【作者】 张汆；

【导师】 魏益民；

【作者基本信息】 西北农林科技大学 ， 食品科学， 2007， 博士

【摘要】 挤压组织化技术是一种较新的食品加工方法,以其高效、节能、环保等特点而广泛用于组织化植物蛋白的生产。中国是世界上花生产量和消费量最高的国家,年总产量已达1471万吨(2005),其中50%～65%用于加工食用花生油,每年产生约300多万吨脱脂花生饼粕,其中含有50%～70%的花生蛋白。花生饼粕色泽浅黄、气味芳香,其中的抗营养物质仅为大豆饼粕中的20%,是一种优质的植物蛋白资源。本文在研究各挤压参数对组织化花生蛋白产品质量影响的基础上,对其挤压参数进行了优化;分析了挤压参数对物料滞留时间的影响;低温脱脂花生粉原料特性对组织化花生蛋白产品质量和结构的影响;研究分析了原料中部分组分在挤压组织化过程中的变化;初步分析了低温脱脂花生粉挤压组织化过程中的美拉德反应及其产物;分析探讨了低温脱脂花生粉挤压组织化过程中纤维状组织结构的形成机理。主要结论如下:在低温脱脂花生粉挤压组织化过程中,挤压温度和喂料水分含量对组织化花生蛋白产品质量的影响最显著,其次是喂料速度和螺杆转速。挤压温度是低温脱脂花生粉组织化的关键因素,喂料水分含量则是影响纤维状组织化结构形成的重要因素,喂料速度和螺杆转速主要影响物料在挤压机内的滞留时间和混合。在本试验条件下,低温脱脂花生粉挤压组织化的最优参数组合为挤压温度为147.0℃～148.0℃,喂料水分含量为49.3%～50.9%,喂料量为9.5～10.4g/min,螺杆转速为95～112r/min。在本试验中,低温脱脂花生粉的平均滞留时间在5.28～10.56min范围内。喂料速度和喂料水分对平均滞留时间的影响最显著,其次是挤压温度和螺杆转速。挤压温度、喂料速度和喂料水分对滞留时间分布曲线的分布范围影响均较明显,螺杆转速的影响较小。物料在挤压机内的流动模式介于柱塞流动和完全混合流动两种模式之间,且随滞留时间的延长,曲线更接近于完全混合流动模式。在挤压组织化过程中,低温脱脂花生粉的原料特性,如蛋白质含量、粒径、pH值、油脂含量及其氮溶解指数均对组织化产品的感官质量、流变学性质及微观结构产生较明显的影响。当低温脱脂花生粉中低变性花生蛋白质含量低于40%时,不能形成具有良好纤维状组织结构的组织化花生蛋白产品。pH值4.5时,挤压产品硬度和咀嚼度达到最大; pH值7～10时,随原料碱性增强而降低。挤压物料中少量油脂(3%～6%)有利于低温脱脂花生粉组织化产品结构的改善和感官质量的提高。挤压后,花生蛋白的溶解性显著降低。十二烷基磺酸钠-聚丙烯酰胺凝胶电泳分析结果表明,构成花生蛋白的亚基共有12个,其相对分子质量分别为63.10、41.64、38.56、36.86、29.95、28.94、24.37、21.98、20.95、19.19、17.62和14.74kD。花生蛋白经挤压后并未发现有新的谱带生成。挤压前后的差示量热扫描图谱显示,花生蛋白起始变性温度为45.01℃,变性高峰温度为95.70℃,表明花生蛋白的热稳定性较高,其分子中可能含有较多的氢键。挤压组织化对低温脱脂花生粉中的碳水化合物(淀粉、小分子糖类)、油脂、氨基酸和矿物质等组分的理化性质有一定影响。在本试验条件下,淀粉除糊化外,一部分发生了降解,使其含量在挤压后有较显著地降低。随挤压温度的升高,游离脂和结合脂均会发生水解、氧化、聚合等反应,致使总脂肪含量降低。在低温脱脂花生粉的挤压过程中,损失较多的是一些含量较高的氨基酸,如谷氨酸、天冬氨酸、丙氨酸和精氨酸等,其中,赖氨酸损失不大(4.93%)。挤压后,产品中铁、锰和铜等元素含量分别增加了11.81%、2.31%和5.42%,主要是挤压过程中挤压机元件的磨损所致,其它元素的变化不大。低温脱脂花生粉挤压过程中美拉德反应产物的乙醚提取物经气相色谱-质谱联合分析后,共分离出33个峰,其中匹配度在60以上的峰共有23个。经分析共检出23种化合物,其中以中长碳链的脂肪酸或其酯(尤其是甲酯)为主,这些酯类物质主要来自低温脱脂花生粉中残留的油脂,也是花生制品特有香味的主要来源。低温脱脂花生粉中添加10%～20%的低温脱脂大豆粕对挤压产品的色度、外形和流变学特性有明显的改善作用,同时也提高了花生蛋白营养价值。氯化钙作为一种二价金属盐,在低温脱脂花生粉中的添加浓度较低时(<1.0%)会有助于挤压产品感官质量和组织结构的改善;当其浓度较高时(1.5%～2.0%)时,产品质量会迅速降低。添加0.2%～3.0%氯化钠对组织化花生蛋白产品质量和结构的影响不明显。低浓度的溴酸钾(10mg/kg)对低温脱脂花生粉的挤压组织化产品质量和结构有一定的改善效果,当浓度>30mg/kg时,挤压产品出现变形,表面变得粗糙,组织化程度降低。添加L-半胱氨酸不利于低温脱脂花生粉挤压组织化结构的形成。研究结果表明,非共价键结合(疏水作用和氢键)是影响花生蛋白高水分挤压组织化结构的主要化学键,其次是二硫键和离子键。在低温脱脂花生粉的挤压组织化过程中,花生蛋白质分子内原有的二硫键可能发生了少量的断裂,且高温可能会加速该反应的进行。此外,花生蛋白分子中维持一定数量的游离氨基,有助于增强蛋白质分子间的聚合作用,从而有利于组织化结构的形成。花生蛋白质中一定比例的长肽链蛋白质分子是组织化花生蛋白产品组织化结构形成所必需的。更多还原

【Abstract】 Extrusion cooking is new processing technology in food industry, it was widely used in processing of texturized plant protein products for its high efficiency, low energy consuming, and cleaning to environment. Peanut seed contained rich oil and protein, and provided plenty of oil and protein for human. China possessed the biggest yield and consumption of peanut seed in the world. The total yield of peanut seed is up to 14,710,000 tons in 2005, and 50%~65% of it was used to extract the edible peanut oil. The byproduct, that is defatted peanut meal, contains protein around 50%~70%. The defatted peanut meal is a good resource of plant protein for its pale color, pleasant smell, and containing fewer antinutrients, about 20% that of in soy bean.In this paper, the extrusion parameters for processing the texturized peanut protein (TPP) products were optimized through analyzing the effects of extrusion parameters on the quality of TPP, at first. Then, the effects of extrusion parameters on the resident time of feed in extruder were investigated. The effects of material characteristics on the qualities and structures of TPP products were studied in detail. The changes of some constituents in feed during the extrusion cooking processing of defatted peanut flour (PF) were also determined and analyzed. About the Maillard reaction and its products formed in extrusion cooking of PF were primarily investigated, too. The mechanisms of the fibrous structures formation during extrusion cooking of PF were analyzed and discussed The main conclusions of above researches