Given the importance of riboflavin in human diets, a rapid riboflavin assay is needed by the food industry to allow simultaneous determination of riboflavin in numerous food sources. The growth responses of Lactobacillus rhamnosus to microaerophilic conditions and three reducing agents were examined as an attempt to reduce riboflavin assay time. Ascorbic acid, dithiothreitol and thioglycollate were applied at three concentrations. None of the concentrations of reducing agents caused a further increase of bacterial optical density (OD) or had a significant effect on the growth rates. More optimal microaerophilic conditions were achieved through the use of an anaerobic chamber. The growth rate of L. rhamnosus under microaerophilic conditions (0.30 ± 0.05/h) was not significantly different (P > 0.05) from the growth rate of the bacteria under aerobic conditions (0.34 ± 0.07/h). However, after 14 h of bacterial growth, the OD of the bacterial culture under anaerobic hood incubation (0.71 ± 0.09) was significantly higher (P < 0.05) than under aerobic incubation conditions (0.58 ± 0.05). Additional research is needed involving more controlled atmospheres for incubation during growth and a wider range of reductants to optimize and shorten the time required for riboflavin microtiter plate assay. PRACTICAL APPLICATIONS Quantifying riboflavin in foods and food ingredients is important to the food industry. Lactobacillus rhamnosus growth response to varying levels of riboflavin is used to estimate the amount of this vitamin. In an effort to optimize growth on microtiter plates and decrease assay time, microaerophilic conditions were examined. Although rate of growth was not altered, cell concentration measured as optical density (OD) did increase. Microaerophilic incubation of microtiter plates represents a potential approach to decrease assay time and provide the food industry with more timely results.

An in vitro study was designed to determine the extent of Salmonella enterica serovar enteritidis survival and growth permissiveness in egg components isolated from shell eggs held at refrigeration temperature over an 8 week time period. Eggs were collected from a commercial laying facility at one-week intervals for eight weeks and stored at refrigeration temperature. After storage, eggs were dipped in ethanol, cracked aseptically and separated into yolk and albumen samples. S. enteritidis resistant to novobiocin and nalidixic acid were inoculated on to the surface of the yolk membrane at a concentration of approximately 10 6 CFU mL¯1. Yolks were then covered with albumen and incubated for 24 hrs at 25ºC. After incubation, eggs were separated into component parts. Samples were removed from yolk, albumen and yolk membrane and diluted 10-fold in sterile phosphate buffered saline. In albumen, S. enteritidis counts were increased in weeks 3 and 8 compared to week 1 (trial 2). The frequency of eggs exhibiting net growth of S. enteritidis in albumen occurred at week 7 versus weeks 0 and 1 in trial 1 and weeks 3 and 8 versus weeks 0 and 2 in trial 2. In the membrane fraction, the frequency of eggs exhibiting net growth of S. enteritidis occurred at weeks 5 and 8 versus week 0 in trial 2. In the yolk fractions, S. enteritidis counts recovered from week 6 eggs were significantly higher (P<0.05) than those of weeks 0, 2, 3 and 7 (trial 2) and the number of detectable S. enteritidis positive eggs were greater in week 8 than week 5 in trial 1. This suggests that egg components recovered from aged eggs stored at refrigeration temperatures infrequently supported S. enteritidis net growth but generally did not inhibit survivability.