Oilseeds are defined as the seed (endosperm) of any of several plants that are used commercially as a source of vegetable oil and can also refer to the plant that yields any such seed. Examples include but are not limited to groundnuts/peanuts, sunflower, sesame, safflower, linseed, soybean, rapeseed/canola, and palm kernel oil (not to be confused with palm oil which is produced from the pulp of the same oil palm fruit). While palm oil is the vegetable oil consumed the most globally, it is not derived from oilseeds and palm kernel oil has a much smaller market segment. The history of oilseeds is closely tied to that of human civilization. Rapeseed and sesame are mentioned in Indian Sanskrit writings from around 2000 BC and sunflower was reported to be present in Arizona and New Mexico around 3000 BC. Whole oilseeds contain high concentrations of energy and moderate amounts of protein and fiber. They are not only an essential source of edible oils but also as a source of meals that are included in diets fed to livestock. Total global oilseed production reached approximately six hundred million tons in 2020/21 and is forecast to grow five percent in 2021/22 to reach six hundred thirty-two million tons from record plantings. Soybeans account for over half of all oilseeds produced worldwide and are forecast to increase in production by twenty-three million tons to three hundred eighty-six million tons, an increase of six percent fueled primarily by output growth in the United States and South America. Production of all oilseeds is forecast to increase, with many types reaching at least ten year records. Global production of oilseeds is forecast to rise by three percent in 2021/22, led by a higher demand for soybeans in China, a direct reflection of the rebuilding of feed demand following African swine fever. Trade is projected to increase as well, mostly because of the greater soybean demand from China, which accounts for around sixty percent of global soybean imports. The production gains and increased demand are also expected to create a modest increase in stock prices as the market rebounds from currently tight stocks that have driven soybean prices to the highest levels in eight years. Soybean oil manufacturing has become so prevalent in the United States that the term “vegetable oil” is synonymous with soybean oil. Another factor in the global expansion and increased demand for oilseeds is the growing need for vegetable oils and biofuels as well as increasing awareness of environmental and sustainable alternative energies.
Oilseeds are crushed to obtain oil for human consumption and biodiesel production and the remainder is processed into meal which is used for high protein livestock and poultry feed. Due to high availability in the United States, soybeans are the dominant biodiesel feedstock while rapeseed oil is the major biodiesel feedstock in Europe. Different oilseeds differ in oil yield and production per crop acre. Soybeans produce approximately 1.5 gallons of oil per bushel of crop and in 2009, U.S. farmers produced a record yield of forty-four bushels per acre, which roughly translates to an oil yield of sixty-six gallons per acre. Although soybeans do not produce as much oil per acre as some other crops, it is the most popular oil in the United States and is commonly grown as a rotation crop with corn. There is an established infrastructure to process soybeans into oil and meal. One regulation is classifying meal into two separate specifications based on the inclusion of hulls during crushing. If soybean hulls are not included in the meal, it is called dehulled soybean meal while inclusion of hulls classifies the meal as non-dehulled soybean meal. This specification is widely used during trading and penalties exist when product deviates from the contract specification. There are also recommendations for certain nutritional parameters within these two classifications. These include protein (47.5-49.0% for dehulled and 44% for non-dehulled), crude fiber (7.0% for dehulled and 3.5% for non-dehulled), moisture (12% for both groups), and fat (0.5% for both groups). Rapeseed and canola produce about seventy-five to two hundred forty gallons of oil per acre. They are excellent rotation crops because of deep root systems that are good at absorbing water and nutrients. Both types use planting and harvesting equipment similar to that used for small grains and they command a high price in the feed market. Mustard is a close relative of canola and rapeseed and produces less oil than canola but is drought tolerant, grows well on marginal soil, and contains compounds that are resistant to soil pathogens. However, mustard oil is not permitted to be imported or sold in the United States and many other countries for cooking use with a few exceptions. This is because of the high level of erucic acid, a monounsaturated omega-9 fatty acid that is about 42% prevalent in mustard oil. Studies on rats in the 1970s showed that erucic acid appears to have toxic effects on the heart at high doses, but more recent research has cast doubt on these results as rats are unusual in their inability to process erucic acid. Studies on other animals have not shown similar results and no definitive link between human heart disease and the consumption of mustard and similar oils has been determined. Despite this, the regulations remain and food-grade rapeseed oil is regulated to a maximum of 2% erucic acid by weight in the United States and 5% in EU, with stricter regulations for infant food. Canola is specifically derived from a variety of rapeseed that is low in erudic acid. Both safflower and sunflower can produce biodiesel oil as well, although these oils are considered more valuable for cooking purposes. As shown in the market analysis here, global demand for oilseeds and its products is increasing at a high rate, creating new challenges in productivity, testing, regulations, and research.
