Lecithin production

The crude oil from which gums are taken for lecithin production still contains nonhydratable phosphatides, but can be treated with a chelating agent before alkali neutralization and will be removed with the soapstock by centrifugation. Provision must be made for the added acid in calculating the amount of neutralizing alkali added. 

TABLE 15. Typical Composition (%) of Commercially Refined Soy Lecithin Products (196). 

Two of the earliest edible applications of lecithin, viscosity reduction in chocolate and confectionery products, and emulsification/antispatter properties in margarine, still enjoy wide popularity and represent outlets for large volumes of lecithin products. In addition, other early uses such as in bakery goods, pasta, textiles, insecticides, and paints, among others, are still active today. 

The simplest method for modifying natural (crude) lecithin is the addition of a non-reactive substance. Plastic lecithins are converted to fluid forms by adding 2% to 5% fatty acids and/or carriers such as soybean oil. If the additives react with the lecithin to alter the chemical structure of one or more of the phospholipid components, the resulting product is referred to as a chemically modified lecithin. Modification can also be achieved by subjecting lecithin to partial controlled enzymatic hydrolysis. Finally, refined lecithin products can be obtained by fractionating the various phospholipid components. 

A method for classifying lecithin to include modified and refined forms has been proposed by Cowell et al. (55). This classification distinguishes between natural (crude) lecithins and those modified by either custom blending or chemical/enzy-matic treatment, e.g., hydroxylation, hydrogenation, acetylation, or refining by acetone or alcohol fractionation. These latter products reflect the state of the art regarding the availability of the various lecithin products on the market and have enhanced properties for specific uses. A listing of soybean lecithin classifications follows (56). 

In practice, commercial lecithin products are not marketed by phospholipid content, but rather by a set of unique chemical and physical properties. These properties, as indicated by product specihcations, must be understood because they are used to characterize specihc lecithin types. 

Moisture. The water content of lecithin products is usually less than 1.0%. As a consequence of lecithin s essentially moisture-free state, lecithin products have very low water activity and do not adversely contribute to the microbiological profile of most food systems. Most lecithin products are preserved well in storage. Higher moisture levels usually indicate a greater potential for spoilage or chemical degradation. Moisture is determined by AOCS Official Method Ja 2b-87 (77). A less accurate moisture level can also be determined by azeotropic toluene distillation (AOCS Official Method Ja 2-46) (77). One cannot determine lecithin moisture by vacuum oven methods. These methods are known to degrade lecithin products and yield false moisture levels. 

HI. The level of HI matter is one measure of the purity of lecithin products. HI matter usually consists of residual fiber, but also particulate contaminants that may be introduced during processing (e.g., filter aids). The level of HI matter in crude lecithin should never exceed 0.3% and rarely exceeds 0.1%. HI matter in lecithin is detrimental to clarity and use in specific applications. HI is measured by an official Food Chemicals Codex (FCC) (1996) method (54) or by AOCS Official Method Ja 3-87 (77). 

The degumming of soybean oil is not an industry-wide practice. Brian (111) estimated that only about one-third of the soybean oil produced in the United States needs to be degummed to meet the U.S. needs for soybean lecithin production. 

Brian (111) describes two methods of miscella filtration, one with and one without filter aids, but both result in a lecithin that still remains somewhat cloudy. Highly clarified lecithin products can be obtained only by filtering the crude oil, usually with the aid of vertical leaf or plate and frame filters, wherein the dry oil is heated to 82°C and 0.1% filter aid is added (33). 

Figure 2. Batch degumming system for lecithin production (115).

Figure 3. Flowsheet for degumming soybean oil and crude lecithin production (111).

The color of most lecithin products will darken on prolonged heating. Color stability can be achieved, however, by avoiding exposure of lecithin to temperatures over 60°C. There are now heat-resistant lecithins on the market that maintain their light color for extended periods even at elevated temperatures (7). 

Because of the sensitivity of lecithin to heat, drying conditions are critical and the product should be cooled to 55-60°C before additional processing, and/or to 35-50°C before storage and packing (33). Shelf life of dried lecithin products in suitable containers is more than 1 year at 21 °C (3). 

