun and rain after a week, and turned into white film bags, and when the fruit was ripe, the peel was yellow-green, and there were no differences in color from the grapefruit in white paper bags and the control without bags. Bagging or not had little effect on the soluble solids, total sugar, titratable acid and edible rate of the fruit, and would not change its appearance, quality and flavor. The bag treatments showed a downward trend in single fruit weight, which is consistent with the research on the decrease of fruit weight performance after bagging［13］. It might be related to factors such as bagging time, bag removal time, fruit bag type, etc., and the specific reasons need to be further studied.
Fruit bagging had good economic benefits, and could effectively improve its economic benefits. According to calculations, the bagging cost of each inner-black outer-yellow paper bag was about 0.18 yuan, and about 60 000 fruit bags were needed per hectare, so the total cost of bagging was about 10 800 yuan. The fruit loss after bagging could be reduced by about 40%, about 15 000 kg, which meant that according to the market price, the economic loss could be saved by about 30 000 yuan. After deducting the cost of fruit bags and bagging labor costs, the income was increased by about 15 000 yuan/hm2, indicating significant economic benefits. Considering the effects of the bagging material on the internal and external quality of the red Massh grapefruit fruit and the cost of use, it is recommended to use the outer-yellow inner-black double-layer pomelo special paper bags with the advantages of ventilation, water proofing, and insect prevention in production.
References
［1］ YANG J, WANG B, YANG CP, et al. Variety characteristics and cultivation techniques of red marsh grapefruit［J］. Chinese Journal of Tropical Agriculture, 2016, 36(5): 17-20. (in Chinese)
［2］ YANG J, WANG B, YANG CP, et al. Breeding of new grapefruit variety "red Massh grapefruit"［J］. Journal of Fruit Science, 2017, 34(5): 646-648. (in Chinese)
［3］ YANG J, WANG B, XU LM, et al. Introduction performance of four grapefruit varieties in Nanning, Guangxi［J］. South China Fruits, 2016, 45(3): 65-67. (in Chinese)
［4］ FENG FM, ZENG LP, JIANG CD, et al. Effects of bagging on fruit quality of ‘Malaysia’ sweet pummelo［J］. Science and Technology of Food Industry, 2017, 38(17): 264-267. (in Chinese)
［5］ BAI ZL, LI SJ, PENG DL, et al. Summary of research on citrus bagging technology［J］. South China Fruits, 2014, 43(3): 57-59.
［6］ LU XH, SUN DQ, WU QS, et al. Effects of bagging with different paper bags on fruit growth and quality of pineapple ［J］. Journal of Fruit Science, 2011, 28(6): 1086-1089. (in Chinese) ［7］ GB/T 8210-2011. Fresh citrus fruit inspection method［S］. Beijing: China Standards Press, 2011. (in Chinese)
［8］ GB/T 6195-1986. Determination of vitamin C in vegetables and fruits (2,6-dichloro-indophenol titration method)［S］. Beijing: Ministry of Agriculture, Liverstock and Fisheries of the Peoples Republic of China, 1986. (in Chinese)
［9］ WANG YG, CHEN DM, LIN HF, et al. The efficacy test of 20% thiodiazole-copper suspension concentrate in preventing and treating citrus canker［J］. Travel to Watch Industry, 2002, 43 (4): 24-25. (in Chinese)
［10］ LIN YJ, LIN QH, LU YQ, et al. Effects of bag types on the appearance and quality of "Huangjinmiyou" fruit［J］. South China Fruits, 2016, 45(3): 68-69. (in Chinese)
［11］ TANG WS. Impact of quality of fruit on different treatments of cover bags of Citrus grandis var Jiangyong［D］. Changsha: Hunan Agricultural University, 2003. (in Chinese)
［12］ ZHANG JY. Effects of fruit bagging treatments on microenvironment and fruit quality of loquat［D］. Fuzhou: Fujian Agriculture and Forestry University, 2017. (in Chinese)
［13］ WU ST. Effects of bagging on color change and quality of pummelo fruit［D］. Fuzhou: Fujian Agriculture and Forestry University, 2019. (in Chinese)
［14］ WANG W, DENG L, HE SL, et al. Effect of different bagging time on the fruit development and internal quality of Zaoxiang hybrid citrus［J］. South China Fruits, 2007(3): 1-3, 22. (in Chinese)
［Methods］Outer-yellow inner-black double-layer pomelo special paper bags, white single-layer paper bags, yellow plastic film bags, and red plastic film bags were used to cover the fruit of red Massh grapefruit. With the fruit free of bagging as a control, the effects of fruit bags with different materials were compared.