Oilseeds Growing, Harvesting, Processing
Oilseed crops are generally grown for the oil in their seeds and can vary considerably in oil content, quality, and composition. These factors are dependent on the crop species and the environmental conditions in which the crop is grown. Soybeans are typically planted in the late spring in rows between thirty-six and forty-two inches apart at a rate of about one viable seed per inch of row. They can be planted in any average, well-drained soil and sprout best when positioned for full sun. Soybeans are known as a good cover crop to add nitrogen to poor soil and mixing a balanced organic fertilizer into soil before planting will improve this process. Harvesting is best done when the plants begin to flower and nitrogen modules left behind in the soil will add fertility. Rapeseeds are members of the brassica family which are cool weather crops and grow best in the spring or autumn. Rapeseed plants are very forgiving and can grow in acidic, neutral, and alkaline soil as long as the soil drains well. Peanuts grow their seeds underground and light-textured soils that do not bake work best. They grow best on soils with a pH between 6.0 and 6.5 if enough lime is available for normal development. Sesame seeds grow best on fertile, well-drained soils of medium texture with a neutral reaction. The seedbed should be mellow, warm, and moist and warm weather is required for growth. Sesame seeds are small and one pound contains about one hundred and fifty thousand seeds. Seedlings emerge quickly under good conditions, but the small plants can grow slowly at first. They are sensitive to cooling during the beginning stages of growth and a heavy rain early after planting may compact the soil, which can require replanting. Regardless of the type of seed, it is important for growers to be aware of environmental factors including weather, pests, and weeds and be sure to take steps to avoid problems with the seeds as they grow and germinate.
The preparation of seeds for oil extraction can vary based on the physical properties and oil content. In general, most oilseeds go through the process of cleaning, drying, dehulling, size reduction, flaking, cooking, and tempering. Oilseeds need to be cleaned to remove plant stems, sticks, leaves, and foreign material before storage. Many foreign materials are separated by a combination of rotating or vibrating screens. Sand and dirt can be removed by fine screening. Magnets can remove ferrous metal contaminants. Some larger oilseeds (such as peanuts) may have stones that are similar in size to the seeds and these stones need to be removed by gravity. Moisture often needs to be reduced before storage to minimize degradation and improve the effectiveness of downstream processing. Soybeans typically have around 13% moisture after harvesting and need to be dried to 10% before dehulling for efficient hull removal. Large, open-flame dryers with multiple columns are used for this purpose and the seeds are dried in the upper section and cooled in the lower section of the columns. The amount of hull on oilseeds varies significantly. Cotton seeds have a hull percentage around 45%, sunflower seeds around 25%, and soybeans around 7%. If hulls are not removed, the total oil yield is reduced by absorbing oil in the pressed cake. Hulls also contain undesirable wax and color compounds that wind up in the extracted oil. There are many types of dehullers that are used depending on the kind of seed. Three common ones are knife, disk, and impact dehullers. If size reduction is required, a cracking mill consisting of two sets of cylindrical corrugated rolls in series is used, although many oilseeds are small enough to not require this. There are three processes that can be used to separate the oil from the protein meal: solvent extraction, continuous pressing, or hydraulic pressing. Solvent extraction is the most common and uses hexane to extract oil from the flaked meal. Before extraction, the flaking process ruptures seed cellular structure and reduces the distance that the solvent has to travel to reach the oil in the cells. A flaking mill has two large diameter rolls that turn in opposite directions and stretch and flatten the seeds. This process also increases the surface area for increased contact between the solvent and seed. Some seeds can be cold-pressed using a screw press at low temperatures and this process uses crushing the seeds to extract the oil instead of hexane extraction. Continuous pressing uses an oil extraction screw pressed to extract the oil from ground and properly conditioned seeds at elevated temperatures. Hydraulic pressing is the oldest method and is an intermittent pressing operation carried out at elevated temperatures in a mechanical press after the seeds have been rolled into flakes and conditioned by heat treatment. Proper storage and transport of the extracted oil is essential to avoid oxidation, hydrolysis, and contamination.
