Functional Properties, Structure And Application Of Flaxseed Gum

Flaxseed gum is a hydrocolloid suitable for a wide range of applications. But thefunctional properties and structure of flaxseed gum has been still understood poorly till now,which restricts the applications of flaxseed gum in food, medicine and cosmetic industry. Theobjective of this dissertation is to develop the functional properties, structure and applicationof flaxseed gum. The main results are as follows.Flaxseed gum was composed of xylose, arabinose, galactose, rhamnose, glucose andfucose, in which xylose was the major monosaccharide, while fucose was the minormonosaccharide. The ratio of xylose and rhamnose was 1.7, which implied that NFG was themain composition in flaxseed gum. Flaxseed gum was an anionic polysaccharide due toionized carboxyl group. M_w and M_n of flaxseed gum were 3.27×10⁶ and 2.77×10⁶,respectively, determined by SEC-MALLS. Flaxseed gum molecule was more homogeneousdue to M_w/M_n was 1.18. Flaxseed gum molecule was more extended when dissolved in waterfor 2>1/2 was 93.6 nm. Water was the θ solvent of flaxseed gum as the value of A2 was 0.Flaxseed gum molecule behaved as random coil chain in aqueous solution deduced by2>/M.AFG-1 and NFG-1 were isolated and purified by CTAB, ion-exchange chromatographyand gel penetration chromatography, of which M_w was 7.62×10⁵ and 1.19×10⁶ by gelpenetration chromatography, respectively. Total sugar content of AFG-1 and NFG-1 was58.92% and 84.93% determined by phenol-sulphate acid method, respectively. Uronic acidcontent of them was 33.55% and 6.58% determined by sulphate acid-carbazole method,respectively. C, H and N contents of AFG-1 were 28.04%, 5.89% and 0.80%, respectively.AFG-1 contained 17 kinds of amino acid. The results of UV, element analysis and amino acidanalysis showed that AFG-1 contained a few proteins. Polysaccharide and protein in AFG-1were combined through O-glycosidic bond by means of β-elimination reaction. NFG-1contained no protein. The structures of both AFG-1 and NFG-1 were determined by IR.AFG-1 was characterized by α-linked glycosidic bonds. NFG-1 was characterized by bothα-linked and β-linked glycosidic bonds.Structure of NFG-1 was analyzed by periodate oxydation, smith degradation, partialhydrolysis, methylation analysis, ¹H and ¹³C NMR, and the conclusions were drawn asfollows: The backbone of NFG-1 was composed of xylose and glucose. Most of arabinosesand part of xyloses were in the side-chain or presented as end group. Xyloses were mainly of1→4 linkage, a few of 1→2 or 1→3 linkage also existed. About 1/3 of xyloses were presentedas reduced end group. Glucoses were mainly of 1→6 or 1→2 linkage. Arabinoses were of1→4, 1→2 or 1→3 linkage. About 1/3 of arabinoses were presented as reduced end group.Galactoses were of 1→4 or 1→6 linkage. About 1/3 of galactoses were presented as reducedend group. Xyloses were characterized by β-linked glycosidic bond, while glucose, galactoseand arabinose were all characterized by α-linked glycosidic bonds.Partial acidic hydrolysis of AFG-1 showed that the backbone of AFG-1 was composed ofrhamnose and galacturonic acid. Most of fucoses were in the side-chain or presented as endgroup. Most of galactoses were in the side-chain, a few galactoses were presented as endgroup.Temperature and time dependence of conformation changes of flaxseed gum moleculesincluding the hydration, swelling and molecules rearrangement and finally formation ofviscous solutions during dissolution process were studied by means of static rheologicalproperties, dynamic rheological properties and molecule conformation. The optimalconditions of flaxseed gum dissolved at different temperatures were preferred as follows: 40℃ for 8h;50℃ for 6h;60℃ for 4h;70℃ for 4h;and 80℃ for 2h. Unusual dissolutionproperties of flaxseed gum were displayed. Flaxseed gum solutions exhibited weak-gelproperties when dissolved at higher temperature.Flaxseed gum solutions exhibited typical pseudoplastic fluid with shear-thinningproperties. Some factors affected the viscosity of flaxseed gum solution. Viscosity of flaxseedgum solution increased with increasing of concentration. Its viscosity decreased withincreasing temperature. Arrhenius equation described the relation of viscosity and temperature,and the activation energy was 27.48 kJ/mol. pH influenced the viscosity of flaxseed gumsolution. Maximum viscosity was obtained at neutral pH. Viscosity decreased with loweringpH at pH2⁶, and raising pH between pH8¹2. Viscosity decreased with addition of mineralsalt. Divalent cations were more effective than monovalent cations at lowering the viscosity.Flaxseed gum solution was characterized with gel properties, which could form a kind ofthermal-reversible gel by means of dynamic rheology measurement and DSC. Both Tgel andTmelt of flaxseed gum were influenced by dissolution temperature (that is initial coolingtemperature), and Tgel was lower than Tmelt. The dissolution temperature, pH value, NaCl,CaCl2 and complex phosphate salt could affect the gel strength of flaxseed gum, which coulddecrease or increase its gel strength.The mechanisms of difference of emulsion properties between flaxseed gum and gumarabic were discussed from molecule structure parameters (molecular weight and mean rootradius), hydrophobic properties (surface hydrophobic properties and hydrophobic amino acidcontent) and absorbed amount of protein at the interface. Compared with gum arabic, Mw and1/2 of flaxseed gum were larger, but surface hydrophobic property was lower, whichresulted in emulsification of flaxseed gum was poorer than that of gum arabic.There were interactions between flaxseed gum and meat protein, or myofibrillar protein,or salt-soluble meat protein by the results of thermal properties, dynamic rheologicalproperties, texture and microstructure. Mechanisms of flaxseed gum interacted with meatprotein were also studied. Electrostatic forces seemed to be the main forced involved in theformation and stability of protein-polysaccharide gel, disulfied bonds and hydrogen bondsplayed minor impacts on the formation and stability of protein-polysaccharide gel.Water-and-oil holding capacities of luncheon meat with addition of flaxseed gum werebetter, while the texture of luncheon meat with single addition of flaxseed gum was poorerthan that addition of gum blend CK. Quality of luncheon meat was significantly improvedwith addition of mixed gum that flaxseed gum and carrageenan were mixed at ratio of 1 : 1(w/w), and close to that addition of gum blend CK. This further verified that synergistic effectexisted between flaxseed gum and carrageenan.Flaxseed gum had significant effects on physicochemical properties of dough. Infarinograph, dough forming time and stability time increased while weak value significantlydecreased with addition of flaxseed gum. This was also verified by SEM and dynamicrheology measurements. The gluten continuous phase of dough with addition of flaxseed gumappeared more denser and uniform than the dough without flaxseed gum, and starch granulesappeared to be securely embedded in modified gluten network. With addition of flaxseed gum,the texture of noodles was improved. Noodles with addition of flaxseed gum had a higherhardness, breaking force, and chewiness than those without flaxseed gum. The solid contentsreleased into the boiling water were reduced by addition of flaxseed gum.