by Michael Bradley and Steve Lowry
AL
Particulate Analysis of Liquid Filtration Materials and Residues in Food Using FTIR Microscopy
To ensure the quality and safety of foods and beverages, analysts and lab personnel must identify components to determine if they are con- taminants that need to be removed or are acceptable by-products of the food production process. Fourier-transform infrared (FTIR) microscopy is a powerful method for identifying traces of material such as particulates and oil droplets. These analyses typically involve the detection of vis- ible irregularities with an approximate lower limit of 25 µm. Two sets of analyses are presented—one involving liquid filtration and the other examining particulate residues in food items—using a simple-to-operate FTIR microscope and attenuated total reflection (ATR) sampling.
Infrared microscopy for food and beverage quality control
The food and beverage industry processes massive quantities of material for direct consumption or as an ingredient for further processing. A single milk truck may transport about 36,000 liters (around 9000 gallons) of liquid milk per load, and even small dairy operations take delivery from several trucks daily. Food processing of all kinds brings the product into contact with containers, impellers, piping, seals, and lubricants.
Modern processing plants are extremely careful to ensure that all sur- faces food comes into contact with are inert, nontoxic, and scrupulously clean. Even so, the food may pick up small amounts of material, includ- ing microparticles of polymers from plastic impellers, lubricants, oils needed for production, or burnt materials from cooking.
For many beverages, a significant control barrier involves filtration. The cost per analysis from testing laboratories may exceed $200 and require 2–14 days to complete. In contrast, dozens of samples can be run per day by a single, moderately trained nonspecialist with the Thermo Scientific Nicolet iN5 FTIR microscope (Figure 1) (Thermo Fisher Scientific, Madison, WI), resulting in a cost-effective and timely solution for the analysis of filters and other particulates.
This article covers the analysis of residues on a liquid filter, particulates on a chip bag, and dark material from cornmeal. A major advantage to infrared spectroscopy is that no sample preparation was needed for any of these, and each analysis required only minutes.
AMERICAN LABORATORY 16 Figure 1 – Nicolet iN5 with the Nicolet iS10 FTIR spectrometer. Experimental
A Nicolet iN5 FTIR microscope attached to a Nicolet iS10 FTIR spectrom- eter (Figure 1) was used for the analysis. The samples were placed on a glass slide, in most cases using double-sided tape to hold them flat. Spectra were collected using the germanium-tip ATR device. Visual illumination using the bright internal LED of the Nicolet iN5 microscope and on-board camera provided large-area targeting images. This, plus intuitive manual controls, enabled rapid movement to the point of col- lection. A round aperture was inserted to target the beam. Aperture size (1 mm), optics magnification (10×), and extra magnification due to the Ge crystal of the ATR (4×) yielded a 25-µm aperture at the sample. The high throughput of the Nicolet iN5 system coupled to the Nicolet iS10 spectrometer means that 1-minute measurements at 8-wavenumber resolution provide very good signal-to-noise results.
The target area was centered in the crosshairs, and the aperture and Ge-ATR were inserted. Background was collected with the ATR inserted
JUNE/JULY 2017
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