［Results］ The four kinds of fruit bag treatments effectively reduced pests and diseases, and increased the good fruit rate, and the effects of paper bag treatments were better than those of film bags. The outer-yellow inner-black double-layer pomelo special paper bags had good air permeability and were easy to operate. The bagged fruit had a smooth and beautiful surface and showed a unique uniform pink color after removing the bags. The fruit had moderate sour and sweet flavor and good overall benefits. It is worthy of popularization and application.
［Conclusions］Fruit bagging has good economic benefits, and it is recommended to use the outer-yellow inner-black double-layer pomelo special paper bags.
Key words Red Massh grapefruit; Bagging type; Fruit appearance; Quality
Received: December 23, 2020 Accepted: February 17, 2021
Supported by 2015 Guangxi Higher Institutions Scientific Research Project (KY2015YB428); Professional (Academic) Leaders and Young and Middle-aged Backbone Teachers (GNZY［2016］33).
Jie YANG (1977-), female, associate professor, master, devoted to research about fruit tree cultivation.
*Corresponding author. Haiyan GAN, E-mail: haiyan68098@163.com.
Red Massh grapefruit is a branch variation of Thompson grapefruit, which was introduced into Nanning, Guangxi in 2005［1］. This variety adapts to the climate of Nanning, Guangxi, and has excellent performance. It was approved by the Guangxi Crop Variety Approval Committee in August 2016 and named "red Massh grapefruit" (Guishenguo 2016016). It has broad market promotion prospects.
The flesh of red Massh grapefruit is pink, soft, moderately sweet and bitter, unique in flavor and rich in nutrition. In Nanning, Guangxi, the fruit development period of red Massh grapefruit is in the season of high temperature and high humidity. There are many diseases such as Phyllocoptruta oleivora and canker on the peel, and the diseases and insect pests are more serious, which reduces the fruit quality and restricts the improvement of fruit farmers economic benefits, so appropriate technical measures should be taken to protect the fruit in production. Bagging plays an important role in protecting fruit skin, improving fruit appearance quality, reducing fruit pesticide residues, and improving economic benefits［1-3］, and has been widely used in fruit tree production［4-6］. In recent years, after small-scale introduction of fruit bagging technique, it has been found that different fruit bag types have affected the color of red Massh grapefruit. In order to explore the types and techniques of fruit bags suitable for red Massh grapefruit, this study was conducted, aiming to provide a theory for the high-quality and high-yield cultivation technology of red Massh grapefruit. Materials and Methods
Materials and agents
Red Massh grapefruit (using sour grapefruit as rootstocks) of 12 years old planted in Yingquan Agricultural Grapefruit Plantation, Dongjiang Village, Fucheng Town, Wuming District, Nanning City, Guangxi, was selected.
The bagging materials were commercially available double-layer waterproof pomelo bags with a black inner layer and a yellow outer layer (the specification of which was 17 cm×19 cm), commercially available white single-layer paper bags (the specification of which 20 cm×30 cm), and commercially available yellow and red plastic film bags (both of which the specification was 30 cm×35 cm).
The agents were carbendazim wettable powder produced by DuPont of the United States and Abamectin EC produced by Chengdu Lvjin Biotechnology Co., Ltd.
Experimental methods
The experiment was set with four treatments using different types of fruit bags, i.e., the outer-yellow inner-black double-layer waterproof grapefruit paper bags, the white single-layer paper bags, the yellow plastic film bags, and the red plastic film bags, respectively, and the non-bagging treatment was set as a control. After the second physiological fruit drop was stable in June 2018, small fruits, diseased fruits, and deformed fruits were removed in 2-3 times. After thinning the fruits, 5 grapefruit trees with relatively uniform growth were selected, and 5 pieces of fruit with uniform sizes were selected in 5 directions in the south, east, north and north sides from each tree for bagging, respectively, that is to say 25 grapefruits were selected from each grapefruit tree for each bagging treatment. The fruit free of bagging was used as the control. One day before bagging, carbendazim and abamectin were sprayed on the tree body, branches, leaf surface, leaf back and fruit surface of the red Massh grapefruit trees thoroughly and evenly in the whole garden for pest control, and the bagging experiment was started immediately after the liquid was dried. Fruit was picked on November 3, and 100 pieces of fruit were randomly selected from each treatment to calculate the good fruit rate, and 10 ripe grapefruits fruit of uniform size were randomly selected for each treatment and were transported back to the laboratory in time. The appearance of fruit such as color and brightness was observed; the single-fruit weight, fruit longitudinal diameter, transverse diameter and peel thickness were determined; and for the internal quality indexes including the soluble solid content, edible rate, titratable acid content, total sugar content and vitamin C content and other fruits, each index was determined repeatedly for 3 times. Determination methods
The weight of the fruit was measured with an electronic balance; the thickness of the peel and the longitudinal and transverse diameters of the fruit were measured with a vernier caliper; the content of soluble solids was determined with a hand-held saccharimeter; the titratable acid content was determined in citric acid with sodium hydroxide titration method［7］; the reducing sugar and total sugar contents were determined by 3,5-dinitrosalicylic acid colorimetric method; the vitamin C content was determined by 2,6-dichlorophenol indophenol sodium titration method［8］; the edible rate was calculated according to Edible rate (%)=(Single fruit juice sac weight/Single fruit weigh)×100; and the good fruit rate was calculated according to Good fruit rate (%)=Normal fruit number/Total fruit number of corresponding treatment×100.
