- Email: [email protected]
Control of postharvest green and blue molds of citrus fruit by application of sodium dehydroacetate
Postharvest Biology and Technology 113 (2016) 17–19
Contents lists available at ScienceDirect
Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Short communication
Control of postharvest green and blue molds of citrus fruit by application of sodium dehydroacetate Xiaofang Duan, Guoxing Jing, Feng Fan, Nengguo Tao* School of Chemical Engineering, Xiangtan University, Xiangtan 411105, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 26 August 2015 Received in revised form 23 October 2015 Accepted 26 October 2015 Available online xxx
Sodium dehydroacetate (SD), a common food preservative, was evaluated against Penicillium digitatum and Penicillium italicum through in vivo and in vitro experiments. SD dramatically inhibited the mycelial growths of P. digitatum and P. italicum, with a minimum inhibitory concentration (MIC) and a minimum fungicidal concentration (MFC) of 0.20 and 0.40 g/L, respectively. In vivo tests demonstrated that various SD concentrations (2, 4, and 8 MFC) significantly reduced the incidence of green and blue molds up to 3 and 5 d at 25 2 C, respectively. As storage time was prolonged, 4 and 8 MFC treatments still drastically inhibited fruit decay caused by P. digitatum and P. italicum. Meanwhile, SD significantly reduced the weight loss rate of citrus fruit during storage, but had minor effect on coloration index, firmness, total soluble solids, pH, and vitamin C content. These data suggested that SD can be used as a good alternative to conventional fungicides in controlling green and blue molds in citrus fruit. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Citrus Sodium dehydroacetate Penicillium digitatum P. italicum Fruit quality
1. Introduction Green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively, are the most economically important postharvest diseases of citrus fruit in all production areas (Regnier et al., 2014). Currently, both diseases are primarily controlled by applying synthetic fungicides such as carbendazim, imazalil, thiabendazole, sodium orthophenyl phenate, fludioxonil or pyrimethanil that were permitted by different countries (Talibi et al., 2014; Shao et al., 2015). Alternative methods are needed because of concerns about environmental contamination and human health risks raised by fungicide residues. Furthermore, the widespread use of these compounds in commercial packing houses has led to the proliferation of resistant strains of the pathogens (Palou et al., 2008). Recently, many salts serving as commercial food additives, such as sodium carbonate, sodium bicarbonate, sodium benzoate, sodium propionate, have been evaluated their corresponding efficacies in controlling pathogens that infect citrus, peach, apple, and grape fruit (Droby et al., 2003; Nigro et al., 2006; Smilanick et al., 2008). Palou et al. (2002) reported that potassium sorbate (0.20 M), sodium benzoate (0.20 M), and ammonium molybdate (1.00 mM) could effectively control P. digitatum- and P. italicum-induced postharvest decay of citrus fruit. In another
* Corresponding author. Fax: +86 731 58293284 E-mail address: [email protected] (N. Tao). http://dx.doi.org/10.1016/j.postharvbio.2015.10.015 0925-5214/ ã 2015 Elsevier B.V. All rights reserved.
study, 3% (w/v) sodium carbonate and sodium bicarbonate were found to totally reduce the incidence of green mold on clementines and oranges (Youssef et al., 2014). Sodium dehydroacetate (SD) is a safe food preservative widely used in noodles, seafood, preserves, beverage, and also in controlling postharvest fungal decay of fruit and vegetables (Joseph and Aworh, 1992; Ni et al., 2010). However, information on the effect of SD on postharvest diseases and fruit quality of citrus is lacking. Therefore, in this study, we aimed to evaluate the antifungal activity of SD against P. digitatum and P. italicum, and to determine the influences of SD on the incidence of green and blue molds in citrus, as well as on the fruit quality parameters, such as weight loss rate, coloration index, firmness, pH, total soluble solids (TSS), and vitamin C (Vc) content. 2. Materials and methods Mature fruits of Ponkan (Citrus reticulata Blanco), one of the most important commercial tangerines extensively cultivated in China, were harvested on 14 December 2014 from a local orchard near Xiangtan University, Xiangtan, China. Defect-free fruits of uniform size and color were selected as experimental materials. P. digitatum and P. italicum were isolated from infected citrus fruit and maintained on potato dextrose agar (PDA). SD (dehydroacetic acid sodium salt, 99%) was obtained from Crystal Pure Biochemical Technology Co., Ltd., Shanghai, China. The effects of SD on the mycelial growths of P. digitatum andP. italicum were determined as described previously (Tao et al., 2014).
