One common method of improving the nutritional quality of certain food proteins is through fortification with necessary amounts of limiting essential amino acids. This simple and convenient method, however, is not the best. Several disadvantages are associated
with the addition of free amino acids to food proteins, such as changes in flavor and color, losses of added amino acids during food processing or cooking, differences in stability and metabolism between free amino acids and amino acids in proteins. Covalent attachment of the limiting amino acids, however, should eliminate these problems, and moreover, could improve the nutritional and functional properties of food proteins. In this study, therefore, an attempt to improve the nutritional value of the soy protein was made by using the carbodiimide condensation reaction to covalently bind methionine and tryptophan to soy protein. In order to confine as much as possible the binding, of amino acid to the protein a-carboxyl groups the soy protein isolate (SPI) was partially hydrolyzed with pepsin to increase the number of a-carboxyls in soy protein. Various conditions of the carbodiimide reaction were analysed by a fractional factorial design in an attempt to determine the factors affecting the amino acid binding to soy protein hydrolysate (SPH). Of the factors investigated, pH, SPH concentration, carbodiimide concentration, activation time and reaction time were found to significantly affect the methionine binding efficiency, whereas pH, SPH concentration, carbodiimide concentration, amino acid concentration and reaction temperature were found to significantly influence the tryptophan binding efficiency to SPH. To determine the best level for each of the selected
factors an optimization of the carbodiimide reaction conditions was conducted by carrying out another factorial experiment. Thus, under the best condition found, the methionine and tryptophan contents of methionine - and tryptophan-bound SPH samples were increased 7.7-fold and 18.0-fold, respectively.
An in vitro pepsin-pancreatin digestion test demonstrated that the bound amino acids were readily released.
In order to improve the low yield of the final product, another analysis of the carbodiimide reaction conditions was carried out. Since the yield could not be markedly improved by this factorial design in which peptic SPH was used, SPI without preliminary hydrolysis was used as the starting material. A product with 95-99% yield was obtained and its methionine or tryptophan content was increased 6.3-fold or 11.3-fold, respectively. High digestibility was still maintained for these products.
Gel filtration chromatography demonstrated that the carbodiimide reaction caused an increase in the molecular weights of soy protein fractions. Furthermore, gel filtration chromatography revealed that, there was no selective amino acid binding among the different soy protein fractions during the carbodiimide reaction. / Land and Food Systems, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/21485 |
| Date | January 1978 |
| Creators | Voutsinas, Leandros Panagis |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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