Preharvest Exposure to UV-C Radiation: Impact on Strawberry Fruit ... treatments, UV-C hormesis has been reported to activate innate plant defenses and.
Preharvest Exposure to UV-C Radiation: Impact on Strawberry Fruit Quality Z. Xie1, M.T. Charles1, D. Charlebois1, D. Rolland1, D. Roussel1, M. Deschênes1, C. Dubé1, S. Khanizadeh2 and J. Fan3 1 Horticulture Research and Development Centre, Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC, J3B 3E6, Canada 2 Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, ON, K1A 0C6, Canada 3 College of Forestry, Northwest A&F University, Yangling‚ Shaanxi‚ 712100, China Keywords: Fragaria × ananassa, ultraviolet, hormesis, preharvest, phytosanitasion Abstract Extending strawberry production season through cultivation in high tunnels or greenhouses offers access opportunities to niche markets. In these confined environments maintaining adequate phytosanitary protection may be very challenging under organic production, since effective chemical pesticides cannot be used. Physical treatments might represent interesting alternatives worthy of consideration to control pests in organically-grown crops. Among these physical treatments, UV-C hormesis has been reported to activate innate plant defenses and to slow down ripening and senescence in postharvest systems. There is however a lack of information on its possible effects on growing plants and how such treatment might impact fruit quality. In the present study, ‘Charlotte’ strawberry plants were exposed to UV-C light (60 mJ/cm2) during growth according to a repeated schedule from flowering until fruit reached commercial maturity. Mature fruits were harvested and quality parameters (firmness, color, anthocyanins and ellagic acid) were assessed. Higher firmness and ellagic acid content are discussed in line with the possible influence of UV-C in delaying ripening and senescence as observed in other fruits treated at the postharvest stage. INTRODUCTION The biocide effect of UV-C as a non-thermal preservation method and a low-cost operation is of significant interest to the food industry (Taze et al., 2014) and could be applied against water, liquid foods and airborne microorganisms. Treatment with UV-C has been demonstrated to be effective in several commodities at the postharvest stage (Shama and Alderson, 2005; Stevens et al., 2006; Charles and Arul, 2007) to delay senescence and induce disease resistance (Charles et al., 2011). However, the potential of UV-C applied directly to growing plants as a protective means against phytopathogens and pests has not been evaluated. In fact, to our knowledge, the preharvest application of UV-C treatment has been considered in only two studies, one on strawberry plants and apple seedling cuttings (Van Hemelrijck et al., 2010), and one on tomatoes (Obande et al., 2011). Both studies reported encouraging results. In the study by Van Hemelrijck et al. (2010), no attention was given to the impact of the treatment on fruit quality. The present work aimed to evaluate the impact of the preharvest application of UV-C light on the chemical components (anthocyanins, flavonols, and ellagic acid) and the physical characteristics (firmness and colour) associated with the quality of strawberry (Fragaria × ananassa Duch.) fruits. MATERIALS AND METHODS ‘Charlotte’ strawberry plants were grown either in a greenhouse (Experiment 1 and 2) or in a growth chamber (Experiment 3). The mean temperature and relative humidity were, respectively, 22°C and 55% in the greenhouse and 25°C and 50% in the growth chamber. In both cases growth occurred under a 15-h photoperiod with a light intensity of 500 µmol m-2 s-1. In each experiment, a total of 90 plants were divided among Proc. Vth International Conference Postharvest Unlimited Eds.: G.A. Manganaris et al. Acta Hort. 1079, ISHS 2015
