AL
(filter background plus the white resi- due) leaves a spectrum showing a strong amide presence (the amide I and amide II bands are seen between 1500 and 1700 cm-1
) plus other signals over the range 1000–1500 cm-1
indicative of sugars and
possibly phosphates, all of which are typi- cal of proteinaceous materials. Milk contains significant amounts of protein such as beta- lactoglobulin, a fat-transport protein. These materials can aggregate under the processing conditions, leading to sticky masses of mate- rial on the filter.
Figures 6–9 show spectra collected from the inside of a snack food bag. Figures 6 and 7 were acquired in reflectance mode (no ATR was used), which was possible because the bag was highly reflective. Again, spectral sub- traction was used to remove the background signals due to the bag itself (predominantly polypropylene), allowing the droplet to be identified as an edible oil. The solid brown particle shown in Figure 8 was analyzed us- ing ATR. Subtraction of the spectrum from the greasy coating on the bag yielded a spectrum dominated by a carbohydrate peak. When searched against a common materials library, this spectrum matched that of dried potato, a remarkably direct conclusion.
Cornmeal often exhibits dark granules among the yellow-colored majority. An analysis of a yellow and dark granule is shown in Figure 9. The yellow granule matches starch, the major- ity constituent in cornmeal. The darker granule is quite different and appears to be corn oil. This is probably caused by overprocessing of a certain part of the sample, and is an example of an acceptable variation in a food product.
Figure 10 shows the spectrum of a fly wing, an undesirable contamination. Like most proteins, the spectrum is dominated by the amide bands, seen between 1300 and 1700 cm-1
. Since all proteins exhibit these bands, careful analysis is required to deter- mine the origin of the material. In this case, the image is a strong clue that the material is a foreign substance. The Nicolet iN5 microscope provides both visual and spectroscopic data to aid in identifications of this type.
Conclusion
Food safety and quality control require continuous monitoring. The importance of
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combining visual and spectroscopic data is demonstrated. In this example, filters were used as the sample, but extraction of particulates from a bulk sample is also a standard analytical procedure. With a well-designed library, the system provides an immediate feedback tool for quality control and diagnostics. The Nicolet iN5 FTIR microscope, combining visual and spectroscopic tools in a cost-effective, simple-to-use package, can drive improvements in quality, regulatory compliance, and cost savings.
Michael Bradley is senior manager, product applications, and Steve Lowry is research scientist, Thermo Fisher Scientific, 525 Verona Rd., Madison, WI 53711, U.S.A.; tel.: 608-276-6100; e-mail:
mike.bradley@
thermofisher.com;
www.thermofisher.com
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