The effect of pH and nitrite concentration on the antimicrobial impact of celery juice compared with sodium nitrite on Listeria monocytogenes
Increasing consumer concerns of harmful preservatives have intensified consumers' demand for natural and organic alternatives. In response to this demand, uncured or no-nitrate-or-nitrite-added meat products which utilize celery juice concentrates as an alternative to sodium nitrite, have emerged on the market to replace conventional nitrite sources. The objective of this study was to evaluate the effect of celery juice pH for the impact of nitrite on L. monocytogenes growth. In addition, equal concentrations of nitrite in celery juice and conventional nitrite were evaluated to determine the impact of nitrite concentration from these sources on L. monocytogenes growth. These objectives were assessed using both a broth and ham system. Celery juice (CJ) was less effective than the conventional nitrite in the broth study at 100 ppm nitrite concentration but in the ham experiment the CJ treatments at both 100 and 200 ppm resulted in similar growth of L. monocytogenes (p>0.05) compared to their counterparts 100 and 200 ppm sodium nitrite. Adjusting the pH of the celery juice proved to be more effective at suppressing L. monocytogenes growth at 200 ppm than 100 ppm in the ham. No differences in growth (p>0.05) were found between the unadjusted 100 ppm celery juice (pH~9.2) and adjusted 100 ppm celery juice (pH~6.0) in either the broth or ham study. Color measurements of the ham indicated that all the CJ treatments were darker (lower L*) and more yellow (higher b*) than the sodium nitrite treatments. As concentration increased within the CJ treatments the L* became significantly lower (p<0.05) and b* values became significantly (p<0.05) greater. Overall, similar redness (a*) values were seen in both the CJ and sodium nitrite treatments. Residual nitrite concentrations were similar for both the 100 and 200 ppm treatments in the ham study, except for the adjusted (pH~ 6.3) 200 ppm CJ treatment which had significantly less (p<0.05) residual nitrite than the unadjusted (pH~6.6) 200 ppm CJ and 200 ppm sodium nitrite treatments.