MICROBIAL CHANGES ON FRESHLY SLAUGHTERED PORK CARCASSES DUE TO HOT LACTIC-ACID DECONTAMINATION

We studied the microbial changes on fresh (still warm) pork carcasses immediately after electrostatic spraying of lactic acid solutions and during chilled storage. Lactic acid decontamination (LAD) included ele ctrostatic spraying of hot (55C) solutions of 1% lactic acidfor 90 s a nd 2%- and 5% lactic acid for 30 and 90 s. The treatments increased th e carcass surface temperature from 22C to about 32-43C. The bactericid al activity of lactic acid killed mainly Gram-negative bacteria. Reduc tions in ''total'' psychrotrophic Gram-negative and Enterobacteriaceae counts were found reliable indicators for the efficacy of LAD. Hot 2- 5% LAD treatments achieved overall reductions in Gram-negative psychro trophs ranging from 0.8 to more than 1.4 log(10) cfu per cm(2). Overal l reductions in mesophilic Enterobacteriaceae counts ranged from appro ximately 1.2 to more than 1.8 log(10) cfu per cm(2). Treatments with 1 % lactic acid achieved marginal 0.5-0.6 overall log(10) reductions in these groups of organisms. Bactericidal effects after LAD occurred dur ing a lag period of whose duration increased with the lactic acid conc entration of the spray solution. The lag lasted less than I day on 1% LAD, 2 days on 2% LAD and 4 days on 5% LAD meat. During these lags the meat surface pH rose from pH 2.7 to 3.2 immediately after LAD to pH 4 .8 to 5.2. During aerobic chilled storage after LAD the growth of Gram -negative psychrotrophs was controlled only temporarily. These organis ms became the dominant group of organisms. The practical utility of el ectrostatic spraying of fresh pork carcasses with hot 1-5% LAD to impr ove the keeping quality is questionable.