Effects of diacetyl and carbon dioxide on spoilage microflora in ground beef

The effect of CO2 and diacetyl, alone or in combination, on spoilage microflora in ground beef was determined. Ground beef was treated with 20, 30, or 40% CO2 for 22 days (study I); 20, 50, or 100 microg/g diacetyl for 26 days (study II); or a combination of 20% CO2 and 100 microglg diacetyl for 40 days (study III). Antimicrobial effectiveness was determined by aerobic plate counts (log10 CFU/g) using plate count agar (total aerobic bacteria), deMan Rogosa Sharpe (MRS) Lactobacillus agar (gram-positive bacteria), MacConkey agar (gram-negative bacteria), pH, and informal organoleptic assessments (by appearance and by odor). In study I, total bacteria and pH increased by day 4 in control meat samples. For all CO2 levels, gram-negative bacteria decreased and gram-positive bacteria increased compared with untreated controls. The pH remained constant for CO2-treated meat. Control samples had an off-odor and a brown appearance, while CO2-treated samples had no off-odor but did have a brown appearance. For samples treated with diacetyl (study II), spoilage was evident by day 7 for samples treated with 0, 20. and 50 microg/g diacetyl for all parameters examined. Ground beef treated with 100 microg/g diacetyl was spoiled on day 12. Diacetyl was detected (by odor) in samples that were treated with 100 microg/g diacetyl and had a brown appearance. Meat samples treated with the combination of CO2 and diacetyl (study III) showed that the addition of diacetyl did not have an additive effect on microbial growth. Combination-treated meat maintained a red appearance and no off-odor. Diacetyl and CO2 could be used in combination to maintain a red color and inhibit spoilage microorganisms.