【作者】 王丽丽；

【导师】 李再贵；

【作者基本信息】 中国农业大学 ， 粮食、油脂及植物蛋白工程， 2014， 博士

【摘要】 豆浆富含多种营养成分,是深受人们喜爱的中国传统植物蛋白饮料。随着家用豆浆机的问世,家庭自制豆浆已成为我国豆浆的主要消费形式之一。而浸泡是家庭豆浆制作中最繁琐和耗时的工序。通过冷冻可以改变大豆组织结构,有利于开发新型免浸泡大豆,实现干豆直接制浆,同时减少干豆直接磨浆可能对豆浆营养成分带来的不利影响。本课题采用电镜扫描、超高速离心、粒径分布(?)(?)SDS-PAGE电泳等方法系统研究了经浸泡-冷冻-干燥处理过程中,特别是冷冻处理对大豆的微观结构、豆浆品质、营养成分、抗营养因子、豆浆中蛋白和油体理化特性的变化的影响。研究结论如下：(1)冷冻处理会导致大豆的组织结构发生改变,诱导油体相互融合,蛋白体被破坏,并与油体发生聚集。冷冻后大豆的子叶内部出现较大空隙和通道,快速冷冻产生的孔隙尺寸小于慢速冷冻。这种多孔结构使得大豆种子在浸泡过程中能够快速地吸收水分,未处理大豆常温浸泡8h后吸水率约为110%,而-10℃冷冻样品浸泡4h吸水率则可达到107%。此外,冷冻还有助于降低大豆的硬度,缩短蒸煮时间。未处理大豆硬度为152.0g,冷冻处理的样品硬度仅为90g左右,降低了40%。(2)对豆浆的品质分析结果表明,冷冻前后豆浆粒度的分布有着相近的趋势,均在0.375-10μm与30-115μm处出现两个明显的峰值。但冷冻处理后,豆浆的粒径在这两个范围内体积百分数降低,而在10-20μm范围内出现较小的峰,且随冷冻时间增加平均粒径显著降低。冷冻使豆浆获得较好的风味,冷冻1天的样品豆腥味评分最低,香甜味和感官评分最高(85.5)。冷冻处理的样品白度增加,这可能是由于浸泡、干燥等处理过程导致了油体含量的增加。冷冻样品的黏度及沉淀离心率均升高可能是由豆浆的提取率和浓度增加所引起。(3)未处理、浸泡和冷冻处理样品中豆浆的营养成分、抗营养成分和蛋白质体外消化率的研究结果表明,冷冻处理样品的油脂、钙和铁提取率最高(15.76mg/mL,68.84mg/kg和4.40mg/kg),蛋白质、碳水化合物、低聚糖、植酸和单宁的提取率显著高于未处理样品,而与浸泡样品的提取率相当。此外,蛋白质体外消化率最高,冷冻4天样品的可溶性蛋白和消化率从未处理组的44.4%和78.5%分别增加到56.2%和85.0%。这可能是由于冷冻后疏松的微观结构使更多的小粒径蛋白溶解在水中,而粒径越小比表面积越大,越容易被蛋白酶消化。(4)分析了冷冻处理对豆浆蛋白的粒径分布、亚基组成及表面疏水性的影响。冷冻使豆浆中蛋白粒径的分布范围从0.04-0.5μm增加到0.04-10μm,这说明冷冻诱导了小粒径蛋白形成较大的蛋白聚集体。利用电泳实验进一步分析了豆浆蛋白及蛋白粒子的亚基组成,结果表明冷冻没有改变豆浆中蛋白质的组成成分,仍然包含β-伴球蛋白的亚基α、β’和β,大豆球蛋白的酸性多肽A和碱性多肽B。超高速离心分离得到不同粒径的蛋白粒子和非粒子亚基组成不同,蛋白粒子包含除了α,α’,之外的几乎所有大豆蛋白亚基组分,而非粒子部分只包含α,α’和大豆球蛋白的酸性多肽。此外,冷冻还导致豆浆蛋白的疏水性指数显著高于未处理组。当pH值从3-5时,蛋白粒子相互作用聚集形成较大粒径的聚集体,而且冷冻处理后的豆浆比未处理组豆浆能在更低的钙离子浓度下凝固。(5)最后研究了冷冻对油体微观结构及理化特性的影响。结果表明,冷冻处理后油体表面的磷脂膜被破坏,相邻的油体相互融合,蛋白体解体并与油体形成聚集体。冷冻后油体的粒径范围为2-4μm,且随冷冻时间的增加,大于4μm的大颗粒油体数量增多。电泳结果发现冷冻后油体表面的结合蛋白oleosin(24kDa)减少,而油体的大小和oleosin含量呈负相关。因此推测形状不规则和较大的油体含有较低含量的油体膜蛋白(oleosin)。此外,冷冻处理还能够轻微地降低油体的等电点,增加油体表面的疏水性。更多还原

