US researchers have discovered a faster, cheaper method for testing the quality and purity of oils, such as flaxseed, used in dietary supplements.
With pressure on the supplement industry to guarantee quality and efficacy, and growing consumer demand for natural food additives, the discovery could prove a more efficient method of meeting quality control.
Lead author Lisa Mauer, assistant professor of food science at Purdue university, said: "Consumers want the salad dressing brand they buy to taste the same every time. The same is true for special types of oils, which are more expensive than a general cooking oil. You expect what you buy to be high quality and contain what is on the label."
For the study, published in the September issue of the Journal of Agricultural and Food Chemistry, the researchers used infrared spectroscopy and statistical analysis to classify samples of 14 dietary supplement oils and five common food oils - canola, corn, peanut, soybean and sunflower. The scientists profiled the chemical make-up of at least two different brands of each.
First, pure oil samples were tested to determine how well the spectroscopy method, called Fourier-transform infrared spectroscopy (FT-IR), could differentiate between each one. Then they mixed various amounts of each cooking oil with one of the dietary oils, such as almond, borage, cod liver and evening primrose, and tested to determine if FT-IR could identify the amounts of individual oils in the compounds.
FT-IR uses wavelengths of light to identify types of chemical bonds. Each type of molecule absorbs light differently, producing a spectrum. Scientists use this spectral information to identify the compound, much the way a fingerprint can identify a person.
"We wanted to see how good FT-IR and common chemical measurement analyses are at differentiating real-world whole samples instead of just one component," Mauer said. "This is the first time this method has been used to differentiate a whole spectrum of food samples, such as the 19 oils used in the study, instead of only comparing two sample types."
Conventional methods for ensuring the make-up of dietary and special use oils are time-consuming and therefore expensive. They involve multiple preparation steps and analysis, which take as much as several hours, after the sample preparation and initial analysis are complete. The FT-IR method took only five minutes once the analytical procedure had been developed, according to Mauer.
The Purdue scientists tested oil mixtures that had 2- 20 per cent by volume of common food oils levels, needed by food makers to determine quality control of oil mixtures. The FT-IR method could identify the adulteration down to 2 per cent, reported the researchers.
Other studies have also shown that FT-IR can be used to identify the region where the oil-producing plant was grown and the variety of plant from which it came.