Effects of postharvest application of Citrocide® PLUS, a peracetic acid based formulation, on tomato decay control
M.C. Mottura, R. Perelló and B. Orihuel-Iranzoa
Abstract
Tomato fruit, considered the second most important vegetable in the world in terms of quantity of vitamins and minerals contributing to the human diet, is affected by postharvest diseases that significantly increase spoilage after harvest. Furthermore, economic losses due to postharvest diseases are even greater than generally realized because the value of the produce increases several-fold while passing from the field to the consumer. Because the increased concerns regarding food safety of fresh vegetables we developed a PAA formulation and application system for the hygienic washing of tomatoes. It turns out that this application is also extremely effective reducing postharvest decay. In the present study, the postharvest application of Citrocide® PLUS on tomatoes was evaluated. Citrocide® PLUS, a PAA based formulation from Productos Citrosol S.A., was applied to three different tomatoes cultivars. In two cultivars, fruit was wounded simulating cracking, while in a third one, tomatoes were harvested from a greenhouse with, presumably, high level of fungi inoculum. The results obtained showed that the proper application of Citrocide® PLUS significantly reduces tomatoes postharvest decay in all cultivars tested. Decay reduction index varies from 85 to even 100% after 10 days at 10°C and 85% RH in wounded tomatoes, while in non-wounded tomatoes decay control was 100% after 13 days at 10°C and 85% RH. In addition, the results showed that the avoidance of washing tomato cannot be considered as an alternative to reduce postharvest decay. This study indicates that the postharvest application of Citrocide® PLUS is a reliable solution to improve postharvest life of tomatoes and therefore, reduce tomato economic losses caused by decay after harvest.
Keywords: tomatoes, postharvest decay, decay control, peracetic acid, Citrocide® PLUS
Despite the use of modern storage facilities and techniques, losses of fresh fruits and vegetables between harvest and consumption are estimated to range from 1 to even 50% (Kader, 2005; Sholberg and Conway, 2004). Most of this spoilage is caused by postharvest diseases. Furthermore, economic losses due to postharvest diseases are even greater than generally realized because the value of fresh fruits and vegetables (F&V) increases severalfold while passing from the field to the consumer (Sholberg and Conway, 2004).
Tomato (Lycopersicon esculentum Mill.), considered the second most important vegetable in the world in terms of quantity of vitamins and minerals it contributes to human diet (Bombelli and Wright, 2006), is affected by postharvest diseases that significantly increase spoilage after harvest. In tomatoes, postharvest losses caused by decay are mainly due to Rhizopus stolonifer infections (Bautista-Baños, 2014). Rhizopus being a wound pathogen, tomato cracking represents an important postharvest problem, mainly because cracks provide entry for this and other pathogens, causing significant income losses in the fresh market and the processing tomato industry (Lichter et al., 2002; Peet, 1992). Management of postharvest decay may include a variety of complementary strategies such as temperature management, handling procedures, sanitation, or application of biocides or
aE-mail: borihuel@citrosol.com
fungicides (Kanetis et al., 2007). Among them, the use of conventional fungicides is considered one of the most effective postharvest disease management strategies (Bautista-Baños, 2014). However, the increasing concern of the public regarding health hazards and environmental pollution have necessitated the intensive search for alternative strategies for the control of postharvest pathogens (Narayanasamy, 2006). Moreover, consumers expect to increase their life expectancy and protect their health by eating healthy and attractive fresh F&V (Dorais et al., 2008). So, the F&V industry is required to combine good agricultural practices and standards of quality in order to ensure horticultural produce demanded by the population (Carrasco and Urrestarazu, 2010). In this sense, peracetic acid (PAA) based biocides, mixed systems of PAA + H2O2 + acetic acid, appears as a reliable and safe solution for decay control during postharvest in many fruits and vegetables (Bautista-Baños, 2014; Kyanko et al., 2010; Alvaro et al., 2009; Mari et al., 2004).
Because the increased concerns regarding food safety of fresh fruits and vegetables, Productos Citrosol S.A. developed a PAA formulation and application system for the hygienic washing of tomatoes. It turns out that this application is also extremely effective reducing postharvest decay. The aim of this study was to establish the efficacy of Citrocide® PLUS, Citrosol’s commercial PAA formulation for tomatoes, in the postharvest decay control of different tomato cultivars in the Almeria area.