Oilseeds and NIR Spectroscopy
NIR spectroscopy has emerged as a tool for rapid, non-invasive, and cost-effective analysis of parameters of interest in oilseeds that could potentially replace traditional reference methods. There are a number of quality parameters in oilseeds that have been studied and predicted with NIR spectroscopy with results suitable for process control purposes. Other parameters have shown results good enough for screening purposes and more study and calibration work could improve the prediction results. A recent comprehensive review discussed in detail the various oilseed quality parameters that have been studied using NIR spectroscopy. These include oil content, protein, moisture, fatty acids, lipids, ash, and lineolic, oleic, erudic, and amino acids. The review also examined specific nutritional components, geographical origin, and adulteration detection. NIR spectroscopy can be used in conjunction with more comprehensive detection methods to create profiles that can predict flavor of peanuts from simple tests. One study determined protein, oil, oleic acid, and linoleic acid using NIR and then identified flavor compounds in the same peanuts using GC-MS. Correlation was determined that allows for the prediction of roasted peanut flavor from the NIR spectra. Moisture and oil content are very important parameters in Chi seeds and these have been correlated with NIR spectra in another study. Similarly, fat, protein, and moisture can be determined in soybeans by using a handheld MEMS FT-NIR spectrometer and calibration models. These parameters are important in sesame seeds as well and one study examined fat, protein, and moisture in sesame seeds of different coat colors, with the results showing that these three quality parameters can be correlated to NIR spectra regardless of coat color. Another study using sesame seeds predicted oil yield in the seeds which is produced by an aqueous extraction process, a known method for producing sesame oil with a pleasant flavor and high nutritional value. Results were good and could provide a method for sorting sesame seeds with a higher oil yield to be used for aqueous extraction. Fatty acid content is an essential parameter in producing high quality rapeseed oil and NIR spectroscopy was shown as a proven method for determining fatty acid composition in rapeseed seeds used in breeding programs. Seed characterization is important as well and NIR spectroscopy has multiple applications for this purpose, including geographical origins, age, seed viability, and seed oil content. One study used NIR spectroscopy to investigate the differences in oil, oleic acid, linoleic acid, and protein in sesame seeds obtained in different countries in Africa and Asia. The results showed high variation in these components, both within these two continents and especially between the two of them. Knowing this variation provides excellent background information for breeding high-nutrition varieties of sesame seeds and to help meet market demand. All these parameters and measurements have been studied using NIR spectroscopy with results showing the potential to replace traditional reference methods.
Oilseeds: World Markets and Trade
Oilseeds: An Overview
Oilseed Crops for Biodiesel Production
Soybeans: A Grow Guide
The University of Vermont Extension: On-Farm Oil Seed Production and Processing
Oil and Oilseed Processing I
Oilseed Processing, Conditioning, and Drying
Common Oilseed Extraction Processes and Equipment