more solid at room temperature; sometimes they are referred as “solid fats” (e.g. coconut).
Linoleic acid (C18:2 n‐6) and α‐linolenic acid (C18:3 n‐3) are called essential because the human body can produce two whole families of polyunsaturated fatty acids from them as a precursors. For example, from n‐6 family (linoleic acid) it can obtain arachidonic acid (ARA) (20:4 n‐6) and docosapentaenoic acid (22:5 n‐6), among others. In the case of n‐3 family (α‐linolenic acid) it can be produced eicosapentaenoic acid (20: 5n‐3) and docosahexaenoic acid (22: 6 n‐3, DHA). Some of these molecules have great importance in human metabolisms. For example ARA is abundant in the brain, muscles, and liver. It has been explained that it is not an essential fatty acid, however if there is a deficiency in linoleic acid, it becomes essential (Smith et al. 2011). This acid is involved in muscle growth and brain. It is present in the brain in similar quantities as DHA both of them are involved in the neurological health. Furthermore, there are studies like Birch et al. (2000) about supplementation of infant formula with DHA + ARA where an increase on the Mental Development Index (MDI) was observed. Also at cognitive and motor subscales of the MDI there was a significant developmental age advantage for supplementation with DHA or DHA + ARA (Birch et al. 2000).
2.2.2 Physicochemical Properties of Oilseeds Oils
Relative density, viscosity, refractive index, smoke point, flash point, fire point, melting point, and crystallization as well as thermal behavior are some of the chemical properties of importance in oilseeds oils to consider for food applications. The crystallization or polymorphisms properties greatly affects the textural and functional properties of oils. Soybean oil tends to form β‐crystals in contrast to the hydrogenated form that can be crystallized in β’, form achieving desired functional properties in the final product (Gunstone 2011). Temperature affects the density of oilseed oils leading to a density decrease with an increment of temperature. Predictions by mathematical model to estimate changes in the viscosity of oils have been developed helping to predict the physical changes (Rodenbush 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 |
