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Evaluation of the ESCA technique as a screening method for the estimation of protein content and quality in seed meals
Author(s) -
Peeling James,
Clark David T.,
Evans I. Marta,
Boulter Donald
Publication year - 1976
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740270406
Subject(s) - kjeldahl method , vigna , chemistry , amino acid , x ray photoelectron spectroscopy , nitrogen , food science , analytical chemistry (journal) , botany , biochemistry , chromatography , biology , organic chemistry , physics , nuclear magnetic resonance
The ESCA (Electron Spectroscopy for Chemical Analysis) technique has been evaluated as an analytical screening method for the determination of protein content and quality of grain meals of some legumes and cereals. To this end the grain meals of a number of different species were analysed for total nitrogen, meals of varieties of cowpea ( Vigna unguiculata ) were examined for sulpho‐amino acid content, and the levels of basic amino acid in meals of some maize and barley varieties were measured by this technique; some amino acids, polyamino acids and pure proteins were also examined as standards. The results obtained for 15 grain meals by the ESCA technique, expressed as the ratio of the intensity of the N 1s photoelectron signal to that of the C 1s signal, were compared with %N as determined by a semi‐automated micro‐Kjeldahl method, and the correlation coefficient between the results from these two methods was r = 0.98. The binding energies of S 2p electrons were determined for some amino acids and proteins, and the amino acid sulphur was differentiated from oxidised sulphur. The N 1s /S 2p intensity ratios for four pure proteins correlated very well with the calculated stoichiometric N/S ratios ( r = 0.999). The N 1s /S 2p intensity ratios were also determined for seven cowpea varieties and the correlation coefficient between these values and the ratios N/S aa , measured by chemical methods, was r = 0.77. The N 1s photoelectron peaks of some varieties of barley and maize meals showed a pronounced shoulder on the high binding energy side. On deconvolution into two components the main peak was assigned to nitrogen in the peptide bond and the smaller peak was assigned to the protonated nitrogen on the side chains of the basic amino acid residues.