【作者】 Irakoze Pierre Claver；

【导师】 周惠明；

【作者基本信息】 江南大学 ， 食品科学， 2010， 博士

【摘要】 高粱含有丰富的微量营养素,如矿物质和维生素；也含有大量的常量营养素,如碳水化合物、蛋白和脂质。高粱中抗性淀粉的存在使得高粱受到糖尿病和肥胖病人的喜爱。此外,高梁还可能是谷朊过敏患者的一种食物选择。发芽高粱表现出可以与发芽大麦相当的淀粉酶活性,因此发芽高粱能够作为原料用于加工多种工业食品。关于以高粱为原料的食品研究在发达及发展中国家都有所研究。这些研究成果主要集中于研究浸泡和发芽对高粱婴儿麦片、颗粒食品、区域性啤酒以及其他农产品工业加工品,如贮藏啤酒、面包等。本文首先对浸泡和发芽条件进行优化,并对发芽和浸泡对高粱颗粒的物重损失、可溶性固形物(SS)含量、冷糊黏度、淀粉酶活性、单宁及蛋白含量的影响进行研究。所研究的影响因素主要有浸泡时间、浸泡温度、发芽时间和发芽温度。经研究分析,发现发芽提高了高粱的物重损失、SS含量、淀粉酶活性和蛋白含量,同时发芽降低了高粱淀粉冷糊黏度和单宁含量；经响应面优化得出高粱浸泡发芽的最佳条件为31℃浸泡24h和30℃发芽4.5d,该条件经试验验证与预测值相符,所优化条件可取。在上述实验条件下,对发芽高粱的出粉率进行研究,发现经发芽后高粱的出粉率显著提高,这主要是因为发芽高粱表皮比较脆弱,从而使得磨粉时出粉率提高；对所得高粱粉的挥发性物质进行研究,在原高粱中共检测到16个峰,检索到14种化合物,经浸泡和发芽处理后产生了一些新的风味物质,在浸泡高粱、发芽3d高粱、发芽5d高粱中分别检测到20、23、25个峰,说明在浸泡和发芽过程中产生一些新的醛类、酮类、酯类和酸类,而且这些风味物质随着发芽时间的延长而增加,发芽后高粱呈甜甜的花香味,这主要是由于其中较高含量的乙酸乙酯、3-甲基丁醛、戊醛、2-戊酮、乙酸、2-甲基丙酯、丁酸乙酯、己醛、1-辛烯-3-醇、安息香醛。高粱天然含有植酸、单宁等抗营养因子,这些抗营养因子的存在降低了高粱营养成分的膳食利用率。因此,本文研究了木灰提取物浸泡法对这些抗营养因子的影响,并评价了浸泡和发芽对高粱粉营养特性的影响。结果得出,采用木灰提取物浸泡24h后单宁含量显著降低了50.2%而且降低的趋势随着随后发芽时间的延长更为显著,发芽5d后高粱中的单宁含量降低了69.3%、植酸降低了66.4%,同时高粱中的灰分、脂质、纤维和淀粉含量也有轻微降低；发芽显著提高了高粱蛋白、必需氨基酸和糖类中果糖、葡萄糖、麦芽糖的含量,高粱蛋白质的体内消化性随着发芽时间的延长显著提高,高粱淀粉呈现更利于淀粉酶作用的多孔形态。发芽对高粱功能特性及对蛋白酶、淀粉酶活性影响研究结果表明：发芽3d时,蛋白酶、淀粉酶活性最高；与未发芽高粱相比,发芽高粱具有较好的蛋白溶出率及蛋白溶解性(pH6时蛋白溶解度最高)、最低凝胶浓度为8%(未发芽的为18%)、较低的容重、较好的吸水(131～142%)吸油性(90～108%)、乳化性及乳化稳定性提高、起泡性及泡沫稳定性得到改善且均随着发芽时间的延长而提高。功能性评价结果进一步表明,发芽能够改善高粱粉的功能特性,这使得发芽高粱粉具有满足制备新食品的条件。采用超声波提取高粱淀粉,并研究以超声功率(X1)、超声时间(X2)、料液比(X3)为考察对象的响应面优化工艺,经统计方差分析得出各因子对淀粉提取率的影响显著性为：X1、X2、X3、X12、X22对淀粉提取率有显著影响,其次为X2X3交互项(p<0.05)。优化后得出最优模型及最优方程,求解后得到最佳提取条件为：超声功率600W、提取时间4min、液料比30(V/W),在此条件下淀粉提取率预测值为17.06%,经验证试验所得实测值为17.08±0.33%,两者无显著差异,模型结果可取。进一步对提取的淀粉进行了物理化学和功能特性研究。结果得出：在低于50℃时浸泡高粱淀粉和发芽高粱淀粉具有相当的溶胀度和溶解指数,然而在高于50℃时发芽高粱淀粉表现出较浸泡高粱淀粉和原淀粉低的溶胀度和较高的溶解指数；采用RVA研究淀粉糊的性质,结果表明发芽高粱淀粉具有较原高粱淀粉(454BU)低的峰值黏度(86BU)；X-射线衍射表明两种淀粉衍射峰均呈典型的谷物淀粉峰A-型,相对结晶度为9.62-15.50%；DSC测得原高粱淀粉的焓变温度为78.06℃,凝胶玻璃化焓值为2.83 J/g,而发芽5d的高粱淀粉焓变温度为47.22℃,凝胶玻璃化焓值为2.06 J/g；流变测定得出所有淀粉悬液的贮存模量和损失模量随测定温度的增加逐渐增加,在70℃时达到最大,之后逐渐降低；对淀粉的表面结构进行研究,发现淀粉表面呈多孔状,这种结构可能更有利于淀粉酶酶解作用。总而言之,浸泡和发芽对高粱淀粉的物理化学和功能特性产生了较大影响。以蛋白提取率为指标,选取超声时间、pH、提取时间和料液比为考察因素,利用响应面优化高粱蛋白的提取率,得到相关性良好的二级模型(R2=0.967),经模型计算最优提取条件为：超声功率400W、pH8、提取时间40min、液料比20(V/W),此条件下蛋白得率预测值为5.36g/100g高粱粉,经试验得实测值为5.43g/100g高粱粉,实测值与预测值无显著差异,说明模型可取。在以上结果基础上,采用SDS-PAGE对所提蛋白进行分析,并采用茚三酮比色法测定了游离氨基酸总量以及采用DSC分析蛋白的热力学特性。SDS-PAGE结果表明经浸泡后高粱中的大分子量蛋白增加,进一步说明由于淀粉的降解使得醇溶蛋白的提取率和含量增加；经浸泡后分子量为66.2KDa条带无明显差异,但是经发芽3d时显著降低,然而继续发芽到5d该条带没有变化,分子量为43.0kDa条带颜色在浸泡后有轻微下降,经发芽后相应的转化为31.0kDa条带；氨基酸总量分析表明发芽5d后总游离氨基酸含量增为原来的四倍,这主要是由于内脂酶、蛋白酶、淀粉酶等水解酶类作用的结果；DSC表征的高粱蛋白的热力学特性结果表明,经发芽后高粱蛋白的热变性温度由原来的70.83℃升高到84.30℃,变性焓值无显著差异由3.09 J/g变为3.05 J/g。采用清除DPPH自由基和ABTS法对浸泡和发芽高粱的抗氧化性进行评价,结果表明浸泡和发芽显著影响高粱的抗氧化性。如前所述,高粱中含有较高含量的单宁和植酸,这些物质赋予高粱具有较高的抗氧化性。原料高粱具有最高的DPPH清除率(21.0μM Trolox/100 g),其次为浸泡高粱(18.8μM Trolox/100 g),然后为发芽3d的高粱(13.0μM Trolox/100 g),最后为发芽5d的高粱(11.2μM Trolox/100 g)。经发芽后,高粱的抗氧化性显著降低。采用ABTS法测定结果得出：原高粱的ABTS清除率为3.1μM Trolox/100 g,而浸泡高粱的为2.3μMTrolox/100 g,发芽5d的最低为1.6μuM Trolox/100 g,其次为发芽3d的。总结以上结果,通过选择适宜的发芽处理时间后,高粱具有用于制备特殊食品的潜在用途和价值。更多还原

