from planting 148 palms/ha on mineral soil, whereas on peat soil income is still on the increase when density is at 200 palms/ha (Latif et al. 2003). Whereas a high plant density may benefit by covering all the areas with leafy tissue to intercept light, a balance must be found, as it may also increase the competition between plants for water or nutrients.
Density of the crop also has a great impact on the uptake of nutrients and nitrogen from the plant. Nitrogen uptake can be improved by using N‐efficient management strategies like choice of variety, form and timing of N‐application adapted to site conditions (Rathke et al. 2006). The canola oil content increased, parallel to the crop yield increase in canola seeds when treated with the adequate proportion of nitrogen and phosphorus 90/60 kg/ha, but when a higher ratio was applied, oil content was inversely proportional to crop yield (Cheema et al. 2001). The amount of N application must be taken into account, as an over‐fertilization can be also negative. For instance in olive trees, an excess of N may lead to polyphenol decrease in oil, which in turn, provokes the decrease in quality and stability to oxidation (Fernández‐Escobar et al. 2006).
Finally, harvest date has to be properly selected in order to optimize the oil content on the fruit or seed. Different parameters are related to harvest, including number of seeds, moisture of the seeds, weight of 1000 seeds, and oil content, which will determine the final oil yield of production. In sunflower, the highest oil content was recorded on late harvesting dates (Miklič et al. 2008), and in olive, it is important to harvest the fruits at full maturation, so they can have the maximum oil content per piece (Lavee and Wodner 2004). In perennial crops, the harvesting frequency also has an impact, with a yield increase of 5–20% when reducing length of harvesting round from 14 to 10 days in palm tree (Woittiez et al. 2017).
2.4 Overview of Oilseed Processing and Current Applications
On the whole, current applications of oilseeds’ oils for food, fats, and oils have been long been used anciently and in many cultures. Most of the oilseeds oils are used for food applications with purposes such as shortenings, texture, flavor, or flavor‐base since most flavors are soluble in oil. For instance, palm oil is well known as cholesterol‐free oil used in cooking, margarines, spreads, confectionary items, ice cream, emulsifiers, and vanaspati (Pande et al. 2012). Sustainable alternatives to palm oil are nowadays on demand in a wide range of food products. Their high level of saturated fatty acids in comparison to other oils such as rapeseed or sunflower oil is still a health issue connected to the cultivation of palm oil (Hinrichsen 2016). A fully hydrogenated fat could potentially be a replacement for palm oil in food applications. For instance, blending liquid rape, sunflower, or soybean oils or coconut oil in combination with fully hydrogenated oils are some options currently in use. As reported by Hinrichsen (2016) recommendations of high level of oleic acid for frying applications such as high oleic sunflower and high oleic rapeseed oil are good alternatives to palm oil. However, other oilseed oils with high flash point are commonly used for frying including canola, safflower, groundnut, or cottonseed oils. On the other hand, the use of partial hydrogenated oils is always under discussion for their content in transfats and the associated health risk (Canada 2016). In addition, the food industry frequently used synthetic antioxidants such as butylated hydro butylated hydroxytoluene, butylated hydroquinone and tert‐butylhydroquinone to inhibit deterioration caused by fats. However, according to Balasubramaniam et al. (2020), finger millet polyphenols delayed the oxidation of both refined and unrefined peanut oils confirming the advantage of providing food safety while maintain quality. Soybean oil is one of the world‐consumed cooking oils offering a neutral flavor and favorable fat profiles used widely in the food industry. Emulsifiers in the food industry are essential for sauces, chocolate, ice cream, and mayonnaise formulations. Commercial lecithin comes from soybean oil and the improvement of food‐grade emulsifiers in the properties and stability is of great interest. Sunflower lecithin extracted by a cold‐press process is an alternative option. Another highly consumed oil is the rapeseed oil, which can be used in salad dressings, mayonnaise, and other emulsified products including biscuits and canning (Perrier et al. 2017).
Regarding animal feed, the remaining part of the seed after oil extraction is called meal fraction and is an important source of high‐protein in animal feed products. Soybean meal is accepted worldwide as the most important protein ingredient in animal diets as a potential source of protein and essential amino acids while making a significant contribution to the dietary energy requirement compared with other oilseed meals. The chicken meat industry is the major user, accounting for 50% of all soybean meal livestock, while the pig industry consumes around 35% (Willis 2003). Also, oilseeds are frequently used as an energy source in diets of lactating dairy cows as ruminal microorganisms highly degraded the protein from whole oilseeds and oilseed meals (Bernard 2016).
Another industrial application is the use of oilseeds in sustainable food packaging. Epoxidized soybean oil has been used to reduce biopolymers hydrophilicity with its low cost, biodegradable and environmentally friendly characteristics, and its renewable origin (Willis 2003; Ciannamea et al. 2018). A partial replacement of glycerol by 20% of epoxidized soybean oil increased the heat seal strength in synthetic polymers as reported by Ciannamea et al. (2018). Other applications are thought highly of in the chemical industry. For instance, cold‐pressed rapeseed meal also has techno‐functional characteristics like emulsification and foaming which are highly valuable for application in adhesives, detergents, paints, varnishes, and are biodegradable (Chew 2020). Linked to industrial applications, flaxseed oil, which is rich in the unsaturated fatty acid linolenic is a drying oil used in protective coatings including paints or varnishes. Other commercial applications are cosmetics, in which oilseed oils suit cosmetic formulations due to their high fatty‐acid composition. Production of lubricants, soaps, and personal care products are some examples of the topical treatments in which oilseeds oils are the main ingredients as base oils (Zimba et al. 2005; Chivandi et al. 2008).
Biotechnology has helped to improve the fatty acid composition of oilseed oils in food, feed, and bio‐based industrial materials. For instance, the production of oilseeds of fish oil‐type omega‐3 polyunsaturated fatty acids resulted in an improvement of oil quality for direct human consumption with health benefits (Wu et al. 2005; Truksa et al. 2006). Metabolic engineering through the synthesis and metabolism of novel fatty acids with hydroxy and epoxy residues has proved valuable for industrial applications including lubricants, plasticizers, and nylon precursor (Burgal et al. 2008; Li et al. 2010).
Rapeseed oil and soybeans are the main oilseed crops for the production of biodiesel in Europe and the United States, respectively. However, other emerging oilseed crops such as mustard or hazelnuts are being explored as promising biodiesel feedstocks (Farm Energy 2019). In the case of rapeseed oil, the production of biodiesel is made through the rapeseed oil methyl ester with a limitation value of contamination lower than 25 mg/kg according to the “Quality standard for rapeseed oil as a fuel” (Fetzer et al. 2018; USDA 2019).
Acknowledgments
Ingrid Aguiló‐Aguayo thanks the National Programme for the Promotion of Talent and Its Employability of the “Ministerio de Economía, Industria y Competitividad” of the Spanish Government and the European Social Fund for the Postdoctoral Senior Grant “Ramon y Cajal” (RYC‐2016‐19949). This work was supported by the CERCA Programme of Generalitat de Catalunya.
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