燕麦发芽过程中主要营养、活性成分的动态变化及其特性研究

【作者】 徐建国；

【导师】 田呈瑞；

【作者基本信息】 陕西师范大学 ， 植物学， 2011， 博士

【摘要】 燕麦(AvenaL.)是禾本科(Gramineae)燕麦属(Avena)一年生草本植物。作为一种人类和动物消费的谷物,燕麦虽然消费量明显低于小麦、大米,但已受到越来越多消费者的青睐,因为燕麦营养价值高,含有大量的优质蛋白质、脂肪、淀粉和可溶性膳食纤维以及一些维生素和矿质元素。此外,燕麦还含有丰富的酚类物质、甾醇、植酸、维生素E等多种生物活性成分,不但可以防止食品腐败,而且赋予燕麦抗氧化、降血压、降血脂、降血液胆固醇和降血糖等多种生理功能。但燕麦食品口感粗糙、不易消化吸收,而且一些加工会导致其生物活性成分含量及其活性的降低,使其开发利用受到限制。已有研究表明,发芽处理不但可以降低一些谷物、豆类中的抗营养因子,提高其营养价值和改善其感官品质,而且可以有效富集生物活性成分。本文以山西产裸燕麦为原料,研究了燕麦发芽过程中主要营养成分和生物活性成分的动态变化,以及发芽对他们相关特性的影响。主要结果如下:1.燕麦发芽过程中,还原糖和可溶性糖含量及α-淀粉酶、β-淀粉酶和总淀粉酶活力明显地先增加后降低;直链淀粉、支链淀粉和总淀粉的含量均随着发芽的进行呈下降趋势。相关性分析表明,燕麦发芽期间还原糖、可溶性糖含量分别与α-淀粉酶、β-淀粉酶及总淀粉酶活力呈显著正相关,而直链淀粉、支链淀粉及总淀粉含量均与淀粉酶活力呈显著负相关。2.燕麦发芽过程中,其残余淀粉颗粒仍保持了原淀粉的外貌形态和X-射线衍射A型图谱特征。发芽处理使燕麦淀粉的溶解度增加,膨胀度减小,同时会导致淀粉冻融稳定性变差,易于老化。但适度的发芽可增加淀粉的透明度,增强淀粉糊的热稳定性、冷稳定性和抗凝沉稳定性,而且能使燕麦淀粉的凝胶质构特性得到较好的改善。3.燕麦发芽过程中,游离氨基酸、总蛋白质、可溶性蛋白、非可溶性蛋白的含量及蛋白酶活力大体上呈增加趋势。燕麦醇溶蛋白组分含量增加,球蛋白和谷蛋白含量先增加后降低,而清蛋白含量变化与此相反。相关性分析表明,燕麦蛋白酶活力与总蛋白、可溶性蛋白、非可溶性蛋白、清蛋白及醇溶蛋白的含量均具有高度的正相关,与谷蛋白含量呈负相关。发芽使蛋白质的营养价值得到提高,但在整个发芽过程中,赖氨酸仍是第一限制性氨基酸。4.燕麦发芽过程中,清蛋白的部分组分降解,其电泳谱带逐渐清晰;球蛋白中的高分子量和中分子量组分随发芽时间的延长而逐渐降解,甚至消失,小分子量组分含量增加,同时蛋白质组分分布区域减小;醇溶蛋白分子量和组分分布在发芽过程中没有明显的变化;谷蛋白的高分子量组分在发芽24～48 h逐渐消失,组分分布区域减小,但再延长发芽时间,其高分子量和低分子量组分逐渐增加,组分分布范围逐渐变宽。5.基于二次回归旋转组合设计,优化燕麦肽的提取工艺。结果表明,在试验范围内,对燕麦肽得率影响程度由大到小的因素依次为:提取温度(X3),料液比(X1),提取时间(X2)。