Comparison of Methods for Determining Coliform and Escherichia coli Levels in Apple Cider
Abstract:The main objective of this research was to determine the easiest and most reliable media for enumerating coliform bacteria and Escherichia coli levels in apple cider. During the autumn of 1994 a total of 59 apple cider samples were collected directly from 12 cider producers and were assessed for bacterial levels and pH. Plate count agar was used to determine heterotrophic bacteria levels. Coliform levels were determined using three different media: violet red bile agar (VRBA), Petrifilm High Sensitivity Coliform Count Plates (PHSCCP), and Trypticase soy agar with a VRBA overlay (TSA/VRBA) for attempted recovery of coliforms injured by the low pH of the apple cider. Eosin methylene blue agar (EMBA) and Petrifilm E. coli Count Plates were used to screen cider samples for E. coli. Apple cider had an average pH of 3.34 ± 0.08. Heterotrophic bacterial levels ranged from 2.30 to 7.11 log CFU/ml. All cider samples contained coliform bacteria with levels varying greatly; on the different media, we found the following: on VRBA, <1.00 to 4.37 log CFU/ml; on TSA/VRBA, 1.20 to 4.40 log CFU/ml; and on PHSCCP, <1.00 to 4.56 log CFU/ml. Coliform levels were most easily determined in apple cider by using PHSCCP. However TSA/VRBA proved to be more reliable; coliform detection was significantly (P < 0.05) increased. EMBA was ineffective for screening apple cider for E. coli, with the low pH of the cider producing many false-positive results. E. coli was only recovered by using Petrifilm E. coli Count Plates with one of the 59 samples positive for E. coli (non-O157:H7) at a level of 10 CFU/ml.
Document Type: Research Article
Affiliations: Department of Animal and Food Sciences, University of Vermont, Bington, Vermont 05405, USA
Publication date: November 1, 1997
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