The Studies On Structural And Functional Properties Of The Hulless Barley Protein

Hulless barley has been topped among all food crops in Tibetan inhabited areas. Not only the high yields, Tibetan hulless barley is also found rich and complete in nutrients. Extracting protein from hulless barley might create opportunity in farm revenue, taking great advantage of this resource can also help with protein supply in protein-based processors. Seven hulless barley proteins obtained by means of alkali-solution and acid-isolation were investigated, and nutritional properties, functional properties and structure were analyzed. The overall experiment focused on one variety, according to some facts, and in which its hydrolysis property was tested, modeling of enzymatic hydrolysis was made using nonlinear regression techniques. Antioxidant activity was also observed in level of hydrolysate rate. The main results were as follows:(1) The content of glutamic acid was the highest and methionine the lowest in amino acid composition among the materials. Ratio of essential amino acids in total amino acid was about 30%, of which protein in Zangqing 25 and Dongqing 8 was relatively higher. In terms of amino acid score analysis, the first restrictive amino of hulless barley acids was lysine, the first restrictive amino of Beiqing 6, Zangqing 320 and Zangqing 25 was sulfur amino acids and the first restrictive amino of Dongqing 8, Xila 19, Kunlun 12 and Zangqing 148 was lysine in terms of chemical score analysis. The essential amino acids component of Dongqing 8 protein got the nearest approach to both two models, ranking highest in essential amino acid index at the same time, which signed its high nutrition value. Free nitrogen content increased with the pepsin digestion time prolonged, then leveled off in the end.(2) Hulless barley protein contained about 20 μmol/g free sulfhydryl and 42.53~52.54 μmol/g disulfide bond; X-ray diffraction spectrum analysis showed all protein had crystalline region and diffraction peaks at 9°and 20°in 2θ; Thermal denaturation endothermic peak had imparity among samples, denaturation temperatures were also different but the differences were not significant. Enthalpy change ranged from 0.67 J/g to 0.77 J/g; From the FTIR spectrum, hulless barley protein had obvious special absorption band, amide areaⅠ,Ⅱand Ⅲ, secondary structure unit of hulless barley protein was given priority to β-angle, about 38.15% ~ 38.15%, followed was β-fold with content 28.76% ~ 28.76%, the sum ranged about 70% ~ 75%, which meant that content of alpha helix and random coil were very low.(3) In the pH range of 3.0~11.0, solubility of hulless barley protein showed a continuous rising trend after its first drop, this number topped over 90%, and the isoelectric point was found at pH 4.5. Water and oil absorption, foamability, surface hydrophobicity and emulsifying activity index differed a lot among the hulless barley protein varieties, different from that of emulsifying stability index, which had very little differences. In all 7 hulless barley proteins, Beiqing 6 had a better solubility in alkaline pH, water absorption ratio, oil absorption rate, foaming ability, emulsibility proved to be good except for its poor surface hydrophobicity. Dongqing 8 had optimal solubility in alkaline pH, its foaming stability, emulsifying stability and surface hydrophobicity was better as well.(4) There existed a structure-activity relation between the functional characteristics and the structural characteristics of hulless barley protein. Water-absorbing capacity had correlation with free sulfhydryl content, total sulphur content, disulfide bond content, and random coil of the secondary structure and denaturation temperature. Oil absorption had correlation with total sulphur content and disulfide bond content. Foamability had positive correlation with total sulphur content, disulfide bond content, α-helix and random coil, and negative correlation with denaturation temperature. Foam stability was positively correlation with sulfur-containing, correlation with each unit of hulless barley protein secondary structure were also significant. Emulsibility also had a certain correlation with protein each unit of secondary structure. Emulsion stability had correlation with sulphur content and denaturation temperature. The surface hydrophobicity had correlation with β-fold and denaturation temperature.(5) Hulless barley protein was hydrolyzed at optimal alcalase-activity comditions: 55 ℃ and pH 10.0, degree of protein hydrolysis droped off along with the initial substrate concentration rose while climbed with the increase of initial enzyme concentration, hydrolysis rate improved over time. The dynamics model of hydrolysis rate was)49.0(p)0209.09358.8(00E ???DHexSV, and the hydrolysis dynamics model was ])0102.0/38.4(1[l041.200 DHE ???tSn. Description alkaline protease inactivation in the controlled enzymolysis process was k4=3.3713 min-1, results from hydrolysis dynamics model met perfectly with former experimental data, could be used to guide and optimize enzymolysis reaction.(6)DH 6% barley proteolytic products showed a strong ability in ferric ion chelating ability, total reducing power, DPPH radical scavenging ability and hydroxyl radical scavenging ability, its total reducing power, DPPH radical scavenging ability and hydroxyl radical scavenging ability were lower than that of Vc, hydroxyl radical scavenging ability of the high concentration peptides was similar with Vc, but its ion chelating ability was better than that of Vc. DPPH radical scavenging rate of DH 6% peptides was 89.26%, with its hydroxyl radical scavenging ability 86.30%, and Fe2+ chelating ability 40%. This proved a strong feasibility to get oxidation resistance polypeptide by hulless barley protease hydrolysis.