【Abstract】 Sorghums are rich sources of micronutrients such as minerals and vitamins; and macronutrients like carbohydrates, proteins and fat. Sorghum has a resistant starch, which makes it interesting for obese and diabetic people. In addition, sorghum may be an alternative food for people who are allergic to gluten. Malts sorghum display a-amylase andβ-amylase activities comparable to those of barley, making them useful for various agro-industrial foods. The feature of sorghum as a food in developing as well as in developed countries is discussed. This work makes a particular emphasis on the impact of soaking and malting on sorghum macromolecules in the use of sorghum for infants thin porridges, granulated foods, local beer, as well agro-industrial foods such as lager beer and bread.The work starts by optimizing steeping and germination condition and their effect on sorghum grain in term of malt loss, soluble solid (SS) yield, cold paste viscosity, amylase activity, tannin and protein content. The factors studied included time and temperature of soaking with temperature and time of germination. Germination significantly affected the increase in malt loss, SS yield, amylase activity, and protein content with a decrease in cold paste viscosity and tannin content of sorghum. Optimum conditions for sorghum were:steeping time for 24 h at 31℃and 4.5-days of germination at 30℃. Values predicted at optimum conditions by the response surface model for all responses were experimentally tested and close agreement between experimental and predicted values was observed. The flour yield was evaluated and sorghum flour was significantly enhanced by 3-days germination of the seeds. The increase in flour yield resulted from the brittle nature of the malted seeds which improved flour extraction. Volatile compounds were detected in the sorghum flour and 16 peaks were detected in raw seed with 14 volatile compounds. Soaking and germination generated some new volatiles and 20,23 and 25 peaks were identified in SSG,3DGS and 5DGS respectively. Some aldehydes, ketones, esters and acids were generated and increased during the time of germination. Malted sorghum flour was sweet and floral due to the higher content of ethyl acetate,3-methylbutanal, pentanal,2-pentanone, acetic acid,2-methylpropyl ester, butyl acetate, hexanal, 1-octen-3-ol, benzaldehyde.Sorghum grains have naturally occurring anti-nutritional factors, such as phytic acid, tannin that decrease their dietary availability. This work determined the effect of wooden ash extract on anti-nutritional factors and also was conducted to assess the effect of soaking and malting on nutritional properties of sorghum flour. The addition of wooden ash extract during 24 h of soaking resulted in significant decrease in tannin by 50.2% and the decrease was observed to be progressive as malting time increases. Five days of malting resulted in significant decrease in tannin by 69.3% and phytic acid by 66.4% with slight decrease in ash, lipid, fiber and starch. Malting significantly improved the quantity of protein and essential amino acids and sugars analysis showed a significant increase of maltose, glucose and fructose. In vitro protein digestibility was markedly increased with the malting time increases and structural analysis of sorghum starch showed porosity on granule’s surface susceptible to the amylolysis.Influence of grain germination on functional properties of sorghum flour was evaluated for five days and protease and amylase activities were measured. Results showed that flour obtained from the 3-days germinated sorghum grain had high protease and amylase activities. The functional properties of flours derived from the germinated sorghum seeds were studied and ungerminated seeds were used as a control. Germinated samples had a higher protein solubility compared with the