FT-NIR spectroscopy for the edible oil industry

Near Infrared Spectroscopy has been a well established technique in the agricultural sector for decades and is recently becoming more and more important in the food industry. Modern multi purpose spectrometers can analyse both, liquid and solid samples and are the ideal tool for the non-destructive and rapid analysis of oilseeds and finished oils throughout the entire manufacturing process.

The FT-NIR technology offers a lot of advantages over classical wet-chemical and chromatographic analyses. It is quick, cost-effective and safe, since no hazardous chemicals are used. It simply measures the absorption of near-infrared light of the sample at different wavelengths. The recorded NIR spectrum is characterized by overtones and combinations of the fundamental molecular vibrations of molecules containing C-H, N-H or O-H groups, making NIR spectroscopy first choice for the analysis of organic materials like oilseeds and edible oils.

FT-NIR also avoids the typical error sources of the classical lab methods, e.g. during the sample preparation stage. With only one measurement, multiple components can be analyzed in less than one minute in solid samples as well as in liquids. Although NIR spectroscopy is not a technology for trace analysis like for toxins, it will help the producer to constantly monitor the quality of the goods along the production chain - from checking the incoming raw materials up to quality testing the finished product. This will soon be in the food industry as important as it is already today in the pharmaceutical industry.

Analysis of Oilseeds

The analysis of oilseeds plays a mayor role in ensuring the right quality of food as well as of agricultural products. Near Infrared spectroscopy offers solutions for oil producers as well as for breeders. To optimize the oil pressing process, the oil seeds as well as the intermediate products, like expellers or extracts can be analyzed for oil and moisture content.  This way, the pressing process can be optimized and the plant runs more efficiently.

Looking at the plant breeding process, at each stage the breeder needs to choose the best seeds for propagation to the nest generation. In the past the breeder has had to sacrifice some of these valuable seeds in order to test for the traits of interest. NIR has become increasingly popular in the plant breeding-sector, as it is a non-destructive method of analysis, capable of measuring many of the important traits. It allows the breeder to analyse seeds quickly and to cost effectively determined the best and successfully grow them on.

Depending on the use of oilseeds, different parameters are of interest: In Asia, soy bean products play a big role and for processing the traditional food like Tofu or Miso, the composition of the incoming soy beans in terms of protein or fat content are crucial. Also the amino acid composition can be monitored with NIR spectroscopy.

For sunflower seeds, the amount of Oleic Acid is an important parameter. Over the last decade, there has been an increased interest in breeding sunflower seeds with high Oleic Acid content. This type of breed is high in mono-saturates and therefore associated with a healthy diet. NIR can determine the content of oleic and Linoleic Acid inside the seed. Rape seed breeders can obtain valuable additional information like fatty acids, including Erucic acid as well as the Glucosinolate content, crucial parameters for the palatability of the finished product.

Quality Control of finished Oils

Edible fats and oils are made up of the esters of glycerol and fatty acids, the so called triglycerides. The softness or hardness of the fats and oils are determined by the composition of the fatty acids. The more saturated the fatty acids are, the harder the fat, the more unsaturated, the softer. The Iodine Value (IV) is defined as the grams of Iodine absorbed by 100g of fat or oil. The higher the IV is, the softer the fat. The analysis of Iodine Value (IV) by FT-NIR is today acknowledged by the AOCS (method Cd1e-01). Other parameters an also be determined simultaneously with only one measurement, e.g. the acidity of the oil. The more fatty acids are freed from the glycerine backbone, the more acidic the material is. This is expressed as the free fatty acid (FFA) content.

This FFA value is, apart from the organoleptic evaluations, a major criterion for the classification of the olive oil into the categories "Virgin" and "Extra Virgin" According to the current EC regulation 1513/01, the maximum level of free acidity of an extra virgin olive oil must not be higher than 0.8 gram per 100 grams (0.8 %). The acidity level in the oil is increased if the olives were attacked by insects. They were collected from the ground instead of straight from the tree or if there was a time lag between harvests and processing to oil.

Since NIR spectroscopy is capable of looking at the complete composition of the molecule, also the fatty acid composition can be determined. This is generally important for the identification of different oils. Further parameters which can be analyzed spectroscopically include the health relevant Trans Fatty Acids (TFA) as well as physical parameters like colour values or Dropping Point.

Testing for Adulteration

A common problem not only for the olive oil industry is the adulteration of high priced oil with cheaper vegetable oils such as sunflower oil or hazelnut oil. Today's public awareness of the health benefit of olive oil makes the adulteration economically attractive. From the chemical point of view, all oils are quite alike and the blend is difficult to identify with common analysis tools like refractive index or iodine value. However the different oils vary in their fatty acid profile and NIR spectroscopy can offer a valuable tool for determining other types of oil in olive oil down to a low percentage range.

Another issue regarding adulteration is to determine the origin of plant oils in order to assign them to geographic regions for certification purposes. One example is the registered designations of origin (RDOs) nomination of extra virgin olive oils of known region, province and variety (cultivar). Here NIR spectroscopy is under review if it can help identifying fraud. First studies indicate that NIR spectroscopy, together with chemometric algorithms shows promising results.

FT-NIR spectroscopy has the potential to substitute a wide range of classical analysis methods in the edible oil industry. Bruker Optics offers ready-to-use calibrations for edible fats and oils as well as for oil seeds to enable a quick and efficient start.