Fluidizing. Fluidizing additives such as soybean oil, fatty acids, or calcium chloride can be added to adjust the viscosity. The viscosity of dried crude lecithin can also be decreased by warming it to a maximum of 60°C. The dried crude lecithin product (unbleached or bleached) can also be used to prepare a variety of grades of lecithin by removing the oil to increase the phospholipid content, or by separating the oil-free lecithin into alcohol-soluble and alcohol-insoluble fractions. 

Producing modified lecithins. The chemistry of lecithin has been reviewed by Pryde (86) and by Wittcoff (4). Schmidt and Orthoefer (58) have discussed the manufacture and use of modified lecithin products. The latter class is represented by chemically or enzymatically modified products that are commercially available in both fluid and de-oiled forms. 

The total acetone insolubles content of commercial acetylated lecithin products can vary from about 52% to about 97%, the remainder being soybean oil (or another food-grade triglyceride or fatty acid as a natural constituent or added diluent), natural pigments, sterols, and other minor constituents present in crude lecithin from the soybean. The acetylated lecithin meets all the compositional requirements of the U.S. Food Chemicals Codex (54). 

Very low temperatures should, however, be avoided when storing liquid lecithin products because physical separation of the phosphohpids and oil may occur. Physical separation is more likely to occur in low AI products. When separation does occur, remixing at 40-60°C will redisperse the oil and lecithin phases. In bulk handling of lecithin, storage temperatures of 30-35°C are acceptable. However, prolonged storage at these temperatures may cause darkening (115). 

FOOD-GRADE LECITHIN PRODUCTS, USES 5.1. Functionality... 

Commercial lecithin products that were sold many decades ago for applications such as chocolate and confectionery products, margarine, bakery goods, pasta products, textiles, insecticides, and paints are still active today because of their emulsifying, wetting, colloidal, antioxidant, and physiological properties. Lecithin s multifunctional properties and its natural status make it an ideal food ingredient. The major applications and functional properties of lecithin products are shown in Table 25 (7). 

The manner in which lecithin is modified to achieve increased hydrophilicity will greatly affect its emulsification properties. Different modifications will create lecithin products with different apparent HLB (hydrophile-lipophile balance) values, a term used to convey the approximate degree of water dispersibility (hydrophilicity) of lecithin products (31). The higher its HLB value, the more water dispersible the lecithin product. In o/w emulsions, the type of fat to be emulsified may require a specific type of hydrophilic lecithin for optimum emulsion stability. Dashiell (31) provides a short listing of fat types, and the corresponding class of lecithin found to give the most stable emulsion in model systems of water/fat/ emulsifier. 

Solid particle dispersions (Sols). Many lecithin products are still the best and most effective surfactants for dispersing sols. This seems to be because of lecithin s affinity for solids—liquid surface interfaces. Phospholipids seem particularly attracted to particles containing metals and metal salts. Examples of food sols include some liquid chocolates, instant drinks, frosting mixes, pigmented foods, and others. The nonfood applications include paints, inks, and other pigmented coatings. 

Foams. Refined lecithins have been employed as effective foam control agents. Examples include whipped toppings, ice creams, and many types of candies. Refined lecithin products have also been employed as effective defoaming agents in foams caused by powdered proteins in water. This is an excellent example of the system specificity of lecithin products (7). 

Manufacturing techniques employed in producing instant products include spray-coating dry powders with fluid lecithin products, cospray drying powders with more hydrophihc lecithins such as the oil-free forms, or hydroxylated lecithin, and agglomeration of the powder with an aqueous dispersion of a hydrophihc lecithin. Some types of powders, for example, starches, gums, and chocolate drink mixes, require agglomeration with an aqueous dispersion of lecithin to achieve optimum wettabihty and dispersibility. 

General food applications of lecithin include margarine, confections, snack foods, soups, instant foods, bakery products, simulated dairy products, processed meat/poultry/seafood products, and dietary apphcations. The most widespread uses of crude lecithin products are in confections and margarine (7, 174). 

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