18
X. Duan et al. / Postharvest Biology and Technology 113 (2016) 17–19
3. Results and discussion
Mycelial growth (mm)
60 A
0 g/L 0.05 g/L 0.10 g/L 0.20 g/L 0.40 g/L 0.80 g/L
40
20
0 Mycelial growth (mm)
B
40
20
0 0
1
2 3 Time (d)
4
5
Fig. 1. Effect of different SD concentrations on the mycelial growths ofP. digitatum (A) andP. italicum(B) incubated at 25 2 C for 5 d.
For in vivo assays, all fresh citrus fruits were surface-sterilized by immersing in 1% sodium hypochlorite solution (v/v) for 2 min, rinsing twice in sterile distilled water, and then drying in air. Thereafter, two wounds (length of 4 mm and depth of 4 mm) were made on the equator of each fruit using a sterilized scalpel. Each incision was inoculated with 10 mL of conidial suspension containing 1 107 spores mL 1 of either P. digitatum or P. italicum. Fruits were then stored at room temperature for 4 h. The fruits were immersed in the SD solution at 2, 4 or 8 MFC for 30 s. The fruit immersed in sterile distilled water was used as a control. The fruits were stored in sealed incubators at 25 2 C and 85–90% relative humidity (RH). A single replicate comprised 20 fruit, and each treatment was performed in triplicate. The incidence rate of each treatment during storage time was measured by counting the number of green or blue mold contaminated fruits and the formula is as follows: number of rotten fruit Disease incidence ð%Þ ¼ 100: number of total fruit The weight of each fruit was recorded on the day of harvest and after the different sampling dates (after storage at an interval of 2 d). Cumulative weight losses were expressed as percentage loss of original weight (n = 20). The Vc content, TSS content, color index, pH and firmness were estimated according to Fan et al. (2014). Each assay was performed in triplicate, and data were processed by analysis of variance. Daily analysis results of the treatments were compared atP = 0.05 according to Duncan’s multiple range tests.
Food additives and low-toxicity compounds with fungitoxic or fungistatic activity can be suitable alternatives to traditional synthetic fungicides to control green and blue molds in citrus (Palou et al., 2008; Smilanick et al., 2008; Talibi et al., 2014; Youssef et al., 2014). Youssef et al. (2012) reported that sodium bicarbonate, sodium carbonate, sodium silicate, potassium bicarbonate, potassium carbonate and potassium sorbate at 0.25% (w/v, 2.50 g/L) could effectively inhibit mycelial growths of P. digitatumandP. italicum in PDA medium at 6 d incubation. In the present study, SD showed a notable antifungal effect on P. digitatum(Fig. 1A) and P. italicum(Fig. 1B). The inhibitory efficacy was enhanced as SD concentration increased. Mycelial growths of P. digitatum and P. italicum were moderately inhibited by SD at low concentration (0.10 g/L). By contrast, 0.20 g/L of SD induced 100% inhibition of the mycelial growths of P. digitatum and P. italicumup to 2 d of culture. Moreover, no mycelial growth was recorded at high concentration (0.40 g/L) after 5 d of culture. Therefore, the MIC and MFC of SD against P. digitatum and P. italicumwere 0.20 and 0.40 g/L, respectively. The ability of SD treatments to reduce disease development in citrus fruit wound-inoculated with P. digitatum or P. italicum is presented in Table 1. When SD was