【作者】 陈锋亮；

【导师】 魏益民；

【作者基本信息】 中国农业科学院 ， 农产品质量与食物安全， 2010， 博士

【摘要】 食品挤压是温度、压力和机械剪切等因素共同作用的过程,水分对挤压过程的顺利实施和挤压产品的特性有着重要影响,物料水分含量是划分中低水分和高水分挤压技术的主要标志。与中低水分蛋白挤压产品相比,高水分挤压组织化产品因具有视觉外观和口感均类似鸡胸脯肉的纤维状结构,已引起人们普遍关注。为此,前人提出高水分挤压产品纤维化结构形成机理的“膜状气腔”理论假设,其中,明确指出挤压过程中水分的变化和作用对挤压产品纤维化结构形成的重要性。在前期相关方法研究和“膜状气腔”理论假设的启示下,本研究以物料水分为切入点,对水分在植物蛋白挤压过程中的作用进行系统分析,旨在探讨高、低水分挤压技术生产纤维状模拟肉蛋白产品的本质差异,进而提出植物蛋白高水分挤压产品纤维化结构形成机理的理论模型。本研究以大豆分离蛋白(SPI)为原料,以DSE-25型同向啮合双螺杆挤压机为加工设备,设计不同物料水分(28%~60%)和挤压温度(140~160℃),通过在线检测和理论模型推导,分析了水分对挤压过程中扭矩、压力降、在线黏度、停留时间分布(RTD)以及单位机械能耗(SME)等系统参数的影响;通过差示量热扫描(DSC)和低场脉冲核磁共振(LF-NMR)技术分析了水分在挤压产品中的形态和分布;通过感官、质构、蛋白质溶解性、电泳和红外光谱等技术,从宏观到微观层面,分析了水分对挤压产品的外观、质构、化学键交联、蛋白质亚基(7S/11S球蛋白比例)和蛋白质二级结构的影响;通过突然停机操作,得到挤压机机筒内不同区段的样品,分析了水分在机筒内对蛋白质特性的影响;最后对水分形态与挤压过程中系统参数、最终挤压产品特性之间进行典型相关分析,系统阐明挤压过程中不同形态水分的作用。主要结论如下:(1)SPI经挤压蒸煮后发生了聚合、交联等变性反应,形成了大分子量聚合物,溶解度降低;挤压组织化产品的结构是由疏水作用、氢键、二硫键以及彼此之间的协同作用共同维持,且非共价键作用大于二硫键作用,4种蛋白二级结构均存在,且β-折叠、β-转角>无规则卷曲>α-螺旋。(2)SPI原料中临界冻结水或自由水含量在35%~38%,这可能是高、低水分挤压组织化技术水分临界值划分的依据。当水分含量高于此临界值时,物料中添加的水主要转化为挤压组织化产品中的冻结水或自由水。挤压蒸煮过程中,主要是冻结水或自由水对挤压过程和组织化产品的特性起作用;水分具有增塑、降黏、导热、熟化、辅助成型以及作为反应溶剂等作用。(3)高水分挤压组织化过程中,存在大量自由水,通过降低SPI在挤压机机筒内的黏度和停留时间,减小物料在挤压机内受到机械作用的大小,从而降低蛋白质亚基聚合交联的程度,增加二硫键与氢键、二硫键与疏水作用之间的协同作用以及7S/11S球蛋白比例,最终使挤压蛋白产品的颜色变浅,产品的纤维化程度提高。这可能是高水分挤压技术较中低水分挤压技术在生产纤维状蛋白模拟肉时更具优势的本质原因。更多还原

【Abstract】 Food extrusion is a multifactors process involving temperature, pressure, mechanical shear, etc. Water is the most important factor affecting successful extrusion operation and the structure and property formation of extrudate. Feed moisture content is the main basis for demarcating high-moisture extrusion and low-intermediate-moisture extrusion. Compared with the textured protein extruded at low-intermediate-moisture content, the meat analogue extruded at high-moisture content has been paid more attention due to its visual texture and fibrous structure resembling chicken breast. Therefor, the hypothesis of―membranous gas cavities‖was proposed to explain the formation mechanism for fibrous structure in high-moisture textured protein, in which the contribution of water change & role to forming the fibrous structure in final product has been emphasized. Inspired by previous related researches and the hypothesis of―membranous gas cavities‖, feed moisture content was separated from numerous extrusion process parameters to further analyze its effects during extrusion texturization for vegetable protein. The objectives of our research are to investigate the essential differences between high-moisture extrusion and low-moisture extrusion in producing protein meat analogue, and further to propose a mechanism model for explaining the forming process of fibrous structure for high-moisture textured vegetable protein.In this research, soybean protein isolate (SPI) was processed using a pilot-scale, co-rotating, intermeshing, twin-screw extruder typed DSE-25 (Brabender GmbH & Co., Germany) under 28-60% moisture content and 140-160℃cooking temperature. By means of on-line sensor detecting and theory model deduction, the effects of moisture content on system parameters such as motor torque, pressure drop, in-line viscosity, residence time distribution (RTD) and specific mechanical energy (SME) were analyzed. By using differential scanning calorimetry (DSC) and low field nuclear magnetic resonance (LF-NMR) techniques together, the change of water states and distribution in textured soybean protein (TSP) extruded under different conditions were investigated. By adopting multiplicate analysis methods and techniques such as sensory, texture, protein solubility, electrophoresis, infrared spectra etc., the effects of moisture content on the product properties (including appearance, texture, chemical cross-linking, protein subunits (7S/11S), protein secondary structure) were analyzed. After dead-stop operation, the samples from different zones of the extruder were obtained to explore the effects of moisture content on protein properties within the extruder barrel. Finally, the canonical correlation analysis between water with different states or mobility, system parameters, product texture and protein properties were investigated, and the specific roles of water with different sates or mobility during extrusion cooking were analyzed systematically. The main conclusions drawn from this research were listed as follows:(1) After extrusion process, soybean isolate protein (SPI) cross-linked and aggregated into macromolecule polymers, resulted in solubility decreasing. The structure of TSP was hold collectively by hydrophobic interactions, hydrogen bonds, disulfide bonds and their interactions, and the contribution of non-covalent bonds outweighed covalent bonds. The four kinds of protein secondary structure all existed in TSP, and the order of their relative percentage was:β-sheet,β-turn>unordered>α-helix.(2) The critical quantity of freezable or mobile water in SPI raw materials was 35%-38% (wet base), which may be the scientific basis of moisture boundary for demarcating low-intermediate moisture extrusion and high moisture extrusion. Above the critical quantity,the water added into the raw materials was mainly converted into the freezable or mobile water in final product. In the extrusion cooking pro- cess, it is the freezable or mobile water that affects the extrusion process and the properties of texturized product. Water performed several important functions such as plastification, reducing- viscosity, con- ducting-heat, cooking, shaping-assist and reaction reagent, etc.(3) There was plenty of freezable water in the texturization process for high moisture extrusion. Water could reduce the viscosity and residence time of SPI dough within extruder, decrease the effect of mechanical energy acting on melt dough, finally the color of extrudate was light. Increasing water content could reduce the degree of aggregation and cross-linking, increase the interactions between disulfide bonds and hydrogen bonds and between disulfide bonds and hydrophobic interactions, increase the ratio of 7S to 11S, consequently increase the degree of fiberization for TSP. These may be the essential reasons why high-moisture extrusion has unique advantage over low-intermediate-moisture extrusion to produce protein meat analogue with fibrous structure.更多还原