This study was undertaken to investigate interference by acids commonly found in fruit juice in Escherichia coli assays involving the use of 4-methylumbelliferyl-β-d-glucuronide (MUG) as a fluorogenic substrate for enzyme reaction. Fluorescence intensity was negatively correlated (P < 0.001) with the volume of fresh citrus juice tested by the lauryl tryptose broth (LST)-MUG assay, and the permissible sample sizes were limited to 0.3 and 0.5 ml for fresh citrus juices with pHs of 3.3 and 3.9, respectively. In addition, false-negative results were visually observed under UV light when the E*Colite assay was used to test large volumes (5 to 10 ml per test) of fresh citrus juice or when the test broth used for the LST-MUG assay was supplemented with citric, malic, or tartaric acid at 2 to 4 g/liter. These results suggest that the size and pH of acidic samples should be controlled in MUG-based fluorogenic assays. The inhibitory effect on fluorescence was due to high acidity, which reduces fluorescence from 4-methylumbelliferone. Buffering improved the assays. When sodium bicarbonate was incorporated in the enrichment broth at 10 g/liter, the permissible sample sizes for fresh grapefruit juice (pH 3.1) increased from 0.3 to 1 ml for the LST-MUG (with 9.9 ml of broth) assay and from 3 to 10 ml for the E*Colite (with 99 ml of broth) assay.
Utilization of Fluorogenic Assay for Rapid Detection of Escherichia coli in Acidic Fruit Juice
- Views Icon Views
- PDF LinkPDF
- Share Icon Share
- Search Site
STEVEN PAO, CRAIG L. DAVIS, LORETTA M. FRIEDRICH, MICKEY E. PARISH; Utilization of Fluorogenic Assay for Rapid Detection of Escherichia coli in Acidic Fruit Juice. J Food Prot 1 December 2002; 65 (12): 1943–1948. doi: https://doi.org/10.4315/0362-028X-65.12.1943
Download citation file: