**2. Utilization potentials of tropical oilseeds**

Many varieties of oilseeds in the tropics particularly, palm kernels, groundnut, sunflower seed, soybean castor seed etc. are some of the sources of the edible oil. The edible oil is the main source of fat taken in daily meals in different developing countries in the tropics and is used for various purposes. Oilseeds are made up of particles called cells while oil glands are embedded in each of the cells which liberate oil from rupturing. Hence, the essence of oilseed processing is to rupture the gland and cell wall which gives a yield of oil by application of heat and pressure during flaking, followed by extraction. The oil extraction processes are designed to achieve high extraction yields, produce value meal/cake and obtain high-quality oil with minimal undesirable components [7]. There are several techniques for extracting oil from oilseeds. However, mechanical extraction using a screw press and solvent extraction are the two common oilseed extraction processes (**Figure 1**).

### **2.1 Preparation, handling and storage**

The physical properties of the seeds, such as bulk density, shape, size and flowability affect the design of oilseed facilities. Typically, in the tropics oilseeds are cleaned and sorted to remove stones, sand, dust, leaves and other contaminants after harvest and before storage. Proper handling and storage of oil-containing materials are vital so as to minimize deterioration and as well as maintain a good quality of both contained oil and meal. All oil-bearing needs to have correct moisture content to maximize the oil yields as the high moisture content in seeds has an adverse effect on oil and meal quality. Whole and low-moisture oilseeds of about 8–10% may be stored for an extended time under suitable conditions [8].

#### **2.2 Unit operations for oilseeds processing**

Although most oilseeds go through pretreatment processes for oil extraction as shown in **Figure 2**, however, the unit operations vary slightly depending on the oil content and physical properties.

**Cleaning:** Oilseeds may contain certain impurities from the field, during storage and or entered on transit. Such impurities include plant stems, leaves, sticks, infected seeds, dust, stones, foreign material etc. Impurities and foreign materials in the seeds are removed by the use of screens, reels, aspiration or separated by gravity.

**Cracking:** Most oilseeds are reduced in size to facilitate other downstream processes such as drying, dehulling, tempering and flaking prior to oil extraction. Cracking mills are used for seed size reduction.

**Drying:** The moisture content of oilseeds is reduced so as to improve the effectiveness of downstream processing particularly, dehulling and tempering.

**Dehulling:** The husk or shell needs to be separated from the oilseeds prior to oil extraction and the amount of hull on the oilseeds varies significantly. Thus, dehulling increases oil production efficiency and its efficiency is measured by the residual fiber content in the meal and the residual oil content in the hulls.

**Tempering:** This is done to facilitate oil recovery by heating to about 90°C in order to denature the proteins, release oil from the cells and inactivate enzymes. It is important to maintain the optimum temperature to avoid the formation of undesirable

**Figure 2.** *Processing of oilseeds into edible oil.*

aromas and coloring compounds. Tempering improves extraction efficiency and flaking performance. The seeds are then pressed to separate oil.

**Flaking:** It involves rupturing of the seed cellular structure while increasing the surface area for increased contact between seed and solvent during the solvent extraction process. It is important to note in order to minimize meal and oil quality deterioration, the oil from the flaked seeds should be extracted within 24 hours after flaking.

**Extraction:** This is the process of separating a liquid from a solid system by either pressing or with the use of a solvent. Although a good percentage of oil is removed by pressing, however, extraction using a low boiling point solvent gives a higher recovery of oil and drier cake than expression. Solvent extraction removes nearly all available oil from oilseed meals. The process provides meals with higher protein qualities and better preservation qualities.

*Processing of Oilseeds in the Tropics: Prospects and Challenges DOI: http://dx.doi.org/10.5772/intechopen.106247*


On the other hand, interesterification is a technique for positioning or rearranging fatty acids on triglycerides. This technique is followed as a means of obtaining trans-free margarine, spreads, and shortenings since controversies exist about the healthfulness of trans-fatty acids produced during hydrogenation.

