Food Safety : Flaws in Fermentation, Part 2

by Food and Drug Administration (FDA)

(Page 3 of 3)

This year, John Roach, an FDA mass spectrometrist, began collaborating with scientists from 20 laboratories worldwide to evaluate Brumley's approach. The collaborative study will determine if the procedure is acceptable for common use within the scientific community.

FDA food scientists continually adapt DNA probes, mass spectrometry, and other procedures to fit the numerous types of food contaminant problems they encounter.

Analytical methods used by FDA have been accepted in courts of law, and studies of most have been published in peer review journals. As FDA geneticist Datta and mass spectrometrist Brumley have shown, if new approaches are needed to solve a contaminant problem, FDA scientists can be called upon to develop them.

Captions — Mass Spectrometry

GC injection port — A food sample is injected through a self-sealing silicon rubber stopper. The heated injection port vaporizes the sample, turning it into a stream of molecules, and a carrier gas sweeps it into the coiled GC column.

GC column — The molecules are separated here. The column is coated with a material that interacts with each molecule. The molecules pass through at varying speeds, depending upon their physical or chemical ability to stick to the material in the column.

Ion Source — A beam emits electrons that strike the molecules as they clear the GC column, producing ions. An electronic field propels the ions toward the quadrupole.

Quadrupole — Four conductive rods separate the ionized material according to their mass/charge ratio. Voltages on the rods can be set to allow ions of a particular weight to pass through and ions of the wrong weight to be pumped away by the vacuum system.

Detector — All ions that pass through the quadrupole are measured here. The information is then passed on to the computer that records the data and generates charts. Using data from the charts, chemists can identify and quantify unknown substances.

Data System — This computer controls the entire GC/MS system. It regulates the temperature in the GC, tunes the MS, controls the voltages on the quadrupole, detects the abundance of each ion, and processes the data.

Captions — DNA Probe Visible colonies of Listeria appear after a dilute food sample is spread on the surface of agar selective for the growth of Listeria.

Bacterial colonies are transferred to filter paper.

Bacterial cells are exposed to microwave irradiation under strong alkaline conditions. This treatment opens the cells, breaks the bonds of the double-stranded DNA, separates them into single strands, and fixes them to the filter paper.

Gene probes (single-strand pieces of synthetic L. monocytogenes DNA) are added. The synthetic strands are labeled with a radioactive compound so their presence can be detected on x-ray film.

The radioactive gene probes couple with complementary regions of the natural DNA and reform the double helices.

The filter paper containing the hybrid DNA is placed on a sheet of x-ray film.

The radioactivity from the hybrid DNA exposes the x-ray film, and dark spots appear after the film is developed. Each dark spot represents a colony of L. monocytogenes and enables the food scientist to know how many bacteria contaminated the original sample.

A Peek in the Toolbox

FDA food scientists use a number of analytical techniques. Grouped into categories according to their function, these tools and some of their applications are:

Chromatography (thin-layer, gas and liquid)

Separates complex mixtures (food extracts of various types) of similar components by measuring migration rates of component molecules through columns and through coatings on chromatography plates.

Analyzes food extracts for pesticide residues, chemical contaminants, and natural toxins; analyzes alcoholic beverages, fats, oils, and direct and indirect food additives.

Spectrometry (mass spectrometry, nuclear magnetic resonance and electron spin resonance, and infra-red and ultraviolet spectroscopy)

Measures molecules or atoms of food components as they are ionized and fragmented in a magnetic field; as they are polarized in a magnetic field; or as they undergo absorption and emission of energy in irradiation.

Analyzes food additives, food contaminants, metals, fats, and oils; confirms the identity of pesticides, natural toxins and other chemical contaminants, and food additives and flavors; assists in identifying unknown complex organic structures.

Radiotracers

Measure isotopes that undergo radioactive decay but that, in all other respects, are identical to atoms normally found in chemicals.

Study food additives, food processing, animal metabolism, and biosynthesis of natural toxins; analyze foods for radioactivity.

Gene probes, enzyme catalysis, antibody-antigen interaction, and immunoassays

Depend on specific properties and interactions of substances being analyzed with antibodies, DNA fragments, and other components.

Analyze foods for amino acids, sugars, microbial toxins, other natural toxins (e.g., aflatoxins), and pesticides.

Analyzers (thermal energy analyzer, amino acid analyzer, and others)

Are specialized instruments, often automatic, that react to specific components or contaminants in food samples.

Analyze contaminants in foods (e.g., nitrosamines) and food packaging; assay vitamins, nutrients, and other food substances.

Electrochemistry (polargraphy, electrophoresis, anodic stripping, voltammetry)

Separates complex mixtures of components in a food product by use of an electric force field.

Analyzes food extracts for metals and pesticide residues; identifies preservatives, color additives, and species of fish.

Bioassays

Measure responses of living organisms (from viruses to bacteria, animal cells in culture to primates) to substances being analyzed.

Analyze food extracts for natural toxins, pesticides, nutrients, and hormones.

Computer-assisted analytical workstations

Control analytical instruments by use of highly sophisticated computers.

Monitor programs; calibrate, record and store information; maintain diagnostic control over analytical and data-gathering systems.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.