applied at various concentrations to artificially inoculated citrus fruit, the percentage of fungal infection was significantly (P < 0.05) delayed relative to the control. With regard to green mold, after 2 d of incubation, decay incidence rate of the control fruit (30.0%) was higher than that in SD (2 MFC)-treated fruit (6.7%), but the fruit treated with SD (4 or 8 MFC) was not infected. After 3 d of storage, the incidence rate of green mold in water-treated fruit reached 100.0%; conversely, the incidence rates in SD-treated (2, 4, and 8 MFC) fruit were only 66.7, 16.7 and 6.7%, respectively. Decay incidence attributed to blue mold in the control fruit was 10.0% after 3 d of storage. By contrast, the fruit treated with SD (2, 4, and 8 MFC) were not infected. After 5 d of storage, the incidence rate of blue mold in the control fruit was 100.0%; conversely, the incidence rates in SDtreated (2, 4, and 8 MFC) fruit were only 60.0, 33.3 and 20.0%, respectively. These data confirmed the results of previous reports that described the antifungal activity of SD in wild mangoes and honey peach (Joseph and Aworh, 1992; Ni et al., 2010). Moreover, higher fungicide concentration was necessary to reduce fungal growth in vivo than in vitro. This phenomenon might probably be attributed to the interactions between film components and vegetative tissues (Cháfer et al., 2012). Another possibility is that chemical fungicides can not easily penetrate living plant tissues to reach fungus-infected sites; therefore, the effective concentration is much lower than the concentration applied onto the fruit surface (Khan et al., 2001). During postharvest storage of fruit, changes related to quality, such as color, weight loss rate, firmness, TSS, total acidity, and Vc content, were generally observed (Fan et al., 2014). In our study, the
Table 1 Decay incidence in citrus fruit inoculated with P. digitatum or P. italicum treated with SD (0, 2, 4 and 8 MFC) during storage time (25 2 C; 85–90% RH). Inoculation period (days)
1 2 3 4 5 6
SD concentration (MFC) 0 2 Green mold incidence (%)
4
8
0 2 Blue mold incidence (%)
4
8
0.0a 30.0a 100.0a 100.0a – –
0.0a 0.0c 16.7c 73.3b – –
0.0a 0.0c 6.7d 50.0c – –
0.0a 0.0a 10.0a 40.0a 100.0a 100.0a
0.0a 0.0a 0.0b 10.0b 33.3c 63.3b
0.0a 0.0a 0.0b 6.7c 20.0d 30.0c
0.0a 6.7b 66.7b 96.7a – –
0.0a 0.0a 0.0b 10.0b 60.0b 100.0a
Data are the means of pooled data (n = 20). Rows with different letters at each time point among different diseases indicate significant differences at (P < 0.05).
X. Duan et al. / Postharvest Biology and Technology 113 (2016) 17–19
0 MFC
4 Weight loss (%)
A
2
b
a
a
This work was supported by National Natural Science Foundation of China (No. 31271964), Research Foundation of Education Bureau of Hunan Province (No. 15A181).
c
b
a a aa
0
2 Time (d)
References
4 B
a
6 Weight loss (%)
Acknowledgments
bc
b
0
b
b b a b bb
3 a
0
b ab b
a a aa
0
alternative to traditional fungicides to control postharvest citrus molds.
a
2 MFC 4 MFC 8 MFC
19
2 4 Time (d)
6
Fig. 2. Effects of SD treatment (0, 2, 4 and 8 MFC) on weight loss rate of postharvest citrus fruit inoculated with P. digitatum (A) or P. italicum (B) during storage at 25 2 C. Values represent the means of the replicates, and error bars represent the standard error of the means (n = 3).
