【作者】 姜梅；

【导师】 董明盛；

【作者基本信息】 南京农业大学 ， 食品科学， 2013， 博士

【摘要】 传统的大豆制品——豆乳、豆腐和豆腐皮,历史悠久,营养价值高,深受消费者的喜爱,是我国大豆加工的支柱产业。传统大豆制品行业规模普遍较小,技术水平低,而且豆乳在加工和贮藏过程中易产生油水分层和沉淀及风味不稳定等质量问题。因此,在保持传统豆制品原有风味和质地前提下,开发能够保持产品风味、质量稳定、品质高的豆制品以及适合于工业化生产的先进技术,是时代发展的迫切需要。超高压均质技术广泛应用于食品行业、医药行业和化妆品行业,是一项极具有发展潜力的技术。超高压均质可以降低豆乳的粒径,提高豆乳的均匀度、颗粒分散性和稳定性,同时也有抑菌、钝酶等效果。另外,超高压均质技术具有处理时间短和可连续化操作等特点,更适合于工业化生产的需要。本研究以传统豆制品——豆乳、豆腐和豆腐皮为研究对象,运用激光粒径分析仪、流变仪、SDS-PAGE电泳等仪器分析超高压均质和热处理对豆乳、豆腐和豆腐皮的物理化学等特性影响,旨在揭示超高压均质和热处理过程中豆乳、豆腐和豆腐皮的品质特性变化规律,为提高豆乳、豆腐和豆腐皮的质量和产率,全面提升豆制品加工综合水平提供基础数据和理论指导。主要的研究结果如下：1.超高压均质对豆乳的物理化学特性和微生物及酶的影响的研究在0～140MPa范围内,升高压力,豆乳温度显著增高；豆乳在进口温度Tin=20℃140MPa2次循环后,温度升高到55.2℃。随着均质压力增加,豆乳色差著下降,140MPa豆乳△E*比未处理的豆乳减少了3.44%,颜色由乳白色变为浅灰白色。此外,超高压均质使豆乳的粘度下降。离心沉淀率测定结果表明：均质压力增加,豆乳物理稳定性增强。DSC测定结果显示,升高均质压力,大豆7S蛋白和11S蛋白的Td变大和AH值变小,豆乳蛋白变性程度和热稳定性增强。豆乳颗粒粒径随压力升高而显著下降；在140MPa下,豆乳(水豆比10：1)粒径D4,3、D3,2、d0,5分别为0.28μm、0.28μm、0.27μm,粒径大小达到了亚微米级。在水豆比6：1～12：1范围内,当均质压力≥100MPa时,豆乳颗粒粒径均达到亚微米级。进口温度和均质次数对豆乳粒径大小有影响。过度均质,豆乳颗粒发生重新聚合,使粒径增大,豆乳不稳定性增强。与热处理(95℃5min)相比,超高压均质的抑菌和钝酶效果较差。豆乳经过140MPa2次循环(Tin=20℃)细菌总数减少了1.77个数量级,大肠菌群数小于3,脲酶相对活力减少19.91%。增加进口温度和均质次数可提高抑菌和钝酶效果,但仍然达不到热处理的效果。2.超高压均质和热处理对豆乳蛋白质溶解性的影响及其机理的研究在0～140MPa范围内,超高压均质可以增加生豆乳的溶解度；在140MPa下,豆乳蛋白溶解度比未处理的提高了63.8%；均质后加热豆乳的溶解度进一步提高,在140MPa下达到了91.1%；均质压力降低了豆乳的粘度和粒径；均质后加热使豆乳的这些特性得到进一步增强。透射电镜观察发现,超高压均质结合热处理能够增加豆乳颗粒的分散度和均匀性,降低豆乳颗粒粒径；粒径的减小增加了豆乳水合作用,从而提高了豆乳的溶解度。内部荧光分析表明,均质和加热改变了大豆蛋白分子的构象,增加了色氨酸微环境的极性,增强了蛋白质分子水合作用。SDS-PAGE结果表明,超高压均质的机械剪切力可以降解蛋白大分子聚集物,解离出蛋白亚基,提高了豆乳蛋白质溶解度；生豆乳均质后增加了A1、A2、A3及B亚基含量,减少了α及β亚基含量。增加均质压力,不仅可以解离大分子蛋白,也可以解离小分子的7S蛋白和11S蛋白(α、β、A、B亚基含量减少)。均质后加热产生了大于130kD的可溶性蛋白小聚集物,提高了豆乳蛋白质溶解度。3.均质压力对经均质(0～140MPa)、均质后加热和加热后均质的豆乳体系乳化性影响的研究均质、均质后加热和加热后均质三种处理方式都能改善豆乳蛋白质的乳化性。随着均质压力增大,三种处理方法能使豆乳蛋白质乳化活性增加；提高均质压力,均质和加热后均质的豆乳蛋白质乳化稳定性先增大再减小,在100MPa时最大；而均质后加热的豆乳蛋白质乳化稳定性随着均质压力增大而增大。均质压力可以增加豆乳蛋白的疏水性和改变豆乳蛋白游离巯基的含量。生豆乳均质后蛋白质乳化活性和乳化稳定性与均质压力和疏水性呈极显著正相关,与粒径大小呈极显著负相关,而与游离巯基含量无相关性。均质后加热的豆乳蛋白质的乳化活性和乳化稳定性与均质压力、疏水性和游离巯基呈极显著正相关,与粒径大小呈极显著负相关。而加热后均质豆乳蛋白质的乳化活性和乳化稳定性与均质压力、疏水性极显著正相关,与粒径大小呈极显著负相关,但只有乳化稳定性与游离巯基呈显著正相关,乳化活性与游离巯基无相关性。4.均质(140MPa)、均质后加热和加热后均质对豆乳风味的影响的研究感官评定结果表明,均质使豆乳口感细腻,加热增加了豆香味。用GS-MS从传统方法制备的生豆乳中鉴定出7种豆腥味化合物(己醛、己醇、1-辛烯-3-醇、反-2-己烯醛、1-辛烯-3-酮、苯甲醛、反,反-2,4-癸烯醛)和3种非豆腥味化合物(反-2-辛烯醛、壬醛、反-2-壬烯醛)。生豆乳的加热及均质后,增加正戊醇、2-正戊基呋喃和己酸三种物质。通过均质,未改变生、熟豆乳的风味物质组成；加热和均质都降低了风味物质的总含量,但加热增加了非豆腥味与豆腥味化合物比值。均质的顺序没有改变熟豆乳风味物质的组成,但先均质后加热的豆乳非豆腥化合物与豆腥味化合物比值高。5.经不同均质压力(0～140MPa)处理豆乳制成豆腐的品质特性研究经过均质处理豆乳凝固过程与未均质豆乳的凝固过程曲线变化过程相同,但140MPa豆乳凝固过程提前；升高均质压力,G’、G”显著增大；且G’>G”,即豆腐的固体性质大于胶体性质。扫描电镜观察表明,豆腐的内部结构是蜂窝状三度网状结构。均质压力增大,网络均匀性、立体性增强,致密性改变。TPA分析表明,豆腐的硬度、弹性、粘聚性和咀嚼性都随均质压力增加而增大。140MPa处理豆腐的咀嚼性比未均质的和20MPa的分别提高了112.7%、87.9%。均质压力达到100MPa时,豆腐保水率有明显的提高；100MPa、140MPa处理豆腐保水率比未均质分别增加了1.47%、2.45%。6.经不同均质压力(20～140MPa)处理豆乳制成豆腐皮的品质特性研究均质压力增加,豆腐皮颜色由浅金黄色变为金黄色；均质压力大于100MPa时,豆腐皮的成膜速度加快,耐煮性增强,豆腐皮品质更加稳定。TPA分析表明,超高压均质提高了豆腐皮的断裂延伸性和抗拉强度及产率,140MPa处理豆腐皮的产率比20MPa处理的提高了31.38%。扫描电镜观察表明,豆腐皮的内部结构是蛋白-脂肪复合物形成的网状层层叠加的结构；在20MPa和60MPa处理的豆乳制成豆腐皮的网状结构中存在游离脂肪球,而脱脂后豆腐皮结构中未出现游离脂肪球；均质压力高于100MPa时,豆腐皮的网状结构中不存在游离脂肪球,豆腐皮的结构更加均匀、致密；140MPa的豆腐皮脱脂前后微观结构无明显变化,蛋白-脂肪复合物更加稳定。这种结构使其贮存过程中减少“浸油”现象,能够防止其氧化产生“哈喇味”,有利于延长产品的货架期。更多还原

