Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 2012
Publication Date: June 1, 2013
Citation: Cox Jr, N.A., Cason, J.A., Buhr, R.J., Richardson, K.E., Richardson, L.J., Rigsby, L.L., Cray, P.J. 2013. Variations in preenrichment pH of poultry feed and feed ingredients after incubation periods up to 48 hours. Journal of Applied Poultry Research. 22(2):190-195. Interpretive Summary: Human salmonellosis outbreaks have been linked to contamination of animal feeds. Therefore, it is critical to use sensitive detection methods. Most Salmonella cells in feed are stressed by dryness and heat used in feed processing. In addition, this study reports that when feeds are tested for Salmonella, the pH of the commonly used media drops during incubation to a level that can kill or severely injure Salmonella which can result in this contamination going undetected.
Technical Abstract: Salmonella sustains acid injury at about pH 4.0-5.0. Since most Salmonella present in feed and feed ingredients are already stressed by desiccation (and heat if pelleted), exposure to low pH may cause death and/or injury and result in contamination going undetected. The objective of this study was to determine if this pH of preenrichment media decreases during incubation with an assortment of feed samples. Five g of 13 different ingredients and 5 types of feed were added to 45 mL of buffered peptone water (BPW), lactose broth (LB), minimal salts medium (M-9) or Universal Preenrichment (UP). Media were incubated at 37oC for 18, 24, and 48 h and the pH of the media was determined after incubation. After 18 hrs of incubation, the pH of the media had decreased to a pH range of 4.0 – 6.1. Lactose broth was observed to have the lowest buffering capacity and UP had the greatest buffering capacity. The pre-enrichment media behaved in a similar fashion when testing oilseed meals (i.e. original pH range was 6.2 - 7.2 and decreased to a pH 4.2 to 5.4 for soya and pH 4.4 - 6.0 for canola). With these ingredients, the buffering capacity of BPW, LB and M-9 were similar. There was more variation with the pH of the pre-enrichment media among the different poultry feed types. The media from broiler and layer feeds had a slightly lower original pH (6.2 - 7.0) than the turkey feed (6.4 to 7.1) and decreased to a lower pH after 18 - 48 hrs incubation (pH 3.9 - 5.6 compared to pH 4.5 - 6.8). In the case of feed, the buffering capacity of BPW, LB and M-9 were similar. UP exhibited the greatest buffering capacity. In light of these data, detection methods for Salmonella in feed and feed ingredients should be re-evaluated.