et al. 1999). Table 2.1 shows some of the key physical characteristics of some of the key oilseed oils comparing to a standard olive oil. Refractive index could help to predict oil viscosity and in turn key physical properties (Gunstone 2011). In the case of flash point (Table 2.1), temperatures of the different oilseed oils around 300 °C differ depending at which temperature the volatiles are produced in amounts that ignite but do not appear as a flame (Gunstone 2011). Peroxide values indicate the level of primary oxidation, which could increase when the oils are exposed to light. The food industry frequently adds sources of antioxidants to enhance oil protection from oxidation changes. Carelli et al. (2005) reported the effectiveness of adding ∝‐ and δ‐tocopherol, citric acid, ascorbic acid, and ascorbyl palmitate in sunflower oil observing that ascorbic acid improved the rancimat oxidative stability of the oil. The measure of iodine value is linked to the degree of unsaturation of fat and oil. Therefore, a low iodine value is related to a high level of saturated and MUFA as observed in palm‐based or coconut oils (Table 2.1).
2.2.3 Nutritional Properties
Oilseeds are a source of fiber and minerals such as phosphorus, iron, and magnesium. Generally, they are a source of vitamin E (an antioxidant), folate, and niacin. Also contain phytoestrogens, which is a group of substances including isoflavones (McKevith 2005). Soybean and sunflower seeds are a rich source of lipids with triacylglycerols as the main constituents. Proteins and phospolipds and bioactive compounds such as vitamin E are also present (White et al. 2006). This is of particular importance in the field of pharmacology, food, and personal care (Sukhotu et al. 2016). Table 2.2 shows the main composition table of the main oilseed oils (USDA 2020). As observed, sunflower oil is a potential source of vitamin E and soybean oil of vitamin K. Regarding the PUFA content, sunflower, soybean, flaxseed, and poppy seed oil present the highest values, whereas coconut has a considerably high saturated fatty acid content (Table 2.2).
Table 2.1 Some physical characteristics of conventional oilseed oils.
| Parameters | Palm kernel oil | Palm oil | Soybean oil | Rapeseed oil | Sunflower oil | Groundnut oil | Olive oil | Coconut oil |
|---|---|---|---|---|---|---|---|---|
| Specific gravity value (relative to pure water) | 0.904 | 0.9020 | 0.9150–0.9280 | 0.9123 | 1.521517 | 0.9155 | 0.910–0.915 | 0.91 |
| Refractive index (t = 40 °C) | 14 490 – 14 520 | 14 530 – 14 560 | 14 660 – 14 700 | 1465–1.469 | 14 610 – 14 680 | 1.47 | 14 670 – 14 710 (at 20 °C) | 14 480 – 14 500 |
| Saponification value (mg KOH/g) | 280.5 | 200.05 | 188–195 | 172.29 | 177.06 | 191.5 | 189.30 | 257.5 |
| Acid value (mg KOH/g) | 2.7 | 0.84 | ≤0.5 | 1.78 | 0.22 | 9.0 | 0.84 | 5.5 |
| Peroxide value (mEq/kg) | 14.3 | 7.98 | ≤10 | 0.63 | 9.99 | 9.99 | 7.98 | – |
| Iodine value (mg KOH/g) | 15.86 | 602.7 | 75–94 | 1198.9 | 94.35 | 9.4 | 831 | 8.5 |
| Viscosity, mPA s (30 °C) | 43 | 45 (at 45 °C) | 45 | 72–82 (at 20 °C) | 47 | 45 | 55 | 39 |
| Flash point, °C | 267 | 314 | 317–324 | 317 | 316 | 315 | 300–330 | 300/288 /270 |
Source: Chadwick 1988; Bailey and Shahidi 2005; Firestone 2006; Tan et al. 2009; Azlan et al. 2010; Neagu et al. 2013; Amira et al. 2014; Roiaini et al. 2015; Alajtal et al. 2018; Godswill et al. 2018; Xu et al. 2018; Beszterda and Nogala‐Kałucka 2019.
Table 2.3 presents the main fatty acids in oilseed oils. Linoleic acid, oleic, and α‐linolenic acids are the primarily unsaturated fatty acids accounting for 88.83% of total lipids. Palmatic acid is the major saturated fatty acid (10.42%). As reported in Ramos et al. (2009), linoleic acid (54.0%), oleic (23.9%), palmitic acid (11.3%), and α‐linolenic acids (6.1%) are the major fatty acids present in soybean oil. Canola oil, also known in Europe as rapeseed oil, has low concentrations of saturated lipids and, in line with soybean, the protein content is high. In particular, percentages of 23 and 40% have been reported in rapeseed and soybean respectively (Bauer and Kostik 2014).
2.2.4 Bioactive Properties
Phenolic, tocopherol, and sterol profiles of oilseed oils are the main important bioactive compounds reported. Palm oil is one of the potential sources of tocotrienol, part of Vitamin E, and in turn, palm oil is a great source of this vitamin helping as antioxidant protector against the oxidation of lipophilic molecules and linked to skin protection when consuming in diet (Enig et al. 1983).
Tocols are synthesized only by plants; however they are very important dietary nutrients for humans and animals (Dunford and Dunford 2004). Tocopherols are present in oilseeds, leaves, and other green parts of higher plants. In the extracted seed oil the main compounds with antioxidant activity are tocopherols and also tocotrienols, which are compounds with vitamin E activity. These compounds protect the oil from oxidative deterioration (Soldo et al. 2019). Furthermore, they prevent metabolic, proliferative, inflammatory, and oxidative damage (Galli and Azzi 2010).
Sunflower,