Food Irradiation Current Research and State of the Art

1. Food IrradiationCurrent Research and State of the Art Brendan A. Niemira, Xuetong Fan, Christopher H. Sommers, Ignacio Alvarez United States Department of Agriculture Agricultural Research Service Eastern Regional Research Ctr. Wyndmoor, PA, USA

2. Food Irradiation • Overview and brief comparison of food irradiation technologies • Research areas • Microbiology of irradiated produce • Biofilms • Sensory and quality properties • Shell eggs and liquid egg products • Ready to eat meats and prepared meals • Toxicology • Summary

3. Food Irradiation - Overview • Treatment of meats, seafood and produce with high-energy particles (gamma, X-ray, E-beam) • inactivate insect pests • eliminate spoilage organisms and human pathogens • extend shelf life • 60+ years of research by governments, industry and academia • Irradiated food is safe, wholesome and nutritious • Endorsed by leading public health organizations (WHO, USDA, FDA, FSIS, ADA, CDC, etc.)

4. How is food irradiated? • Product to be irradiated is handled with the same care and attention to cleanliness as ever • Irradiation is intended to complement, not substitute for, proper food handling procedures • Product is exposed to high energy electrons or high energy photons, either on-site, or at another location • Contracting, shipment, transshipment add costs to final product

5. High energy electrons Electron Source LINEAR ACCELERATOR High energy electrons Electron beam

6. High-energy photons Electron Source LINEAR ACCELERATOR High-energy photons X-rays High-density metal target (must be cooled)

7. Photon Source High-energy photons High-energy photons High-energy photons High-energy photons Gamma rays Radioactive material: cobalt-60 or cesium-137

8. Technologies - Summary

9. Mode of Action • Largest target in organisms is water • High energy electrons break water molecules into OH• and O• radicals, which disrupt membranes, proteins and nucleic acids • DNA is also broken directly • High energy photons interact with atoms to eject high energy electrons • Penetration of photons is much greater than for electrons - implications for how material is processed

10. E-BEAM E-BEAM The Max/Min Ratio Maximum dose (GROUND BEEF PATTIES) Minimum dose

11. The Max/Min Ratio • Packaging is appropriate • complete penetration of e-beam from above and below • relatively even dosage, low Max/Min ratio • Improper packaging & processing - too thick! • incomplete penetration of e-beam • uneven dosage, high Max/Min ratio

12. Microbiology of Irradiated Produce

13. Response and efficacy • Lettuce • D10 values on shredded iceberg lettuce • E. coli O157:H7: ~0.11 kGy • Salmonella: ~0.2 kGy (Goularte et al., 2004, Rad Phys Chem 71:155-159) • D10 values on green leaf lettuce • NalSE. coli O157:H7: ~0.18 kGy • NalRE. coli O157:H7: ~0.10-0.12 kGy (Niemira 2005. J. Food Sci 79(2):M121-4) • 5.5 kGy + chlorination 5.4 log reduction of E. coli O157:H7 (Foley et al., 2002. Rad Phys Chem 63:391-396.) B. Niemira

14. B. Niemira

15. Post-irradiation phenomena L. mono. • Endive • L. monocytogenes regrew to control levels in storage following 0.42kGy (a 2 log10 reduction). • Higher dose (0.84 kGy) suppressed the pathogen throughout the 19 d of the storage period (Niemira et al., 2003. J Food Prot 66:993-998.) TAPC B. Niemira

16. Post-irradiation phenomena • Respiration rates of most MAP vegetables are not significantly affected by low dose irradiation • changes to packaging are not indicated • Endive + MAP • Dose equivalent to 1-3 log10 reductions allowed regrowth of L. monocytogenes • Irradiation + reduced-O2, enhanced-CO2 packaging scheme effectively suppressed this capacity, and prevented the pathogen from regrowing. (Niemira et al., 2004. Rad Phys Chem 72(1):41-48.) B. Niemira

17. L. mono. on endive: Irradiation + MAP B. Niemira

18. Biofilms: the great unknown • Phytoplane bacteria are biofilm associated • Biofilms protect against chemical and many physical antimicrobial processes • Often requires 10x, 100x, 1000x exposure to get equivalent kill • Planktonic and biofilm-associated Salmonella are equally susceptible to irradiation (Niemira and Solomon. 2005. Appl. Environ. Microbiol. 71(5):2732-2736) • Effect on structure? Attachment strength? Efficacy of co-applied antimicrobials? B. Niemira

19. Irradiated biofilms • Irradiation changes the internal structure of Salmonella biofilms • shifts in region of highest density • cell distributions • Behavior of commensal & background microflora biofilms not known B. Niemira