【Abstract】 Soymilk, rich in nutrients, is a kind of traditional and popular plant protein beverage. With the invention of soymilk grinder, homemade soymilk has become one of the main way of soymilk consumption. In soymilk making, soaking is the most time-cost processing. Therefore, we tried to modify the texture of soybean by freezing and developed a new kind of instant soybean which can be direct grinded in water without soaking. The soymilk from instant soybean is simple, convenient and rich of nutrients. The effect of freezing on soybean microscopic structure, quality, nutrients composition, protein digestibility, anti-nutritional factors and the physical and chemical properties of protein and oilbodiesof soymilk were investigated. Electron microscopic technique, laser light-scattering, ultracentrifugation and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) etc. were used for the examination.Main results are as follows:(1) Freezing caused significant deformation of soybean structure and induced fusion of oilbodies. Protein body is destroyed, and aggregated each other or with oilbodies. Larger internal voids and channels appeared in cotyledons, which could attributeto the quickly hydrate during soaking. The water absorption rate of untreated soybeans was about110%after8h. While the value of freezing sample was107%after3h at same conditions. In addition, freezing can reduce the hardness of soybeans and shorten the cooking time. Thehardness of freezing sample was90.0g, a40%reduction from untreated sample (152.0g).(2) The particle size distributionsof soymilks have similar trends with two distribution peaks (range of about0.375-10μm and30-115μm). But a small distribution peak from10μm to20μm was found for freezing sample and the average particle size decreased significantly with the increasing of freezing time. Freezing made soymilk get better flavor. The sample from freezing1day has the lowest beany score and highest sweet and sensory scores (85.5). Freezing also increased the whiteness of soymilk, probably by the degradation of the pigment during soaking, drying processes and content of oil bodies increase resulted from freezing. The increase of viscosity and centrifugal sedimentation rate may be related with increasing extraction rate and concentration of soymilk.(3) Soymilks made from untreated soybeans, soaked soybeans, and frozen soybeans were compared on nutritional components, in vitro protein digestibility and some functional components. It was found that frozen sample was the best at extracting of lipid, Ca and Fe (15.76mg/mL,68.84mg/kg and4.40mg/kg, respectively), good at extracting of protein, carbohydrate, oligosaccharides, phytic acids and tannins, and excellent inin vitro protein digestibility. The soluble protein and protein digestibility of freezing4day sample increased significantly from44.4%and78.5%of untreated soybean to56.2%and85.0%, respectively. The reason may be the increasing of smaller protein particles dissolved in water resulted fron the loose structure of freezing sample.(4) The particle size distribution, protein subunit composition and the surface hydrophobicity of soy protein were analyzed. Distribution trends of protein particle size in frozen and untreated sampleswere significantly different. Protein particles of untreated sample were mainly0.04to0.5μm, while that of frozen samples were mainly0.04to10μm. This indicated that freezing induced the formation of protein aggregates. SDS-PAGE analysis shows that the soy protein subunits were not changed by freezing. Protein particles not only contain basic peptides and β, but also acidic peptides and some whey protein (lipoxygenase and β-amylase). The soluble protein mainly contain α and α’ subunits and acidic peptides. The hydrophobicity index of frozen samples was higher than that of untreated sample. When the pH changed from3-5, proteins aggregated because of the interaction among protein particles. In addition, the soymilk of frozen samples solidified at a lower calcium iron concentrationscompared with untreated sample.(5) Finally, this paper studied the effect of freezing on microscopic structure and the physical, chemical properties of soybean oilbodies. Results showed that the phospholipid membrane of oilbodies was destroyed and protein bodies disintegrated. Freezing induced the fusion and coalescence of oilbodies and protein, which resulted in a larger particle size of2to4μm.Moreover, percentage of oil bodies sizelarger than4μm increased with freezing. Electrophoretic results showed that the amount of oleosin decreased after freezing. The size of oilbodys was negative correlated with oleosin contentin seeds. Thus, oilbodies from freezing samples with irregular shape and enlarged size had the lower levels of oleosins. In addition, freezing can slightly decrease isoelectric point (pI) and increased the hydrophobicity of oil bodies from freezing samples更多还原