Plant material
Studies were carried out in a packinghouse in the Nijar area, Almerı́a, Spain. In the experiments, mature light-red to red (ripeness stage 5-6) tomatoes (Solanum lycopersicum L.) harvested from commercial greenhouses in Nijar area were used. Fruit was harvested following local practices and transported at room temperature to the packing house within 2 h after harvest. Fruit was not washed neither disinfected prior to treatment application to mimic current practices in the fresh fruit industry, where typically a single-stage washing process with or without sanitizing agents is applied. In the first two experiments, tomatoes were wounded simulating cracking, using a 1-mm long × 1-mm wide needle. A 1-cm long (approximately) longitudinal wound was performed in each single fruit. Afterward tomatoes were inoculated by leaving the fruit below the dumper for 4 h, in this way the tomatoes accumulated more inoculum. After inoculation, fruit was randomly divided in replicates and the treatment described below was applied. These two experiments were performed using 5 replicates of 30 fruits each of round ‘Dreamer’ cherry tomatoes and 4 replicates of 12 fruits each of ‘Daniela’ round tomatoes. After treatment, fruit was air-dried and packed in cardboard boxes. Boxes were stored at 10°C and decay was evaluated as the number of fruit affected by decay. In a third experiment, ‘Sunstream’ baby plum tomatoes were harvested from a greenhouse with clear decay problems. In this case, tomatoes were not wounded neither inoculated, and the treatment described below was applied within 6 h after harvest. After treatment and drying, fruit was packed in 250 g commercial plastic punnets, with 12 punnets per treatment and a range of fruits per punnet of 15-24 tomatoes. Punnets were stored at 10°C, simulating transport temperature, and decay was evaluated over the number of punnets affected by decay.
In all three experiments treatment was applied by dipping the tomatoes for 30 s in a 100-L water solution containing 0.20% Citrocide® PLUS (15% w/w peracetic acid + 23% H2O2 w/w, Productos Citrosol S.A). Two controls were established, one washed with tap water and the other without washing. After treatment, all fruits were air-dried. In the first two experiments, wounded tomatoes, fruit was packed in cardboard boxes. In the third experiment, baby plum tomatoes, fruit was packed in 250 g commercial punnets. All experimental fruit was stored at 10°C (±2°C) and 85% RH. In wounded tomatoes rotting was assessed over the total number of fruits after 6 and 9 days of storage. While in baby plum tomatoes the incidence of decay was evaluated over the number of punnets affected by decay,
i.e., punnet with one or more rotten fruit, after 6, 9 and 13 days at 10°C. Pathogen identification was performed through visual observation of the symptoms. Efficacy was calculated as decay reduction index (DRI) as follows: 100×(no. of decayed fruit in the control – no. of decayed fruit in the treatment)/no. of decayed fruit in the control.
In wounded tomatoes analysis of variance (ANOVA) applied to the arsin of the square root of the proportion of infected wounds over the total number of fruits was used. While in baby plum tomatoes the incidence of decay was evaluated by ANOVA applied to the number of punnets affected by decay. Fisher’s protected least significant difference test (P≤0.05) was used to separate means on the basis of statistically significant differences. StatGraphics 5.0 Plus software was used.
Figures 1 and 2 show the results obtained in the trials with wounded and inoculated round ‘Dreamer’ cherry tomatoes and ‘Daniela’ round tomato, respectively. In both tomato cultivars tested, results indicated that Citrocide® PLUS at 0.20% significantly reduces the percentage of wounds affected by decay. While in not washed round cherry tomatoes the percentage of wounds affected by decay reached 40.67% after 6 days at 10°C, and increased up to 60.67 after 9 days under the same conditions (Figure 1), in the fruit washed with Citrocide® PLUS at 0.20% the percentage of rotten wounds was 6.67 and 14.67% after 6 and 9 days at 10°C, respectively. This represents a decay reduction index (DRI) of more than 80% after 6 days, and over 75% after 9 days of storage. In addition, when comparing round cherry tomatoes washed with Citrocide® PLUS with the same cultivar washed with tap water, DRI of Citrocide® PLUS was even higher, because decay levels in fruit washed with tap water were significantly higher than those levels registered in not washed tomatoes (Figure 1).
Figure 1 Percentage of wounds affected by decay on wounded round ‘Dreamer’ cherry tomatoes after 6 and 9 days at 10°C and 85% RH. NW = not washed; WW = washed with water; Citrocide PLUS = washed with Citrocide® PLUS 0.20%. Means of five replicates. Vertical bars represent ± standard error of the mean. Bars within each count with unlike letters are significantly different by Fisher’s protected LSD test (P≤0.05) performed over the arsin of the square root of the proportion of infected wounds.
