Deodorisation

Field of application

Chemical neutralisation is applied in the refining process of vegetable oils, such as soybean oil, sunflower oil, rapeseed oil, and of animal oils and fats such as tallow or fish oil. Neutralisation is also used in processes such as HPP manufacture.

Description of techniques, methods and equipment

The process makes the free fatty acids separable from oil by saponification and increases the water-solubility of both the free fatty acids and the phosphatides rests so that both components can be easily separated from the oil. The fatty acids are transformed into soaps by adding lye. These fatty acids can be separated from the water afterwards in a soap-stock splitting process, where the water-solubility of the fatty acids is decreased after boiling the soap-stock in an acid environment. The recovered phosphatides are utilised as lecithin in human food or in animal feed.

Methods and equipment

A neutralisation process basically requires, depending on the type of process (i.e. whether ist is batch or continuous): mixing equipment, separation equipment (continuous process: centrifuges) and heating (steam). A soap-stock splitting process also requires heating and mixing equipment, in addition to decanting vessels. After preheating the oil, phosphoric acid or citric acid is mixed with the oil to increase the water-solubility of the phosphatides. The acidified oil is further mixed with a caustic solution, which neutralises both free fatty acids (crude oil content of: 0.5 to 6 %) and the phosphoric or citric acid and further increases the water-solubility of the phosphatides. The mixture of soap and phosphatides, is separated from the oil by a centrifuge. Finally the oil is mixed with water to wash off the rests of the soaps. Again the water is removed from the oil by a centrifuge. The alkali-refined oil may be dried under vacuum conditions and is then pumped to a storage tank. The process is mostly operated in a continuous way (see Figure 2.2), but it can also be carried out in a semi-continuous way or in batch, using long-period mixing and settling equipment.

The combined-centrifuge aqueous discharges (soap-stock), are further treated in a soap-stock splitting system. This is an acidulation process, used to recover the fatty acids after treatment with concentrated acid (i.e. sulphuric acid or (in a few cases) hydrochloric acid) and heating with steam. The separated fatty acids are removed in a decantation vessel. In integrated plants, the soap-stock can be added to the meal toasting process.

Bleaching

Objective

The objective of bleaching the oil is to remove pigments, metals (nickel or iron, from other oilrefinery processes), residual soaps and phospholipids from the oil or fat.

Field of application

Bleaching is applied in the refining of edible oils and fats.

Description of techniques, methods and equipment

Edible oils and/or fats are mixed with bleaching earth that has an affinity for adsorbing the above mentioned undesirable compounds. The oil is mixed under vacuum conditions with 0.1 to 3 % of bleaching earth. This is a clay mineral, such as bentonite or montmorrillonite, that has been activated by thermal and/or acidic or other treatments. These earths (sometimes mixed up with small amounts of activated carbon) have a very high adsorbing capacity. After bleaching for 30 – 90 minutes, the oil is separated from the bleaching earth, using filters. The spent earth contains high amounts of oil (up to 30 %). A steam stripping process can recover a part of the oil or fat. Used bleaching earth can be added to the meal in integrated plants. The bleached oil is further processed in other refinery processes. The equipment used for bleaching consists of mixing vessels, vacuum generators and filters.

Deodorisation by steam stripping

Objective

The objective of deodorisation is to remove free fatty acids and other highly volatile compounds from crude degummed and/or alkali refined edible oils and fats after bleaching.

Field of application

Deodorising is applied in the refining of edible oils and fats.

Description of techniques, methods and equipment

Deodorisation is the use of steam distillation to strip fatty free acids and other highly volatile components, under vacuum conditions, from oils and fats. The equipment used for deodorisation consists of a steam distillation column, barometric condenser, demisters and scrubbers. Steam is injected into the heated oil (>200°C) at the bottom of the distillation column, which is under vacuum conditions. The steam strips the fatty acids and other impurities from the oils and fats (gums are not removed by this process). The steam is condensed afterwards, using a barometric condenser of either “once-through” or closed loop design (see also U.4, 9.4). The separation of the volatile components from this steam can be enhanced by one stage of a twostage scrubbing/condensation system and by demisters. Deodorisation can be operated in batch or continuous deodorising vessels.

Decolourisation

Objective

Decolourisation is carried out to improve the colour, purity, ageing, microbiological stability and shelf-life of certain food products.

Field of application

Decolourisation is used in the sugar, glucose, syrup and fermentation industries

Description of techniques, methods and equipment

Decolourisation can be carried out in two ways:
1) by the addition of an active powder (e.g. powdered activated carbon) to the product in aqueous solution, which is then mixed under controlled conditions. The powder is then removed by filtration (static filters, rotary vacuum filters) while the decoloured product is processed further. This process is often carried out in multiple stages with the active material being re-used until exhausted, often using a countercurrent system.

2) by passing the food product in aqueous solution through a column of active material (e.g. granular activated carbon or ion exchange resin beads). Here only minimal filtration is required after the process as the active material is held in place. Active material is withdrawn from the column at regular intervals and replaced by new or reactivated material. The main purpose of both these operations is to remove colour molecules from the product as well as precursors, which may give rise to colour formation on storage (known as ageing). The majority of the impurities removed are organic in nature. Passage over activated carbon may also be helpful in removing phenolic material (which may cause taints), pesticide residues and some heavy metals.