A collaborative study was conducted to compare a proposed LSTMUG method with the AOAC official method for Escherichia coli detection. E. coli produces an enzyme, β-glucuronidase, which cleaves the substrate, 4-methyl-umbelliferyl-β-D-glucuronide (MUG), to yield a fluorescent end product. Incorporation of the MUG substrate into lauryl tryptose broth (LST) enables a rapid quantitative method for screening E. coli, which is detected by fluorescence of the medium under longwave UV light. In this collaborative study, 5 food samples, 2 frozen (entree sauce/gravy and dairy topping) and 3 chilled (hamburger, pork sausage, and cheese), were tested for E. coli detection by 17 collaborating laboratories. Results indicate that the LST-MUG method is equal to or better than the current AOAC method for detecting E. coli. The LST-MUG method has been adopted official first action
Sodium nitrite, sorbic acid, potassium sorbate and polyphosphates (sodium acid pyrophosphate, SAPP; sodium hexametaphosphate, SHMP; and sodium tripolyphosphate, STPP) were tested at similar preadjusted (before cooking) pH levels (in the range of pH 5.78 to 6.19 after cooking) to determine effective combinations capable of controlling Clostridium botulinum growth and toxin production in mechanically deboned chicken meat frankfurter emulsions incubated at 27°C. In combination with low levels of nitrite (40 ppm), potassium sorbate (0.26%, pH 6.06) was more effective than sorbic acid (0.20%, pH 6.03) in delaying toxin production (>27 d vs. 6 d) and in controlling growth. In formulations containing combinations of nitrite (40 ppm) and sorbic acid (0.20%) or nitrite (40 ppm) and potassium sorbate (0.26%), the addition of polyphosphates (0.4%) resulted in a greater delay of toxin production (8 to 25 d for nitrite-sorbic acid-SAPP vs. 28 d for nitrite-potassium sorbate-SAPP) at similar pH levels. Under these conditions, SAPP delayed production of detectable toxin longer (25 d) than did either SHMP (6 to 11 d) or STPP (4 to 14 d). The addition of polyphosphates to nitrite-free emulsions containing sorbic acid (0.20%) or potassium sorbate (0.26%) did not delay the development of botulinal toxin when the pH was essentially equivalent in the range of 5.78 to 6.07.
Combinations of sodium acid pyrophosphate (SAPP) with added sodium nitrite and/or potassium sorbate were tested at various pH levels to determine effectiveness in delaying Clostridium botulinurn growth and toxin production in frankfurter emulsions. Formulations containing sodium nitrite (40 ppm), potassium sorbate (0.26%) and SAPP (0.4%) resulted in a greater delay of toxin production (12-18 days) than other combinations (6-12 days) having similar pH values. Treatments containing 0.4% SAPP appeared to be more inhibitory than their counterparts without SAPP, displaying less numbers of toxic samples during the 53~day storage period at 27°C. Aerobic mesophilic colony counts and residual nitrite data showed little difference among treatments.
The effects of two pH levels (5.55 or 5.85) in combination with 0.4% sodium acid pyrophosphate (SAPP), NaH2PO4 * H20, Na2HPO4 * 7H20, or NaCl on the growth and toxicity of Clostridium botulinum 52A were studied. Absorbancy measurements at 630 nm, microscopic observations, and the mouse bioassay procedure were used to observe the effects. At pH 5.55 and 5.85 most control cultures exhibited toxicity when cell lysis began. Vegetative cell development was normal (4 ,im long; 1 ,um wide). SAPP-containing (0.4%) treatment cultures displayed similar growth and lysis but no or delayed (48 h) toxicity. Cells grown in the SAPP treatment culture were longer and wider (6 jim long; 1.5 jim wide) than in most other treatment cultures. Trypsinization of nontoxic supernatants from 0.4% SAPP resulted in toxicity. Addition of 0.4% SAPP to toxic C. botulinum supernatant delayed but did not prevent death of mice. The addition of various levels of SAPP to toxic supernatants resulted in a decrease in zone size with an increase in the level of SAPP (9 mm with 0.4% SAPP to 7 mm with 1.0% SAPP), using a dual substrate protease assay. A decrease in the zone size also occurred with the supernatant from cultures grown in the presence of SAPP and with Bacillus polymyxa protease dilutions containing 0.4% SAPP. Results suggest that the actual production or function of the protease responsible for toxin activation may have been inhibited by the presence of SAPP.
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