Effects of Acid Adaptation, Product pH, and Heating on Survival of Escherichia coli O157:H7 in Pepperoni

Abstract

The thermotolerance of E. coli O157:H7 cells (strain 380-94) heated in pepperoni is reported. Information on the pattern of thermal inactivation of E. coli O157:H7 in pepperoni was applied in the development of heating processes designed to reduce E. coli O157:H7 numbers therein by 5 log 10 units.The identification of fermented meat as a vehicle of infection for Escherichia coli O157:H7 (4) has led to the development of heat treatments for such products (3,8,10) such that a 5-log 10 -unit reduction in E. coli O157:H7 numbers can be achieved during processing. Fermented meat had traditionally relied on its low pH status as its primary preservative mechanism; however, E. coli O157:H7 has been shown to be unusually resistant to inactivation at low pHs (9, 12, 13). Thus, it is imperative that this factor be borne in mind when heat treatments are designed. Previous studies involving E. coli O157:H7 (5, 16) have shown that cross-protection, i.e., preadaptation to one stress encountered in the environment, e.g., acid, can lead to enhanced resistance to a different, and possibly previously unencountered, stress, e.g., heat. Therefore, the possibility that cross-protection could occur must be considered in the development of thermal inactivation protocols. This study aimed to elucidate the effects of prior acid adaptation and final product pH on the thermotolerance of E. coli O157:H7 in pepperoni. The information derived was used to develop a commercially applicable postfermentation heating process capable of inducing a 5-log 10 -unit reduction in E. coli O157:H7 numbers.E. coli O157:H7 (strain 380-94) was obtained from the Centers for Disease Control and Prevention, Atlanta, Ga., maintained on tryptone soya agar (TSA; Oxoid, Basingstoke, England) at 4°C, and recultured monthly. Inocula were prepared by adding one loopful of culture from TSA into (i) 50 ml of brain heart infusion broth (BHI; Oxoid) (0.2% [wt/vol] glucose) or (ii) 50 ml of BHI supplemented with 1% (wt/vol) glucose (1.2% [wt/vol] glucose). Cultures were grown at 37°C (18 h) to provide non-acid-adapted organisms and acidadapted organisms, respectively (2). pH was estimated using a model 210 pH meter (Orion Research Corp., Boston, Mass.). Pepperoni batters were prepared and fermented by the following modifications of the method previously described (18). Meat mixtures were inoculated with acid-adapted and nonacid-adapted E. coli O157:H7, as previously outlined, and stored at 4°C overnight. The meat mixtures were then incorporated into standard-and low-pH batter mixes. The standardfinal-pH product was formulated to ferment to a final pH of 4.8 by the addition of 0.625% sodium nitrite (0.01%), Pediococcus spp. starter culture (0.028%), sodium ascorbate (0.048%), spice mix (0.302%), dextrose (0.625%), mustard flour (1.5%), and salt (2.5%) (all wt/wt) with other ingredients previously described (18). The low-final-pH product was formulated to ferment to a final pH of 4.4 by the addition of dextrose at 1% (wt/wt). Approximately 12 sausages per batch (150 by 30 mm...

Determination of the survival levels of acid-adapted Escherichia coli O157:H7in sucuk (Turkish-type fermented sausage)

“…Contrary to this research, in a study conducted by Riordan et al (28) it was detected that acid adaptation did not result in any increase in the survival rate of E. coli O157:H7 in pepperoni, another fermented meat product. Dlamini and Buys (13) claimed that a significant difference did not exist between survival levels of acid-adapted and nontreated E. coli O157:H7 cells in amasi, also a traditional fermented dairy product, but that in commercial amasi the nontreated cells had a higher survival rate.…”

Health and Safety Considerations of Fermented Sausages

“…Other studies have reported variable quality and sensory effects, ranging from unacceptable to improved sensory scores, due to heat treatments at higher temperatures (≥approx. 50 ∘ C) [105,221,275,276]. Combinations of high temperature and reduced treatment times may be regarded as most feasible in industrial production.…”

“…Combinations of high temperature and reduced treatment times may be regarded as most feasible in industrial production. Optimal treatment regimes are likely to differ between products with different characteristics [102,221,273,274,276].…”

Predicting the Concentration of Verotoxin-Producing Escherichia coli Bacteria during Processing and Storage of Fermented Raw-Meat Sausages

“…The data sets used for developing the models for VTEC were obtained from the ComBase database (15) or from the literature (13,20,22,(35)(36)(37)(38) or were kindly provided by the Food Safety Centre, University of Tasmania (39,40). Additional data were generated in this work to address data gaps (see Table S1 in the supplemental material).…”