20. Biofilms: the great unknown • Response of other pathogen biofims • Complex microecologies • mixed species biofilms of pathogens + commensal/phytoplane background organisms • recovery, injury repair, regrowth, predation, competition? • Synergy of multiple interventions • Substrate effects

21. Sensory and Quality Attributes of Irradiated Foods

22. Dose Threshold and Endogenous Antioxidant Capacity of Fresh-cut Vegetables X. Fan

23. X. Fan

24. Nutritional Quality of Alfalfa Sprouts Grown from Irradiated Seeds X. Fan

25. X. Fan

26. 0 kGy 3 kGy Volatile Sulfur Compounds from Turkey Bologna Irradiated at 0 and at 3 kGy 4 5 2 3 1 6 X. Fan

27. Irradiation-Induced malondialdehyde, formaldehdye, and acetaldehdye in Fresh Apple Juice X. Fan

28. Irradiation and Heat Treatment of Whole and Liquid Eggs

29. Irradiation of eggs: background Eggs and egg products are responsible for an estimated 230,000 cases of foodborne illnesses each year, resulting in economic losses and representing a consistent and serious obstacle to the well-being of consumers Salmonella and mainly serovar Enteritidis is the leading cause of all egg-related foodborne illnesses Ionizing radiation can inactivate Salmonella spp. in shell eggs and egg products. I. Alvarez

30. Whole Shell Egg 137Cs irradiator, dose rate of 0.095 kGy/min, 4ºC I. Alvarez

31. Liquid whole egg 137Cs irradiator, dose rate of 0.095 kGy/min, 4ºC I. Alvarez

32. Shell eggs - US FDA Approves Irradiation of Shell Eggs £ 3.0 kGy (21 CFR Part 179, vol. 65, No. 141, p. 45280) - Problem: Internal quality properties decreases with irradiation dose. 0 kGy 0.3 kGy 0.5 kGy 2.0 kGy 3.0 kGy 1.0 kGy Will consumers accept IR shell egg? I. Alvarez

33. 9 log FDA (60ºC/3.5 min) • Egg products – LIQUID WHOLE EGG • Heat pasteurization to obtain Salmonella-free LWE: 60ºC/3.5 min (FDA) (CFR 590.570, p. 765). • Very heat resistant Salmonella serotypes • More intensive treatments reduce LWE quality (57ºC – coagulation of some soluble proteins) I. Alvarez

34. Egg products – LIQUID WHOLE EGG • 3.0 kGy enables to reduce 9 log cycles population of Salmonella. • However, doses > 1.5 kGy reduce LWE quality properties (color, off-flavor) • HEAT followed by IRRADIATION – additive lethal effect not available equipment for the industrial process • - IRRADIATION followed by HEAT • - synergistic lethal effect • - most viable immediate industrial option • - available equipment for the industrial process LWE Heat pasteurizer Holding tuve I. Alvarez

35. Egg products – LIQUID WHOLE EGG COMBINING TREATMENTS IRRADIATION followed by HEAT - synergistic lethal effect - most viable immediate industrial option: available equipment for the industrial process I. Alvarez

36. S. senftenberg S. enteritidis – S. typhimurium 0.1 kGy 0.3 kGy 0.5 kGy 3.5 min 1.0 kGy 1.5 kGy Egg products – LIQUID WHOLE EGG - COMBINING TREATMENTS: IRRADIATION followed by HEAT MODELIZATION OF THE COMBINING TREATMENTS Salmonellainactivation= IR/0.67 kGy + Time/(299-9.8T+0.08T^2+4.4*IR+0.07*IR*T) T: temperature (55 – 57ºC) IR: irradiation dose (0.1 – 1.5 kGy) Dotted and thick lines represents the TDT curves for Salmonella Enteritidis-Typhimurium and for Senftenberg, respectively. Combinations time-temperature to inactivate 5 log of any Salmonella Enteritidis, Senftenberg or Typhimurium I. Alvarez

37. Irradiation + HeatSalmonella enteritidis (A) Non-treated native cells (B) subcultured cells after 1.5 kGy (C) subcultured cells after 1.5 kGy and 55ºC/21 min (D) subcultured cells after 1.5 kGy and 60ºC/2 min. I. Alvarez

38. Egg products – LIQUID WHOLE EGG COMBINING TREATMENTS - IRRADIATION followed by HEAT in LWE added with ADDITIVES - Nisin - Nisin + carvacrol - Carvacrol - EDTA + carvacrol - EDTA - EDTA + nisin - Sorbic acid - EDTA + nisin + carvacrol I. Alvarez

