News and analysis on the global poultry
and animal feed industries.
on June 24, 2009

Research Digest: June 2008

Reviews of research on listeria control and dealing with heat stess

Controlling Listeria With Lactic Acid, Sodium Lauryl Sulfate

Contamination of thermally treated product with Listeria monocytogenes (LM) can lead to foodborne illness, listeriosis, in humans. Therefore, non-reheated frankfurters are considered a high-risk product. USDA and FSIS enforce a zero tolerance rule for LM in ready-to-eat (RTE) meats. Various control measures for LM in RTE products can be put in place by processors including (1) a post-lethality treatment combined with a LM growth inhibitor, (2) a post-lethality inactivation treatment or a growth inhibitor, or (3) sanitation measures and environmental testing. Depending on which alternative is used by the processor, processors may be subject to less frequent verification testing by FSIS.

Lactic acid (LA) is a compound that is generally recognized as safe and it has bacteriocidal and bacteriostatic effects against LM that are well documented. Sodium lauryl sulfate (SLS) is an acid anionic surfactant that is approved for use by FDA as a wetting or whipping agent in many foods, though it is not currently not included in FSIS list of “safe and suitable ingredients used in the production of meat and poultry products.” However, SLS does have bacteriocidal and bacteriostatic properties. The objective of this study was to determine the effect of spraying with LA or SLS, individually or as a mixture, on LM on frankfurters.

Frankfurters were prepared and inoculated with 0.2 ml of a 10-strain cocktail of LM. The inoculum covered the entire surface of the frankfurter to obtain a target level of 4.8 log CFU/cm2. After inoculation, frankfurters were kept at 4 C for 15 min to allow attachment of the cells. Frankfurters were sprayed with 5 percent (vol/vol) LA or 0.5 percent (vol/vol) SLS after inoculation. Frankfurters were also sprayed before and after inoculation with a mixture of LA and SLS (LASLS) or distilled water (DW). Inoculated frankfurters without any spray treatment served as a control.

All spraying solutions applied after inoculation resulted in a reduction in pathogen levels including the DW treatment compared to the control. The authors explained that this decrease was due to a physical removal of cells. Spraying the frankfurters with LASLS after inoculation resulted in a greater reduction (approximately 2.8 CFU/cm2) of LM compared to LA or DW. The authors explained that the antimicrobial effects of SLS increase at a low pH. There seemed to be an additive effect of SLS and LA because when these compounds were used alone, the bacterial levels did not differ from DW alone. When applying the LASLS before inoculation, a reduction in LM was observed compared to DW, and this reduction was similar to when compounds were sprayed after inoculation. The authors suggested that this was due to bacteriocidal effects of SLS rather that physical removal of cells.

None of the treatments reduced LM levels during storage; however, treatments including LA sprayed after inoculation had a reduced growth rate compared to the DW (after inoculation) treatment.

The results of this study suggest that using LA and SLS in combination may improve effectiveness of the antimicrobial properties of each. The authors suggested that the SLS decreases surface tension of the solution on the frankfurter thereby allowing better distribution of LA on the product. Furthermore, antimicrobial properties (e.g., damage to cytosolic membrane) of SLS are enhanced at low pH (provided by LA). The authors suggest that using LA and SLS in combination may be useful as a post-lethality treatment for reducing LM levels and suppressing growth of surviving LM. Furthermore, this treatment may allow processors to operate under alternative 1 resulting in less frequent FSIS verification testing. Processors would have to validate the effectiveness of these antimicrobials in their products. Sensory properties of products containing these compounds would also need to be evaluated.


O.A. Byelashov, P.A. Kendall, K.E. Belk, J.A. Scanga and J.N. Sofos; 2008. Control of Listeria monocytogenes on vacuum-packaged frankfurters sprayed with lactic acid alone or in combination with sodium lauryl sulfate. Journal of Food Protection, 71 (4): 728-734.



Water Supplements Improve Heat Stress Performance

Heat stress on broilers is a major concern to poultry growers/integrators as it can lead to decreased body weight, increased feed conversion, decreased yield at the processing plant, and even poor meat quality. Mortality can also increase due to heat stress. All of these effects can result in poor performance and thus, economic loss. Using strategies to prevent or reduce heat stress on birds can improve these negative effects. Appropriate housing design, proper ventilation and cooling systems, and proper feed formulations can help reduce heat stress. Additionally, the uses of electrolytes, ascorbic acid, acetylsalicylic acid, potassium chloride and sodium bicarbonate have all been used to reduce the effects of heat stress. The purpose of this study was to evaluate the combined effects of ascorbic acid (AA), acetylysalicyclic acid (ASA), potassium chloride (KCl), and sodium bicarbonate (NaHCO3) supplemented in water on the performance of heat-exposed broilers.

Over three replications, 225 broilers were divided into three groups: 1) non-heat stressed control (control), 2) heat stressed supplemented (HS-SUP), and 3) heat stressed non-supplemented (HS-NON). Birds in the heat stressed treatments were subjected to elevated temperatures (30-33 C for 12 h) for seven days beginning at day 35. Control birds were kept at thermoneutral conditions (21-23 C). The HS-SUP birds were supplemented ad libitum with AA (62.5 mg/L), ASA (62.5 mg/L), KCl (125 mg/L) and NaHCO3 (75 mg/L) in the water. Body weight (BW), BW gain, total feed consumption feed conversion (FCR) and mortality were evaluated.

Heat stress resulted in inferior performance factors including lower live body weight, body weight gain, total feed consumption, and increased feed conversion and mortality compared to the control. Growth rates of heat stressed broilers were also slowed compared to control. However, supplementing water (HS-SUP) with AA, ASA, KCl and NaHCO3 resulted in improved performance factors over the HS-NON and control treatments. Previous research has shown that these supplementations have improved performance when used individually.

The results of this study suggest that the water supplementation with the combination of AA, ASA, KCl and NaHCO3 improved performance of heat stressed broilers. The authors recommend this combination for use with broilers under heat stress conditions.


Comment: A comparison of this supplement combination and the individual ingredients would be useful in determining if there are any additive effects when using these ingredients in combination. If there are no additive effects, it may be worthwhile to concentrate on a single ingredient or a combination of fewer ingredients.


D.A. Roussan, G.Y. Khwaldeh, R.R. Haddad, I.A. Shaheen, G. Salmeh and R. Al Rifai; 2008. Effect of ascorbic acid, acetylsalicylic acid, sodium bicarbonate, and potassium chloride supplementation in water on the performance of broiler chickens exposed to heat stress. Journal of Applied Poultry Research, 17: 141-144.

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