Buffering capacity comparison of tris-phosphate-carbonate (TPC) and buffered peptone water (BPW) Salmonella pre-enrichments for manufactured feed and feed ingredients

Authors: ESCOBAR, CESAR - Auburn University; MUNOZ, LUIS - Auburn University; BAILEY, MATEHEW - Auburn University; KREHLINGS, JAMES - Auburn University; PACHECO, WILMER - Auburn University; HAUCK, RUEDIGER - Auburn University; Buhr, Richard - Jeff; MACKLIN, KENETH - Auburn University

Submitted to: Poultry Science Association
Publication Type: Abstract Only
Publication Acceptance Date: 5/26/2022
Publication Date: 7/11/2022
Citation: Escobar, C., Munoz, L.R., Bailey, M.A., Krehlings, J.T., Pacheco, W.J., Hauck, R., Buhr, R.J., Macklin, K.S. 2022. Buffering capacity comparison of tris-phosphate-carbonate (TPC) and buffered peptone water (BPW) Salmonella pre-enrichments for manufactured feed and feed ingredients. Poultry Science Association. p. 145.

Interpretive Summary:

Technical Abstract: Various comprehensive culture-based methods to detect Salmonella in animal feed have been developed due to the impact of this bacterium on public and animal health; these methods generally include pre-enrichment (non-selective medium), enrichment (selective medium), sample isolation and serological confirmation. Recovery of Salmonella depends on the type of sample, level of stress/injury on the bacteria by the sample environment, presence of competitive bacteria, and level of Salmonella contamination. A pH 6.5 is near the ideal pH range for Salmonella growth and pH values below 5 could affect detection and recovery. Tris-phosphate-carbonate (TPC) is a new pre-enrichment buffer that demonstrated a strong buffering capacity. For this project, buffered peptone water (BPW) and TPC buffering capacity were evaluated as pre-enrichment mediums for detection of Salmonella in animal feed and feed ingredients. A total of 185 samples (feed ingredients and finished feed) were collected from 5 commercial feed mills (A, B, C, D and E), 2.5 g of sample were mixed with 22.5 mL of pre-enrichment and incubated, pH was measured at 0 and 24 h. Data was analyzed using one-way ANOVA (GLM) (significant P = 0.05), means were separated using Tukey’s HSD and pH change in time (initial to final) was analyzed using independent t-test for each sample type in SPSS® software. Differences were observed in pH values (P < 0.001), post mixing samples of feed mill A and ground corn of feed mill C reported higher initial pH value (0 h) for TPC (8.29) and BPW (7.24) respectively. Meat & bone meal of feed mill E reported higher final pH value (24 h) for TPC (7.39) and ground corn of feed mill A for final BPW (6.64). Pellet loadout of feed mill E reported lower pH value for final TPC (6.18) and final BPW (4.81). Moreover, differences were observed comparing pH values by type of sample (P < 0.001), Corn DDGs samples presented lower initial pH values for TPC (6.97) and BPW (5.75), while pellet loadout presented lower final pH values for TPC (6.26) and BPW (5.12). In addition, using t-test, ground corn and mash loadout samples reported differences in pH change (P < 0.002) for both, BPW and TPC. Pellet loadout and wheat midds experienced the greatest pH change (21.6% and 27.4% respectively) at 24 h using BPW, whereas pellet loadout (21.6%) and post cooling (20.2%) had the greatest change using TPC. From meat & bone meal samples, 4 were positive for Salmonella (3 from BPW and 1 from TPC). Results show the buffer capacity of two-pre-enrichments and how some feed ingredients and finished feeds change pH during incubation. Samples from additional feed mills will be collected and analyzed to complete this project.