Results and Analysis
Effects of different bagging treatments on fruit diseases and pests
The four kinds of fruit bag treatments increased the good fruit rate of grapefruit, reduced the number of fruits suffered from diseases and pests, and achieved the expected control effect. Compared with the control, the fruit disease and insect rates of the outer-yellow inner-black double-layer paper bags, white single-layer plastic film bags, yellow plastic film bags and red plastic film bags were reduced by 30, 26, 21 and 21 percentage points, respectively, and the good fruit rates were 95%, 91%, 86% and 86%, respectively, indicating that various types of bagging treatments had good effects in protecting fruits and preventing diseases and pests. Among them, the outer-yellow inner-black double-layer paper bags showed the best control effect, followed by the white single-layer plastic film bags, while the yellow plastic film bags and red plastic film bags had poor control effects (Table 1). According to the investigation, the damaged parts of the bagged grapefruit fruit were the skin and outer flesh, while the damaged parts of the control fruit were as deep as the inner flesh and even rotten fruit and fruit dropping appeared. It can be seen that bagging during the development of grapefruit effectively reduced pests and diseases, and increased the rate of good fruit, and the effect of paper bag treatment was better than that of film bags.
Effects of different bagging treatments on fruit appearance quality
Compared with the control, all the four bag treatments improved the appearance quality of the fruit. Specifically, the fruit with yellow outer and inner black double-layer paper bags had pink peel when ripe, which was uniform in color, fine in oil vacuoles, and was smooth, bright, moist, and the effect was the best, reaching the color standard of superior fruit. The fruit treated with white single-layer paper bags was yellow-green when ripe, and the peel was rather uniform in color, fine in oil bubble, and was rather smooth, so the effect was rather good. For the fruit treated with yellow and red plastic film bags, the peel was yellow-green, not uniform in color, rough in oil vacuoles, dull, and had more P. oleivora and canker spots thereon, and there was no significant difference in fruit appearance between the two. From the perspective of the smoothness of the peel, the bagging treatments were better than the non-bagging control, and the paper bag treatment effect was better than film bags (Table 1). Compared with the control, after bagging, the single fruit weight, longitudinal diameter, transverse diameter and peel thickness of grapefruit all showed a downward trend. The fruit weight, longitudinal diameter and transverse diameter of the fruit did not decrease significantly in the outer-yellow and inner-black double-layer paper bag treatment, but the values of the fruit treated with white single-layer paper bags, red plastic film bags and yellow plastic film bags were particularly reduced, reaching a significant level. The two paper bag treatments were not significantly different in single fruit weight, but were significantly higher than other two film bag treatments. It can be seen that the effects of bagging on the individual fruit quality, fruit longitudinal diameter and fruit transverse diameter of grapefruit fruit had a decreasing trend. Bagging also had the effect of thinning the peel of red Massh grapefruit. The differences between film bag treatments from the control were significant, and the differences caused by the paper bag treatments did not reach a significant level (Table 1). The control showed the highest edible rate, followed by the treatments of the outer-yellow and inner-black double-layer paper bags, white single-layer paper bags, yellow plastic film bags, and red plastic film bags sequentially, but none of them reached a significant level (Table 2).
Based on the above analysis, the outer-yellow inner-black double-layer paper bag treatment caused no significant differences in single fruit weight, fruit longitudinal diameter, transverse diameter, edible rate and other indicators, but better formed the unique pink appearance of red Massh grapefruit peel, improved glossiness, and showed the best peel appearance, followed by white paper bags, and film bags had the worst effect in improving appearance quality.
