Controlling growth of Listeria monocytogenes and Pseudomonas fluorescens in thermally processed ground beef by sodium lactate, encapsulated or unencapsulated polyphosphates incorporation

Abstract

This work was undertaken to evaluate the effectiveness of using sodium lactate (SL), encapsulated (e) and unencapsulated (u) polyphosphates (PP; sodium tripolyphosphate, STP; sodium acid pyrophosphate, SPP), and various combinations of these additives on growth of Listeria monocytogenes and Pseudomonas fluorescens in cooked ground beef during 30 d refrigerated storage. The study consisted of two independent work packages as L. monocytogenes and P. fluorescens in the same experimental settings. During storage, analysis of oxidation-reduction potential (ORP), water activity (aw), pH, and counts of L. monocytogenes and P. fluorescens were carried out. Results indicated that there was no difference among the groups in terms of L. monocytogenes or P. fluorescens counts on processing day. Although only PP incorporated groups had higher (P < 0.05) P. fluorescens counts compared to those groups formulated with only SL at the end of storage, there were no differences among these groups regarding L. monocytogenes load. The lowest L. monocytogenes and P. fluorescens counts were determined in the samples containing a combination of SL with uSPP or eSPP or ueSPP at the end of storage (P < 0.05). A combinations of SL with uSTP or eSTP or ueSTP did not create further reduction in L. monocytogenes load then reduction level obtained by SL which had lower (P < 0.05) load compared to MO. The same combination groups had lower (P < 0.05) P. fluorescens counts then those of MO and SL groups. The lower (P < 0.05) ORP values were determined in all PP added groups during storage compared to control, MO and SL groups. ORP in all treatments generally increased (P < 0.05) with storage. There was no significant changes in pH during storage. A slight decrease (P < 0.05) in aw was determined during storage in P. fluorescens experiments, whereas aw levels was stable in case of L. monocytogenes. In general, the use of ePP did not create any significant changes on pH, aw, ORP values and counts of L. monocytogenes and P. fluorescens compared to that of uPP.This study showed that encapsulation is not a factor affecting antimicrobial efficiency of PP and using PP-SL combinations have synergistic effect on reducing the viability of L. monocytogenes and P. fluorescens and their subsequent growth ability in cooked ground beef. Therefore, cross-contamination of L. monocytogenes or P. fluorescens cells on RTE meat products may be controlled more effectively with combinations of SL with ePP or uPP or uePP.