【Abstract】 Traditional soy products-soymilk, tofu and Yuba, favorite Chinese foodstuffs of high nutritional value and a long history form a pillar of China’s soybean industry. Traditional soy industry is generally in small scale and contains little modern technology. In addition, several quality problems, such as oil-water stratification, precipitation, flavor instability and other quality problems occur during the processing and storage of soymilk. Therefore, development of an advanced technology suitable for industrial scale production, which also cable of producing products with sufficient and stable quality, maintaining the original flavor and texture of traditional soybean, is an urgent need currently.Ultra high pressure homogenization technology is with great development potential which have already widely used in food industry, pharmaceutical industry and the cosmetics industry. Ultra high pressure homogenization is cable of producing soymilk with reduced particle size, improved uniformity and stability, and with antibacterial effects and reduced enzymatic activity. In addition, the high pressure homogenization technology is suitable for industrial scale production due to the typical features such as short processing time and continuously operating.In this study, traditional soybean products-soymilk, tofu and Yuba treated with heat and high-pressure homogenization were studied for the physical-chemistry properties changes using a laser particle size analyzer, rheometer, SDS-PAGE analysis. The objective of this study was to reveal the typical characteristics changes during high-pressure homogenization and heat treatment of soymilk, tofu and Yuba, as to improve the overall quality and yield of the three traditional soybean products. The study will also provide data basis and theoretical guidance for future elevation of soybean processing techniques. 1. Effects of ultra high pressure homogenization on the physicochemical properties, micro-organisms and enzymes of soymilkThe temperature of soymilk significantly increased along with the improving pressure in the range of0-140Mpa; Two cycles of soymilk at Tin=20℃,140MPa resulted a temperature rise up to55.2℃. With the increasing of homogenization pressure, decreased soymilk color differences observed. A decrease of3.44%obtained in140MPa soymilk AE*than the untreated samples, in which the color turned milky white to light gray. In addition, Ultra high pressure homogenization soymilk resulted viscosity decreasing. Centrifugal sedimentation rate measurements showed that physical stability increased along with the homogenization pressure. DSC measurement results demonstrated that the higher homogenization pressure gave higher Td and smaller AH value of both7S and11S soy protein, which indicated enhanced degree of denaturation and thermal stability.Soymilk particle size increased significantly with the pressure decreased; at140MPa, the soymilk (water:soybean ratio of10:1) particle size D4,3, D3,2, and d0,5were respectively0.28μm,0.28μm,0.27μm, which have achieved submicron size level. The soymilk particle size reached submicron level when the homogenization pressure≥1OOMpa using: water:soybean ratio among6:1to12:1. Inlet temperature and homogeneous times affected soymilk particle sizes. Excessive homogenization induced soymilk particles repolymerisation, thus resulted in an unstable soymilk system.Compared with heat treatment (95℃,5min), ultra high pressure homogenization was less effective in enzyme inhibition and microorganism inhibition. After2cycles (Tin=20℃) of high pressure homogenization at140MPa the total number of bacteria decreased1.77magnitude, coliform group was less than3, and the relative activity of urease