【作者】 甘晓玲；

【导师】 朱松明；

【作者基本信息】 浙江大学 ， 生物系统工程， 2012， 硕士

【摘要】 虾因其美味和营养丰富而备受大众喜爱。南美白对虾是世界上养殖产量最高的三种虾之一在我国南方也大量养殖。虾仁是优质蛋白和矿物质的来源,因此虾仁的产后加工引起了食品行业的广泛关注。超高压加工技术不同于传统热加工技术,可以保证食品的安全与质量,其应用前景广阔。目前,超高压技术被越来越多地应用于水产品的产后加工。本课题研究了超高压技术对虾仁颜色、硬度、pH、可溶性蛋白质含量的影响,并应用低场核磁共振技术分析虾仁的水分变化,利用凝胶电泳技术分析蛋白及其交联作用,最后对比了热处理与超高压处理对虾仁品质的影响。高压处理条件为100-600MPa,保压时间为3min、5min、10min,具体结果如下：1.与对照相比,超高压处理后虾仁的L*值增大、a*值减小。白度与总色差随压力的升高呈现增大趋势,其中200MPa-400MPa的增幅最明显。与对照相比,超高压处理使虾仁硬度增大,且硬度随压力上升而不断增大。而虾仁pH随着压力呈现先减小后增大的趋势。保压时间对虾仁理化性质的影响没有压力变化显著。2.低场核磁共振分析显示高压处理下虾仁弛豫时间缩短,水分子与蛋白分子的相互结合作用增强,水分流动性减弱。超高压处理显著降低了虾仁可溶性蛋白质的含量(P<0.01),而SDS对变性蛋白有很好的溶解性。SDS-PAGE对虾仁蛋白的分析表明超高压处理下虾仁蛋白质间的交联反应与分子间非共价键的形成有关,且非共价键的交联程度随压力增大而加剧。超高压处理后虾仁的水分变化与其它品质存在着不同程度的关联性。高压会引起水分分布及水分形式的改变,从而对蛋白结构造成影响,引起蛋白变性,而蛋白变性又会导致其它诸如颜色、硬度等物化性质发生改变。3.高于40℃的热处理使虾仁由透明转至不透明,50℃时开始变白,60℃处理后体表颜色变红。随着温度的升高,L*值逐步增大,a*、b*值先减小后增大,WI与△E整体呈增大趋势,而硬度与pH呈倒”S”型变化。热处理后虾仁不易流动水向结合水转化,水分流动性减弱。电泳结果表明,热处理的虾仁蛋白条带与对照相比有明显变化,随温度升高,蛋白质分子间非共价键交联程度加剧,60℃处理下低分子量的蛋白条带增多,而较高温度下部分蛋白通过分子间双硫键形成高分子聚合物。4.超高压与热处理都在不同程度上引起虾仁品质的改变,但高温引起的品质改变程度更大。超高压处理在一定程度上可以减少对虾仁颜色、蛋白质的改变,维持一定的pH值,减少水分损失,并延缓质构的改变。要达到相同程度的品质改变,超高压所需的能耗更少。作为一种环境友好型加工技术,将超高压技术应用于虾仁产后加工前景广阔。更多还原

【Abstract】 Shrimp is popular sea food for its delicious taste and rich nutrition. White shrimp (Penaeus Vannamei) is one of the top three high yield shrimp species in the world. It is also commonly cultured in South China. Shrimp meat is an excellent source of protein and minerals, so its post-harvest processing is of great interest to many researchers. High pressure processing (HPP), an alternative to traditional thermal processing, is considered a promising emerging technology for insuring food quality and safety. Recently, HPP is being increasingly used by the aquaculture as a post-processing technology.In this study, the effect of high pressure processing on the quality of white shrimp meat based on color, hardness, pH value, content of soluble-protein was studied. Low-field nuclear magnetic resonance (LF-NMR) technology was used to assay changes in water. Changes in protein and its crosslink was analyzed by electrophoresis technology. The differences of meat quality between HP-treated samples and heated ones were also compared. Shrimp samples were treated at different pressures (100-600 MPa) with various pressure holding time (3,5 or 10 min). The specific results are as follows:1. HP-treated samples had higher L* values but lower a* values compared to that of untreated samples. An increase in pressure resulted in an increase in whiteness (WI) and total color difference, more pronounced between 200-400 MPa. The hardness of shrimp meat presented an overall trend of increase with increasing pressures, while pH value decreased first and then increased. These results indicated that the variation of pressure holding time had less impact on the quality of shrimp meat than that of pressure.2. Analysis of the LF-NMR T2 relaxation data revealed that HP-treated sample has slower T2 relaxation time. Free water turning into bound water was also observed. These results indicated lower mobility of water due to enhanced interactions between water and protein molecules. HP induced a significant decrease (P<0.01) in protein solubility, while SDS has the power of solubilization for denatured protein. Electrophoresis analysis demonstrated that intermolecular cross-links by non-covalent bond enhanced with increasing pressures. Changes in water have a liner relationship with other qualities of shrimp meat. HP induced modification in water distribution and water phase existence, which had a compact on conformation of protein molecular. And protein denaturation will also influence physicochemical parameters, such as color and hardness.3. Temperature higher than 40℃gave the shrimp meat a brighter and less transparent appearance. Shrimp meat turned white at 50℃and the surface color turned red at 60℃.The whiteness (WI) and total color difference (ΔE) of shrimp meat showed an overall trend of increase with increasing temperature conditions. While the pH and hardness presented a change of inverted s-type. Immobilized water turned into bound water after heat treatment, indicating that the mobility of water become lower. Electrophoresis analysis demonstrated that intermolecular cross-links by non-covalent bond enhanced with increasing temperatures. Protein bands in low molecular weight area were more abundant in sample heated at 60℃. The aggregation of unfolded protein was induced by intermolecular disulfide bond at a higher temperature. 4. HPP and heat treatment caused quality changes in shrimp meat to different extent, while heat treatment resulted in a more sever impact. HPP can minimize the changes in color, water and protein denaturation, maintain pH value and texture. To obtain the same quality changes, energy consumption of high-pressure processing is much lower than that of conventional thermal processing. As an environment friendly technology, HPP has high potential for its application in post-harvest processing of shrimp meat.更多还原