Microgard, a commercially-available pasteurized
fermented milk, was found inhibitory to gram negative
bacteria such as Pseudomonas putida, some well-known foodborne
pathogens (e.g. Salmonella, Yersinia and Aeromonas)
and some fungi as revealed by an agar incorporation assay
method. Gram positive bacteria, however, were not
inhibited. Rather, some bacteria in this group were
stimulated by Microgard. The inhibitory activity of
Microgard was optimum at pH 5.3 and below.
Thermal stability and protease sensitivity were
characteristic of Microgard. Addition of albumin or some
emulsifying substances antagonized Microgard whereas
treatment with proteases at an initial pH of 11.0 enhanced
its inhibitory ability. Purified eluates of Microgard from
a Sephadex Column (gel filtration) exhibited thermal
stability and maximum UV absorbance. Furthermore, they gave positive results with the Biuret test, indicating the
presence of protein type substance(s). Diacetyl, known to
be inhibitory for psychotrophic bacteria, was present in
Microgard as well as several organic acids.
Filter-sterilized fermentation growth metabolites of
Pediococcus spp., Propionibacterium spp., Bifidobacterium
longum, Lactobacillus plantarum and a black-pigmented yeast
were tested for antimicrobial activity as Microgard had
been tested. Results revealed that some of these
metabolites were inhibitory to Pseudomonas putida and
Listeria monocytogenes, which represented food spoilage and
pathogenic bacteria, respectively. / Graduation date: 1989
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27115 |
| Date | 05 July 1988 |
| Creators | Al-Zoreky, Nageb |
| Contributors | Sandine, William E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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