Efficacy of buffered propionic acid against Salmonella Typhimurium in ground pork stored at 4ÃÂ°C and 10ÃÂ°C and inhibition of Listeria monocytogenes by buffered dry vinegar in ready-to-eat uncured turkey stored at 4ÃÂ°C
Date of Award
Doctor of Philosophy
James S. Dickson
Joseph G. Sebranek
The objective of the first study was to evaluate the antimicrobial efficacy of buffered propionic acid-based antimicrobials (BP-6 buffered to pH 6; BP-5 buffered to pH 5) against Salmonella Typhimurium (ST) inoculated by two methods in ground pork (1) Addition of antimicrobial to ground pork followed by inoculation with Salmonella Typhimurium (2) Addition of Salmonella Typhimurium to ground pork followed by addition of antimicrobial. This study was undertaken to check if there would be any difference in the antimicrobial efficacy of buffered propionic acid if added before or after Salmonella addition to ground pork. Ground pork treatments consisted of 0.2% BP-6, 0.2% BP-5 and an untreated control without any antimicrobial. The treatments were challenged with a 5-strain inoculum of ST with a target of 3-4 log CFU/g. Storage was at 4 ÃÂ°C for 4 weeks and ST populations were tested at weekly intervals. The study was conducted as a single replication. Results showed that in method-1, the initial ST populations in all the treatments were within the expected range. In method-2, the initial ST populations were lower (~ 1 log) than expected. In both methods of addition, a decline in ST populations was seen in the antimicrobial treatments as well as untreated control throughout 4 weeks. The probable reason for the decline could be the low incubation temperature (4 ÃÂ°C) that might have reduced survival. The propionic acid levels in both the antimicrobial treatments were within the expected range (0.09-0.1%). This study suggests that in method-1 and method-2, there was no difference in the log change of ST populations between the treatments throughout the testing period. However, 4 ÃÂ°C is not an optimum temperature for growth of ST because both antimicrobial treatments and untreated control resulted in restricted the growth of ST. Additional research has to be conducted to evaluate the efficacy of buffered propionic acid against ST in ground pork stored at temperatures optimal for ST growth.
The objectives of the second study are to evaluate the antimicrobial efficacy of two buffered propionic acid (BP) formulations (BP-6 buffered to pH 6; BP-5 buffered to pH 5) against Salmonella Typhimurium (ST) in ground pork stored at 4 ÃÂ°C and 10 ÃÂ°C for 3 weeks and to determine the effects on spoilage microflora, color, cook loss and sensory characteristics on uninoculated pork patties stored at 4 ÃÂ°C for 3 weeks. ST inhibition results at 4 ÃÂ°C showed no significant differences (p=0.9948) in the microbial change of ST populations between untreated control and buffered propionic acid treatments. All the treatments showed a drop of 0.1-0.4 log CFU/ml rinse in ST populations by the end of three weeks with sporadic growth in a few samples treatments at 4ÃÂ°C. ST results at 10ÃÂ°C showed that buffered propionic acid treatments resulted in a drop of 0.3-1.4 log and 0.2-1.8 log CFU/ml rinse respectively by the end of 3 weeks whereas, ST population in untreated control declined after one week and no significant ST microbial differences (p=0.9982) were seen throughout the testing period. Lactic acid bacteria results showed that untreated control and antimicrobial treatments reached >7 log CFU/ml rinse by the end of 2 and 3 weeks. Aerobic plate counts of untreated control and the antimicrobial treatments reached 7-8 log and 6-7 log CFU/ml rinse respectively by the end of 3 weeks. pH results showed significant differences (p<0.05) between the treatments at 0 and 1 week but no significant differences were seen at the remaining test intervals. Statistical analysis of the instrumental L*, a* and b* values showed significant differences (p<0.05) between the treatments at few testing intervals. The a* values declined, as the color of the ground pork changed from bright red to pale red/brown and significant differences (p<0.05) were seen between the treatments at 1 and 2 weeks. Cook loss results showed no significant differences (p=0.1517) between untreated and antimicrobial treatments. Overall sensory scores showed no significant differences between the treatments at week-0 whereas; significant differences (p<0.05) were seen between some of the treatments at week-1 and week-2. Overall, this study demonstrated that 4 ÃÂ°C is not an optimum temperature for ST growth because both untreated and antimicrobial treatments restricted the growth of ST in ground pork. At 10 ÃÂ°C, it is not possible to compare the ST inhibition results between the untreated and antimicrobial treatments because no growth of ST was seen throughout three weeks in buffered propionic acid formulations whereas; in untreated control ST growth was inhibited by the outgrowth of spoilage and non ST populations after one week. Both antimicrobial formulations delayed the growth of lactic acid bacteria and aerobic bacteria by one week compared to untreated control without negatively impacting the sensory parameters of ground pork stored at 4 ÃÂ°C for 3 weeks.
In the third study, a reduced sodium ready-to-eat (RTE) uncured turkey was manufactured with buffered dry vinegar treatments to validate the inhibition of Listeria monocytogenes and spoilage microflora, and to determine the effects on sensory and quality attributes. Samples were stored at 4 ÃÂ°C for 12 weeks, and the study was independently replicated three times. Two different 5-strain inoculum of L. monocytogenes obtained from different sources were used for evaluating the efficacy of the buffered dry vinegar treatments. The results showed that 0.6% and 0.8% buffered dry vinegar sodium-based (BDV-SB) and potassium–based buffered dry vinegar (BDV-PB) at 0.7% and 0.9% controlled L. monocytogenes for 12 weeks. Untreated control product containing no buffered dry vinegar showed >1 log increase in L. monocytogenes populations counts at the end of 2 weeks. Statistical analysis confirmed that the dry vinegar treatments inhibited (P<0.05) the growth of L. monocytogenes compared to the untreated control. No significant differences (P>0.05) were seen in the inhibition of L. monocytogenes between the two different 5-strain inocula. Instrumental color results showed no significant differences between the treatments. Purge loss results showed no significant differences between the dry vinegar treatments but significant differences were seen between untreated control and dry vinegar treatments at few testing intervals. The overall results indicated that the dry vinegar ingredients (6.66 mM – 8.83 mM acetic acid in finished product) were effective in inhibiting L. monocytogenes obtained from multiple sources in reduced-sodium RTE uncured turkey stored at 4ÃÂ°C without adversely impacting the quality attributes
Mani Kumar Badvela
Badvela, Mani Kumar, "Efficacy of buffered propionic acid against Salmonella Typhimurium in ground pork stored at 4ÃÂ°C and 10ÃÂ°C and inhibition of Listeria monocytogenes by buffered dry vinegar in ready-to-eat uncured turkey stored at 4ÃÂ°C" (2016). Graduate Theses and Dissertations. 16505.