Growth and Production of Enterotoxin by Staphylococcus aureus S-6 in Soy Proteins and Soy-Supplemented Beef and Pork Sausage

Abstract

The effect of three commercial soy proteins on growth and production of enterotoxin by Staphylococcus aureus S-6 was determined. Sterile isolated soy protein (ISP), soy protein concentrate (SPC), and textured soy protein (TSP) were adjusted to 20% protein by diluting with sterile nutrient medium, inoculated with S. aureus S-6 and incubated at 37 C. Generation times of S. aureus S-6 in ISP, SPC, and TSP were 41, 38, and 33 min, respectively. At 48 h, log 8.4 – 8.5 organisms/g were found in the soy products, and staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin B (SEB) were produced. Each of three hydrated soy protein products was added to ground beef or pork sausage to attain 20% (wt/wt) and cooked to 71 C. Each product was then inoculated and incubated at 37 C. Generation times of S. aureus S-6 did not differ significantly for any beef-soy or pork-soy samples compared to beef or pork sausage controls. Production of SEB (12–72 h) was similar in most beef-soy and pork-soy samples compared to controls, but was significantly lower in the beef-SPC product and beef-TSP and significantly higher in pork-ISP. Small quantities of SEA were produced in beef, beef-soy, pork, and pork-soy samples. Possibly reduction of enterotoxin production in some meat-soy samples was due to outgrowth and competition by spore contaminants of the soy proteins that survived cooking. Production of SEB in all beef-soy and beef control samples was not significantly different when raw samples were autoclaved before inoculation.