as follows:Extrusion temperature and moisture content in feed have the most significant effects on the qualities of TPP products during the extrusion cooking of PF, and the effects of feed rate and screw speed are second. Extrusion temperature is the key parameter for PF can be texturized or not. While the effects of moisture content in feed is important condition for the texturized quality of TPP products. The roles of feed rate and screw speed are mainly about to the resident time of feed in the extruder, and therefore bring effects on the texturized structures and sensory qualities of TPP products. In the test conditions, the optimal extrusion parameters is 147.0℃～148.0℃, 49.3%～50.9%moisture content in feed, feed rate at9.5～10.4g/min and the screw speed at 95～112r/min. The mean residence time (MRT) is in the range of 5.28~10.56 min during the extrusion cooking of PF. the effects of feed rate and moisture content on the MRT is the most significant, and the effects of extrusion temperature and screw speed is the second. Extrusion temperature, feed rate and moisture content have more effects on the curve breadth of residence time distribution (RTD), the effect of screw speed is less. The MRT would be prolonged and get broader curve of RTD when decreasing feed rate and screw speed or increasing the extrusion temperature and moisture content in feed. There are evident interaction effects on MRT between extrusion temperature and moisture content, extrusion temperature and screw speed. The flow mode of the melt in extruder is between plug flow mode and perfect mixing flow mode, and the curve of RTD would be close to the perfect mixing flow mode with increasing the residence time of feed in extruder..The material characteristics of PF, such as protein content, size diameter, pH value, oil content and the nitrogen solubility index (NSI)of protein in feed have significantly effects on the sensory qualities, rheological properties and microstructures of TPP products. The TPP products don’t possess the good fibrous structure when protein content lower than 40% in feed. The TPP would keep proper hardness and chewiness, and have good texturized structures when PF size diameters in the range of 0.2~0.3mm. The hardness and chewiness of TPP products would be the highest at the pH 4.5; in the range of pH value 7~10, its would be lower increasing the pH value. Few of oil content (3%~6%) in feed is helpful to improving the structure and sensory qualities of TPP products. It is not proper to extrusion cooking when the NSI lower than 20% in PF.The solubility, structure of submits and thermodynamic property of peanut protein were obviously affected by the extrusion processing. The solubility of peanut protein sharply decreased after extrusion. The results of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that peanut protein molecule is composed of 12 submits, and its molecule weight were 63.10, 41.64, 38.56, 36.86, 29.95, 28.94, 24.37, 21.98, 20.95, 19.19, 17.62kD and14.74kD, respectively. Some of low molecule weight submits would be degraded at high extrusion temperature, such as 155℃. But there is no new brand present in the results of SDS-PAGE. The results of differential scanning calorimetry (DSC) of peanut protein before and after extrusion showed that the onset denature temperature of peanut protein is 45.01℃, top denature temperature is 95.70℃, and the results indicated that peanut protein possessed high stability and would be much hydrogen bonds in its molecules. The physicochemical characteristics of the carbohydrates (starch and small molecule sugars), lipids, amino acids and minerals in PF are also affected by the extrusion processing. In the test conditions, some starch molecules were degraded besides gelatinizing during extrusion, so the starch content in PF