Edible oils are used in a wide variety of food products such as margarines, salad, cooking oils, mayonnaise, salad dressings, and confectioners’ coatings. They play a major role in determining the taste, texture, nutrient profile, and shelf life of food products.
Explore this issueFebruary/March 2008
Characterizing an unknown sample of edible oil and checking for its purity or for its possible blending with other edible oils are common problems facing oil chemists, because the respective chemical compositions of different edible oils are extremely similar. This article will examine the capability of encoded photometric near infrared (EP-NIR) spectroscopy to collect sufficient NIR information to differentiate samples of three edible oils—canola, corn, and olive.
Three Edible Oils
Canola oil derives from rapeseeds. Compared with other edible oils, canola oil has the lowest level of saturated fat and one of the highest levels of heart-healthy monounsaturated fat. It also contains high levels of omega-3 fatty acids, which can help decrease the risk of heart disease and lower blood pressure. Research has demonstrated that 19 grams of canola oil—about 1 1/2 tablespoons per day—may reduce the risk of coronary heart disease due to its unsaturated fat content if it replaces a similar amount of saturated fat in the diet without increasing calories. Canola oil is thin compared with corn oil and, unlike olive oil, it is flavorless.
Corn oil, which is extracted from the germ of corn, is high in polyunsaturated fat. Corn oil is perfect for frying because it has a high smoke point. It is almost tasteless and odorless. Studies using typical American foods have found that no vegetable oil is more effective than corn oil in lowering blood cholesterol levels.
Olive oil is considered healthier than many others because it has high levels of monounsaturated fat and polyphenols. Evidence from epidemiological studies suggests that a higher proportion of monounsaturated fats in the diet is linked to a reduction in the risk of coronary heart disease.
EP-NIR spectroscopy technology (Aspectrics; Pleasanton, Calif.) covers a wide spectral range of 1,375-2,750 nanometers, whereas traditional NIR systems typically stop at 2,100 nanometers. EP-NIR facilitates fast scanning operation and is capable of simultaneously measuring multiple components in the parts per million range at a rate of 100 scans per second. This rate results in high sample throughput, real-time quality control monitoring, and a high degree of sensitivity through spectral averaging.
Furthermore, EP-NIR units do not utilize hygroscopic optical components or internal lasers. The EP-NIR spectrometers have been designed to encode analytical information in the same way as Fourier transform NIR interferometers, without the environmentally sensitive components of such instruments.
EP-NIR technology is military certified for vibration insensitive operation under Military 202G Method 204D. A high frequency vibration resistance test was performed to determine the effect of vibration on component parts of the analyzer in sweeping frequency ranges of 0.5 to 30 hertz. The units demonstrated no degradation in electrical or photometric performance either during or after the test. Moreover, the photometric performance was further tested by collecting spectra as these vibrations were applied to the analyzer. Even under the stress of such vibrations, the EP-NIR analyzer retained photometric performance and met root mean square signal-to-noise specifications greater than 50,000:1.
EP-NIR spectroscopy relies upon a simple, flexible, and efficient photometric design in which the incoming near infrared beam from a sample is imaged onto a diffraction grating-based spectrograph. The dispersed radiation from the grating is then imaged across an aperture onto the surface of an encoder disk, which is spinning at 6,000 revolutions per minute (100 hertz), providing fast real-time detection. The encoder disk has a series of reflective tracks spatially located within the dispersed grating image to correspond to the wavelengths and wavelength regions used for the analysis.