PATHOGEN DETECTION IN FOOD MICROBIOLOGY LABORATORIES: AN ANALYSIS OF QUALITATIVE PROFICIENCY TEST DATA, 1999–2007

The objective of this study was to assess laboratories' ability to detect or rule out the presence of four common food pathogens: Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes and Campylobacter spp. To do this, qualitative proficiency test data provided by one proficiency test provider from 1999 to 2007 were examined. The annual and cumulative 9-year percentages of false-negative and false-positive responses were calculated.
The cumulative 9-year false-negative rates were 7.8% for E. coli O157:H7, 5.9% for Salmonella spp., 7.2% for L. monocytogenes and 13.6% for Campylobacter spp. Atypical strains and low concentrations of bacteria were more likely to be missed, and the data showed no trend of improving performance over time. Percentages of false-positive results were below 5.0% for all four pathogens.

PRACTICAL APPLICATIONS

The results imply that food testing laboratories often fail to detect the presence of these four food pathogens in real food specimens. To improve pathogen detection, supervisors should ensure that testing personnel are adequately trained, that recommended procedures are followed correctly, that samples are properly prepared, that proper conditions (temperature, atmosphere and incubation time) are maintained for good bacterial growth and that recommended quality control procedures are followed. Supervisors should also always investigate reasons for unsatisfactory proficiency test results and take corrective action. Finally, more research is needed into testing practices and proficiency test performance in food testing laboratories.     

PARTICLE COUNTING OIL AND WATER EMULSIONS

ABSTRACT

Because of their speed and convenience, optical particle counters are widely used for particle size analysis of liquid samples. In some cases, both solid particles and emulsified water or oil may be present in a sample. Since emulsion droplets are counted as if they are solid particles, analysis and data interpretation for these samples are difficult. Until recently, no suitable method existed for distinguishing solid contaminants from emulsion droplets. This paper discusses a method which overcomes this limitation. Through the use of a surfactant-laden nonpolar dilution fluid, water is incorporated into reverse micelles too small to be seen by most optical particle counters. As a result, only solid contaminants are counted, and many problems associated with the analysis of emulsions are overcome. Results obtained from a wide range of oil and water emulsions are used to evaluate the merits and possible applications of the new technique.     

Frozen Hake Fillets Quality as Related to Texture and Viscosity By Mechanical Methods

This work aimed to develop a textural quality classification function for frozen hake fillets using instrumental measurements. Frozen hake fillets were stored to provide a wide range of textures. Raw and cooked fillets were analyzed for texture using Kramer and Warner-Bratzler shear cells and a puncture device. Apparent viscosity, dimethylamine and protein solubility were also measured. Principal Component Analysis indicated three factors accounted for 86.5% of the variance. Four clusters were found, ranging from excellent quality (low texture, high viscosity) to very poor (high texture, low viscosity). Parameters required for classification were viscosity, maximum force from Kramer and maximum force and energy from the puncture test.     

SPICES AND HERBS: THEIR ANTIMICROBIAL ACTIVITY AND ITS DETERMINATION1

Throughout the years numerous investigations concerning the inhibition of microorganisms by spices, herbs, their extracts, essential oils and various constituents have been reported. Many of these materials possess significant antimicrobial activity, which in many cases is due primarily to a particular constituent. Interpretation and comparison of results of various studies is complicated by variations in the methodology used for the determination of antimicrobial activity. The antimicrobial activity varies depending on the microorganism, the spice or herb and the test medium. These and other factors are examined in the light of their effect on the outcome of the test method.     

Inhibitory and Stimulatory Effects of Oregano on Lactobacillus Plantarum and Pediococcus Cerevisiae

Increasing concentrations of oregano from 0.5 to 8 g/L in a liquid medium resulted in stimulation, delay, or inhibition of acid production and viability of Lactobacillus plantarum and Pediococcus cerevisiae. The inhibitory factor could be removed from oregano by solvent extraction or autoclaving; residues from these treatments stimulated acid production by the organisms. Organisms growing in media containing sublethal oregano concentrations that had delayed growth and acid production developed resistance to the deleterious effects of the spice. L. plantarum was more resistant than P. cerevisiae to the inhibitory effects of oregano.