通过DPS软件分析,建立了以3个因素为自变量、以燕麦肽得率(Y)为因变量的回归模型为:Y= 5.3712+0.2633X1+0.2454X2+0.3092X3-0.3301X12-0.1958X22-0.1710X32-0.1363X1X3。得到燕麦肽的最优提取条件为:液料比16:1(v/m),提取时间72 min,提取温度34℃。在此条件下,试验得到的燕麦肽得率为5.54 mg/g,和预测肽得率(5.60 mg/g)接近。6.燕麦发芽过程中,肽含量大体上呈现增加的趋势。燕麦肽具有一定的抗氧化和降血压活性,其生物活性与含量呈高度正相关。综合比较,发芽60 h时,燕麦肽的含量和生物活性(抗氧化性及抑制血管紧张素转化酶活性)较高。燕麦肽提取物经过截留分子量为1 KDa和5 KDa的超滤膜分离后,分子量低于1 KDa的组分含量最少,但其ACE抑制活性最高。Sephadex G-25葡聚糖凝胶柱层析分离燕麦肽(<1KDa),得到2个较好的洗脱峰,第一个洗脱峰对应的分子量范围大约为472.3～819.5 Da,第二个洗脱峰对应的分子量范围大约为178.8～419.2 Da。7.燕麦肽具有较高的营养价值,但其溶解性和ACE抑制活性会受到pH、温度和消化酶的影响。在pH 2.0～12.0范围内,燕麦肽显示出较高的溶解度。在中性和酸性条件下,燕麦肽的ACE抑制活性基本没有变化,pH值高于9.0时,ACE抑制率明显降低。燕麦肽的溶解度随着温度的升高缓慢增加,但当温度高于80℃时,溶解度开始下降;燕麦肽的ACE抑制活性随着温度的升高呈下降趋势,温度在20～60℃之间,燕麦肽的ACE抑制活性没有明显变化,当温度高于60℃时,其ACE抑制活性迅速下降。燕麦肽经胃蛋白酶或胃蛋白酶-胰酶联合作用后,其ACE抑制活性变化不大。8.燕麦发芽过程中,酚类物质及其抗氧化活性随着发芽阶段和品种的差异呈现不同的变化。相比于原粮,发芽处理燕麦的游离酚、结合酚及总酚含量均有不同程度的增加。总体上来看,燕麦游离酚、结合酚的铁还原能力及其对DPPH和ABTS自由基的清除能力随着发芽的进行逐渐增加,而对Fe2+的螯合能力、羟基自由基的清除能力及对脂质过氧化的抑制作用在发芽过程中先降低后增加。发芽过程中除坝莜一号的游离酚外,多酚提取物对质粒DNA损伤的保护作用均优于原粮。相关性分析表明,游离酚和结合酚均高度正相关于DPPH、ABTS、FRAP试验所确定的抗氧化能力;游离酚适度正相关于Fe2+的螯合作用和对定位羟基自由基的-清除能力及脂质抗氧化能力,但与非定位羟基自由基的清除能力呈现负相关;结合酚与Fe2+的螯合能力、对定位羟基自由基和非定位羟基自由基的清除能力及脂质抗氧化能力均表现为适度的负相关。这些结果说明,发芽过程中燕麦多酚提取物的抗氧化能力的变化不单单与其含量及抗氧化体系有关,更与其成分有关,包括提取物中的非酚类物质的抗氧化成分。更多还原

