Rapid Microbiology Testing of Dairy Products using the BioLumix Instrument

Background

Testing Dairy Products using Rapid Microbiology with the BioLumix InstrumentCommercial Dairy Products need to be tested for microbial contaminants.  Dairy products include: cultured dairy products (kefir, cultured buttermilk, sour cream, and yogurt), cheeses (soft cheese products, semi-hard, hard, and extra hard cheeses), processed cheeses, butters, butter creams, dried milks, and ice creams.

Manufacturers require a simple, cost effective and rapid microbiological method to assess samples for the presence of specific organisms as an indication of the sanitary conditions.  The most common dairy microbiology tests include: Aerobic plate count, Yeast and Molds, Coliforms, and could also include some indicator of cold spoilage such as Pseudomonads.  Rapid and early testing for microorganisms can reduce product quarantine time, allows for faster response to contamination, decreases inventory holding and cold warehouse costs, and aids in prediction of product shelf-life for manufacturers.

Troublesome spoilage microorganisms include aerobic Psychrotrophic bacteria, yeasts, molds, heterofermentative lactobacilli, and spore-forming bacteria (Ledenbach and Marshall 2009).  Psychrotrophic bacteria can produce large amounts of extracellular hydrolytic enzymes, and the extent of recontamination of pasteurized fluid milk products with these bacteria is a major determinant of the milk products shelf life. Fungal spoilage of dairy foods is manifested by the presence of a wide variety of metabolic by-products, causing off-odors and flavors, in addition to visible changes in either color or texture and may also cause gassing.

BioLumix has developed a simple rapid microbiological method for the detection of various groups of bacteria, yeasts and molds.  The system can make the microbiology testing simpler, faster and automated, saving manufacturers time, labor and money. BioLumix has a comprehensive range of microbiological tests, including specific vials for Coliforms and Pseudomonas.  The system is designed to accelerate product release in a simplified automated approach.  Complete coliform test results are obtained within 12 hours with one vial substituting for nine or more MPN (Most Probable Number) test tubes.  Yeast and mold results are obtained in 48 hours rather than 5-7 days using plate methods.  Many products can be introduced directly into the BioLumix test vial without the need of a dilution step.  These include yogurts and sour cream, as well as milks.

BioLumix Applications

Yogurt Testing

Yogurt is a dairy product, which is made by blending fermented milk with various ingredients that provide flavor and color.  Manufacturers have responded to the growth in the yogurt market by introducing many different types of yogurt including low fat and no-fat, creamy, bio-yogurt, organic, baby, and frozen.  BioLumix has developed assay methods for measuring contaminating microorganisms in dairy products.

The yogurt can be directly added (Figure 1) into BioLumix vials to measure growth of Coliforms or Yeast and Molds.  Specialized high pH BioLumix vials can also be used for yogurt samples.  When a low pH yogurt sample is added to the BioLumix high pH Coliform vial (CC), the pH conditions become near neutral.  This ensures the yogurt manufacturer to be able to correctly test for coliforms using a direct (without dilution) sample of product.  As much as 1 gram of product can be directly tested in each BioLumix test vial.

Coliform organisms generally include four key groups of enteric bacteria.  They comprise of the following species: Escherichia, Citrobacter, Klebsiella and Enterobacter.  Each of these organisms can grow in the BioLumix high pH CC vial.  Figure 2 illustrates the growth of a coliform (Citrobacter) in the BioLumix CC vial (green) while the Dark Blue curve shows a clean sample.

A clear advantage of the BioLumix vial is that it can be used on the same work-day to yield data about the status of any contamination in dairy samples and thus enable the manufacturer to make a decision on the acceptability of the lot of product for sale and consumption.

Fermented Dairy Products

Yeast and Mold Testing: An example of the growth of a mold in cream cheese is shown below. Figure 3 illustrates the clean test result, using BioLumix Yeast & Mold vials, for the cream cheese product as shown in the Green curve.  The Dark Blue curve illustrates the growth curve in BioLumix YM vials when cream cheese was inoculated with the mold organism Geotrichum candidum.

Coliforms Testing:Similarly, testing of sour cream showed the lack of Coliforms in the product as illustrated in the Dark Blue curve in Figure 4.  The sour cream product sample was found to have other flora as shown by growth in the BioLumix TAC vial which detected total aerobic bacterial counts.  Thus, the BioLumix high pH CC vial was used to show selectivity for the presence or absence of Coliform organisms.

Rapid Detection of Pseudomonas in Dairy Products as an Indicator of Product Shelf-Life
Pseudomonad organisms are a major cause of bacterial spoilage of pasteurized milk and dairy products due to post process contamination.  Early detection of Pseudomonas in can be a predictor of product shelf-life as it is the predominant psychotropic bacteria present.  BioLumix has developed a rapid method for the detection of Pseudomonads in dairy products; the method is also applicable to detection of Pseudomonads in process water.

The BioLumix system was directly compared to the plate count methodology for milk samples stored at refrigerated temperatures and held overnight at room temperatures and to detected Pseudomonads in process water and other dairy products.

Commercial milk products were used to measure the presence of Pseudomonads during refrigerated and elevated temperature storage.  Pseudomonads were present at varying levels in dairy samples and were detected within 16-24 hours using BioLumix vials.  All process water samples tested were free of Pseudomonads by both methods.  Process water samples inoculated with different Pseudomonads strains were found to detect in the BioLumix system.  The vial were selective enough not allowing for growth of unrelated gram positive and gram negative bacteria, mold or yeast.  The combination of the Pseudomonas vial with overnight pre-incubation could serve as an indicator of shelf-life of products.

The data in this study suggests that the BioLumix Pseudomonas vials are capable of early detection of Pseudomonads in dairy products and in processing water. The system offers a reduction in time to results as compared to the plate methodology and eliminates any product interference.  It allows for rapid assessment of problems associated post processing problems.

BioLumix has developed a vial specific for testing of Pseudomonads that are known to commonly contaminate milk and also survive pasteurization, albeit in low numbers. These Pseudomonads may include P aeruginosa, P fluorescens, P putida, and P stutzeri.  Each of these species of pseudomonas was found to grow readily in the BioLumix PSE-B vials.

Summary

The BioLumix System is designed to accelerate product release with a simplified, automated approach.  This yields fast, accurate, real-time results while reducing costs and eliminates the time required for the assays to be completed.  The system offers real-time results of contaminated samples saving hours, possibly days.  The Coliform or Enterobacteriaceae results can be available within 12 hours; Yeast and Mold results within 48 hours.  Thus the BioLumix system allows for rapid detection of Coliforms and Yeast and mold.  For low coliform numbers, one vial can substitute for 9+ MPN tubes.  BioLumix will streamline and simplify the microbiological procedures, save labor and create a paperless laboratory, while generating results that correlate well with plate count methodology.

Reference
Ledenbach L. H. and R.T. Marshall. 2009 In “Compendium of the Microbiological Spoilage of Foods and Beverages” . Chapter Microbiological Spoilage of Dairy Products.