effects of SD treatment on fruit quality were further investigated (Fig. 2). The weight loss rate of SD-treated samples was significantly lower (P < 0.05) than that of the control samples. At the end of storage period, the weight loss rates of P. digitatum and P. italicum control samples reached the highest levels at 3.62 and 5.81%, respectively. Meanwhile, no significant differences in the Vc content, coloration index, firmness, TSS content, and pH were found among all treatments in P. digitatum and P. italicum, respectively (data not shown). Joseph and Aworh (1992) also found that SD can control decay in wild mangoes, decrease weight loss and extend the shelf life of the fruit without adverse effects on the visual and chemical qualities. Similar result was obtained in honey peach (Ni et al., 2010). Therefore, SD is an effective moisture barrier to fruit. These results indicated that SD can reduce postharvest green and blue decay and had no negative effect on citrus fruit quality. In conclusion, SD exhibited notable antifungal activity against P. digitatum and P. italicumin in vitro and in vivo tests. Moreover, SD treatment did not affect fruit qualities, but significantly decreased weight loss rate. These results confirmed that SD can be used as an
Cháfer, M., Sánchez-González, L., González-Martínez, C., Chiralt, A., 2012. Fungal decay and shelf life of oranges coated with chitosan and bergamot, thyme, and tea tree essential oils. J. Food Sci. 77 (8), E182–E187. Droby, S., Wisniewski, M., El Ghaouth, A., Wilson, C., 2003. Influence of food additives on the control of postharvest rots of apple and peach and efficacy of the yeast-based biocontrol product Aspire. Postharvest Biol. Technol. 27 (2), 127–135. Fan, F., Tao, N.G., Jia, L., He, X.L., 2014. Use of citral incorporated in postharvest wax of citrus fruit as a botanical fungicide against Penicillium digitatum. Postharvest Biol. Technol. 90, 52–55. Joseph, K., Aworh, O.C., 1992. Postharvest treatment of wild mango (Irvingia gabonensis) for improved shelf life. Food Chem. 44 (1), 45–48. Khan, S.H., Aked, J., Magan, N., 2001. Control of the anthracnose pathogen of banana (Colletotrichum musae) using antioxidants alone and in combination with thiabendazole or imazalil. Plant Pathol. 50 (5), 601–608. Ni, Y., Ding, Z.P., Liu, Z.H., 2010. Effects of different fresh-keeping agent treatment on the storage of honey peach. Food Res. Dev. 36 (1), 162–165 in Chinese with English abstract. Nigro, F., Schena, L., Ligorio, A., Pentimone, I., Ippolito, A., Salerno, M.G., 2006. Control of table grape storage rots by pre-harvest applications of salts. Postharvest Biol. Technol. 42 (2), 142–149. Palou, L., Smilanick, J.L., Droby, S., 2008. Alternatives to conventional fungicides for the control of citrus postharvest green and blue mold. Stewart Postharvest Rev. 4 (2), 1–16. Palou, L., Usall, J., Smilanick, J.L., Aguilar, M.J., Vinas, I., 2002. Evaluation of food additives and low-toxicity compounds as alternative chemicals for the control of Penicillium digitatum and Penicillium italicum on citrus fruit. Pest Manag. Sci. 58 (5), 459–466. Regnier, T., Combrinck, S., Veldman, W., Du Plooy, W., 2014. Application of essential oils as multi-target fungicides for the control of Geotrichum citri-aurantii and other postharvest pathogens of citrus. Ind. Crop Prod. 61, 151–159. Shao, X.F., Cao, B.Y., Xu, F., Xie, S.H., Yu, D.D., Wang, H.F., 2015. Effect of postharvest application of chitosan combined with clove oil against citrus green mold. Postharvest Biol. Technol. 99, 37–43. Smilanick, J.L., Mansour, M.F., Gabler, F.M., Sorenson, D., 2008. Control of citrus postharvest green mold and sour rot by potassium sorbate combined with heat and fungicides. Postharvest Biol. Technol. 47 (2), 226–238. Talibi, I., Boubaker, H., Boudyach, E.H., Ait Ben Aoumar, A., 2014. Alternative methods for the control of postharvest citrus diseases. J. Appl. Microbiol. 117 (1), 1–17. Tao, N.G., Fan, F., Jia, L., Zhang, M.L., 2014. Octanal incorporated in postharvest wax of satsuma mandarin fruit as a botanical fungicide against Penicillium digitatum. Food Control 45, 56–61. Youssef, K., Ligorio, A., Sanzani, S.M., Nigro, F., Ippolito, A., 2012. Control of storage diseases of citrus by pre- and postharvest application of salts. Postharvest Biol. Technol. 72, 57–63. Youssef, K., Sanzani, S.M., Ligorio, A., Ippolito, A., Terry, L.A., 2014. Sodium carbonate and bicarbonate treatments induce resistance to postharvest green mould on citrus fruit. Postharvest Biol. Technol. 87, 61–69.
