Rapid optical measurements of microbial contamination in raw ground beef and effects of citrate and lactate

The levels of microbial contamination in purchased pre-wrapped fresh ground beef samples were estimated by using the BioSys automated optical system for rapid detection of the presence of microorganisms. Additionally, the response of the system to the activity of antimicrobial agents in meat was evaluated after adding (separately) the sodium salts of lactic and citric acid to meat samples. Meat homogenates in peptone water were incubated at 30°C in broth containing the indicators bromcresol purple (pH) or resazurin (redox potential). Curves (light transmittance versus time) generated by the instrument showed significant and rapid changes in the indicator color, and times of detection of the initial changes were inversely proportional to the standard plate counts in the meat samples. This relationship indicated that the detection time can provide a good estimate of the microbial quality of fresh meat. Treatment of meat with 2% citrate or 2% lactate extended the shelf life by about 2 and 4 days. respectively. Detection time values confirmed the ability of the salts to delay the microbial spoilage of meat.