reduced19.91%. Increasing of the inlet temperature and homogenization cycles could increase the effects of inhibitions of microorganisms and enzymes, yet not comparable to heat treatment.2. Effects of ultra high high pressure homogenization and heat treatment on soy protein solubility and its mechanismUltra high pressure homogenization in the range of0-140MPa can increase the solubility of raw soy protein; At140MPa, the soymilk protein solubility improved63.8%than the untreated ones; Thermal processing after homogenization further improved the solubility and reached91.1%(140MPa). Homogenization reduced viscosity and particle size of soymilk; Heating after homogenization further enhanced these properties. TEM observation demonstrated that a combination of thermal treatment and ultra high pressure homogenization increased the dispersion and uniformity of soymilk particles, decreased the particle size; particle size decrease improved the soymilk hydration, thereby increased the solubility of the soy protein. Internal fluorescence analysis showed that homogeneous and heating changed soy protein conformation, improved the polarity of tryptophan microenvironment, enhanced hydration of protein molecules.SDS-PAGE results showed that ultra high pressure homogenization mechanical shear force could degrade protein aggregates, dissociation of protein subunits, improved soymilk protein solubility; After homogenization, the raw soymilk had higher contents for A1, A2, A3and B subgroup, with reduced a and P subunits contents. Increasing homogenization pressure not only dissociate large protein molecules, small proteins7S and11S protein might also dissociate (α,β,A, B subunit content decreased). Heating after homogenization induced protein aggregates larger than130kD, which improved the soymilk protein solubility.3. Effects of homogenizing pressure on homogenized (0-140MPa), heating after homogenization, and homogenization after heating soymilk protein emulsification propertiesAll three approaches could improve soymilk protein emulsification properties. With higher homogenization pressure, all three treatment had increased soymilk protein emulsifying activity; emulsifying stability of homogenization and heating after homogenization samples indicated trends of first increases and then decreases curves, and maximized at lOOMpa, whereas homogenization after heating samples increases. Homogenization pressure could improve the raw milk proteins hydrophobicity and influence the free sulfurdryl group contents.Emulsifying activity and stability was significantly positively correlated with homogenization pressure and hydrophobicity, but significantly negatively correlated with particle sized, and with no correlation with free sulfhydryl groups. Samples of heating after homogenization had emulsifying activity and emulsion stability significantly positively correlated with homogenization pressure, hydrophobicity and free sulfhydryl groups, significantly negatively correlated with the particle sizes. Whereas the samples heating before homogenization had emulsifying activity and emulsion stability significantly positively correlated with homogenization pressure, hydrophobicity, significantly negatively correlated with the particle sizes. The emulsion stability significantly positively correlated with free sulfhydryl groups; however, the emulsion activity