Contents lists available at ScienceDirect
Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Short communication
Control of postharvest green and blue molds of citrus fruit by application of sodium dehydroacetate Xiaofang Duan, Guoxing Jing, Feng Fan, Nengguo Tao* School of Chemical Engineering, Xiangtan University, Xiangtan 411105, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 26 August 2015 Received in revised form 23 October 2015 Accepted 26 October 2015 Available online xxx
Sodium dehydroacetate (SD), a common food preservative, was evaluated against Penicillium digitatum and Penicillium italicum through in vivo and in vitro experiments. SD dramatically inhibited the mycelial growths of P. digitatum and P. italicum, with a minimum inhibitory concentration (MIC) and a minimum fungicidal concentration (MFC) of 0.20 and 0.40 g/L, respectively. In vivo tests demonstrated that various SD concentrations (2, 4, and 8 MFC) significantly reduced the incidence of green and blue molds up to 3 and 5 d at 25 2 C, respectively. As storage time was prolonged, 4 and 8 MFC treatments still drastically inhibited fruit decay caused by P. digitatum and P. italicum. Meanwhile, SD significantly reduced the weight loss rate of citrus fruit during storage, but had minor effect on coloration index, firmness, total soluble solids, pH, and vitamin C content. These data suggested that SD can be used as a good alternative to conventional fungicides in controlling green and blue molds in citrus fruit. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Citrus Sodium dehydroacetate Penicillium digitatum P. italicum Fruit quality
1. Introduction Green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively, are the most economically important postharvest diseases of citrus fruit in all production areas (Regnier et al., 2014). Currently, both diseases are primarily controlled by applying synthetic fungicides such as carbendazim, imazalil, thiabendazole, sodium orthophenyl phenate, fludioxonil or pyrimethanil that were permitted by different countries (Talibi et al., 2014; Shao et al., 2015). Alternative methods are needed because of concerns about environmental contamination and human health risks raised by fungicide residues. Furthermore, the widespread use of these compounds in commercial packing houses has led to the proliferation of resistant strains of the pathogens (Palou et al., 2008). Recently, many salts serving as commercial food additives, such as sodium carbonate, sodium bicarbonate, sodium benzoate, sodium propionate, have been evaluated their corresponding efficacies in controlling pathogens that infect citrus, peach, apple, and grape fruit (Droby et al., 2003; Nigro et al., 2006; Smilanick et al., 2008). Palou et al. (2002) reported that potassium sorbate (0.20 M), sodium benzoate (0.20 M), and ammonium molybdate (1.00 mM) could effectively control P. digitatum- and P. italicum-induced postharvest decay of citrus fruit. In another
* Corresponding author. Fax: +86 731 58293284 E-mail address: [email protected] (N. Tao). http://dx.doi.org/10.1016/j.postharvbio.2015.10.015 0925-5214/ ã 2015 Elsevier B.V. All rights reserved.
study, 3% (w/v) sodium carbonate and sodium bicarbonate were found to totally reduce the incidence of green mold on clementines and oranges (Youssef et al., 2014). Sodium dehydroacetate (SD) is a safe food preservative widely used in noodles, seafood, preserves, beverage, and also in controlling postharvest fungal decay of fruit and vegetables (Joseph and Aworh, 1992; Ni et al., 2010). However, information on the effect of SD on postharvest diseases and fruit quality of citrus is lacking. Therefore, in this study, we aimed to evaluate the antifungal activity of SD against P. digitatum and P. italicum, and to determine the influences of SD on the incidence of green and blue molds in citrus, as well as on the fruit quality parameters, such as weight loss rate, coloration index, firmness, pH, total soluble solids (TSS), and vitamin C (Vc) content. 2. Materials and methods Mature fruits of Ponkan (Citrus reticulata Blanco), one of the most important commercial tangerines extensively cultivated in China, were harvested on 14 December 2014 from a local orchard near Xiangtan University, Xiangtan, China. Defect-free fruits of uniform size and color were selected as experimental materials. P. digitatum and P. italicum were isolated from infected citrus fruit and maintained on potato dextrose agar (PDA). SD (dehydroacetic acid sodium salt, 99%) was obtained from Crystal Pure Biochemical Technology Co., Ltd., Shanghai, China. The effects of SD on the mycelial growths of P. digitatum andP. italicum were determined as described previously (Tao et al., 2014).
