| Oat,as a healthy food,is rich in several components beneficial to health.It has a variety of health care effects,such as lower blood lipid levels,regulated blood glucose levels,weight loss,less constipation and a reduced risk of tumour.The health awareness among people has been improved gradually,so the consumption of oat and oat-based products has on the rise.For oat food,its health-oriented efficacy and nutritional characteristics have close link with the destruction degree of grain structure.The diversity of processing methods will result in the unpredictability of the health efficacy of oat products.As an emerging technology to deal with raw materials,steam explosion has the advantages of environmental protection,low cost and high efficiency.In this study,under the background of whole grain,the effects of steam explosion treatments with different pressure(0.3 MPa,0.5 MPa and 0.7 MPa)and time(30 s,60 s and 90 s)on the microstructure and composition of oats were discussed,and the relationship between oat structure,nutrition quality and processing features were further analyzed,so as to provide a theoretical basis for the production and processing of whole grain oats.The main results are as follows:(1)Effect of steam explosion on the microstructure of whole grain oats.The structure of steam exploded whole grain oats,crystal structure and thermodynamic characteristics were studied by scanning electron microscope,polarizing light microscope,x-ray diffractometer and differential scanning calorimeter.The correlated analysis demonstrated that the internal structure of whole grain oats of the untreated group was closely and orderly arranged.After steam explosion,the structure of whole grain oats was destroyed,showing honeycomb shape and the internal specific surface area and porosity were on gradual increases with the augment of steam explosion treatment intensity.The crystalline area and ordered structure of steam-exploded whole grain oats were broken,the amorphous area was hydrolyzed,the crystallinity decreased,some starch was gelatinized,and the crystalline structure transformed from A-type to V-type,and produced starch-lipid complex.Therefore,the gelatinization enthalpy of whole grain oats gradually inclined with the increase of steam explosion treatment pressure and pressure holding time.When the steam explosion conditions were 0.7 MPa and 30 s,the heat energy for gelatinization of whole grain oats was only about 73.61%of that of the untreated group.(2)Effects of steam explosion on the nutrition quality of whole grain oats.In comparison with the untreated group,steam exploded whole grain oats boasted basically stable water,protein and total β-glucan content.With the increasing intensity of steam explosion treatment,the total starch content of whole grain oats showed a decreasing trend,and the amylose content showed ascending tendency,but there was no significant change.After steam explosion,whole grain oats had significant changes in fat content,water-soluble β-glucan content,β-glucan dissolution rate,gelatinization characteristics,and digestion characteristics of starch.With the increase of steam explosion treatment pressure and pressure holding time,the damage degree of whole grain oats tissue structure saw increases,giving rise to continuously increased watersoluble β-glucan content,β-glucan dissolution rate and rapidly digestible starch content.When the steam explosion conditions were 0.7 MPa and 90 s,water-soluble β-glucan content were on increases by 0.76% compared with untreated group and β-glucan dissolution rate and the content of rapidly digestible starch increased to around 19.77 times and 11 times of the untreated group respectively.The contents of fat and slowly digestible starch of steam exploded whole grain oats increased first and then decreased,and reached the maximum of 8.81 ± 0.05% and 52.18 ± 0.95% at 0.5 MPa,90 s and 60 s respectively.After steam explosion treatment,the content of resistant starch of whole grain oats decreased constantly,and the starch digestibility increased ceaselessly.In addition,the starch-lipid complex was produced during steam explosion of whole grain oats,and some starch was aged and degraded.Thus,the peak viscosity,trough viscosity,disintegration value,final viscosity,and setback value of whole grain oats significantly declined after steam explosion treatment,which was 35.35%,40.74%,22.55%,38.23%and 36.88% lower than that of the untreated group respectively under 0.7 MPa and 90 s.(3)Effects of steam explosion on the processing characteristics of whole grain oats.The solubility,water absorption,swelling power,texture,gelatinization degree and cooking quality of whole grain oats by steam explosion with different intensity were further studied.The results showed that with the increase of steam explosion intensity,the internal specific surface area and porosity of whole grain oats added,some fibers and starch were degraded into small molecular substances,the external substances became easier to penetrate,the internal substances became easier to dissolve,and the content of dissolved substances was on the rise.Therefore,the solubility,water absorption and swelling of whole grain oats flour increased constantly,and increased by 1.67 times,2.39 times and 46.83 times of the untreated group respectively under 0.7MPa and 90 s.The viscosity,gelatinization,water absorption,expansion volume,solids content and starch-iodine-blue in steam exploded whole grain oats after cooking were also on increases,and rose by 20.18 times,16.4 times,1.89 times,1.42 times,5.29 times and 2.86 times of the untreated group respectively under 0.7 MPa and 90 s.The hardness,chewability and p H value in steam exploded whole grain oats after cooking decreased continuously.When the steam explosion conditions were 0.7 MPa and 90 s,the hardness and chewability decreased to about 25.19% and 15.13% of the untreated group,and the p H decreased from 6.47 ± 0.02 to 6.17 ± 0.02.Hence,steam explosion can change the processing quality of whole grain oats by affecting the structure and composition of oats. |
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