October 25, 2007
US study shows organic acids controls E. coli O157:H7 in ground beef.
Organic acids are already widely used to reduce the number of bacterial pathogens on meat carcasses and some meat products despite the vague acceptance of antibacterial mechanism in meat. Research from the Texas A&M University shows that generally accepted that undissociated molecule is mostly responsible for the antimicrobial activity.
The accumulation of a weak acid in the bacterial cytosol--the internal fluid of the cell--will result in acid dissociation if the acid dissociation constant (pKa) is lower than the intracellular pH. This will release a proton and acidify the cytosol.
Acetic and lactic acids are among the acids most frequently used to decontaminate carcasses. By combining a high-pressure water wash and spray with 2 percent L-lactic acid at 55'C, university scientists were able to reduce counts of E. coli O157:H7 by 5-log cycles on-beef carcass surfaces before they were chilled. A secondary spray using 4 percent L-lactic acid at 55'C led to an additional 2-log reduction in E. coli O157:H7 populations. The overall reduction reached 7 log cycles.
When beef obtained from these carcasses was ground, E. coli O157:H7 appeared at low levels and remained viable for 21 days of refrigerated storage. The same results were obtained when the researchers inoculated the trimmings with E. coli O157:H7, treated them with lactic acid and ground them. This indicates that carcass sprays are limited only to superficial contamination. So, bacteria lodged in crevices or other areas not reached by the antimicrobial solution may not be exposed to treatment, and could remain viable in the ground beef.
The use of organic acids for controlling pathogens in ground beef presents challenges including, but not limited to, the use of the acids at low temperatures, the pH of the meat and the large contact surface on the ground meat. To address these challenges, the acid can be incorporated into the product and use slow acid-release mechanisms for extended effect.
