GAMMA RADIATION EFFECTS ON MICROBIAL INACTIVATION AND ANTIOXIDANT ACTIVITY OF CHERRY TOMATOES Duarte Guerreiro, Telma Silva*, Márcia Meneses, Joana Madureira, Rita Melo, Sandra Cabo Verde, Fernanda Margaça Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Portugal *
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Introduction
Experimental
The tomato fruit has strong antioxidant action, preventing degenerative and heart diseases and cancer. Fresh fruits and vegetables can be contaminated during and after harvest. Particularly, Salmonella serotypes are the most commonly reported pathogens. Food irradiation is one of the few technologies that address both food quality and safety by virtue of its ability to control spoilage and foodborne pathogenic microorganisms without significantly affecting sensory or other organoleptic attributes of the food. Food irradiation is well established as a physical, nonthermal treatment that processes foods at ambient temperature in the final packaging, reducing the possibility of cross contamination. [1,2]
Inactivation Studies 4
Morphotypes - before irradiation: gramnegative, oxidase-negative, rods (88%); after irradiation: gram-negative, oxidase-positive, rods (78-100%).
3 2 1 0 0
7 Storage time (days)
0 kGy
1.3 kGy
3.2 kGy
14 5.7 kGy
Total aerobic mesophilic counts for non-irradiated and irradiated fruits during storage time.
Challenging Tests
Survivor population mainly constituted by gram-positive rods and yeast during storage time. Target bacteria followed an exponential gamma radiation inactivation kinetics on cherry tomatoes:
7 6 4
Microorganism
D-10 value (kGy)
3
Salmonella Typhimurium ATCC 14028
0.30 ± 0.01
2
Escherichia coli ATCC 8739
0.71 ± 0.04
Staphylococcus aureus ATCC 6538
0.45 ± 0.02
1 0 0,2
0,4
0,6 0,8 1 1,2 1,4 Dose (kGy) Salmonella Typhimurium Escherichia coli Sthapylococcus aureus
A decontamination dose of 3 kGy pointed out to 4 10 log- reduction in survival of the tested biohazards contaminants and 1 log-cycle reduction of natural microbiota.
Antioxidant Activity Antioxidant activity (mM FeSO4.7H2O)
GAE (mM)
1,6 1,2 0,8 0,4 0,0 0
1 t0
2
3 4 Dose (kGy) t7
14028); Escherichia coli (ATCC 8739); Staphylococcus aureus (ATCC 6538)
• Antioxidant Activity: Folin-Ciocalteau and FRAP assays Folin-Ciocalteau
FRAP
• Shelf-life assessment after 7 and 14 days storage at 4°C
Inactivation Studies Microbial load reduction of 2 log (99%) after irradiation at 3.2 kGy and 14 days of storage at 4°C, comparatively with the non-irradiated cherry tomatoes. The results indicated a potential shelf-life extension for irradiated cherry tomatoes.
Challenging Tests
The results indicated an improvement of the antioxidant activity after storage for the irradiated tomatoes. Storage seems to influence positively the antioxidant activity.
FRAP
Total Phenolics
2,0
Analyzed parameters: Challenging Tests • Inactivation studies of natural microbiota • Challenging tests of potential pathogenic microorganisms - Salmonella enterica serotype Typhimurium (ATCC
Antioxidant Activity
1,6
Comparison of the sensitivities of S. Typhimurium, E. coli and S. aureus to gamma radiation in cherry tomatoes.
Co-60 source Dose rate: 1.1 kGy.h-1
Inactivation efficiencies ≥ 99.99% for the tested biohazards.
5
0
Inactivation Studies
Conclusions
Bioburden - Total microbiota: ̴500 CFU/g; Fungal population: < 4 CFU/g.
5 Log CFU/g
The aim of this study was to evaluate the effects of gamma radiation on microbial inactivation and antioxidant activity of cherry tomatoes, assessing the potential shelflife extension of ionizing radiation as a conservation treatment.
Sub-lethal doses: 0.5 kGy up to 6 kGy
Results
6
Log CFU/g
Goals
Sub-lethal doses: 0.5 kGy up to 1.5 kGy
5
6
Total phenolics content for non-irradiated and irradiated fruits during storage time.
GAMMA IRRADIATION TREATMENT
4 3
THESE RESULTS SUGGEST THAT THE
2 1 0 0
1 t0
2 3 Dose (kGy)
4
5
6
t7
Antioxidant activity for non-irradiated and irradiated fruits during storage time .
The phenolic content decrease with the The results show that the antioxidant activity has the same tendency of total phenolics. shelf-life is lower for irradiated fruits.
IRRADIATION TREATMENT COULD BE ADVANTAGEOUS IN IMPROVING MICROBIAL SAFETY OF CHERRY TOMATOES DURING STORAGE WITH THE POTENTIAL ADDEDBENEFIT OF INCREASING ITS ANTIOXIDANT CONTENT.
References: [1] Diehl, J. F. 2002. Food irradiation—Past, present and future. Radiat. Phys. Chem, 63: 211–215. [2] FAO/IAEA/ WHO. 1999. High-dose irradiation: Wholesomeness of food irradiated with doses above 10 kGy. Report of a Joint FAO IAEA WHO Study Group, Rome, Italy. Acknowledgments: The authors are grateful to IAEA (CRP D6-RC-1163.2) and FCT (RECI/AAG-TEC/0400/2012) for financial support.
