The potential of oilseeds crop is built on its ability to deliver oil yield of consistent quality. The quality of oilseeds is assured through the varietals development and registration system which encourages the development of cultivars with quality factors demanded by the end-user as well as good agronomic performance. One of the roles of the Oilseed Brassica Group of Plant Breeding and Genetics Division at NIFA, Peshawar is to provide information on the quality of oilseed crops to all stakeholders. The Oilseed Quality Laboratory assesses utilization quality of different oilseed crops with chemical or physical tests which measure important quality parameters in the seed or the final product.
Oil content can be defined as the maximum amount of material (lipid) that can be removed from the seed by extraction with specific solvents (usually hexane or petroleum ether). This test estimates the amount of oil which could optimally be obtained in industrial crushing. An estimated 97% to 99% of the oil content estimated analytically may be removed by commercial solvent extraction or Prepress solvent extraction systems. Direct pressing or cold pressing usually removes about 90% to 92% of the oil. The quality of the oil removed analytically also differs greatly from the quality of the oil removed in industrial processing. Oil removed analytically usually consists of about 99% triacylglycerol molecules (the desired end product of oil processing) and is relatively colourless. Pre-treatment of the seed to increase the efficiency of industrial extraction results in a highly coloured crude oil which consists of about 96% of the desired triacylglycerol molecules. The undesired material and colour is removed by refining and bleaching.
Oil content is measured directly by grinding the seed and extracting the oil in a continuous extractor. The official methods call for extracting for periods of 1 to 3 hours followed by further grinding and extraction periods until no further oil is removed. Total analysis time is in the order of 6 to 8 hours per sample with a maximum throughput of 18 samples per day. Indirect oil content analysis can be carried out using Near Infrared Reflectance Spectroscopy (NIRS). The NIRS technique measures the energy absorbed (1100-2500 nm) in the whole seed sample. Sample throughput is increased to about 300 per day for NIRS. The precision of NIRS methods is dependent on reference method and oil contents are expressed on 6 to 8% moisture basis.
Oilseed crops produce a meal after commercial extraction of the oil that is a valuable source of protein for compound feeds. The analysis of protein content is based on an estimation of the nitrogen in the seed. As protein is the major nitrogen containing component in seeds its content can be estimated by multiplying the nitrogen content by a factor (by convention, 6.25 for oilseeds). Some trading specifications call for protein to be specified as nitrogen or ammonia (1.21 x N).
Protein is traditionally determined by the Kjeldahl method in which the ground, dried material is digested or dissolved in concentrated sulfuric acid converting all the nitrogen to ammonia. The ammonia is distilled into a standardized acid solution and is determined analytically by titration.
Traditionally, oilseed protein is expressed on an oil-free basis. Protein is also estimated by NIRS with good precision in Oilseed Quality Laboratory.
|Fatty Acid Composition
The functional and nutritional values of different vegetable oils are dependent on the nature of the different fatty acids which are incorporated like building blocks into the oil (triacylglycerols). For example, erucic acid (C22:1) makes up about 50% of the fatty acids of traditional rapeseed and mustard oil. Canola oil, on the other hand, is designed to contain zero erucic acid for nutritional reasons. By definition, erucic acid must make up less than 2% of all fatty acids in canola oil. Recent sales of canola oil products in the international markets have been based upon this oils' low level of saturated fatty acids (mostly palmitic and stearic acid), its high level of mono-unsaturated fatty acids (mostly oleic acid), and its good ratio of polyunsaturated fatty acids (linoleic and linolenic acids).
Fatty acid composition is mostly effected by variety and growing environment. It is important to know the effect of environment on the fatty acid composition of canola in order to determine where seed can be drawn which will make oils meeting the specifications for saturated fatty acids required by processors. Fatty acid composition is determined by a process which starts with extraction of a portion of the oil and its chemical conversion into individual fatty acids (taking apart the triacylglycerols). The fatty acids are then converted to methyl esters, compounds which can easily be converted to gases. The different fatty acids are then separated and analyzed on a Gas Chromatograph (GC). The method is rapid and accurate. Starting from seed, a single sample can be analyzed within 30 minutes. Using GC complete fatty acid profile can be obtained on as many as 15 samples per day in NIFA Oilseed Quality Laboratory. The NIRS technique predicts with good precision the fatty acid profile in the whole seed sample. NIRS seed testing is increased to about 300 samples per day.
Glucosinolates (GSL) are natural components of canola, rapeseed, and mustard seed. These compounds are found in all Brassica vegetables (cabbage, Brussels sprouts, radishes, broccoli, and cauliflower) and are responsible for the desirable pungent smell and sharp flavour associated with these foodstuffs. GSL are also natural toxicants, being associated with goitre and liver damage when consumed in large quantities. Brassica seeds such as rapeseed and mustard are particularly rich in GSL. While high levels of GSL may be desirable in the case of mustard seed destined for condiment use, the high levels of GSL found in rapeseed meal have restricted the use of this seed as a source of protein in compound feeds. Plant breeding to reduce the level of GSL in rapeseed resulted in canola seed. Nutritional studies have demonstrated that substantially more canola meal can be used in compound feeds than rapeseed meal.
GSL are ionic, that is they are charged molecules. They are determined by first extracting them from the seed into water, then isolating them from interfering components. They are then converted into an uncharged molecule with an enzyme, and are analyzed by UV vis Spectroscopy. The current definition of canola requires that only part of the total GSL in a sample (the aliphatic GSL) be measured. Canola seed contains less than 30 micromoles per gram of these aliphatic compounds expressed on an oil-free. The GSL in whole seeds of brassicas are predicted through more rapid and less expensive methodologies “NIRS” at NIFA.
GSL levels are highly dependent on environment with up to 3- fold differences being noted between seed planted and seed harvested. It is important that the GSL level in the crop be monitored closely to determine if the canola specification is being met.