【Abstract】 Oat(Avena L.),belonging to Avena of Gramineae,is an annual herb.As a cereal for human or animal consumption,although consumed in considerably lower quantities worldwide than wheat and rice,oat has received increased interest because of its excellent health-related properties,such as high contents of well-balanced protein and solube dietary fibre,energy in the form of carbohydrate and oil,and several vitamins and minerals.In addition,oats contained abundant biological active compounds such as tocols,phytic acid,sterols,phenolic compounds and so on,which contribute towards protecting foods from rancidity and may also provides its extensive physiologieal functions such as antioxidant activity,reducing blood pressure,blood lipids,blood cholesterol and blood sugar.However,foods from oats have unpleasant taste and difficult to be digested,in addition,the content and bioactivity of biological active compounds were decreased by some processing methods,which limited the development and utilization of oats.Some reported studies demonstrated that germination of seeds from some cereals and beans can decrease antinutritional compounds and enhance the nutritive value and improve sensory quality.Besides,germination can effectively accumulate biological active compounds.The main aim of this research was to study dynamic changes in main nutrient components and biological active compounds in oat groats during germination,as well as to investigate the effect of a highly controlled germination process on their related properties.The main research results of this paper are as follows:1.The content of reduced,soluble sugar and the activity of α-amylase,β-amylase and total amylase from oat groats increased at first and then decreased rapidly during germination.The content of amylose,amylopectin,total starch from oat groats decreased with the processing of the germintion.During germination,the content of reduced and soluble sugar were highly correlated to the the activity of a-amylase,β-amylase and total amylase,however,the content of amylose,amylopectin and total starch were negativly correlated to the the activity of amylase.2.During germination,the starch granules from oats still maintained the original shape,the A-type characteristics of the X-ray diffraction pattern.Germination increased the solubility and decreased swelling value of starch,and resulted in the poor freeze-thawing stability,which starch is easily gelatinized starch.Moderately germination increased the transparency of starch from oats and enhanced the hot paste stability,cool paste stability and anti-retrogradation,as well as improving starch gel texture properties.3.During germination,the contents of free amino acids,total protein,soluble and insoluble protein and protease activity in oats increased,as well as prolamin.The levels of globulin and glutelin first increased and then decreased,albumin however is quite opposite.The protease activity correlated highly to the content of total,soluble,insoluble protein,albumin,and prolamin,contrary to it for glutelin.The nutritional value of protein from oat groats was improved,but ’lysine was till restricted amino acid during germination.4.With the processing of germination,some albumin subunits in oat groats were degraded and then albumin electrophoretic bands became clear in electrophoresis picture.The higher and medium molecular weight of the globulin subunits were also degraded gradually,the higher molecular weight of band even disappeared and the lower molecular weight of the globulin subunit increased in their content while the molecular weight distribution narrowed,but there were no significant change in the molecular weight and distribution of prolamin.The higher molecular weight of glutelin subunits caused to disappear gradually from 24 h to 48 h of germination,while the molecular weight distribution narrowed.However,with the prolongation of germination time,The higher and lower molecular weight of glutelin subunits increased at the same time,the same as the molecular weight distribution.5.The optimum parameters for extraction technology of peptides from oat groats were determined by quadratic orthogonal rotation regression combination design.The result showed that the effect sequences of three factors for peptide yield were as follows:extraction temperature(X3),liquid-to-solid ratio(X1),extraction time(X2).The regression equation between peptide yield(Y)and three variables was determined by by Data Processing System(DPS),as given in the following equation:Y=5.3712+0.2633X1+0.2454X2+0.3092X3-0.3301X12-0.1958X22-0.1710X32-0.1363 X1X3.The optimal extraction parameters were as follows:liquid-to-solid ratio of 16:1(v/m),extraction time of 72 min,extraction temperature of 34℃,and the number of extraction times was one.Under the optimal extract parameters,the peptide yield was 5.54 mg/g,which was in agreement with the predicted value(5.60 mg/g).6.During germination,the content of peptide from oat groats increased significantly as compared with raw groats.The peptide from oat groats exhibited better antioxidant activity and effect of reducing blood pressure,which was highly correlated with the content of peptide.Compared comprehensively,the content and bioactivity(antioxidant activity and angiotensin converting enzyme(ACE)inhibitory activity)of peptide were higher when oat groats were germinated for 60 h.The ultrafiltration membranes with MWCO of 5 KDa and 1KDa were used to classify the extracts of peptide from oat groats.The extracts with lower molecular weights was the lowest in the content,but had higher ACE inhibitory activity.Sephadex G-25 gel filtration chromatography was employed to investigate the molecular weight of the ACE inhibitory peptides(<1 KDa).The result showed that there were two eluting peak with its corresponding molecular weight being 472.3～819.5 Da and 173.3～411.3 Da respectively.7.The peptide from germinared oat groats possessed excellent nutritional values,but its solubility and ACE inhibitory activity were influence by different pH,temperatue,and digestive enzyme.They has higher solubility in range of pH 2.0^12.0,while the ACE inhibitory activity decreased obviously until pH was higher than 9.0.The solubility of peptide first increased to the maximum at 80℃ then decreased while its ACE inhibitory activity decreased slowly at 20～60℃and it decreased sharply at 60℃ with temperature increasing.The peptides showed no obvious change in ACE inhibitory activity after digested by pepsin or pepsin-trypsin.8.The contents of phenolics and antioxidant activity of oat groats varied with the difference in germination stages and oat cultivars.Compared with raw groats,the contents of free,bound and total phenolics increased in varying degrees during germination.Over all,reducing ability and scavenging ability on DPPH and ABTS radicals of phenolic extracts from oat groats increased along with prolonging the germination time,while the scavenging effects on hydroxyl free radicals and chelating ability on ferrous ions of phenolic extracts first decreased and then increased during germination,as well as inhibition effects on lipid peroxidation.The DNA damage protective effects of phenolic extracts in oats but for free phenolics from Bayou I during germination was better than that of raw groats.The correlation between phenolic content and antioxidant activity indicated that the contents for free,and bound phenolics were highly correlated to the antioxidant activity determined by DPPH,ABTS,FRAP assays.The free phenolics were moderatly correlated to the scavenging activity on site-specific hydroxyl free radicals,chelating ability on ferrous ions and inhibition effects on lipid peroxidation,but negativly correlated to the scavenging activity on non-site-specific hydroxyl free radicals.Conversely,bound phenolics were negativly correlated to antioxidant activity mentioned above.From the regression analysis it can be concluded that changes of antioxidant activity of phenolic extracts from oats during germination can be not only attributed to phenolic contents and assessment methods for antioxidation,but also to phenolic components,including some antioxidative substances contained in extracts besides phenolic compounds.更多还原