Tels.: +351 214403500 Fax: +351 214413208 – E-mail: mjptrigo@gmail.com Home Page: http://www.iniap.min-agricultura.pt

1. LOW-DOSE GAMMA RADIATION EFFECTS ON WATERMELON SHELF LIFE1M. J. Trigo, 1M. B. Sousa, 1M. M. Sapata, 1A. Ferreira, 1T. Curado, 1L. Andrada, 1E.S. Ferreira, 2M. L. Botelho, 3G. Veloso1INIAP - EAN – DTPA, Quinta do Marquês, 2784-505 Oeiras2Nuclear and Technological Institute, E.N. 10, 2696 Sacavém, Portugal3Technical University of Lisbon, Faculty of Veterinary Medicine, Lisbon, Portugal INTRODUCTION Fruits can be contaminated with pathogenic microorganisms during the growing season, harvest, processing and distribution. Ionizing radiation is a promising technology to be applied for assuring safety and quality of food products and do not present harmful toxic residues. The objective of this study was to analyse gamma radiation’s effect on quality and safety of ready-to-eat watermelon [Citrullus lanatus (thunb.) Mansfeld]. MATERIALS AND METHODS Raw material: Watermelon [Citrullus lanatus (thunb.) Mansfeld]; Packaging: Nutrip-PS tray and polymeric film bags - Cryovac - PE65S, passive atmosphere (20.9% O2 - 0.03% CO2);Irradiation:  irradiation in UTR (dose rate - 4.7 kGy. h-1) – 0.5 and 1 kGy;Storage: 4ºC for 11 days; Sampling: 1, 3, 4, 7, 9 and 11 storage days. Quality Parameters: Atmosphere composition - food pack gas analyser PBI Dansensor. Soluble solids content - hand refractometer ATAGO on juice extract. pH - potentiometer Crison- Micro pH 2002 with a glass electrode. Textural attributes - texturometer TA-Hdi with a 50 N load cell, crosshead at 1.5mm.sec-1, and 6mm plunger and penetration distance of 10mm. Colour analysis - Minolta Chroma Meter CR 200b, with a diameter area of 8 mm, standardised with a white tile. Sensorial analysis - test panel made up of 8 trained people. The general overall visual quality and aroma are scored using a scale of 1 to 5 (1 - very bad and 5 - excellent). A score of 3 is considered the limit of saleability. Microbiological analysis - Aerobic total count mesophilic - PCA, 30ºC, 48h; Psycrothrophics - PCA, 7ºC, 10 days; Enterobactereaceae - VRBGA, 30ºC, 48h; Coliforms - VRBA, 30ºC, 48h. RESULTS Atmosphere Composition Texture Sensorial Analysis Irradiated and non irradiated samples showed a significant decrease of O2 (%) to values near zero, inside the watermelon packages during the first four days; the CO2 concentration values increase to 5% and remained constant until the end of storage. Irradiation at 0.5 and 1 kGy did not affect significantly the samples’ firmness when comparing to non irradiated samples. Microbiological Analysis Sensorial analysis of irradiated samples at 0. 5 kGy point out to an extended shelf life (up to 9 days) compared with non-irradiated (4 days). Sensorial analysis after irradiation at 1 kGy revealed less quality in the tested samples. The radiation impact on mesophilic and psycrotrophic bacteria counts showed a decrease of ≤ 1 log to 0.5 kGy. The juice leakage, Brixº and pH values did not showed significant differences during the time of storage of irradiated and non irradiated samples. Immediately after irradiation it was noticed a slight colour change into a darker shade, nevertheless this difference disappeared along storage time. Enterobacteriaceae and coliforms counts decreased ≤ 2 log at the same dose. This trend remained constant during the trial period. CONCLUSIONS LITERATURE • Hygienic quality of minimal processed watermelon improved after irradiation at 0.5 kGy; • The self-life of minimal processed watermelon was extended with more 5 days after irradiation at 0.5 kGy. Akamine, E.K., Moy, J.H., Delay in post-harvest ripening and senescence of fruits In E.S. Josephson, M.S. Peterson (eds) - Preservation of Food by Ionizing Radiation, Vol. III, CRC Press, Boca Raton, FL. (1983) 129-158. Bhushan, B., Thomas, P., Quality of apples following gamma irradiation and cold storage. Intern. J. Food Sci. Nutr. 49 (1998) 485-492. Fonseca, J.M., Rushing, J.W, Effect of ultraviolet-C light on quality and microbial population of fresh-cut watermelon, Postharvest Biol. Technol. 40 (2006) 256–261 Gombas, D.E, Chen, Y., Clavero, R.S., Scott, V.N., Survey of Listeria monocytogenes in ready-to-eat foods. J. Food Prot. 66 (003) 559-569. Horby, P.W, O’brien, S.J, Adak, G.K, Graham, C., Hawaker, J.I, Hunter, P., Lane, C., Lawson, A.J, Mictchell, R.T, Reacher, M.H, Threlfall, E.J., Ward, L.R., A national outbreak of multi-resistent Salmonella enterica serovar Typhimurium definitive phage type (DT) 104 associated with consumption of lettuce. Epidemiology and Infection (2003) 169-178. Lalaguma, F., Response of ‘Galia’ muskmelons to irradiation as a quarantine treatment. HortScience, 33 (1998) 118-120. Monge, R., Chinchilla, M., Presence of Cryptosporium Oocysts in fresh vegetables. J. Food Prot. 59 (1996) 202-203. Niemira, B.A., Fan, X., Sokoray, K.J.B., Irradiation and modified atmosphere packaging of endive influences survival and regrowth of Listeria monocytogenes and sensory qualities. Radiat. Phys. Chem. 72 (2005) 41-48. Paull, R.E., Response of tropical horticultural commodities to insect disinfestation treatments. HortScience 29 (1994) 988-996. Paull, R.E., Ripening behavior of papaya (Carica papaya L.) exposed to gamma irradiation. Postharvest Biol. Technol. 7 (1999) 359-370. Prakash, A., Inthajak, P., Huibregtse, H., Caporaso, F., Foley, D.M., Effects of low-dose gamma irradiation and conventional treatments on shelf life and quality characteristics of diced celery. J. Food Sci. 65 (2000) 1070-1075. Yu, L., Reitmeier, C.A, Gleason, M.L., Nonnecke, G.R. Olson, D.G., Gladon, R.J., Quality of electron beam irradiated strawberries. J. Food Sci. 60 (1995) 1084-1087. Zhang, S., Farber, J.M., The effects of various disinfectants against Listeria monocytogenes on fresh-cut vegetables. Food Microbiology 13 (1996) 311-321. Tels.: +351 214403500 Fax: +351 214413208 – E-mail: mjptrigo@gmail.com Home Page: http://www.iniap.min-agricultura.pt ACKNOWLEDGMENT Partial support of this work by International Atomic Energy Agency under the research contract nº 11682