Effects of different bagging treatments on the internal quality of fruit
Compared with the control, the soluble solid and the total sugar contents in the flesh showed a downward trend after bagging. Specifically, the soluble solid contents of the red plastic film bags and the yellow plastic film bags were less than 10%, and the differences were significant. In particular, the treatments of the outer-yellow inner-black double-layer paper bags and white single-layer paper bags showed the soluble solid contents, respectively of 10.38% and 10.31%, which were both higher than 10%, and were very close to the value of the control at 10.57%. The differences in the total sugar content of the flesh between different bag types were similar to the soluble solid content (Table 2). It can be seen that the fruit maturity of the paper bag treatment was better, but the fruit maturity of the film bag treatments were poor. It can be seen that the fruit maturity of the paper bag treatments was better, but the fruit maturity of the film bag treatments was poor. Titratable acid is one of the important factors affecting fruit flavor quality. Compared with the control, the titratable acid content of the fruit after bagging showed an upward trend. Specifically, the titratable acid content of the fruit treated with the outer-yellow inner-black double-layer paper bags rose up to 0.94 g, followed by white single-layer paper bags, yellow plastic film bags, and red plastic film bags, but the differences in the titratable acid content of the fruit after the treatment with the 4 kinds of fruit bags did not reach a significant level. The ratio of soluble solids to acids is an important index to measure the flavor of the fruit. The ratios of soluble solids to acids of various treatments were close to 11, but the ratios of soluble solids to acids after bagging showed a downward trend. Among them, the values of paper bag treatments only decreased by 0.03%-0.08%, and were very close to the control (Table 2). It can be seen that bagging had little effect on the flavor of the fruit.
Vitamin C
Compared with the control, the vitamin C contents of the treatments of the outer-yellow inner-black double-layer paper bags, white single-layer paper bags, red plastic film bags and yellow plastic film bags decreased by 1.65, 2.67, 3.73 and 4.62 mg/100 g, respectively. Among them, the outer-yellow inner-black double-layer paper bag treatment had the least decrease, which did not reach a significant level, and the next was the white single-layer paper bag, red plastic film bag and yellow plastic film bag treatments, which all reached a significant level. It is consistent with the conclusion that the vitamin C content of fruit decreases after bagging［10-11］.
Conclusions and Discussion
Bagging affects fruit growth and fruit quality by changing the microenvironments of the fruit growth such as light, temperature and humidity［11］. Paper bags of different colors, materials and thicknesses will affect the quality of bagged fruit［12-13］. In the process of fruit development, the double-layer pomelo special waterproof paper bags with a yellow outer layer and a black inner layer selected were not easy to be washed out by rain or bitten by pests, and could be used for a long time with a more secure effect. Meanwhile, the inner-black outer-yellow double-layer paper bags had a certain shading effect, which prevented the synthesis of chlorophyll on the fruit surface, made the fruit surface turn color faster, and could avoid sunburn during high temperature and drought in summer and autumn. When the fruit was mature, the surface of the fruit had a high gloss and presented a unique pink skin color, and the appearance quality was good. The white single-layer paper bags were not as effective as the inner-black outer-yellow double-layer paper bags, and especially when the fruit was ripe, the peel was yellow-green, which might be due to the good light transmission performance of the white paper bags and the normal synthesis of chlorophyll on the fruit surface. The red single-layer film bags and yellow single-layer film bags were not as effective as the inner-black outer-yellow double-layer paper bags and single-layer paper bags, which might be related to environmental factors such as the quality, thickness, and airtightness of the film bags. According to observation, the red and yellow film bags faded due to the sun and rain after a week, and turned into white film bags, and when the fruit was ripe, the peel was yellow-green, and there were no differences in color from the grapefruit in white paper bags and the control without bags. Bagging or not had little effect on the soluble solids, total sugar, titratable acid and edible rate of the fruit, and would not change its appearance, quality and flavor. The bag treatments showed a downward trend in single fruit weight, which is consistent with the research on the decrease of fruit weight performance after bagging［13］. It might be related to factors such as bagging time, bag removal time, fruit bag type, etc., and the specific reasons need to be further studied.
Fruit bagging had good economic benefits, and could effectively improve its economic benefits. According to calculations, the bagging cost of each inner-black outer-yellow paper bag was about 0.18 yuan, and about 60 000 fruit bags were needed per hectare, so the total cost of bagging was about 10 800 yuan. The fruit loss after bagging could be reduced by about 40%, about 15 000 kg, which meant that according to the market price, the economic loss could be saved by about 30 000 yuan. After deducting the cost of fruit bags and bagging labor costs, the income was increased by about 15 000 yuan/hm2, indicating significant economic benefits. Considering the effects of the bagging material on the internal and external quality of the red Massh grapefruit fruit and the cost of use, it is recommended to use the outer-yellow inner-black double-layer pomelo special paper bags with the advantages of ventilation, water proofing, and insect prevention in production.
References
［1］ YANG J, WANG B, YANG CP, et al. Variety characteristics and cultivation techniques of red marsh grapefruit［J］. Chinese Journal of Tropical Agriculture, 2016, 36(5): 17-20. (in Chinese)
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