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two groups (45 control plants and 45 UV-C-treated plants). Treatment with UV-C was done with a device composed of three germicidal lamps (Cleanlight, Inc., Vineland, ON, Canada) with peak emission at 254 nm. Treatment started when the first flush of flowers were wide open. The distance between the plants and the lamps was 40 cm. The plants received a dose of 60 mJ cm-2 two times a week until the fruits reached optimum maturity. Firmness was measured with a universal testing machine (LRX; Lloyd Instruments, Hampshire, UK) and compression force, expressed in Newtons (N), was measured at a deflection limit of 12 mm. Colour was measured with a Minolta Chroma Meter CR-400 (Minolta Co., Ltd., Osaka, Japan). The recorded parameters were lightness (L*), hue angle (H°), and chroma (C). Chemical components were analyzed as described by Fan et al. (2012) with a Varian HPLC system (Varian, Inc., Palo Alto, CA, USA) equipped with a quaternary pump and a photodiode array detector. The detector was set at 254 nm to monitor for ellagic acid, at 280 nm for kaempferol (kaempferol glucuronide, K3Gr), at 350 nm for quercetin (quercetin glucoside, Q3G; and quercetin glucuronide, Q3Gr), and at 510 nm for anthocyanins (cyanidin glucoside, C3G; pelargonidin glucoside, P3G; and pelargonidin rutinoside, P3R). Experimental layout was a completely randomized design in a factorial arrangement (2 factors: Experiment and Treatment at 3 and 2 levels, respectively) with three replications of 15 plants. Statistical analysis was performed with the SAS software package (2010). After an analysis of variance (ANOVA) was carried out, means were separated with the least significant difference (LSD) test at α=0.05. RESULTS The application of UV-C at the preharvest stage did not cause any visible damage to the leaves, flowers, or fruits. Similar colour index values (Table 1) between the fruits of the control group and those of the UV-treated group were observed when the experiment was conducted in the greenhouse (Experiments 1 and 2). When the experiment was conducted in the growth chamber (Experiment 3), however, significant dissimilarities between the two groups were obtained for L* and C. The L* values in Experiment 3 indicate that the UV-treated fruits were lighter, while the C* values indicate that they were more vivid than the control fruits. Although not statistically significant, the lower H° value of the UV-treated fruits from the greenhouse tends to indicate that those fruits were redder than the control fruits. The fruits of the UV-C-treated group tended to be firmer than the control fruits, but there was no significant impact of either experiment or treatment on this parameter. Individual anthocyanins (Table 2) tended to be lower in the UV-C-treated fruits than the control fruits, but significant differences were observed only in Experiment 3 for minor anthocyanins, namely C3G (36%) and P3R (53%). No significant impact of UV-C was observed on total anthocyanins within each experiment. The latter observation is in accordance with the data reported for H° and indicates that the differences in pigment content would be barely perceptible by the naked eye. It should be noted that total anthocyanin content varied significantly between the experiments, with a higher content recorded in Experiment 1. Ellagic acid (Table 3) was generally higher in the fruits from the UV-C-treated plants than control plants. However, a significant difference was observed only for data from Experiment 3, where ellagic acid was found to be 32.7% higher in the treated group. Non-significant increases of 22.4 and 20.5% of ellagic acid were recorded in Experiments 1 and 2, respectively. Considering the figures reported for the control, experiment had no significant effect on ellagic acid content. There was no significant effect of UV-C or experiment on total flavonol content. DISCUSSION The present study found that the fruits from the UV-C plants tended to have higher ellagic acid content and lower anthocyanin content, but were firmer than the fruits from the control plants. Ellagic acid content decreases and anthocyanin content increases 590
(Pineli et al., 2011) as strawberry fruits ripen, with a concomitant decrease in firmness (Ornelas-Paz et al., 2013). Taken together, these observations might be indicative of a delay in the ripening process. This hypothesis is sustained by reports on the impact of using UV-C on postharvest commodities as an approach to delay processes associated with ripening and senescence. At the postharvest stage, Li et al. (2014) recorded a lower accumulation of anthocyanins in UV-C-treated strawberry fruits, and Pombo et al. (2009) reported a delay in fruit softening. CONCLUSION The proposed approach holds promise for application in integrated pest management programs in greenhouses under organic production. However, more research is needed to assess the optimum treatment conditions (doses and timing) and to evaluate the real impact of UV-C in controlling diseases during both growth and the postharvest period of strawberries. ACKNOWLEDGEMENTS This work