| To investigate the effects of different heat treatments on nutrients(especially the dietary fiber component) and digestibility of oat, this paper used normal steaming, autoclaving, dry roasting and microwaving to process wholegrain oat. Then extracted soluble dietary fiber(SDF) out of the wholegrain oat to study effects of heat treatments on the SDF components,structural characteristics and physicochemical properties such as dissolution/swelling, holding water/oil, cation exchange and adsorption capacity, and rheological property. Finally, we explored the antioxidant activity of wholegrain oat SDF and the impacts of heat treatments on it. Main results are as follows:Four heat treatments affected nutritional quality and digestibility of wholegrain oat to varying degrees. Compared with the control group, contents of total dietary fiber(TDF) andβ-glucan of wholegrain oat were significant lower after steaming and microwaving, TDF content was higher while β-glucan lower after autoclaving, and contents of TDF, β-glucan were increased after dry roasting(p<0.05). Rapidly digestible starch contents of the wholegrain oat were all significant higher after different heat treatments, while contents of resistant starch(RS) were all decreased except dry roasting, after which the RS was 7.4%higher(p<0.05). Protein digestibility of the wholegrain was significant higher after normal steaming and microwaving, lower after autoclaving, while had no significant change after dry roasting(p>0.05).The main ingredient of SDF extracted from wholegrain oat is β- glucan, and contents decreased after heat treatments(p<0.05), in which the microwaving decline the largest. The average molecular weight of oat SDF increased after different heat treatments, and the order was autoclaving > steaming > dry roasting > microwaving > control, which was basically consistent with the results of particle size distribution changes. Scanning electron microscopy pictures showed that SDF of dry roasting and control group had similar structure, which was fine particles and sheet shape of polysaccharides was not obvious. While the remaining heat-treated groups had significantly sheet shape structure and signs of mutual aggregation.Infrared spectra showed oat SDF had characteristic absorption peaks of polysaccharide and had no significant changes after different heat treatments.Oat SDF had good solubility, which decreased after heat treatment. The water/oil holding capacity of SDF were significantly decreased after heat treatments(p<0.05). The emulsibility of SDF improved after heat treatments and emulsion stability was good. Heat treatments except steaming made the cation exchange capacity of SDF increase significantly while glucose absorption decrease(p<0.05). Adsorption of cholesterol of Oat SDF under neutral condition was significantly higher than that under acidic conditions(pH 2.0), and after microwaving the cholesterol absorption of SDF was significantly higher than the other groups(p<0.05). The apparent viscosity of SDF by different heat treatments were all decreased with the increase of shear rate, showing pseudoplastic fluid properties, and all increased with the increase of concentration and decreased gradually with increasing temperature. Compared the viscosity of SDF under the same conditions, we found it was significantly increased after steaming, and autoclaving and microwaving followed, while dry roasting had no significant difference with the control group.The total phenol content of oat SDF was 2.14mg/g, and significantly decreased after heat treatments(p<0.05). The total antioxidant capacity of SDF was 3.07μmol Trolox equivalent/g,and autoclaving, dry roasting and microwaving made it decreased significantly while steaming increased(p<0.05). The SDF had a certain capacity scavenging DPPH·, HO·, O2-·.The clearance rate of DPPH· of SDF significantly increased and that of HO· decreased after steaming(p<0.05). The other heat treatments made the clearance rate of DPPH· and HO· decreased significantly, and dry roasting and microwaving also decreased the O2-· clearance rate(p<0.05). The SDF had a good reducing capacity and increased after steaming while decreased after the other heat treatments(p<0.05). Oat SDF also had a good iron chelating ability, but decreased significantly after heat treatments(p<0.05). There were significantly correlations among the antioxidant indices of SDF. The total antioxidant capacity,DPPH· clearance rate, O2-· clearance rate and reducing capacity were positively associated with total phenol content of SDF( p<0.05), and iron chelating ability and HO· clearance rate had no significant correlation with total phenolic content(p>0.05). What’s more, the DPPH·,O2-· clearance rate, reducing capacity had significant positive correlation with total antioxidant capacity(p<0.01). |
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