The presence and metabolic activity of psychrotrophic microorganisms in milk and dairy products are reviewed. Problems involved in adequately defining the microorganisms and temperatures of growth are discussed. The sources and incidences of psychrotrophs in milk and dairy products and methods to control these microorganisms are presented. Methods ranging from simple plate counting techniques to detection of metabolites produced by the psychrotrophs are reviewed. Alterations of protein, lipid and carbohydrate fractions of milk and their effects on the keeping quality of milk and dairy products are discussed. Finally, additional research areas are suggested.

The genus Fusarium comprises a diverse group of fungi including several species that produce mycotoxins in food commodities. In this study, a multiplex polymerase chain reaction (PCR) assay was developed for the group-specific detection of fumonisin-producing and trichothecene-producing species of Fusarium. Primers for genus-level recognition of Fusarium spp. were designed from the internal transcribed spacer regions (ITS1 and ITS2) of rDNA. Primers for group-specific detection were designed from the TRI6 gene involved in trichothecene biosynthesis and the FUM5 gene involved in fumonisin biosynthesis. Primer specificity was determined by testing for cross-reactivity against purified genomic DNA from 43 fungal species representing 14 genera, including 9 Aspergillus spp., 9 Fusarium spp., and 10 Penicillium spp. With purified genomic DNA as a template, genus-specific recognition was observed at 10 pg per reaction; group-specific recognition occurred at 100 pg of template per reaction for the trichothecene producer Fusarium graminearum and at 1 ng of template per reaction for the fumonisin producer Fusarium verticillioides. For the application of the PCR assay, a protocol was developed to isolate fungal DNA from cornmeal. The detection of F. graminearum and its differentiation from F. verticillioides were accomplished prior to visible fungal growth at <10(5) CFU/g of cornmeal. This level of detection is comparable to those of other methods such as enzyme-linked immunosorbent assay, and the assay described here can be used in the food industry's effort to monitor quality and safety.

Fourier transform‐infrared spectroscopy (FT‐IR) methods enable chemical discrimination of intact bacterial cells and produce complex whole‐organism biochemical fingerprints (spectra), which are reproducible and distinct for different bacteria. Numerous researchers indicate that there is great potential for using FT‐IR methods in combination with multivariate statistics (chemometrics) to detect and identify bacteria in water, culture media and foods. This article presents a review of the FT‐IR techniques, sample preparation procedures and experimental conditions used in these studies, as well as advantages, disadvantages and challenges that remain for the development of FT‐IR detection methods.

Some species of Fusarium can produce mycotoxins during food processing procedures that facilitate fungal growth, such as the malting of barley. The objectives of this study were to develop a 5' fluorogenic (Taqman) real-time PCR assay for group-specific detection of trichothecene- and fumonisin-producing Fusarium spp. and to identify Fusarium graminearum and Fusarium verticillioides in field-collected barley and corn samples. Primers and probes were designed from genes involved in mycotoxin biosynthesis (TRI6 and FUM1), and for a genus-specific internal positive control, primers and a probe were designed from Fusarium rDNA sequences. Real-time PCR conditions were optimized for amplification of the three products in a single reaction format. The specificity of the assay was confirmed by testing 9 Fusarium spp. and 33 non-Fusarium fungal species. With serial dilutions of purified genomic DNA from F. verticillioides, F. graminearum, or both as the template, the detection limit of the assay was 5 pg of genomic DNA per reaction. The three products were detectable over four orders of magnitude of template concentration (5 pg to 5 ng of genomic DNA per reaction); at 50 ng template per reaction, only the TRI6 and FUM1 PCR products were detected. Barley and corn samples were evaluated for the presence of Fusarium spp. with traditional microbiological methods and with the real-time PCR assay. The 20 barley samples and 1 corn sample that contained F. graminearum by traditional methods of analysis tested positive for the TRI6 and internal transcribed spacer (ITS) PCR products. The five corn samples that tested positive for F. verticillioides by traditional methods also were positive for the FUMI and ITS PCR products. These results indicate that the described multiplex real-time PCR assay provides sensitive and accurate differential detection of fumonisin- and trichothecene-producing groups of Fusarium spp. in complex matrices.

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An enzyme-linked immunosorbent assay was developed for the detection of molds in dairy products. New Zealand White female rabbits were immunized with .45 mg of partially purified extracellular antigen from freeze-dried culture filtrates of Aspergillus versicolor, Cladosporium herbarum, Geotrichum candidum, Mucor circinelloides, and Penicillium chrysogenum. Blood was drawn at various intervals, and antibodies were separated and purified. Antibody-peroxidase conjugates were prepared with the following ratios being the optimum ones: A. versicolor 10:20; C. herbarum 5:10; G. candidum 1:10; M. circinelloides 5:5; and P. chrysogenum 10:10. The assays were sensitive within a range of 1 ng to 1 microgram/ml, depending on the mold used. Inhibition tests were done for each mold with concentrations of 0 to 5000 micrograms/ml of antigen. The enzyme-linked immunosorbent assay tests for Cladosporium, Geotrichum, and Mucor were only inhibited by antigens from other species of the same genus; whereas there was crossreaction between antibodies and antigens of species of Penicillium and of Aspergillus. Citrate buffer was best for extracting the mold from cheese and yogurt. The extract was adjusted to pH 7.2 and ELISA was performed. Results showed that these molds can be detected in Cheddar and cottage cheeses and yogurt within 2 d, which is before mold growth is visible in these products.

Listeria monocytogenes is a foodborne pathogen of significance because of its comparatively high heat resistance, zero tolerance in ready-to-eat foods, and growth at refrigeration temperatures. A 3 x 3 x 3 factorial study was done to determine the effects of milkfat (0%, 2.5%, 5.0%), pH (5.0, 6.0, 7.0), and processing temperature (55 degrees C, 60 degrees C, 65 degrees C) on the thermal resistance of L. monocytogenes in a formulated and homogenized milk system. Data were fit to a modified Gompertz equation where parameter estimates characterized three regions of a survival curve: the shoulder, maximum slope, and tail. Statistical analysis was done for each of the 27 individual treatment sets to visualize individual effects on parameter estimates and to evaluate how well the Gompertz equation represented the data. A regression model for the Gompertz equation was generated to predict the logarithmic surviving fraction of L. monocytogenes based on all 27 treatments and their single and interactive effects. The shoulder region of the survival curve was affected by pH; however, the maximum slope was affected by temperature, milkfat, and the interaction of temperature x milkfat. Validation of the model suggests that the predictions are best suited for processing above 62 degrees C. Trends over time for a 4-log reduction in cells (4D values) were evaluated using results from the 27 individual treatment sets, the regression model for the Gompertz equation, and a linear equation. At lower temperatures, 4D values by the three methods varied by twofold. At higher temperatures, all methods gave similar 4D values, suggesting that death became more linear. Based on this study all three factors affect heat resistance for specific regions of a survival curve, and a predictive model was developed that can be used as a preliminary estimate for L. monocytogenes inactivation.

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