Amaguaña R M, Sherrod P S, Hammack T S, June G A, Andrews W H
US Food and Drug Administration, Division of Microbiological Studies, Washington, DC 20204, USA.
J AOAC Int. 1996 Jul-Aug;79(4):853-7.
Most foods examined for Salmonella spp. by the procedure described in the U.S. Food and Drug Administration's Bacteriological Analytical Manual are preenriched at a 1:9 sample/broth ratio. However, 25 g guar gum (an emulsifying agent) is not wetted completely in 225 mL of preenrichment broth, and after a 24 h incubation at 35 degrees C, the product is transformed into a viscous, nonpipettable mass. The effects of 4 factors (inorganic salts, pH, temperature, and various enzymes) on the viscosity of the sample/preenrichment mixture during incubation were determined. Addition of various inorganic salts or adjustment of pH from 4.0 to 9.0 had no significant effect on the viscosity of the incubated mixture. Elevated incubation temperatures of 42 degrees, 44 degrees, and 46 degrees C reduced viscosity but were well above the optimal growth temperature for Salmonella, 35 degrees C. Addition of cellulose to lactose broth at a final concentration of 0.01% reduced viscosity of the mixture, making it readily pipettable. At least one Salmonella cell was consistently recovered from 25 g samples of guar gum, which represents a most probable number value of 0.04 cell per g.