control, and the highest solubility occurred at pH 6. Germination also increased the protein solubility index of sorghum flour. Germinated sorghum flour had a least gelation concentration of 8% compared with 18% for the control. The bulk densities of germinated flours were lower compared to the ungerminated one. Water and oil capacities were increased by germination from 131% and 90% to 142% and 108%, respectively after three days of germination. The emulsifying activities and stabilities of the germinated samples increased significantly. In addition, germination improved the foamability of sorghum flour from unfoam flour to a flour with foam after three days of germination; and the foaming capacity and stability increased significantly with increasing germination time. Thus, the study indicated that germination improved the functional properties of sorghum and it would be possible to design new foods using germinated sorghum.Ultrasonic technology was applied for starch extraction from the malted sorghum and response surface methodology (RSM) was used to optimize the effects of processing parameters on starch yields. Three independent variables were ultrasonic power (X1), extraction time (X2) and ratio of water to raw material (X3), respectively. The statistical analysis indicated that three variables and the quadratic of X1 and X2 had significant effects on the yields, and followed by the significant interaction effects between the variables of X2 and X3 (p<0.05). A mathematical model with high determination coefficient was gained and could be employed to optimize starch extraction. The optimal extraction conditions of starch were determined as follows:Ultrasonic power 600 W, extraction time 4 min, ratio of water to raw material 30:1 (v/w). Under these conditions, the experimental yield of starch was 17.08±0.33%, which was agreed closely with the predicted value 17.06%. Extracted starch from soaked and malted sorghum was studied to understand their physicochemical and functional properties. The swelling power (SP) and the water solubility index (WSI) of both starches were nearly similar at temperatures below 50℃, but at more than 50℃, the starch isolated from malted sorghum showed lower SP and high WSI than those isolated from raw and soaked sorghum. The pasting properties of starches determined by rapid visco-analyzer (RVA) showed that malted sorghum starch had a lower viscosity peak value (86 BU) than raw sorghum starch (454 BU). For both sorghum, X-ray diffractograms exhibited an A-type diffraction pattern, typical of cereal starches and the relative degrees of crystallinity ranged from 9.62 to 15.50%. Differential scanning calorimetry (DSC) revealed that raw sorghum starch showed an endotherm with a peak temperature (Tp) at 78.06℃and gelatinization enthalpies of 2.83 J/g whereas five-day malted sorghum starch had a Tp at 47.22℃and gelatinization enthalpies of 2.06 J/g. Storage modulus (G’) and loss modulus (G") of all starch suspensions increased steeply to a maximum at 70℃and then decreased with continuous heating. The structural analysis of malted sorghum starch showed porosity on the granule’s surface susceptible to the amylolysis. The results showed that physicochemical and functional properties of sorghum starches are influenced by soaking and malting methods.A mathematical model with high determination coefficient was gained and could be employed