Browsing by Author "Byrne, Robert Duane"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- Assessment of dairy product quality by selective incubation and rapid techniquesByrne, Robert Duane (Virginia Tech, 1989-12-05)A study was conducted to investigate the use of bacterial numbers and metabolites for their Value in predicting potential shelf-life of pasteurized fluid milk. The study consisted of two phases. In the first phase, chemical inhibitors were evaluated for their ability to allow growth of gram-negative psychrotrophic bacteria while inhibiting growth of gram-positive organisms. Crystal violet, benzalkonium chloride, a mixture of crystal violet and benzalkonium chloride, and alkylaryl sulfonate were tested. These were incubated with milk samples separately inoculated with gram-negative and gram-positive bacteria, at 2l°C for 18 hours. Alkylaryl sulfonate allowed growth of gram-positive organisms. Crystal violet inhibited gram-positive organisms but was not as effective as the mixture of crystal violet and benzalkonium chloride, The inhibitor of choice was benzalkonium chloride as it inhibited growth of all gram-positive organisms tested and allowed growth of the gram-negative psychrotrophic organisms.
- Capture filtration for concentration and detection of selected microorganisms in milkByrne, Robert Duane (Virginia Tech, 1994-05-04)The effectiveness of an adsorption filter in retaining bacteria present in milk was examined. Skim milk and whole milk (100ml) were separately filtered through a 47mm adsorption filter. No significant change in total solids, total fat, and solids-not-fat percentages of skim and whole milk permeates was observed after filtration. Adsorption of Pseudomonas fluorescens at target concentrations of 103 , 102 , and 101 cells/ml was determined in 100ml of dairy standard methods buffer, nutrient broth, whole milk, and skim milk. The average percentage bacterial retentions were 95 ± 5.5%, 95 ± 2.6%, 28 ± 22.1%, and 62 ± 15.5%, respectively. A treatment was developed for milk to increase the bacterial retention of ~ fluorescens after filtration. The preferred treatment for 100ml of skim milk involved the following final concentrations (v/v): 0.80% disodium ethylenediamine-tetraacetic acid, 0.02% sodium dodecyl sulfate, pH to 7.5 with 1N sodium hydroxide. The average bacterial retention of ~ fluorescens using the treatment was 91 ± 7.1%. Enumeration of bacteria adsorbed to the filter was then conducted using impedance microbiology. When milk was inoculated with ~ fluorescens at target concentrations of 103 , 102 , and 101 cells/ml, an average log bacterial increase of 1.4 ± 0.1 (25x) was obtained. This method will allow for rapid detection of microorganisms in milk by increasing microbial load in the tested sample and eliminating the need for pre-enrichment.