Figure 2. Percentage
wounded ‘Daniela’ round tomatoes after 6 and 9 days at 10°C and 85% RH. NW = not washed; WW = washed with water; Citrocide PLUS = washed with Citrocide® PLUS 0.20%. Means of four replicates. Vertical bars represent ± standard error of the mean. Bars within each count with unlike letters are significantly different by Fisher’s protected LSD test (P≤0.05) performed over the arsin of the square root of the proportion of infected wounds.
wounds affected by decay
In ‘Daniela’ tomato, the number of wounds that were decayed after 6 and 9 days at 10°C was similar between unwashed and tap water washed tomatoes, with no significant differences between these two controls (Figure 2). While in not washed tomatoes the level of decay reached 50.00 and 58.33% after 6 and 9 days, respectively, in those tomatoes washed with tap water decay percentage were 41.67 and 70.83 for the same periods (Figure 2). On the other hand, when wounded ‘Daniela’ tomatoes were washed with Citrocide® PLUS at 0.20% no decay was detected neither at 6 nor at 9 days at 10°C (Figure 2). In this cultivar, Citrocide® PLUS controlled decay with a DRI of 100% (Figure 2).
To further study the efficacy of Citrocide® PLUS on tomato decay control, the same treatments applied above were applied in a third tomato cultivar, ‘Sunstream’ baby plum. In this case tomatoes were not wounded neither inoculated, but fruit was harvested from a greenhouse where many decayed fruits were seen. After treatment and drying, fruit was packed in 250-g commercial plastic punnets, and stored at 10°C simulating transport temperature. Decay was evaluated over the number of punnets with decay. This analysis is particularly important from a practical and economical point of view considering that, when tomatoes are commercialized in such packaging that contains more than one fruit per unit, the package as a whole is considered the sales unit. Therefore, the presence of just one fruit with decay makes the punnet unsaleable. This fact multiplies several-fold the losses. This can be called the “multiplier effect” of the packaging. As it is shown in Table 1, after 6 days at 10°C decay was detected in one out of 12 punnets (8.33%) in baby plum tomatoes washed with water as well as in those unwashed, while no decay was detected when tomatoes were washed with Citrocide® PLUS at 0.20%. The same levels where observed after 9 days of conservation in all treatments. However, no statistical differences were observed between treatments at 6 neither at 9 days storage. On the other hand, after 13 days at 10°C the percentage of punnets affected by decay raised up to 58.3 in unwashed tomatoes as well as in those washed with water (Table 1). That is 7 out of 12 punnets had one or more rotten tomato. On the other side, punnets with tomatoes washed with Citrocide® PLUS still did not show decay symptoms, what represents an DRI of 100%. In practice, this result is highly relevant because it establishes the possibility to reach further distance markets which implies longer shipping times.
Table 1. % of punnets (± standard error) with one or more tomatoes affected by decay after 6; 9 and 13 days of conservation at 10°C and 85%RH for ‘Sunstream’ baby plum tomatoes not washed, washed with tap water or washed with Citrocide® PLUS at 0.20%. Total number of punnets per treatment = 12.
Different letters within the same column indicates statistical differences by Fisher’s protected LSD test (P≤0.05).
In all trials performed, most of the decay was caused by Rhizopus spp. (data not shown), that was easily identified for its characteristics tufts of white aerial erect hyphae which end into a large number of black spots, named sporangiophores (Bautista-Baños, 2014). Only in a few cases Geotrichum spp. decay symptoms were observed.
The results obtained in this study agree with those reported by several authors (Bautista-Baños, 2014; Sisquella et al., 2013; Kyanko et al., 2010; Alvaro et al., 2009; Mari et al., 2004) that report clear evidences that PAA-based formulations may represent a reliable solution for postharvest decay control in several fruits and vegetables. Furthermore, results obtained by Alvaro et al. (2009) indicate that, washing tomatoes with a PAA solution at 400 mg L-1, did not alter the organoleptic quality of tomatoes when they came to the final consumer, neither depreciated fruit quality nor caused phytotoxic effects. Moreover, regarding food safety issues, the use of PAA has not been associated with the formation of harmful disinfection by-products (DBPs). The only decomposition products reported appears to be acetic acid and oxygen (Santoro et al., 2007; Monarca et al., 2002). These properties make it attractive for use in vegetables washing processes and it has been studied as disinfectant for washing a variety of fruits and vegetables (González-Aguilar et al., 2012).
The results of this study demonstrate that the postharvest application of Citrocide® PLUS significantly reduces tomato decay with very high levels of efficacy, that reach 100% in some cases. Moreover, results obtained in wounded tomatoes show that with the application of Citrocide® PLUS at 0.20% it is possible to reduce and even eliminate decay formation in the cracks. Since tomato cracking represents an important postharvest problem mainly because cracks provide entry for pathogens and therefore decay, the proper use of Citrocide® PLUS in the postharvest washing process of tomatoes appears as a very valuable tool to reduce economic losses caused by decay. On the other hand, the results show that to avoid the washing of tomato on the basis that it will lead to decay, is a wrong idea. Finally, these results endorse the conclusions of Carrasco and Urrestarazu (2010), that it is possible to incorporate green chemistry strategies, such as the use of Citrocide® PLUS, a PAA based formulation, in the cultural practices of horticulture and food industry, and to release biodegradable elements that do not pollute the environment.