had no correlation with free sulfhydryl groups.4. The effect of homogenization (140MPa), heating before homogenization and heating after homogenization on the soymilk flavorSensory evaluations showed that the soymilk homogenization had better taste, and heating increased the nice bean flavor. Seven compounds attributed to beany flavor was identified using GS-MS (hexanal, hexanol,1-octen-3-ol, trans-2-hexenal,1-octen-3-one, benzaldehyde, trans, trans-2,4-decene aldehyde) and three non-beany flavor compounds (trans-2-octyl aldehyde, nonyl aldehyde, trans-2-nonenal). After heating and homogenization of raw soymilk, increase of n-amyl alcohol,2-n-pentyl furan, and hexanoic acid was observed. Homogenization barely changed the raw or cooked soymilk flavor compounds composition; heating and homogenization have reduced the total content of flavor compounds, but heating increased the ratio of non-beany and beany flavor compounds. Heating before or after homogenization did not change composition of the flavor compounds, however, heating after homogenization had higher ratio for the nice bean flavor/non-beany flavor compounds.5.Effect of different homogenization pressure (0-140MPa) on the tofu propertiesThe gel formation curves between non-homogenized soymilk and homogenized soymilk was the same, but the gel formation time was shorter in the140MPa treated soymilk; increased homogenization pressure improved G’, G" significantly, and G’> G" This means tofu had a nature of more solid than colloid. Scanning electron microscopy showed that the internal structure of tofu was a honeycomb structure. As higher the homogenization pressure was, the network had higher uniformity, enhanced three-dimensional properties, and changed density properties. TPA analysis showed that tofu hardness, elasticity, cohesiveness and chewiness were improved with homogenization pressure increases.140MPa processed tofu chewiness were112.7%,87.9%higher than that of non-homogenization and20MPa treated samples, respectively. The tofu water retention properties increased significantly when homogenization pressure reached lOOMPa; Compared to non-homogenization samples, water retention properties of tofu underwent1OOMPa and140MPa increased1.47%and2.45%, respectively.6. Effect of different homogenization pressure (20-140MPa) on the Yuba propertiesAs increase of homogenization pressure, Yuba became changed from light golden yellow to golden; when homogenizing pressure was greater than1OOMPa, the Yuba forming speeded, higher thermal stability obtained, and more stable Yuba quality observed. TPA analysis showed that high pressure homogenization improved tensile strength, elongation at break and yield of Yuba. The yield of140MPa treated Yuba was improved31.38%than that20MPa. Scanning electron microscopy showed that the internal structure of the Yuba was protein-fat complex which formed superimposed layers of mesh structure;20MPa and60MPa treated Yuba in presence of free fat globules, whereas the free fat globules were degraded when using homogenization pressure higher than1OOMPa;140MPa treated Yuba had no significant changes in the microstructure before and after defatted treatments, the protein-fat complex was more stable. This structure reduced the "oil-exuding" phenomenon and prevented its oxidation "rancid smell", which eventually helped extend product shelf life.更多还原