18
X. Duan et al. / Postharvest Biology and Technology 113 (2016) 17–19
3. Results and discussion
Mycelial growth (mm)
60 A
0 g/L 0.05 g/L 0.10 g/L 0.20 g/L 0.40 g/L 0.80 g/L
40
20
0 Mycelial growth (mm)
B
40
20
0 0
1
2 3 Time (d)
4
5
Fig. 1. Effect of different SD concentrations on the mycelial growths ofP. digitatum (A) andP. italicum(B) incubated at 25 2 C for 5 d.
For in vivo assays, all fresh citrus fruits were surface-sterilized by immersing in 1% sodium hypochlorite solution (v/v) for 2 min, rinsing twice in sterile distilled water, and then drying in air. Thereafter, two wounds (length of 4 mm and depth of 4 mm) were made on the equator of each fruit using a sterilized scalpel. Each incision was inoculated with 10 mL of conidial suspension containing 1 107 spores mL 1 of either P. digitatum or P. italicum. Fruits were then stored at room temperature for 4 h. The fruits were immersed in the SD solution at 2, 4 or 8 MFC for 30 s. The fruit immersed in sterile distilled water was used as a control. The fruits were stored in sealed incubators at 25 2 C and 85–90% relative humidity (RH). A single replicate comprised 20 fruit, and each treatment was performed in triplicate. The incidence rate of each treatment during storage time was measured by counting the number of green or blue mold contaminated fruits and the formula is as follows: number of rotten fruit Disease incidence ð%Þ ¼ 100: number of total fruit The weight of each fruit was recorded on the day of harvest and after the different sampling dates (after storage at an interval of 2 d). Cumulative weight losses were expressed as percentage loss of original weight (n = 20). The Vc content, TSS content, color index, pH and firmness were estimated according to Fan et al. (2014). Each assay was performed in triplicate, and data were processed by analysis of variance. Daily analysis results of the treatments were compared atP = 0.05 according to Duncan’s multiple range tests.
Food additives and low-toxicity compounds with fungitoxic or fungistatic activity can be suitable alternatives to traditional synthetic fungicides to control green and blue molds in citrus (Palou et al., 2008; Smilanick et al., 2008; Talibi et al., 2014; Youssef et al., 2014). Youssef et al. (2012) reported that sodium bicarbonate, sodium carbonate, sodium silicate, potassium bicarbonate, potassium carbonate and potassium sorbate at 0.25% (w/v, 2.50 g/L) could effectively inhibit mycelial growths of P. digitatumandP. italicum in PDA medium at 6 d incubation. In the present study, SD showed a notable antifungal effect on P. digitatum(Fig. 1A) and P. italicum(Fig. 1B). The inhibitory efficacy was enhanced as SD concentration increased. Mycelial growths of P. digitatum and P. italicum were moderately inhibited by SD at low concentration (0.10 g/L). By contrast, 0.20 g/L of SD induced 100% inhibition of the mycelial growths of P. digitatum and P. italicumup to 2 d of culture. Moreover, no mycelial growth was recorded at high concentration (0.40 g/L) after 5 d of culture. Therefore, the MIC and MFC of SD against P. digitatum and P. italicumwere 0.20 and 0.40 g/L, respectively. The ability of SD treatments to reduce disease development in citrus fruit wound-inoculated with P. digitatum or P. italicum is presented in Table 1. When SD was