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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


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].


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.


Atmosphere Composition


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.



  • 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.

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Partial support of this work by International Atomic Energy Agency under the research contract nº 11682