was funded by Agriculture and Agri-Food Canada. Zhichun Xie held a scholarship from the China Scholarship Council. Literature Cited Charles, M.T., Arul, J. and Benhamou, N. 2011. UV-C-induced disease resistance in tomato fruit is a multi-component and time-dependent system. Acta Hort. 905:251260. Charles, M.T. and Arul, J. 2007. UV treatment of fresh fruits and vegetables for improved quality: a status report. Stewart Postharvest Review 3(8):1-8. Fan, L., Dubé, C., Fang, C., Roussel, D., Charles, M.T., Desjardins, Y. and Khanizadeh, S. 2012. Effect of production systems on phenolic composition and oxygen radical absorbance capacity of ‘Orleans’ strawberry. LWT-Food Sci. Technol. 45:241-245. Li, D., Luo, Z., Mou, W., Wang, Y., Ying, T. and Mao, L. 2014. ABA and UV-C effects on quality, antioxidant capacity and anthocyanin contents of strawberry fruit (Fragaria ananassa Duch.). Postharvest Biol. Technol. 90:56-62. Maharaj, R., Arul, J. and Nadeau, P. 1999. Effect of photochemical treatment in the preservation of fresh tomato (Lycopersicon esculentum cv. Capello) by delaying senescence. Postharvest Biol. Technol. 15:13-23. Obande, M.A., Tucker, G.A. and Shama, G. 2011. Effect of preharvest UV-C treatment of tomatoes (Solanum lycopersicon Mill.) on ripening and pathogen resistance. Postharvest Biol. Technol. 62:188-192. Ornelas-Paz, J.J., Yahia, E.M., Ramírez-Bustamante, N., Pérez-Martínez, J.D., EscalanteMinakata, M.P., Ibarra-Junquera, V., Acosta-Muñiz, C., Guerrero-Prieto, V. and Ochoa-Reyes, E. 2013. Physical attributes and chemical composition of organic strawberry fruit (Fragaria × ananassa Duch, cv. Albion) at six stages of ripening. Food Chem. 138:372-381. Pineli, L.L.O., Moretti, C.L., dos Santos, M.S., Campos, A.B., Brasileiro, A.V., Córdova, A.C. and Chiarello, M.D. 2011. Antioxidants and other chemical and physical characteristics of two strawberry cultivars at different ripeness stages. J. Food Comp. Anal. 24:11-16. Pombo, M.A., Dotto, M.C., Martínez, G.A. and Civello, P.M. 2009. UV-C irradiation delays strawberry fruit softening and modifies the expression of genes involved in cell wall degradation. Postharvest Biol. Technol. 51:141-148. Shama, G. and Alderson, P. 2005. UV hormesis in fruits: a concept ripe for commercialisation. Trends Food Sci. Technol. 16:128-136. Stevens, C., Khan, V.A., Wilson, C.L., Lu, J.Y., Pusey, L., Bassett, C.L., Igwegbe, E.C.K., Wisniewski, M., Chalutz, E., Droby, S. and El-Ghaouth, A. 2006. The use of low dose UV-C light technology to control postharvest storage decay and delayed ripening and senescence of fruits and vegetables. p.199-205. In: B. Noureddine and S. 591
Norio (eds.), Advances in Postharvest Technologies for Horticultural Crops. Research Signpost, Kerala, India. Taze, B.H., Unluturk, S., Buzrul, S. and Alpas, H. 2014. The impact of UV-C irradiation on spoilage microorganisms and colour of orange juice. J. Food Sci. Technol. doi 10.1007/s13197-013-1095-7. Van Hemelrijck, W., Van Laer, S., Hoekstra, S., Aiking, A. Creemers, P. 2010. UV-C radiation as an alternative tool to control powdery mildew on apple and strawberry Proceedings Ecofruit, 14th International Conference on Organic Fruit-Growing. Hohenheim, Germany 22-24 February 2010. p.99-105. Tables Table 1. Effect of preharvest UV-C on physical parameters of strawberry. Experiment 1 2 3
Treatment Control UV Control UV Control UV
LSD0.05
1
L*1 34.7b 34.3b 36.8ab 38.1a 30.4c 35.1b 3
Hue 34.3b 32.4b 40.4a 39.4a 32.4b 35.8b 3.7
Chroma Firmness2 40bc 11.4b c 38.1 12.2ab 36.5c 13.4ab bc 40.3 14.2a 43.4b a 50.3 4.6 2.81
Values are means of 3 replicates; 2 Firmness is expressed in Newtons.
Table 2. Effect of preharvest UV-C on anthocyanins in strawberry. Experiment 1 2 3 LSD0.05
1
Treatment Control UV Control UV Control UV
C3G1 6.8b 6.3b 2.3c 3.1c 8.9a 5.7b 1.6
P3G 454.8a 446.3ab 311.8c 347.2bc 353.4abc 268.7c 107.5
P3R 1.2bc 1.3ab 1.2bc 1.5ab 1.7a 0.8c 0.4
Total 462.9a 454ab 315.3c 351.8bc 364abc 275.2c 109.4
Values are means of 3 replicates and are expressed in µg/g fresh weight.
Table 3. Effect of preharvest UV-C ellagic acid and flavonols in strawberry. Experiment Treatment Ellagic1 Q3G+Q3Gr K3Gr Total flavonols 2.6a 2.5a 5.1a Control 4.9bc 1 UV 6ab 2.8a 2.5a 5.3a Control 4.4c 2.4a 2.1ab 4.5a 2 bc a a UV 5.3 2.7 2.6 5.3a 3.1a 1.7bc 4.8a Control 5.5bc 3 a a c UV 7.3 2.9 1.3 4.2a 1.4 0.7 0.4 1.2 LSD0.05
1
Values are means of 3 replicates and are expressed in µg/g fresh weight.
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