Food Protection Trends - March 2010 - 163

TABLE 3. Relation of can abuse and microbial count on double seam areas1 to rate of spoilage (cans taken at caser)2 Severe Can Abuse Microorganisms Per Can 23,000 32,000 35,000 69,000 73,000 130,000 327,000 1 2 Minimum Can Abuse Spoilage Rate (Cans/1,000) 18 30 23 22 24 25 25 Microorganisms Per Can 1,000 1,600 25,000 52,000 209,000 900,000* 1,790,000* Spoilage Rate (Cans/1,000) 0 0 <1 <1 <1 <1 <1 Seams inoculated with Aerobacter aerogenes From Weddig, L. M. et al. (24, 28) * Seams inoculated with Aerobacter aerogenes dence of total coliforms and enterococci in cooling water. The results showed a trend in which the frequency of coliform detection increased as the APC counts increased. Enterococci were also recovered with greater frequency at the higher APC levels, but no significant trend was noted. The study showed the frequency of aerobic spore detection increased as the APC counts increased. Odlaug and Pflug (19) reported that the anaerobic spore means were 0.5 CFU/ ml for hydrostatic retorts and 0.4 CFU/ ml for the cooling canal. The number of C. botulinum spores in the cooling water was not directly measured, but it was assumed that the number was very low, since it would be only a fraction of the total anaerobic spores in the water (19). BACTERIOLOGICAL TESTING METHODS FOR MONITORING BACTERIAL COUNTS IN CANNERy COOLING WATER Recontamination of thermally processed cans during the cooling process is the most common cause of microbial spoilage in canned food products (7). Recontamination is dependent upon the condition of the container seam, the condition of the container handling system and the condition of the water (21). Incidences of spoilage are corre- lated to the number of bacteria in container cooling water (20). As the count in the water increases, the probability of spoilage organisms entering the can also increases. In most cases, water from municipal supplies and deep wells is low in bacterial counts and surface waters are frequently high in bacterial counts. Bacteria multiply rapidly in reused cooling water that is not chlorinated (16). Although determination of free residual chlorine can be used as a guideline for water quality, counting of bacteria is the most reliable and direct procedure for monitoring the purity of can cooling water (16). Aerobic plate counts (APC) are sufficient indicators of the bacterial content of can cooling water. For testing a city water supply, well water, single pass continuous coolers and cooling canals, where the water is not reused, an appropriate sample should be taken from the source and 1, 0.1 and 0.01 ml tested in duplicate. For water from continuous coolers and cooling canals, an appropriate sample should be taken and the following dilutions tested: 0.1, 0.01, 0.001 and 0.0001 ml. Each dilution should be plated at least in duplicate and incubated at 48 ± 2 h at 35°C (1, 14). If the water has been chlorinated, the chlorine should be neutralized by addition of 1.5% sodium thiosulfate solution (16). The American Water Works Association and Water Environment Federation recommend the het- erotrophic plate count (HPC), formerly known as the standard plate count, be used (4). Three different methods, such as a pour plate method, a spread plate method and a membrane filter method, may be used to determine the HPC. In the pour plate method, submerged bacterial colonies in agar medium may be exposed to heat shock from the transient exposure of the sample to 45oC agar. The spread plate method causes no heat shock, and all colonies are on the agar surface, where they can be distinguished readily from particles and bubbles. The membrane filter method permits testing large volumes of low-turbidity water and is the method of choice for lowcolony waters (< 1 to 10 CFU/ml). This method produces no shock but adds the expense of the membrane filter (4). Many thermal processing plants do not have the facilities and trained workforce required for aseptic microbial testing. Simplified and rapid microbial testing methods might be the solution for this situation. Currently, there are several modified methods of conventional microbiological testing that can be used for monitoring bacteria in canning plants. This includes the use of 3M Petrifilm™, which uses disposable cardboard disks containing dehydrated media, designated for enumerating specific bacteria. This test eliminates the need for preparing media and agar plates, economizes storage and incubation MARCH 2010 | FOOD PROTECTION TRENDS

Food Protection Trends - March 2010

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