Lecithin AOCS methods

The standard methods (26) of analysis for commercial lecithin, as embodied in the Official and Tentative Methods of the American Oil Chemists Society (AOCS), generally are used in the technical evaluation of lecithin (27). Eor example, the AOCS Ja 4-46 method determines the acetone-insoluble matter under the conditions of the test, free from sand, meal, and other petroleum ether-insoluble material. The phosphoHpids are included in the acetone-insoluble fraction. The substances insoluble in hexane are determined by method AOCS Ja 3-87. 

The total phosphoms content of the sample is determined by method AOCS Ja 5-55. Analysis of phosphoUpid in lecithin concentrates (AOCS Ja 7-86) is performed by fractionation with two-dimensional thin-layer chromatography (tic) followed by acid digestion and reaction with molybdate to measure total phosphorous for each fraction at 310 nm. It is a semiquantitative method for PC, PE, PI, PA, LPC, and LPE. Method AOCS Ja 7b-91 is for the direct deterrnination of single phosphoHpids PE, PA, PI, PC in lecithin by high performance Hquid chromatography (hplc). The method is appHcable to oil-containing lecithins, deoiled lecithins, lecithin fractions, but not appHcable to lyso-PC and lyso-PE. 

Up to now, however, HPLC has remained the method of choice. This is due mainly to the fact that this technique is much easier to automate as compared to TLC. Besides, a wide variety of stationary and mobile phases are available, so the technique is highly flexible. Besides, the investment cost is much lower as compared to P-NMR, whereas quantitation is more straightforward than in MEKC. Hence, the more recent official methods for the analysis of phospholipids, as proposed by the American Oil Chemists Society (AOCS), by the International Union for Pure and Applied Chemistry (IUPAC), and by the International Lecithin and Phospholipid Society (ILPS), all use HPLC. In this chapter, a review is presented of HPLC procedures that have been described during the past 10 years the older literature was discussed in a previous edition of this handbook (21). 

By any appropriate conventional viscosimeter, or by AOCS Bubble Time Method Tq 1A-64, assuming density to be unity. Fluid lecithin having a viscosity less than 7,500 centipoises may be considered a premium grade. Using Precision cone 73525, Penetrometer 73510 sample conditioned 24 hours at 25°C. 

AI. The amount of acetone-insoluble matter (%A1) is a measure of the polar material found in lecithin. In soybean lecithin, the acetone-insolubles typically contain 70-75% phospholipids, with the remaining portion consisting of glycolipids, carbohydrates, and a small amount of residual triglyceride oil. The amount of acetone-insoluble matter is determined by the AOCS Official Method Ja-4-46 (77). 

AS/. The AV is the number of milligrams of potassium hydroxide necessary to neutralize the acids in 1 g of lecithin (62). A product s AV is representative of the acidity contributed by both the phospholipids and any free fatty acids that are present. The AV is usually not indicative of pH, as the chemical nature of the phospholipid imparts buffering quahties to most systems. Lecithins typically exhibit a neutral pH value in aqueous media. An AV above 36 may indicate degradation of the lecithin because of improper processing or substandard quality soybeans. AV should not be confused with free fatty acid content, pH, or mineral acids. The correct method to assay for free fatty acids is to titrate only the acetone-soluble portion of the lecithin, whereby any contribution from the phospholipids in the acetone-insoluble portion is eliminated. AV is determined by the AOCS Official Method Ja 6-55 (77). 

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). 

A number of methods are routinely used for determining the specifications during lecithin production, trading and incoming quality control. In Table 10.3 the most used approved methods by the AOCS and the DGF are now given. 

Lecithin is analyzed according to the AOCS Ja method series (28). For food uses, the Food Chemicals Codex should also be consulted. These procedures are mainly based on gross physical properties, such as acetone solubility. An exception is the TLC method, which gives the composition in terms of individual phosphatides (29). Because of their importance in biology, phosphatides are the focus of intense method development. Mass spectrometry is the most powerful tool to characterize mixtures of phophatides (see Chapter 15), but there is usually no need to perform a complete MS analysis of lecithin. Commercial lecithin is a complex mixture, the properties of which are profoundly influenced by the considerable amount of nonphosphatide materials present. Further information on lecithin can be found in specialized publications (30). 

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