Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 19, 1997
Publication Date: N/A
Interpretive Summary: Nisin, a naturally occurring, antimicrobial protein associated with cheese making, was investigated as a means of killing bacteria attached to beef. For this experiment, the protein was incorporated into an edible gel and applied to beef lean and fat tissue which had been experimentally inoculated with a meat spoilage organism, Brochothrix thermosphacta, to obtain approximately 50,000 bacteria/cm**2. Samples were left untreated (U), or treated with the edible gel known as calcium alginate (A), an antimicrobial compound, nisin (N), or nisin incorporated in the edible calcium alginate gel (AN). Treated tissues were processed into ground beef, held under refrigeration, and sampled for bacterial populations and antimicrobial activity at days 0, 7, and 14. U, A, and N treatments of lean and adipose beef did not affect bacterial growth, whereas AN treatments suppressed bacterial growth at day 0. By day 7, nisin titers from AN-treated ground beef were diminished considerably and bacterial populations had increased. At day 14 of the study, all treatments exhibited bacterial populations greater than 10,000,000 CFU/g and antimicrobial activity was virtually undetectable in any of the ground beef samples. This study demonstrates that incorporation of nisin with an edible gel on the surface of beef can be used to reduce undesirable bacteria in ground beef such that the shelf life can be extended.
Technical Abstract: Sterilized, lean and adipose beef carcass tissues were inoculated with Brochothrix thermosphacta, left untreated (U), or treated with 100 ug/ml nisin (N), calcium alginate (A), or 100 ug/ml nisin immobilized in a calcium alginate gel (AN). Treated tissues were aseptically processed into ground beef and populations of B. thermosphacta and nisin activity were determined during refrigerated storage (4 deg C) at 0, 7, and 14 days. At day 0, bacterial populations of U- and A-treated ground beef were 3.24 and 3.17 log10 CFU/g respectively. Ground beef treated with N exhibited populations of 2.80 log10 CFU/g while AN significantly suppressed the organism to undetectable levels (<1.30 log10 CFU/g) at day 0. In contrast to high nisin titers from AN-treated ground beef at day 0, nisin titers were undetectable in N-treated ground beef. By day 7, B. thermosphacta had grown to 7.18, 7.04, and 6.92 log10 CFU/g in U-, A-, or N-treated ground beef, respectively, while AN-treated ground beef exhibited significantly different (P </= 0.05) populations of 6.56 log10 CFU/g. By day 7, nisin titers from AN- treated ground beef were diminished considerably. At day 14 of the study, all treatments exhibited bacterial populations >7 log10 CFU/g and nisin titers were virtually undetectable in any of the ground beef samples. This study demonstrates that immobilization of a bacteriocin on the surface of beef with an edible gel can be used to reduce undesirable bacteria in ground beef.