Microbiological testing of OILS

Edible oils are an important part of the dietary supplement industry. Oils are also used extensively in cosmetics and of course, hydrocarbon based oils, are used in heavy machinery.

Oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes plant (vegetable) oils, fish or animal derived oils, volatile essential oils, petrochemical oils, and synthetic oils. Plant derived oils are used frequently in the Dietary Supplement industry and may include examples such as Flax and Sunflower oils. Fish derived oils may include the infamous Cod Liver Oil and Krill (omega 3) oils. Essential oils are generally aromatic oils and are extracted by distillation. They are used in perfumes, cosmetics, soaps and other personal care products, and occasionally for flavoring food and drink. Petrochemical oils include crude oils as an example and are naturally occurring, flammable liquids consisting of a complex mixture of hydrocarbons of various molecular weights, and other liquid organic compounds. Synthetic oils are lubricants consisting of chemical compounds that are artificially made (synthesized). Many are very similar in function to hydrocarbon based motor oils.

Plant and fish-derived oil based products are common in the dietary supplement industry and are most commonly tested in the form of liquids, soft-gels, and capsules. Cosmetic oil based-products may be in the form of creams, lotions, washes, to name a few. Oils used in products for the dietary supplement industry and in cosmetics will require testing for the presence of microorganisms.

Problems Associated with Microbial Testing of Oils

Oils can be difficult to handle due to their hydrophobic composition. An example of an oil micelle (oil present in aqueous solutions) is represented in the cartoon shown in Figure 1.

For sampling of oils for the presence of microorganisms (microbial content), it is generally necessary to first dilute the oil material 1/10 into an aqueous buffer. The material can then be mixed thoroughly (mechanically or by hand) followed by a series of decimal dilutions. Due to the lack of mixing of oil and water it is difficult to remove the organisms from micelles and transfer them to the diluent prior to making the decimal dilution and to disperse them evenly in the agar medium, all steps required for the plate count method.

The BioLumix Advantage

The BioLumix system is based upon detection of color or fluorescence variations due to microbial metabolism in liquid medium within a novel two-zone test vial. An optical sensor monitors changes in color and fluorescence within the vial’s reading zone, which is physically separated from the incubation zone. This two-zone approach prevents masking of the optical pathway by product or microbial turbidity and therefore, eliminates product interference. Separate test vials are also used to automatically detect the presence of viable microorganisms and/or to estimate the concentration of viable counts by monitoring changes in CO2 production during cellular growth.

For the BioLumix assay, oil materials diluted into TSB (1/10) and can either be used directly or pre-enriched overnight to gain sensitivity. The diluted sample is added into BioLumix vials containing broth media. A variety of vials are available to conduct any necessary assay. After the inoculation of the vials, they are inserted into the instrument that serves as an incubator and a reader. The inoculated vials are analyzed every 6 minutes and the end results are reported in an automated certificate of analysis. Most assays are completed overnight and all the results are available in 48 hours.

Results Obtained Using The BioLumix System

Table 1 includes examples of oil-containing products successfully tested using the BioLumix method including plant derived, fish derived, cosmetic oils, essential oils, industrial and synthetic oils.

TABLE 1- Types of oil tested

Plant Derived Fish Oil Cosmetic/Essential Oils Industrial/Synthetic
Flax Krill Oil Facial soaps/lotions Motor Oil
Safflower Cod Liver Oil Body (massage) VITE (dl-alpha-tocopherol)
Sunflower Omega 3 Oil Suppositories
Soybean Vitamin E Lotions
Sesame Primrose Oil

Figure 2

The clean product yields a flat curve whereas products that contain bacteria show an increase in the optical curves allowing the system to detect the presence of the microorganisms.

Similar results were obtained with motor oil (Figure 3).

The data indicates that the system works very well in distinguishing between contaminated and clean samples. It can be also used to determine the level of contamination.

High precision or repeatability was obtained for all samples tested. The BioLumix system can be used to detect the presence or absence of organisms. Assays include Total Aerobic Count, Yeast and Mold, Enterobacterial count and absence of objectionable organisms in 10 grams of product, such as E. coli, S. aureus, and Salmonella. The system is designed to speed up product release and simplify the microbiological testing of oil containing products, generating an automated certificate of analysis for all assays in 48 hours.

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