Flour samples, examination

Beuchat et al. (24) also examined the nitrogen solubility profiles for enzymatically hydrolyzed and control peanut flour samples in 0.03M Ca2+ (as CaCl2). Solubilities of controls between pH 2.0 and 5.0 in 0.034 Ca solutions were similar to those noted for water however, very little increase in nitrogen solubility of controls was noted in the pH 5.0 tc 11.0 range. 

Extraction is an essential step when analyzing solid samples. In some cases homogenization with a solvent suffices, but in others the sample must first be coimninuted. Water, solutions of acetic acid or sodium chloride, or more complex saline solutions are used as solvents. Mixtures of water and methanol or water and ethanol are also employed. The choice of solvent depends on the degree of selectivity desired in the extraction and whether the extraction yield is intended for quantitative analysis. Optimization of the extraction procedure is required in all cases, to fit the nature of the sample to be analyzed and the range of molecular weights of the peptides to be separated. For example, water has been used as the extraction solvent for cheese (33) and legumes (34). Saline solutions have been utilized to extract peptides from meat (35-38) and flour (39,40). Benedito de Barber et al. (41) examined differences in the extractability of amino acids and short peptides in various solvents (1M acetic acid, 70% ethanol, and distilled water) they concluded that extraction with 1M acetic acid yielded the maximum amino acid and peptide contents. 

Sensitivity The declared limit of quantification is 2.5mg/kg as soy protein. Nevertheless, sensitivity has been tested on real samples (Table 17.3) to verify possible interferences by analyzing different types of matrices spiked with soy at decreasing levels of contamination. For the final calculation we consider a content of about 40% of protein in soy flour determined with the same kit by diluting the spiking matrix. For the matrix examined, LOQ was verified similar tests should be carried out with other matrices to verify the effective sensitivity of the assay (at least three spike levels are recommended). 

Experimentally, however, the spectra are easy to observe, thick samples being tractable in either transmission or reflection without preparation. As the spectra seldom possess many narrow features that could be unduly affected by instrumental or other factors, robust methods for quantitation were possible. With the arrival of cheap instrumental computing from the 1980s onwards and the development of multivariate analysis methodology, NIR spectroscopy has undergone considerable expansion in use. It is now widely applied to automated, rapid and precise quantitative analyses in agriculture, industrial process control and noninvasive medical examinations. A typical and early example was determination of the protein content of grain and flour. 

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