| In this research,corn starch,wheat starch and tapioca starch were used as raw materials for freeze-thawing treatment and frying freeze-thawing starches with starch-oil model system.The starches after two freeze-thawing cycles with low oil absorption were selected to study.The effects of freeze-thawing treatment and frying treatment on the structure and properties of starches with low oil absorption were studied,and the reason for the decrease of oil absorption of starches was explained.It is very important for the application and development of freeze-thawing starches in starch-based food and fried starch-based food.In this study,the oil absorption of three starches were determined by freeze-thawing treatment with different cycles,and the lowest oil absorption was selected as the standard to prepare freeze-thawing starches.After two freeze-thawing cycles,the oil absorption of three starches were the lowest.The total oil absorption decreased from 80.34%?73.12% and 74.12% to 68.23%?60.78% and 68.27%,respectively.The structure and properties of raw starches and freeze-thawing starches were compared.The adsorption properties,amylose content,wettability,functional groups,microstructure,specific surface area and crystallinity of starches granules were discussed.The reason for the decrease of total oil absorption was also analyzed.After freeze-thawing,amylose content decreased,from 13.47%?18.02% and 15.56% to 12.98%?16.54% and 15.07%,respectively.Total water absorption increased,from 88.17%?97.12% and 82.04% to 98.41%?110.37% and 91.13%,respectively.And matrix oil adsorption increased slightly,from 1.78%?2.33% and 2.41% to 1.85%?2.56% and 2.46%,respectively.Contact angle(CA),fourier transform infrared spectroscopy(FT-IR),and scanning electron microscopy(SEM)showed that the change in groups and the rougher surface was correlated with oleophobicity.Rough surface can improve the oleophobicity of starch granules,the increase of hydrophilic groups and the decrease of lipophilic groups confirm the increase of total water absorption and the decrease of total oil absorption.The result of particle size showed that the surface area of freeze-thawing starches decreased,while the D10,D50,D90 and maximum particle size increased,which also increased the oleophobicity of starch granules.X-ray diffraction(XRD)showed that all samples were A-type,and the crystallinity of freeze-thawing starches decreased,which led to the increase of matrix oil adsorption.However,the increase of matrix oil adsorption had little effect on the decrease of total oil absorption.In other words,freeze-thawing treatment can effectively improve the properties of starch and reduce the lipophilicity of freeze-thawing starches.In this study,three raw starches and three freeze-thawing starches were fried with starch-oil model system,and the structure and properties of the fried raw starch and the fried freeze-thawing starches were compared.After frying,and compared with the raw starches,the total oil absorption of freeze-thawing starches were still decreased.The oil absorption of three fried freeze-thawing starches decreased from 78.72%?71.76% and 71.01% to 70.25%?61.12% and 67.18%,respectively.Amylose content,matrix oil adsorption and total water absorption increased.Amylose content increased from 8.34%,5.01% and 9.64% to 9.58%,5.66% and 10.22%,respectively.Matrix oil adsorption increased from 1.30%,1.91% and 1.57% to 1.62%,2.11% and 2.29%,respectively.And total water absorption increased from 92.55%,86.47% and 82.27% to 99.22%,99.18% and 87.12%,respectively.Fourier transform infrared spectroscopy(FT-IR)and scanning electron microscopy(SEM)showed that the functional groups on the surface of fried starch granules did not change,the hydrophilic groups increased significantly,and the lipophilic groups decreased.Rough particle surface reduced lipophilicity,and looser structure made the matrix oil adsorption slightly increased.Particle size analysis showed that compared with fried raw starches,D10,D50,D90 and maximum particle size of fried freeze-thawing starches were similar or slightly increased,and the specific surface area of fried freeze-thawing starches was significantly reduced,which would reduce the lipophilicity of starch.X-ray diffraction(XRD)showed that freeze-thawing starches were still A-type after frying,but the crystallinity decreased,which also led to an increase of matrix oil adsorption.However,the increase of matrix oil adsorption had little effect on the decrease of total oil absorption.In conclusion,the reduction of total oil absorption of freeze-thawing starches was not affected by frying treatment. |
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