Sample preparation cereal proteins

The use of NIR reflectance has gained considerable interest for process analysis in the food, pharmaceutical, petrochemical, and other chemical industries. This method requires little or no sample preparation and involves measurement of the reflectance of a liquid or solid sample relative to that of a standard in the same wavelength series. As illustrated in Table 3, process NIR has gained considerable use for moisture determination in coal, cosmetics, and detergent powders, as well as for protein contents of cereal and grain, and hydrogenation of unsaturated fats and oils. 

Sample Preparation and Injection. Most cereal proteins are rich in glutamine and are subject to deamidation in acidic solvents. It is thus best to minimize exposure to acidic solvents, including ones containing TFA [21]. Similarly, alkaline extraction should be avoided because of potential peptide bond hydrolysis. As noted earlier, high temperature may also dissociate polypeptides. Most extracts are, however, quite stable [18-19,21]. 

From the outset, it was apparent that HPLC was a valuable preparative method for cereal proteins. Up to 5 mg of samples can be fractionated on analytical columns with good resolution [7], and this can be scaled up considerably. Electrophoresis of resulting fractions is a complementary technique that confirms the resolution of RP-HPLC and further fractionates by size or charge [7,94]. 

In this way, correlations with around 50 reference samples, very similar to those to be measured, is not unusual. Many products (proteins, oils in cereals, meat), can routinely be analysed by this method and often without preparation beforehand. In general, a relation is sought between certain absorptions and the presence of constituents in the mixtures to be analysed. This is the domain of correlation analysis. 

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