decreased significantly after extrusion. Some of small molecules sugars started to degrade even at low temperature (120℃), part of it changed into reducing sugars, and other part of it would be decomposed into smaller molecules, such as pigment or flavor substances. Free lipids and combined lipids in PF would be hydrolyzed, oxidized and aggregated, and lead to their content decreased in TPP products at high extrusion temperature. The amino acids losing much in extrusion are the high content amino acids in PF, such as glutamic acid, asparaginic acid, alanine and arginine et al. While the lysine losing is relatively little, only lose 4.93%, may be caused by the high moisture content (50%) in feed during extrusion. Some minerals, such as iron, manganese and copper, their contents increased 11.81%, 2.31% and 5.42%, respectively, after extrusion, which mainly originated from the extruder and screws. And the other minerals contents has no change. Moreover, the minerals content from elements of extruder would increase with the extrusion temperature increasing.Ether extractions from different extrusion samples were detected and analyzed by gas chromatographs-mass spectrometer (GC-MS) system. The results showed that the extractions exhibit 33 peaks, in which there are 23 peaks their match quality above 60, and 23 kinds of compounds were analyzed by GC-MS. The results indicated that the ether extraction are mainly composed of middle and long chain fatty acids or its esters, especially methyl esters. These esters mainly originate from the lipids in PF, and they play a main role in the special fragrant of peanut seed and its products.The 10%~20% addition of defatted soy meal in PF could improve the color, morphology and rheological properties of TPP products during extrusion cooking of PF, as well as increase the nutritional value of peanut protein of TPP products. As a kind of bivalent salts, lower level calcium chloride addition (<1.0%) is benefit to the sensory quality and structures of TPP products, but higher level addition (1.5%～2.0%) is harmful and make the sharply qualities decreased of TPP products. While, in the range of 0.2%~3.0% sodium chloride addition in PF have little effect on the quality of the TPP products. Low concentration potassium bromate (10mg/kg) addition in feed has definite effect on the quality and structure of TPP products. While, the TPP products appeared distortion in morphology, roughness in surface, and poor texturized degree when the potassium bromate addition above 30mg/kg. As well as addition of L-cysine in feed, even very low (0.01%), is harmful to the teturization of PF. The results indicated that the electrovalent and disulfide bonds may be not important to the formation of fibrous structure during PF extrusion cooking.The results of solubility test of peanut protein in different solvents showed that noncovalent bonds (hydrophobic interaction and hydrogen bond) play important roles in the formation of fibrous structures during PF high moisture extrusion cooking, and the effects of disulfide and electrovalent bonds are the second. Some of the disulfide bonds in the peanut protein molecules would be ruptured during extrusion texturization of PF, and the reaction would be accelerated at higher temperature. The total sulfhydryl group content in TPP products shows little change increasing the extrusion temperature. Moreover, it is benefit for enhancing the aggregation between protein molecules that possess certain number of free amino groups in the protein molecules, and this also helpful to the information of fibrous structure in TPP products. The results of SDS-PAGE indicated that it is necessary to the information of fibrous structure in TPP products that contain proper rate of long chain protein molecules in peanut protein material.更多还原