复合湿热处理对苦荞全粉理化特性及体外消化性的影响

采用湿热处理(HM-T)、湿热复合普鲁兰酶处理(HM-E-T)、湿热复合微波处理(HM-M-T)、湿热复合柠檬酸处理(HM-C-T)4种方法,研究不同湿热处理对苦荞全粉(N-T) 理化特性及消化性的影响。结果表明:经处理后苦荞全粉总膳食纤维和直链淀粉含量显著增加(P>0.05),其中HM-E-T效果最显著,HM-C-T次之；差示热量扫描仪检测结果显示,湿热处理后苦荞全粉黏度均显著降低且相变峰消失；X射线衍射结果表明,HM-T淀粉仍为A型结晶,HM-E-T淀粉由A型淀粉转变为A+B+V的多晶型,而HM-M-T和HM-C-T淀粉失去了原有晶形结构,淀粉相对结晶度从23.0%(N-T)下降至20.9%(HM-T)、18.4%(HM-E-T)、12.6%(HM-M-T)和10.6%(HM-C-T)；扫描电子显微镜和激光共聚焦电子显微镜观察结果表明,处理后的苦荞全粉微观结构发生不同程度的变化,蛋白质和淀粉发生一定程度复合。体外消化结果显示,苦荞全粉中抗性淀粉质量分数从9.69%(N-T)分别增加到11.49%(HM-T)、14.12%(HM-E-T)、11.97%(HM-M-T)、13.01%(HM-C-T)；预估血糖生成指数(eGI)出现不同程度的降低,即57.85(N-T)>56.03(HM-T)>55.65(HM-M-T)>55.18(HM-C-T)>50.22(HM-E-T),特别是HM-E-T后的苦荞全粉eGI值降低效果最明显。复合湿热处理比湿热处理更能有效降低餐后谷物血糖生成指数(GI)值,其中HM-E-T后的苦荞全粉可作为低GI食品的理想原料。

Effect of Combined Heat-Moisture Treatments on Physicochemical Properties and in Vitro Digestibility of Whole Tartary Buckwheat Flour

Changes in physicochemical properties and in vitro digestibility of native whole tartary buckwheat flour (N-T) were studied after heat-moisture treatment (HM-T), heat-moisture-enzyme treatment (HM-E-T), heat-moisture-microwave treatment (HM-M-T), or heat-moisture-citric acid treatment (HM-C-T). The results showed that the contents of total dietary fiber and amylose in whole tartary buckwheat flour increased significantly after treatment (P>0.05), among which HM-E-T was the most effective, and seconded by HM-C-T. Differential scanning calorimetry analysis indicated that the viscosity of tartary buckwheat powder decreased significantly and the phase transition peak disappeared after treatment. The results of X-ray diffraction showed that the starch after HM-T was still type A, and which was converted to A+B+V polymorph starch after HM-E-T. While the starch after HM-M-T and HM-C-T lost the original crystal structure, and the relative crystallinity of starch decreased from 23.0 (N-T) to 20.9 (HM-T), 18.4 (HM-E-T), 12.6 (HM-M-T) and 10.6 (HM-C-T), respectively. Images from scanning electron microscopy and laser confocal electron microscopy displayed that the microstructure of the whole tartary buckwheat flour changed in varying degrees, and the protein and starch were compounded in a certain extent. In vitro digestion assay showed that the content of resistant starch in whole tartary buckwheat flour increased from 9.69 (N-T) to 11.49 (HM-T), 14.12 (HM-E-T), 11.97 (HM-M-T), 13.01 (HM-C-T), respectively. And the estimated glycemic index (eGI) decreased in varying degrees:57.85 (N-T)>56.03 (HM-T)>55.65 (HM-M-T)>55.18 (HM-C-T)>50.22 (HM-E-T). In particular, HM-E-T had the greatest effect on reducing the eGI value of whole tartary buckwheat flour. Therefore, the combined heat-moisture treatment might more effectively reduce the postprandial grain blood glucose generation index (GI) than HM-T, and the whole tartary buckwheat flour after HM-E-T could be used as an ideal raw material for low GI food.