| Mineral calcium is an important element for human health. Deficiency of dietary calciumcan lead to numerous diseases. Mineral chelating peptides have shown potential application inthe management of mineral deficiencies. An increasing number of chelating peptides with theability to facilitate and enhance the bioavailability of minerals are being discovered andidentified. Food-derived chelating peptides have been used for development of functionalfoods and health products fortified with calcium due to their safety and multi-functionality. Inthis work, wheat germ protein is going to be hydrolyzed by proteinase to release the calciumchelating peptides, which might provide an experimental evidence for the related research anddevelopment of food-derived chelating peptides.A central composite design with two independent variables (solubilisation pH andprecipitation pH) and bivariate correlations were selected for the correlation analysis of theprotein separation conditions and the functional properties. The results showed that wheatgerm protein yield was sensitive to both solubilisation pH and precipitation pH (p<0.05). Theyield (r=0.785, p=0.000), fat absorption (FA, r=0.752, p=0.000) and emulsification (EA,r=0.697, p=0.697) of isolates showed a high positive linear correlation with solubilisation pH;whereas water absorption (r=0.863, p=0.000) showed a negative correlation to precipitationpH; For all the functional properties of wheat germ protein, only fat absorption toemulsification (r=0.753, p=0.753), water absorption to foaming capacity (r=0.503, p=0.503)were linear correlation; The protein yield showed high positive correlation with FA (r=0.820,p=0.000) and EA (r=0.683, p=0.683) but did not have significant correlations with otherproperties. In addition, when wheat germprotein showed the highest yield (36.64%) in9.5/4.0(solubilisation pH and precipitation pH), only foaming stability showed maximum (91.67%)and other functional properties were not necessarily the best, such as the maximum of waterabsorption (3.99g g-1) was at the extraction condition of10.2/3.3, while fat absorption,emulsifying activity, foaming capacity were at9.5/3.0(2.98g g-1,0.207,150%, respectively),and the maximum value of emulsifying stability (76.09%) was at10.5/4.0. This allowsprocessers to adjust pH values according to the protein isolate property requirements withoutaffecting the yields greatly.Metal salt was used to control the formation of protein aggregates to improve thesolubility, it is very important for the application of the protein in food. Effects of CaCl2ondisaggregation of wheat germ globulin (WGG) solution heat-treated ranging from55°C to95°C at pH2.0were investigated by turbidity, solubility, H0(surface hydrophobicity),-potential and microstructure. Maximum turbidity (A400=1.3) and minimum solubility (20.3%)occurred at the isoelectric point (pI5.0) and95°C. The turbidity of WGG at pH ranging from1.0to5.0(below pI) in the presence of CaCl2was rapidly decreased, while significantincrease in pH ranging from6.0to9.0(above pI). The addition of CaCl2to dispersions ofWGG produced an increase and followed a decrease in solubility: for pH<pI (pH5.0~1.0) thesolubility began to rise from38.9%to76.3%, compared with their controls without calcium(p<0.05), andat pH>pI (pH6.0~9.0) the decrease was20.3%to12.2%(p<0.05). A strong increase in the turbidity during heating was observed at low pH (2.0) for proteins with nocalcium ion. In the presence of50mmol/L CaCl2, solubility of thermally treatednative WGGsignificantly increased. The disaggregation extent of the aggregations, reported as thedisaggregation index, was observed as a constant (y=0.5) between pH-induced (from pH1.0to the pI) treatment or heat-induced (from55to95°C) treatment for WGG. At Ca100mmol/L a significant increase in the solubility of WGG was detected (66.8%at95°C)compared with its control without calcium (26.9%); The chages of hydrophobic (H0), zetapotential and the protein microstructure (SEM) of WGG during theaggregation-disaggregation process were investigated. The results suggested that theelectrostatic repulsion between the particles issufficiently strong to disintegrate proteinaggregates, leading to a degradation of large lumps and ahomogeneous distribution of WGGparticles.To produce and evaluate wheat germ protein-calcium complex from enzymatichydrolysis of wheat germ protein, the restrictive enzymolysis technology, metal chelatetechnology and analytical techniques such asultraviolet-visible (UV-vis) spectroscopy andFourier transforminfrared (FTIR) spectroscopy had been accepted. It is demonstrated that theamount of Ca bound depended greatly on the type of enzyme, degree of hydrolysis (DH),amino acid composition, and molecular mass distribution of different hydrolysates. Wheatgerm protein hydrolysate prepared by Alcalase2.4L at DH of21.5%had the maximum levelof Ca bound and the highest yield of complex (18.0mg (g protein)-1,32.5%), and wassubsequently fractionated through ultrafiltration membranes with molecular weight cutoffs.Calcium binding capacity of portions P2(3K<Mw<5K) was significantly higher (p<0.05)than other portions, its calcium content increased to67.5mg (g protein)-1; Peptide fragmentsexhibiting high calcium-binding capacity had molecular mass <2000Da. The calcium-bindingpeptides mainly consisted of Glu, Arg, Asp, and Gly, and the level of Ca bound was related tothe hydrophobic amino acid content in WGPHs. UV-visible and Fourier transform infraredspectrademonstrate that amino nitrogen atoms and oxygen atoms on the carboxylgroup wereinvolved in complexation. Therefore, wheat germ protein is a promising proteinsource for theproduction of calcium binding peptides and could be utilized as a bioactive ingredient fornutraceutical food production.In vitro gastrointestinal digestion experimentwas used to evaluate the wheat germpeptides on calcium bioavailability, comparing inorganic calcium and calcium gluconate. Thecalcium bioavailability included the release quantity, solubility and dialyzability. The resultsshowed that wheat germ peptide-calcium complex had a higher bioavailability: The releaserate of peptide-calcium complex was more than90%after2h of the stomach digestion; In thegastrointestinal digestion after8h the solubility and dialyzability remained at ahigh level with80%and43%, respectively; Wheat germ peptide-calcium complex was more slowly torelease of Ca2+under the gastricacid than CaCO3and calcium gluconate, which could reducethe stimulation of the stomach; Under the influence of inhibitors such as phytic acid, oxalicacid and dietary fiber, wheat germ peptide-calcium complex still had a high bioavailability;At the present of phytic acid, its solubility and dialyzability reduced to77%and35%respectively during gastrointestinal digestion for2h; After adding oxalic acid, reduced to75% and24%, respectively; Dietary fiber, reduced to45%and21%respectively; However, thebioavailability of wheat germ peptide-calcium complexwere higher than CaCO3and calciumgluconate. It means that wheat germ peptide-calcium complex is the ideal calciumsupplements; Wheat germ peptide-calcium complex had remarkable biological stabilityduring simulated gastrointestinal digestion, thus the calcium chelating peptides from wheatgerm protein is a good indicator for enhancement of calcium absorption. |
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