applied at various concentrations to artificially inoculated citrus fruit, the percentage of fungal infection was significantly (P < 0.05) delayed relative to the control. With regard to green mold, after 2 d of incubation, decay incidence rate of the control fruit (30.0%) was higher than that in SD (2 MFC)-treated fruit (6.7%), but the fruit treated with SD (4 or 8 MFC) was not infected. After 3 d of storage, the incidence rate of green mold in water-treated fruit reached 100.0%; conversely, the incidence rates in SD-treated (2, 4, and 8 MFC) fruit were only 66.7, 16.7 and 6.7%, respectively. Decay incidence attributed to blue mold in the control fruit was 10.0% after 3 d of storage. By contrast, the fruit treated with SD (2, 4, and 8 MFC) were not infected. After 5 d of storage, the incidence rate of blue mold in the control fruit was 100.0%; conversely, the incidence rates in SDtreated (2, 4, and 8 MFC) fruit were only 60.0, 33.3 and 20.0%, respectively. These data confirmed the results of previous reports that described the antifungal activity of SD in wild mangoes and honey peach (Joseph and Aworh, 1992; Ni et al., 2010). Moreover, higher fungicide concentration was necessary to reduce fungal growth in vivo than in vitro. This phenomenon might probably be attributed to the interactions between film components and vegetative tissues (Cháfer et al., 2012). Another possibility is that chemical fungicides can not easily penetrate living plant tissues to reach fungus-infected sites; therefore, the effective concentration is much lower than the concentration applied onto the fruit surface (Khan et al., 2001). During postharvest storage of fruit, changes related to quality, such as color, weight loss rate, firmness, TSS, total acidity, and Vc content, were generally observed (Fan et al., 2014). In our study, the
Table 1 Decay incidence in citrus fruit inoculated with P. digitatum or P. italicum treated with SD (0, 2, 4 and 8 MFC) during storage time (25 2 C; 85–90% RH). Inoculation period (days)
1 2 3 4 5 6
SD concentration (MFC) 0 2 Green mold incidence (%)
4
8
0 2 Blue mold incidence (%)
4
8
0.0a 30.0a 100.0a 100.0a – –
0.0a 0.0c 16.7c 73.3b – –
0.0a 0.0c 6.7d 50.0c – –
0.0a 0.0a 10.0a 40.0a 100.0a 100.0a
0.0a 0.0a 0.0b 10.0b 33.3c 63.3b
0.0a 0.0a 0.0b 6.7c 20.0d 30.0c
0.0a 6.7b 66.7b 96.7a – –
0.0a 0.0a 0.0b 10.0b 60.0b 100.0a
Data are the means of pooled data (n = 20). Rows with different letters at each time point among different diseases indicate significant differences at (P < 0.05).
X. Duan et al. / Postharvest Biology and Technology 113 (2016) 17–19
0 MFC
4 Weight loss (%)
A
2
b
a
a
This work was supported by National Natural Science Foundation of China (No. 31271964), Research Foundation of Education Bureau of Hunan Province (No. 15A181).
c
b
a a aa
0
2 Time (d)
References
4 B
a
6 Weight loss (%)
Acknowledgments
bc
b
0
b
b b a b bb
3 a
0
b ab b
a a aa
0
alternative to traditional fungicides to control postharvest citrus molds.
a
2 MFC 4 MFC 8 MFC
19
2 4 Time (d)
6
Fig. 2. Effects of SD treatment (0, 2, 4 and 8 MFC) on weight loss rate of postharvest citrus fruit inoculated with P. digitatum (A) or P. italicum (B) during storage at 25 2 C. Values represent the means of the replicates, and error bars represent the standard error of the means (n = 3).
