Amino acids have their lowest solubility at their isoelectric point
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Retrieved literature confirms that proteins and protein derivatives exhibit their minimum solubility at their isoelectric point, which mirrors the fundamental biochemical behavior of zwitterionic amino acids.
The functional properties of protein isolate and major protein fractions prepared from Changbai Mountain pine nuts were investigated. Albumin, globulin, glutelin, and protein isolates were obtained after the Osborne method and alkaline dissolution and acid precipitation, and protein contents of the fractions are 48.02%, 81.93%, 83.02%, and 89.69%, respectively. For the sulfhydryl contents, albumin is the highest, and glutelin is the lowest. In a disulphide bond, the protein isolate content is the highest with a value of 28.74 μmol/g, and the glutelin content is the lowest with the value of 13.46 μmol/g. For the four kinds of proteins, the essential amino acids in percentage of total amino acids are 31.13%, 34.22%, 30.30%, and 34.54%, respectively. The pH dependent protein solubility profile reveals that the minimum solubility is at pH 5.0, which corresponds to the isoelectric point. Protein isolate has the minimum water absorption capacity with a value of 0.59 ml/g. On the other hand, albumin has the minimum oil absorption capacity with a value of 2.11 ml/g. The emulsifying activity and stability and the foaming activity and stability increased with increasing concentration of four kinds of proteins. SDS-PAGE results showed that these four kinds of proteins have different molecules.
Abstract Quinoa protein with great functional properties has been considered a potential source for food fortification or the production of functional foods. In this study, quinoa protein hydrolysate (QPH) was prepared from quinoa protein concentrate (QPC) after hydrolysis by pancreatin (pancreatic) enzyme. The emulsifying, foaming, and antioxidant activities, the emulsion and foam stabilization, as well as amino acid profile and chemical composition were evaluated. The highest degree of hydrolysis (19.17%) was obtained after 180 min. The amino acid profile (by high-performance liquid chromatography: HPLC) showed that glutamic acid and lysine had the highest contents and all essential (limiting) amino acids were recorded. Fourier-transform infrared (FTIR) spectroscopy showed hydroxylic and aromatic amino acid residues in the QPC and it was inferred that different functional groups have originated in QPH that confirms the hydrolyzing action of pancreatin enzyme. QPH had the lowest solubility at the isoelectric pH of 5 (pI~5) and had better emulsifying, foaming, and antioxidant properties compared to QPC. In contrast, QPC had better emulsion/foam stabilizing properties. Overall, this study suggests that pancreatin could be employed for hydrolysis of quinoa protein and its hydrolysate with functional properties could be possibly considered for food fortification or production of functional foods.
The chemical composition and the food properties of shell and flesh of Penaeus notabilis were evaluated. The protein, ash and energy were high whereas carbohydrate and fibre were low in the proximate composition. In the mineral composition, the mineral elements in shell were corresponding higher than the level in flesh. The total essential amino acids in shell was 740mg/g protein and 865mg/g protein in flesh. The limiting amino acid in both shell and flesh was threonine. In the functional properties, both water absorption, oil absorption and oil emulsion capacities were all high with foaming stability at 25% (90min) in both tissues. The lowest gelation was low in both tissues. The protein solubility was high at both sides of pH with isoelectric point being 5.0 (shell) and 7.0 (flesh). The followings: proximate, mineral, amino acids and essential amino acids composition, functional properties and protein solubility, all showed that correlation coefficients r-values > t , n-2 meaning that the correlations were significant with high positive values at r0.05.
For this reason proteins have their lowest solubility at their isoelectric points. This relationship … varies from amino acid to amino acid. Thus phenyl alanine (or some other amino acid) might … of Some RNA Triplets to Amino Acids* Amino Acid Triplets Amino Acid Triplets Alanine CUG
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