Mechanism For Removing Oat Lipids And Improving Cold Water Swelling Performance Of Oat Starch Based On Sub-critical Fluid

Oats is a whole grain healthy food recognised globally,and it has a wide range of application prospects in the processing of the staple food of Chinese noodles.How to improve the“high fat,no gluten”defect of whole oat flour,to make it suitable for processing Chinese traditional noodles,is the common challenge of cereal industry.In this study,we are focusing on the two key technical bottlenecks:removing oat structured lipids and modifying the oat starch,to improve the adaptability of oat flour.Firstly,a rapid,accurate,and simultaneous measurement of oat lipids and moisture was established.Then,the oat lipids was removed by subcritical fluid extraction technology,and the correlation between lipids contents and the structure,gelatinization and retrogradation properties of oat starch was investigated.Secondly the Granule Cold Water Swelling（GCWS）starch was prepared using subcritical ethanol-water solution,and to explore the influence of ethanol concentraction and treatment temperature on the crystalline structure of starch granules on molecular level.Then,the defatted oat flour and GCWS oat flour were used to produce oat noodles,and the processing quality was evaluated.We hope that eventually to provide technological support to oat food processing.The main findings of this study are as follows:（1）Establishing a novel method for determining moisture and lipid contents in oats using low-field nuclear magnetic resonance（LF-NMR）.The independent peaks of T₂₁（0.01–3.0 ms）and T₂₂（9.01–410.27 ms）in the T₂ spectral curves of oat flour represented water and lipid,respectively.Analysis of moisture content with the internal standard method was more accurate than with the external standard method,which uses 3%Mn Cl₂·4H₂O as a standard.There was a linear correlation between T₂₁peak area and water weight,and the correlation coefficient（R²）was 0.9893.There was also a linear correlation between T₂₂ peak area and lipid weight,and R² was0.9955.The results of the LF-NMR method were consistent with the results of the oven method（for moisture content）and the Bligh method（for total lipid content）.Moreover,the endosperm was found to contain 0.58–1.36%of the bound lipid,which was slightly lower than the value for the oat bran.（2）The effects of subcritical solvents（propane,dimethyl ether（DME）,and their 1:1 mixed solvents）and extraction temperatures（30°C to 60°C）on oat lipids and phospholipid extraction was investigated using the Patricelli kinetic model and thermodynamic analysis.The mass-transfer coefficient（k₁）of the washing stage under different solvents and temperature conditions ranged from 0.26min^–1 to 0.53 min^–1,which was approximately 10 times higher than that in the diffusion stage.Compared with the subcritical propane and mixed solvents,the maximum equilibrium yield of oat lipids and phospholipids were obtained using subcritical DME.With increased extraction temperature from 30°C to 60°C,the equilibrium yield of phospholipids increased,whereas the equilibrium yield of lipids increased to 5.30%at 40°C and then decreased.The enthalpy and entropy changes for phospholipid extraction were higher than those for lipid extraction.The Gibbs free energy for phospholipid extraction rapidly decreased with increased extraction temperature.A loose endosperm structure of oat grain was observed in the fluorescent microscope image,and the concentration of lipids in the bran layer was higher than those in the endosperm.In conclusion,kinetic and thermodynamic analyses statistically proved that DME was more effective than propane and mixed solvents for the extraction of lipids and phospholipids from oat flakes,and that phospholipid extraction strongly depended on temperature.（3）Understanding how oat lipids affecting the functional properties of oat flour and starch is of great importance for oat products.The rheological and thermal properties of oat flours and starch affected by oat lipids were investigated.The peak viscosity of oat flour and starch increased as lipid content decreased.Dynamic rheological measurements showed that the storage modulus of oat flour increased,whereas that of oat starch decreased as the lipid content decreased.The gel strength of oat flour and starch increased with decreasing in lipid content.Differential scanning calorimetry results suggested that decrease in non-starch lipid content had little influence on the properties and the formation of amylose-lipid complexes both of oat flour and starch during gelatinization and retrogradation.The removal of non-starch lipids from oats increased the peak viscosity and retrogradation behavior of oat flour and starch.（4）The changes on cold water swelling properties,structure of oat starch during subcritical ethanol-water treatment.As the treatment temperature increased from 75°C to 150°C,the cold water swelling ability of oat starch firstly increase and then decrease.The cold water solubility showed no significant changes,but the treatment temperature increased into 150°C,in which the cold water solubility changed from 2.93%to 54.55%.The cold water swelling ability of oat starch decreases with the increase of ethanol concentration.The cold water swellability of oat starch_{（95°C/48%）}is 24.09±1.30 g/g.Compared with the raw oat starch,GCW oat starch has larger granular size,and becoming larger when exposed to the water.The gelatinization enthalpy of GCWS oat starch is 0 J/g,and it can form a uniform gel in cold water.During the modification process,the surface of GCWS oat starch granules was honeycomb and porous,the crystalline changed from A-type to V-type,the ratio of 1047 cm^-1/1022 cm^-1 in the Fourier transform infrared spectroscopy（FT-IR）decreased,the amylose content increased from 27.49%to 47.08%.Therefore,the ethanol concentration of 48%and the treatment temperature of 95°C can be used as the process conditions for improving the cold-water swelling ability of oat starch.The molecular chain of oat starch will be degraded during the subcritical ethanol-water treatment.（5）Improving the cold-water swelling properties of oat flour and its effects on processing quality of oat dough sheets.The modified oat flour showed the intact starch granules,the gelatinization peak and the starch-lipid complex dissociation peak disappeared,the room temperature viscosity increased,and the peak viscosity decreased from 1293 cp to 403 cp.Addition of GCWS oat flour,the propotion of bound water peak(A₂₁)of the noodle sheet is significantly increased from 12.07%to16.31%,and the propotion of weakly bound water(A₂₂)was significantly reduced from 86.20%to 82.18%.Addition of 5%GCWS oat flour,the optimum added water of dough sheet（containing 50%oat）increased from 40%to 41%,and the tensile strength increased significantly from 345.57 g to 365.93 g.Therefore,the room temperature viscosity of GCWS oat flour is significantly increased.The amount of water added for noodle making should be increased when addition of GCWS oat flour.Addition of 5%GCWS oat flour,the tensile strength of dough sheet（containing 50%oat flour）has been significantly improved.