to optimize protein extraction of malted sorghum flour. Four independent variables were ultrasonic power, pH, extraction time and solvent/meal ratio was used. Selected response which evaluated the extraction process was protein yield and the second-order model obtained from protein yield revealed a coefficient of determination of 0.967%. The optimal extraction conditions of protein were determined as follows: Ultrasonic power, pH, and extraction time and solvent/meal ratio were 400 W,8,40 min, and 20:1 (v/w), respectively. Protein yield was primarily affected by ultrasonic power, pH and solvent/meal ratio. These conditions resulted in protein yield of 5.43 g of soluble protein from extract/100 g malted sorghum flour which was agreed closely with the predicted value 5.36%. The adequacy of the model was confirmed by extracting the protein under optimum values given by the model and the results may help in designing the process of optimal protein extraction from malted sorghum flour. Sorghum protein extracted was followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The quantitative measurement of free amino acids in the sample was made using the ninhydrin reaction and thermal properties of protein were evaluated using DSC. The SDS-PAGE results showed that levels of high-molecular-weight aggregates increased after soaking. This behavior shows the enhancement of prolamin extractability and concentration in sorghum as a result of starch degradation. The 66.2 kDa oligomer concentration remained constant when sorghum is soaked and showed a significant decrease after 3 days of germination and remain constant after 5days malting. The 43.0 kDa oligomer concentration remained constant when the sorghum is soaked thereafter decreases slightly, reaching 31.0 after 3 and 5 days of germination. It was also found that 5 day malt led to a fourfold increase in free amino acid content. These modifications are due to intrinsic lipases, proteases and amylases. Germinated sorghum protein possessed the highest differential scanning calorimetry result (peak temperature of 84.30℃, delta H = 3.05 J/g) and raw seed protein had the lowest (peak temperature 70.83℃, delta H= 3.09 J/g). Germinated sorghum proteins are potential functional food ingredients.To estimate the antioxidant activity of soaked and malted sorghum, the DPPH and ABTS were used. Antioxidant activity was significantly affected by sorghum soaking and germination. As studied before raw sorghum grain had high content (p<0.05) in tannin and phytic acid. These sorghums had significantly high antioxidant activity. Raw sorghum grain had the highest (P< 0.05) DPPH radical scavenging activity (21.0μM Trolox/100 g of dw), followed by soaked sorghum (18.8μM Trolox/100 g of dw), then 3-days malted sorghum (13.0μM Trolox/100 g of dw) and lastly 5-days malted sorghum (11.2μM Trolox/100 g of dw). Malted sorghum had significantly decreased antioxidant activity. Antioxidant activities of malted sorghum as measured by ABTS ranged from 3.1μM Trolox/100 g of dw for the raw sorghum grain to 2.3μM Trolox/100 g of dw for the soaked sorghum. The 5-days malted sorghum gave the lowest ABTS radical scavenging (1.6μM Trolox/100 g of dw) followed by 3-days malted sorghum grainThese findings show that it is possible to use the sorghum macromolecules and selecting the most suitable sorghum flour properties for specific food processing.更多还原