Study On The Properties Of Limited Enzymatic Hydrolysis Rice Glutelin And The Effects Of Polysaccharides On Its Properties

Rice protein is rich in essential amino acids,has a high nutritive value,lowers cholesterol,and is hypoallergenic.The low solubility limited the application in industry.Rice glutelin is the major protein in rice.In this study,the effects of degree of hydrolysis(DH)on the structure and functional properties of rice glutelin was studied.The stability of rice glutelin emulsion with different DH was compared.The stability of the limited enzymolysis rice glutelin emulsion and whey protein emulsion,which was the common emulsifier in food industry,was also compared.The influence of addition of polysaccharide on stability of limited enzymolysis rice glutelin emulsion was investigated.The interaction between polysaccharide and rice glutelin in solution,and the effects of polysaccharide on solubility of rice glutelin in solution were analyzed.The major conclusions were listed as the following:The influence of the degree of hydrolysis(DH)on the structure and functional properties of rice glutelin was investigated.The molecular weight of rice glutelin decreased gradually with increasing of degree of hydrolysis,and the formation of soluble peptide aggregates at high degrees of hydrolysis;Surface hydrophobicity and intrinsic fluorescence intensity increased firstly and then decreased;enzyme hydrolysis led to a more extended form of the RG secondary structure.Compared with the native RG,the ?-sheet regions in the RGH decreased from 30.9% to 21.1% by hydrolysis with DH of 6%,whereas the contents of random coil and ?-helix regions increased from 29.7% to 38.6% and from 17.7% to 22.8%,respectively.The emulsifying activity,emulsifying stability,foaming ability and foaming stability increased firstly and then decreased with increasing of degree of hydrolysis.The influence of the degree of hydrolysis(DH)on storage,pH,salt,and temperature stability,and rheometer properties of rice glutelin emulsion.The storage,pH,salt,and temperature stability of the emulsions increased firstly and decreased with decreasing hydrolysis.Emulsions prepared with 2% DH rice glutelin were stable over a range of environmental conditions: pH 7-9;NaCl<100 mmol/L(pH 7);temperatures < 90(pH 7,0 mmol/L NaCl)studied.After 7 days of storage,there ?was little change in the K and n values of the emulsions stabilized by the 2% DH rice glutelin.Conversely,there was an ppreciable increase in the consistency index of the other two emulsions,and shear-thinning behaviour was observed.The emulsifying properties of partially hydrolyzed rice glutelin(HRG,2% degree of hydrolysis)were compared to those of whey isolate protein(WPI),a commonly used protein-based emulsifier.The surface load of WPI(1% emulsifier,d32 = 167.5 nm)was 2.8 times lower than that of HRG(3% emulsifier,d32 = 159.0 nm).Emulsions containing WPI-coated lipid droplets had better stability to pH changes(2–8),NaCl addition(0–500 mmol/L)and thermal processing(30–90 ?,0 or 200 mmol/L NaCl).Nevertheless,HRG emulsions were stable over a range of conditions: pH 6–8;NaCl ?200 mmol/L(pH 7);temperatures ?90 in the abse? nce of salt(pH 7);and temperatures ? 50 in the presence of 200 m? mol/L NaCl(pH 7).The objective of this study was to improve the physical stability of emulsionscontaining oil droplets stabilized by hydrolyzed rice glutelin(HRG)by coating them with anionic polysaccharides.Polysaccharide type and concentration had a strong influence on the properties of the coated droplets.Smaller particles with better pH-stability could be formed from xanthan gum or pectin than from alginate or gum arabic.The impact of environmental stresses on the stability of oil droplets coated with HRG-xanthan gum or HRG-pectin complexes was tested by measuring the impact of salt addition(0-500 mmol/L NaCl,pH 3.5)and thermal processing(30-90 oC 30 min,0 mmol/L NaCl,pH 3.5).The emulsions containing xanthan gum were stable at all NaCl concentrations,whereas those containing pectin were only stable at low salt levels.Compared with pectin,the oil droplets covered with xanthan gum had relatively high stability to salt addition across the whole range studied.There was actually an initial decrease in mean particle diameter in the emulsions containing xanthan gum with increasing salt content.Emulsions containing xanthan gum or pectin were stable to thermal processing.The influence of arabic gum and alginate on the properties of hydrolyzed rice glutelin(HRG)were studied.There is no significant changes for HRG properties when arabic gum was added,while soluble or insoluble complexes could be formed between HRG and alginate by manipulating solution conditions such as HRG:alginate ratio,pH,and ionic strength.Relatively small complexes that were relatively stable to aggregation and sedimentation over a wide range of pH conditions could be formed using a 3:1 HRG to alginate mass ratio.The addition of salt(NaCl)to solutions containing HRG-alginate complexes weakened the electrostatic attraction between them,which led to release of the protein.As a result,the protein molecules tended to interact with other protein molecules(rather than polysaccharide molecules)leading to the formation of precipitates and sediments.The influence of amylose on the structure and solibility of rice glutelin(RG)was characterized.The binding sites,binding constant and thermodynamic features indicated that binding process was spontaneous and the main driving force of the interaction was hydrophobic interaction.Furthermore,synchronous fluorescence and circular dichroism(CD)spectra provided data concerning conformational and micro-environmental changes of RG.With the concentration of amylose increasing,the polarity around the tyrosine residues increased while the hydrophobicity decreased.Alteration of protein conformation was observed with increasing of ?-helix and reducing of ?-sheet.Finally,a visual representation of two binding sites located in the amorphous area of RG was presented by molecular modeling studies.