Alvaro, J.E., Moreno, S., Dianez, F., Santos, M., Carrasco, G., and Urrestarazu, M. (2009). Effects of peracetic acid disinfectant on the postharvest of some fresh vegetables. J. Food Eng. 95 (1), 11–15 https://doi.org/10. 1016/j.jfoodeng.2009.05.003
Bautista-Baños, S., ed. (2014). Postharvest Decay. Control Strategies (Mexico: National Polytechnic Institute; Academic Press, Elsevier Inc.).
Bombelli, E.C., and Wright, E.R. (2006). Tomato fruit quality conservation during postharvest by application of potassium bicarbonate and its effect on Botrytis cinerea. Cienc. Investig. Agrar. 33 (3), 167–172 https://doi.org/ 10.7764/rcia.v33i3.346
Carrasco, G., and Urrestarazu, M. (2010). Green chemistry in protected horticulture: the use of peroxyacetic acid as a sustainable strategy. Int. J. Mol. Sci. 11 (5), 1999–2009 https://doi.org/10.3390/ijms11051999 PubMed
Dorais, M., Ehret, D.L., and Papadopoulos, A.P. (2008). Tomato (Solanum lycopersicum) health component: from the seed to the consumer. Phytochem. Rev. 7 (2), 231–250 https://doi.org/10.1007/s11101-007-9085-x.
González-Aguilar, G., Ayala-Zavala, J.F., Chaidez-Quiroz, C., Heredia, J.B., and Campo, N.C.-D. (2012). Peroxyacetic acid. In Decontamination of Fresh and Minimally Processed Produce (Wiley-Blackwell), p.215–223.
Kader, A.A. (2005). Increasing food availability by reducing postharvest losses of fresh produce. Acta Hortic. 682, 2169–2176 https://doi.org/10.17660/ActaHortic.2005.682.296.
Kanetis, L., Förster, H., and Adaskaveg, J.E. (2007). Comparative efficacy of the new postharvest fungicides Azoxystrobin, Fludioxonil, and Pyrimethanil for managing citrus green mold. Plant Dis. 91 (11), 1502–1511 https://doi.org/10.1094/PDIS-91-11-1502 PubMed
Kyanko, M.V., Russo, M.L., Fernández, M., and Pose, G. (2010). Effectiveness of peracetic acid on fungal spore reduction of moulds causing rotting in fruits and vegetables. Inf. Tecnol. 21 (4).
Lichter, A., Dvir, O., Fallik, E., Cohen, S., Golan, R., Shemer, Z., and Sagi, M. (2002). Cracking of cherry tomatoes in solution. Postharvest Biol. Technol. 26 (3), 305–312 https://doi.org/10.1016/S0925-5214(02)00061-3
Mari, M., Gregori, R., and Donati, I. (2004). Postharvest control of Monilinia laxa and Rhizopus stolonifera in stone fruit by peracetic acid. Postharvest Biol. Technol. 33 (3), 319–325 https://doi.org/10.1016/j.postharvbio. 2004.02.011
Monarca, S., Richardso, S.D., Feretti, D., Grottolo, M., Thruston, A.D., Jr., Zani, C., Navazio, G., Ragazzo, P., Zerbini, I., and Alberti, A. (2002). Mutagenicity and disinfection by-products in surface drinking water disinfected with peracetic acid. Environ. Toxicol. Chem. 21 (2), 309–318 https://doi.org/10.1002/etc.5620210212. PubMed
Narayanasamy, P. (2006). Postharvest Pathogens and Disease Management (Hoboken, New Jersey: John Wiley & Sons, Inc.), pp.578
Peet, M.M. (1992). Fruit cracking in tomato. Horttechnology 2 (2), 216–223 https://doi.org/10.21273/HORTTECH. 2.2.216
Santoro, D., Gehr, R., Bartrand, T.A., Liberti, L., Notarnicola, M., Dell’Erba, A., Falsanisi, D., and Haas, C.N. (2007). Wastewater disinfection by peracetic acid: assessment of models for tracking residual measurements and inactivation. Water Environ. Res. 79 (7), 775–787 https://doi.org/10.2175/106143007X156817 PubMed
Sholberg, P.L., and Conway, W.S. (2004). Postharvest pathology. In The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks, USDA-ARS Agriculture Handbook Number 66. Draft – revised April 2004.
Sisquella, M., Casals, C., Vinas, I., Teixido, N., and Usall, J. (2013). Combination of peracetic acid and hot water treatment to control postharvest brown rot on peaches and nectarines. Postharvest Biol. Technol. 83, 1–8 https://doi.org/10.1016/j.postharvbio.2013.03.003.