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Salmonella Enteritidis has been recognized as the cause of over 60% of reported salmonellosis cases, associated with shell eggs and egg products (CDC, 2013). In order to reduce occurrence of salmonellosis, egg washing on an industrial scale was mandated in some countries such as the United States of America and Japan (Hutchinson et al., 2003). Chemical sanitizers like quaternary ammonia (QA), used in commercial egg washing have been seen to cause degradation of the egg cuticle, which is a natural protectant against bacterial penetration (Bialka et al., 2004). So as to preserve the cuticle, and not compromise on microbial safety, plasma activated water (PAW) was investigated as a possible sanitizer on the basis of microbial reduction on artificially contaminated eggs, as well as its effect on the quality of cuticle and egg shell strength. PAW was generated by exposing distilled water to atmospheric pressure plasma jet from filtered dry air. PAW and QA were then used to wash eggs artificially contaminated with Enterobacter aerogenes (non-pathogenic Salmonella surrogate), to compare their effectiveness in microbial reduction on egg surface as well as in wash water. Colorimetric analysis was performed on eggs washed with sanitizers and stained with a cuticle sensitive dye, to evaluate loss of cuticle. Additionally, damage to cuticle was studied using microscopic analysis of egg shells. Damage to shell integrity was studied by means of texture analysis of sanitized eggs, to ensure that the acidic nature of PAW did not affect egg shell strength. Preliminary planktonic-cell experiments with distilled water (DW) which served as control, caused bacterial reduction of 0.2±0.1 log CFU/ml from initial concentration of 9.2±0.1 log CFU/ml. On the other hand, treatment with equal volumes of PAW or QA resulted in bacterial concentration below detection limit (3.2 log CFU/ml). This proved that microbial reduction was not due to osmotic pressure generated by water. This was further enforced by analysis of artificially contaminated shell egg surface, with an initial bacterial concentration of 7.9±0.3 log CFU/egg, sanitized with PAW, QA and DW. Upon exposure of eggs to sanitizers by massaging of egg surface, it was noted that bacterial survival after treatment with both PAW and QA was below detection limit (2.3 log CFU/egg). Thus, the microbial reduction efficiencies of PAW and QA were comparable, at over 5.3 log CFU/egg. Conversely, treatment with DW showed survival of 3.7±0.1 log CFU/egg on the surface of egg. Colorimetric analysis showed statistically significant difference between un-sanitized farm eggs, and farm-eggs treated with PAW and, QA and store-bought eggs suggesting that eggs treated with PAW retained their cuticle layer better. Texture analysis of treated whole eggs revealed that the acidic nature of PAW did not affect the peak force needed to crack eggs. Eggs sanitized with both QA and PAW showed highest peak strength at the small-end up position and lowest peak force at the equatorial positions. A significant difference was observed between the orientations of eggs; however, the difference in strength within a given orientation, among different sanitizing treatments was not significant. This study showed that PAW possessed both comparable anti-microbial efficacy and effect on egg shell strength as QA, while being better at cuticle retention on shell egg surface. QA was observed to erode the cuticle layer, while similar treatment with PAW showed that the cuticle coverage was relatively intact and comparable to unsanitized eggs. Thus, PAW appeared to show promise for use in egg washing process to replace current chemical sanitizers (QA) with minimal cuticle loss.

ETD_8595

M.S.

Includes bibliographical references

by Shruthi Lakshmi Narasimhan

doi:10.7282/T3HD7ZWS

ETD graduate

The author owns the copyright to this work.