E: Food Engineering & Physical Properties Microencapsulated Antimicrobial Compounds as a Means to Enhance Electron Beam Irradiation Treatment for Inactivation of Pathogens on Fresh Spinach Leaves Carmen Gomes, Rosana G. Moreira, and Elena Castell-Perez Abstract: Recent outbreaks associated to the consumption of raw or minimally processed vegetable products that have resulted in several illnesses and a few deaths call for urgent actions aimed at improving the safety of those products. Electron beam irradiation can extend shelf-life and assure safety of fresh produce. However, undesirable effects on the organoleptic quality at doses required to achieve pathogen inactivation limit irradiation. Ways to increase pathogen radiation sensitivity could reduce the dose required for a certain level of microbial kill. The objective of this study was to evaluate the effectiveness of using natural antimicrobials when irradiating fresh produce. The minimum inhibitory concentration of 5 natural compounds and extracts (trans-cinnamaldehyde, eugenol, garlic extract, propolis extract, and lysozyme with ethylenediaminetetraacetate acid (disodium salt dihydrate) was determined against Salmonella spp. and Listeria spp. In order to mask odor and off-flavor inherent of several compounds, and to increase their solubility, complexes of these compounds and extracts with β -cyclodextrin were prepared by the freeze-drying method. All compounds showed bacteriostatic effect at different levels for both bacteria. The effectiveness of the microencapsulated compounds was tested by spraying them on the surface of baby spinach inoculated with Salmonella spp. The dose (D 10 value) required to reduce the bacterial population by 1 log was 0.190 kGy without antimicrobial addition. The increase in radiation sensitivity (up to 40%) varied with the antimicrobial compound. These results confirm that the combination of spraying microencapsulated antimicrobials with electron beam irradiation was effective in increasing the killing effect of irradiation. Keywords: antimicrobial efficiency, fresh produce, ionizing radiation, Listeria spp., Salmonella spp. Practical Application: Foodborne illness outbreaks attributed to fresh produce consumption have increased and present new challenges to food safety. Current technologies (water washing or treating with 200 ppm chlorine) cannot eliminate internalized pathogens. Ionizing radiation is a viable alternative for eliminating pathogens; however, the dose required to inactivate these pathogens is often too high to be tolerated by the fresh produce without undesirable quality changes. This study uses natural antimicrobial ingredients as radiosensitizers. These ingredients were encapsulated and applied to fresh produce that was subsequently irradiated. The process results in high level of microorganism inactivation using lower doses than the conventional irradiation treatments. Introduction Several bacterial pathogens have caused fresh produce- associated epidemics of enteric illness, including Salmonella en- terica, pathogenic Escherichia coli, Shigella spp., Campylobacter spp., Listeria monocytogenes, Staphylococcus aureus, Yersinia spp., and Bacil- lus cereus (Brandl 2006). While decontamination procedures may be applied to fresh produce, current procedures cannot elim- inate the contaminating microorganisms (Takeuchi and others 2000). It is well known that the difference of total microbial counts between vegetables either water washed or treated with 200 ppm chlorine is usually not more than 1 log CFU/g (Beuchat 2002). MS 20110324 Submitted 3/14/2011, Accepted 5/12/2011. Authors are with Dept. of Biological & Agricultural Engineering, College Station, TX 77843-2117, U.S.A. Direct inquiries to author Gomes (E-mail: carmen@tamu.edu). Irradiation is a nonthermal process, which can effectively inac- tivate pathogenic bacteria. Radiation can be applied after pack- aging, thus avoiding recontamination and reinsfestation (Farkas 1997). Two of the most promising applications of this technology are the assurance of safety and shelf life extension. In 2008, the U.S. Food and Drug administration (USFDA 2008) published a final rule that allows the use of irradiation up to a dose of 4 kGy to make fresh Iceberg lettuce and spinach safer and last longer. However, previous studies have shown that doses above 1.5 kGy are detrimental to the quality of lettuce and spinach (Han and oth- ers 2004; Gomes and others 2008). Therefore, the actual radiation dose used should be a balance between what is needed and what can be tolerated by the product without unwanted changes. Thus, radiosensitization of microorganisms can be obtained by physi- cal and chemical means in combination with other preservation methods such as mild heat treatment, modified atmosphere pack- aging, addition of antimicrobial agents, and their combinations (Lacroix and Ouattara 2000). C  2011 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2011.02264.x Vol. 76, Nr. 6, 2011  Journal of Food Science E479 Further reproduction without permission is prohibited