39. Microbiological Safety of Irradiated Ready-To-Eat Foods

40. Irradiated Ready to Eat Meals • Reduction of pathogens in complex ready-to-eat (RTE) foods • deli meats, assembled meals, sandwiches • New challenge from a food safety standpoint • highly processed • typically eaten with little or no preparation • must have a low in-package risk profile • Influences on efficacy • composition of meal • physical location of the contaminating bacteria C. Sommers

41. Proliferation of L. monocytogenes on beef fine emulsion sausage at 0. 1.5 and 3.0 kGy during 8 weeks refrigerated storage (9oC). L. monocytogenes can proliferate following a radiation dose of 1.5 kGy, that provides a 2.5 log reduction, but not at 3.0 kGy, a 5 log reduction. Sommers et al. 2003. J Food Prot. 66(11):2051-2056 C. Sommers

42. Proliferation of L. monocytogenes on beef fine emulsion sausage that contains sodium diacetate and potassium lactate at 0. 1.5 and 3.0 kGy during 8 weeks refrigerated storage (9oC). Use of 0.15% sodium diacetate and 2% potassium lactate prevents growth of L. monocytogenes and spoilage bacteria in combination with irradiation during long-term storage. Sommers et al. 2003. J Food Prot. 66(11):2051-2056 C. Sommers

43. How virulent is irradiated Listeria monocytogenes? L. monocytogenes inoculated onto beef frankfurters, irradiated, and plated on blood agar to assess function of the hylA (hemolysin) virulence gene. Significant inactivation of hlyA was achieved only at radiation dose (>2 kGy) sufficient to achieve a 3-4 log reduction of the pathogen. Sommers et al. 2003. J Food Prot. 66(11):2051-2056 C. Sommers

44. Toxicological Safety of Irradiated Foods

45. Toxicological Safety • Irradiated foods have tested exhaustively • Numerous short-term, medium-term and long-term (multigenerational) animal feeding studies • Chemical and biochemical analyses • WHO determined in 1998 that foods treated at any dose posed no exceptional risk to consumers • As chemical analysis methods improve, the debate on the toxicological safety of irradiated foods continues. C. Sommers

46. Toxicological Safety • IR induces changes in the chemistry of treated foods • formation of chemical byproducts, some of which are known toxins • Vast majority of radiolytic products are also found in unprocessed foods and in foods treated with conventional processing techniques • Unique radiolytic products, i.e. chemicals byproducts which are only formed in foods by IR, have been a topic of recurrent attention. C. Sommers

47. Toxicological Safety • 2-alkylcyclobutanones (2-ACBs) • Generated at low levels in irradiated meats and poultry • Observed to cause damage to DNA under certain laboratory conditions • Most significant is 2-dodecylcyclobutanone (2-DCB) C. Sommers

48. O CH2 CH2 CH2 CH2 CH2 CH2 CH2 C OH CH2 H3C CH2 CH2 CH2 CH2 CH2 CH2 Palmitic Acid CH2 CH2 2-DCB CH2 CH2 CH2 CH2 CH2 CH2 C O H3C CH2 CH CH2 CH2 CH2 CH2 Genotoxicity of 2-dodecylcyclobutanone (2-DCB) • Produced by irradiation of fat containing foods.1 • 0.1 – 0.2 mg/g of fat in meats. • Produced equivocal results for genotoxicity in the Comet Assay.2, 3 • LeTellier and Nawar. (1972) Lipids. 1: 75-76. • Delincee and Pool-Zobel. (1998) Radiat. Phys. Chem. 52: 39-42. • Delincee et al. (1999) Lebensmittelbestralung 5. Deustche Tagung, Kahlruhe, Behichte der Bundesforcheshungsanstalt fur Ernarung. BFE-R—99-01. 11- 12 Nov. 1999, pp 262 – 269. C. Sommers

49. Toxicological Safety • 2-dodecylcyclobutanone (2-DCB) • review of literature suggests that improper tests do not allow any conclusions to be drawn(Smith and Pillai. 2004. Food Technology. 58 (11), 48-55.) • analysis using more appropriate tests indicates no meaningful risk posed (Sommers and Mackay. 2005. J Food Sci. 70:C254-257) • In vitro toxicology is one piece of information • accurate, appropriate tests are essential • Many factors determine actual potential for risk C. Sommers

50. Summary • Irradiation has shown promise to improve the safety, sensory properties and shelf-life of a wide variety of foods • An underutilized tool • Consumer understanding, acceptance is key • Challenge for processors and food scientists: derive benefits within limitations of technology • Singly or in combination with other treatments • Varying preparation methods, storage conditions, and market forces