Microbiological control of food spoilage and pathogenic microorganisms in refrigerated foods

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

Limited survey on aflatoxin contamination in rice

Aflatoxins (AFS) are toxic and carcinogenic fungal metabolites. Aflatoxin B1 is the most toxic and has been classified as a Group I carcinogen by the International Agency for Research on Cancer (IARC). Samples of imported rice were analyzed for their AFS content. Finley ground rice subsamples were extracted with water/methanol (100:150 v/v) followed by purification with Immunoaffinity columns (IAC). AFS purified from extracts were determined with RP-HPLC-FLD using post column electrochemical derivatization with a Kobra Cell. Concentrations of aflatoxin B1 and total AFS in test rice samples were ≤0.123 and ≤2.58 µg/kg, respectively. Tween 80 improved recoveries (86 and 106%) of aflatoxin B1 and aflatoxin G1 from brown rice. Recoveries of Aflatoxin B2 and aflatoxin G2 were substantially reduced (non-detected to 27%) by Tween 80 used in IAC cleanup of brown rice extracts. Visible dense growth of Aspergillus parasiticus (food isolate) occurred at 25 °C but higher aflatoxin B1amounts (23.9–39.3 µg/kg) accumulated when the mold grew at 37 °C in rice seeds stored for three weeks. It could be concluded that levels of aflatoxin B1 and total AFS in rice samples were within the permissible amounts of the EU and other international legislations. Keywords: Rice, Brown rice, Saudi Arabia, Aflatoxins, Aflatoxin B1, HPLC-FLD, Aspergillus parasiticus, Tween 8

Laboratory antimicrobial activity of cinnamaldehyde and pomegranate-based polycaprolactone films

Polycaprolactone (PCL) was incorporated separately with cinnamaldehyde (CNMA), pomegranate methanolic extract (PME), freeze dried arils of pomegranate (FDAP), and seed flour of pomegranate (SF) to form antimicrobial films to be used for active food packaging. PCL–CNMA films completely inactivated growth of the artificially inoculated Escherichia coli and Staphylococcus aureus, whether at 5% or 10% concentrations (wt/wt of polymer), at all studied temperatures (4, 20, and 37 °C). PCL–PME films (10% wt/wt of polymer) delayed the growth of E. coli and S. aureus for up to 7 and 6 days, respectively, at 37 °C. Two-day delays in the growth of both bacteria were achieved with FDAP and SF films (10% wt/wt of polymer) at 20 °C. The release of CNMA was slower than the release of PME during film processing, as measured by Fourier transform infrared spectroscopy. Thus, CNMA and pomegranate-based films perhaps should be planned further for use in controlled release food packaging

Lyophilized Preparations Of Bacteriocinogenic Lactobacillus Curvatus And Lactococcus Lactis Subsp Lactis As Potential Protective Adjuncts To Control Listeria Monocytogenes In Dry-Fermented Sausages

Methyl oleate was used as a primary carbon source and as an alternative inducer for the production of an extracellular lipase, Lip2, in Y. lipol.vtica strain LgX64.81 grown in a 20-1 bioreactor. The lipase-encoding gene, LIP2, was investigated during culture on methyl oleate using a pLIP2-LacZ reporter fusion and we provide evidence for the involvement of methyl oleate in its regulation