effects of SD treatment on fruit quality were further investigated (Fig. 2). The weight loss rate of SD-treated samples was significantly lower (P < 0.05) than that of the control samples. At the end of storage period, the weight loss rates of P. digitatum and P. italicum control samples reached the highest levels at 3.62 and 5.81%, respectively. Meanwhile, no significant differences in the Vc content, coloration index, firmness, TSS content, and pH were found among all treatments in P. digitatum and P. italicum, respectively (data not shown). Joseph and Aworh (1992) also found that SD can control decay in wild mangoes, decrease weight loss and extend the shelf life of the fruit without adverse effects on the visual and chemical qualities. Similar result was obtained in honey peach (Ni et al., 2010). Therefore, SD is an effective moisture barrier to fruit. These results indicated that SD can reduce postharvest green and blue decay and had no negative effect on citrus fruit quality. In conclusion, SD exhibited notable antifungal activity against P. digitatum and P. italicumin in vitro and in vivo tests. Moreover, SD treatment did not affect fruit qualities, but significantly decreased weight loss rate. These results confirmed that SD can be used as an
Cháfer, M., Sánchez-González, L., González-Martínez, C., Chiralt, A., 2012. Fungal decay and shelf life of oranges coated with chitosan and bergamot, thyme, and tea tree essential oils. J. Food Sci. 77 (8), E182–E187. Droby, S., Wisniewski, M., El Ghaouth, A., Wilson, C., 2003. Influence of food additives on the control of postharvest rots of apple and peach and efficacy of the yeast-based biocontrol product Aspire. Postharvest Biol. Technol. 27 (2), 127–135. Fan, F., Tao, N.G., Jia, L., He, X.L., 2014. Use of citral incorporated in postharvest wax of citrus fruit as a botanical fungicide against Penicillium digitatum. Postharvest Biol. Technol. 90, 52–55. Joseph, K., Aworh, O.C., 1992. Postharvest treatment of wild mango (Irvingia gabonensis) for improved shelf life. Food Chem. 44 (1), 45–48. Khan, S.H., Aked, J., Magan, N., 2001. Control of the anthracnose pathogen of banana (Colletotrichum musae) using antioxidants alone and in combination with thiabendazole or imazalil. Plant Pathol. 50 (5), 601–608. Ni, Y., Ding, Z.P., Liu, Z.H., 2010. Effects of different fresh-keeping agent treatment on the storage of honey peach. Food Res. Dev. 36 (1), 162–165 in Chinese with English abstract. Nigro, F., Schena, L., Ligorio, A., Pentimone, I., Ippolito, A., Salerno, M.G., 2006. Control of table grape storage rots by pre-harvest applications of salts. Postharvest Biol. Technol. 42 (2), 142–149. Palou, L., Smilanick, J.L., Droby, S., 2008. Alternatives to conventional fungicides for the control of citrus postharvest green and blue mold. Stewart Postharvest Rev. 4 (2), 1–16. Palou, L., Usall, J., Smilanick, J.L., Aguilar, M.J., Vinas, I., 2002. Evaluation of food additives and low-toxicity compounds as alternative chemicals for the control of Penicillium digitatum and Penicillium italicum on citrus fruit. Pest Manag. Sci. 58 (5), 459–466. Regnier, T., Combrinck, S., Veldman, W., Du Plooy, W., 2014. Application of essential oils as multi-target fungicides for the control of Geotrichum citri-aurantii and other postharvest pathogens of citrus. Ind. Crop Prod. 61, 151–159. Shao, X.F., Cao, B.Y., Xu, F., Xie, S.H., Yu, D.D., Wang, H.F., 2015. Effect of postharvest application of chitosan combined with clove oil against citrus green mold. Postharvest Biol. Technol. 99, 37–43. Smilanick, J.L., Mansour, M.F., Gabler, F.M., Sorenson, D., 2008. Control of citrus postharvest green mold and sour rot by potassium sorbate combined with heat and fungicides. Postharvest Biol. Technol. 47 (2), 226–238. Talibi, I., Boubaker, H., Boudyach, E.H., Ait Ben Aoumar, A., 2014. Alternative methods for the control of postharvest citrus diseases. J. Appl. Microbiol. 117 (1), 1–17. Tao, N.G., Fan, F., Jia, L., Zhang, M.L., 2014. Octanal incorporated in postharvest wax of satsuma mandarin fruit as a botanical fungicide against Penicillium digitatum. Food Control 45, 56–61. Youssef, K., Ligorio, A., Sanzani, S.M., Nigro, F., Ippolito, A., 2012. Control of storage diseases of citrus by pre- and postharvest application of salts. Postharvest Biol. Technol. 72, 57–63. Youssef, K., Sanzani, S.M., Ligorio, A., Ippolito, A., Terry, L.A., 2014. Sodium carbonate and bicarbonate treatments induce resistance to postharvest green mould on citrus fruit. Postharvest Biol. Technol. 87, 61–69.