It is well known that extreme temperatures may affect oil content, and also oil composition. In sunflower, high temperature during the development of the seed leads to stress on the biosynthesis of fatty acids, and not only is the yield decreased, but also the percentage of linoleic acid is decreased (Harris et al. 1978). For olive crops, the beginning of the oil accumulation period is the most sensitive to temperature increases. (García‐Inza et al. 2014) found that olive oil content decreased 1.1% for each 1 °C increase. Moreover, even a tropical crop such as coconut its resistance to extremely high temperatures depends on the humidity of the zone, being less productive in a dry zone than it is in a wet one (Pathmeswaran et al. 2018).
Salt stress alters the morphological, physiological, and biochemical performance of crops. It occurs as result of limited water uptake, which is caused by a reduction in hydrolysis and translocation of the nutrient reserves, thus reducing seedling vigor (Parveen et al. 2016). For instance, soybean grain yield decreased by 20% when salinity was 4.0 dS/m and by 56% at 6.7 dS/m. There are some methods, which can prevent salt stress, such as the addition of glutathione, which takes part in the detoxification system of the plant. When applied at 50 mM at the reproductive stage of soybean, it improved plant growth, yield, number of pods, and number of seeds (Akram et al. 2017).
Crops can be classified according to their lifecycle: annual or biannual, such as sunflower, groundnut, or rapeseed, or perennial, such as olive, coconut, or palm (Sharma et al. 2012). There are structural differences in several ways. In annual crops, new seeds for each growing season might be advantageous, while the potential yield for perennial ones is fixed for each planting cycle (Woittiez et al. 2017). The perennial crops have a yield cycle which depends on the age of the tree, and varies among the species. Four yield phases have been described: (i) the immature or building phase, before harvestable production, (ii) the young mature phase, when yield increases linearly along the years, (iii) the mature phase, when yield remains stable, and (iv) the phase of yield decline (Díez et al. 2016). In palm oil tree, the mature phase is reached at the eighth year after plantation and stands for eight years more (Goh et al. 2003). In coconut oil tree, full production is reached between the 15th and 20th years after plantation, and lasts until the plant's 80th year (Broschat and Crane 2017). On the other hand, as calculated by Vega et al. (2001), seed number per plant in annual crops can be related with their growth rate. Seed number varied from 0 to 890 in soybean, which was directly related with the growth rate of the plant. In sunflower it varied from 0 to 4096 in sunflower, and from 0 to 1348 in maize, which both have a curvilinear relationship with the growth rate.
Variety is an important factor that affects the average oil yield of a crop, which will be later affected by stresses. The oil yield has been one of the main objectives in genetics and breeding studies in oil crops all over the years (Knowles 1983; Murphy 2014). In soybeans, oil content between varieties may range from 0.9 to 11.9% (Kim et al. 2013). Regarding palm, the variety determines the thickness of the endocarp, whose development depends on the major effect shell gene. The thickness of the endocarp is highly correlated with the oil content, which may vary by 30% between varieties (Barcelos et al. 2015). Apart from the oil content of the seed, the amount of formed seeds per area unit also contributes to the yield of a crop. For instance, it is clear for sunflower that variety affects this trait (Khan et al. 2007), but some authors report that this is not a significant factor affecting sesame yield (Mesera and Mitiku 2015). However, breeders not only look for maximum yields, but also the stability of the cultivars across a range of production environments, including the cases where several stresses occur. Sometimes, maximum and stable yields do not occur in the same genotypes, soybean cultivars being an example (Gurmu et al. 2009).
Radiation also plays a role in potential yields, as it is the driving force for photosynthesis, which will allow converting carbon dioxide into organic compounds. Regions with eight sunshine hours/day would have 60% higher potential yield than regions with only three hours/day (Van Kraalingen et al. 1989). In palm‐oil, for instance, productivity is constrained if radiation is less than 5.5 hours a day. Above this, one additional hour a day yields an additional 15–20 kg bunch dry matter/palm/year compared with productivity under cloudy conditions (Paramananthan 2003). Light incidence has also a direct relationship with the cell number and cell expansion of olives, with the ones at the top of the canopy being the ones that yield the most oil (Reale et al. 2019). So, in general, under no‐stressed environmental conditions, the amount of dry matter produced by a crop is linearly related to the amount of solar radiation, specifically photo synthetically active radiation, intercepted by the crop (Campillo et al. 2012).
The ability of a plant to intercept the incident radiation depends on the leaf area available. To maximize it, most production strategies relay on achieving an optimal distribution of the plants in a way that canopies can capture sufficient solar energy (Hemming et al. 2007). In rapeseed crops, plant density has the greatest effect on yield. Seedling rate establishes the competition for nutrients and water within the canopy, and evenly distribution makes yield more stable because there are fewer losses in seed growth (Diepenbrock 2000). In olive orchards, density between 200 and 550 tree/ha is translated into a higher fraction of intercepted radiation per area, which leads to higher productivity (Gucci et al. 2012). Optimal density also depends on the type of soil. For palm oil, a maximum income can be obtained 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