Graduate Thesis Or Dissertation
 

Growth and enterotoxin production of Staphylococcus aureus in papain-treated beef and ham

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  • Growth and enterotoxin production of Staphylococcus aureus in papain-treated beef and ham were studied. In addition to an untreated control, four treatments were used in the beef experiment including two levels of papain, a commercial tenderizer preparation, and commercially tenderized beef. Two levels of papain treatment and an untreated control were used for the ham study. Both raw and cooked samples were tested. Proteolysis was determined by 280 nm readings in a spectrophotometer for total UV absorbing materials and for UV absorbing materials in a trichloroacetic acid soluble meat solution. The third method, a more sensitive analysis, used trinitrobenzene sulfonic acid to determine the amount of free amino nitrogen present. With the latter method some differences in the amount of amino groups present could be detected among the various treatments. Strain S-6 which produces both enterotoxins A and B was used for the experiment. The inoculum level for studies of meat slices held at 30 and 42 C was 1 x 10⁷ colony forming units per gram. Sampling times for the number of colony forming units and for enterotoxin production by microslide and Oudin assays were 5, 8, and 24 hr. The action of papain did not significantly affect the number of colony forming units nor the amount of enterotoxin produced in treated versus untreated control meat samples. The number of colony forming units at 30 C increased at a slower initial rate than at 42 C although higher numbers of viable cells were detected after 24 hr in the samples incubated at 30 C. Cooked samples supported a faster initial growth than raw samples. Earlier and greater enterotoxin B production occurred when cooked samples, especially of beef, were the substrates. Enterotoxin B concentrations in cooked beef held at 42 C were estimated to be 0.06, 0.9 - 1.0, and 0.2 - 2 μg per g for 5, 8, and 24 hr respectively. Raw beef samples contained no detectable enterotoxin until after 24 hr (0.2 - 0.9 μg per g). At 30 C approximately 1 μg per g of enterotoxin B was detected in the cooked samples and only 0.02 (μg per g in some raw samples after 24 hr. The cooked and "not fully cooked" hams were similar in support of growth and enterotoxin production. Enterotoxin B concentrations present in "hot fully cooked" samples held at 42 C were approximately 0 - 0.9 (μg per g at 5 hr, 0 - 1 μg per g at 8 hr, and from 0.05 - 1.8 μg per g at 24 hr. Enterotoxin levels in the cooked samples were 0.2 - 0.9 μg, 0.25 - 1 ug, and 1 - 6.2 μg per g after 5, 8, and 24 hr respectively. Isolated samples, positive for enterotoxin A (0.05 μg per g), were detected in cooked beef held at 42 C for 24 hr. Detectable amounts (0.05 - 0.2 μg per g) were found, however, in both the cooked and "not fully cooked" cured hams, especially at the higher incubation temperature.
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