果品蔬菜射频烫漂护色及其分子细胞作用机理研究

Concentrated apple juice, dehydrated fruits and vegetables (FV), deep freeze FV and canned FV are the main products from fruits and vegetables. Blanching is an important operation when processing FV. There exist short backs of blanching FV with hot water or steam such as slow heat conduction, large loss of soluble nutrients, huge water wastage and difficulty of sewerage management. Similar to microwave, radio frequency (RF) is a no ionizing radiation with larger penetration depth. Heating uniformity, cellular morphology, texture, color change and kinetics of enzyme inactivation are the key issues facing FV blanching using RF energy. There appeared little research on the discipline of RF blanching, which is of urgent need to be revealed. In this project, inactivation kinetics of enzymes in solution and FV tissues，secondary structure change of enzyme protein would be studied using specially made cells for heating and circular dichroism (CD) spectra. Cellular morphology change is to be observed under fluorescent light conditions in an upright microscope. Damage of cell membrane is to be discovered with the help of atomic force microscope (AFM) and laser scanning confocal microscopy (LSCM). Damaging effects mechanism due to heat or non-thermal of RF to enzyme and cell will be explored. Control method of RF blanching of FV will be revealed. Heating uniformity will be studied using temperature measurement technology of infrared photography and Chemical Marker (CM). Fast RF blanching techniques of FV such as apple, potato and green bean will be optimized. This research work will provide a solid theoretical and technical support for the industrialized application of RF blanching of FV.

浓缩汁、脱水、速冻果蔬和罐头是主要的果蔬加工品。烫漂护色是果蔬加工中的一个重要工序。热水及蒸汽烫漂存在：传热速度慢、营养损失大、水消耗量巨大、污水处理困难等缺点。射频与微波类似，为非电离辐射，但穿透力更大。加热均匀性、细胞形态、质构、颜色变化和灭酶动力学是果蔬射频烫漂的关键问题，目前研究较少，规律有待揭示。本课题拟采用射频加热控制单元结合圆二色谱分析，研究射频对酶液及果蔬组织中酶的钝化动力学和酶蛋白二级结构的变化；采用荧光显微照相法观察细胞形态变化；采用原子力显微镜、激光扫描共聚焦显微镜研究细胞膜破损情况。探索射频对于酶及细胞的热或非热破坏作用机理，揭示基于射频加热的果蔬烫漂控制方法。获得射频烫漂对果蔬颜色和质构变化影响的动力学。采用红外和化学标记等测温技术，研究加热均匀性，获得苹果、马铃薯和豆角射频快速烫漂工艺。为果蔬射频烫漂技术工业化应用提供理论和技术支撑。

浓缩汁、脱水、速冻果蔬和罐头是主要的果蔬加工品。烫漂护色是果蔬加工中的一个重要工序。热水及蒸汽烫漂存在：传热速度慢、营养损失大、水消耗量巨大、污水处理困难等缺点。射频与微波类似，为非电离辐射，但穿透力更大。加热均匀性、细胞形态、质构、颜色变化和灭酶动力学是果蔬射频烫漂的关键问题，目前研究较少，规律有待揭示。研究内容和结果：（1）采用射频加热设备，研究了马铃薯块射频加热均匀性。结果表明：介电常数随温度升高先升高后降低，介电损耗因子随温度升高而增大。极板间距、物料高度和氯化钠溶液电导率对加热均匀性均有显著性影响(P<0.05)。（2）研究了板间距和电导率对加热速度及酶灭活效果的影响，进行了酶灭活动力学模型研究。结果表明：在极板间距120 mm，电导率0.1 S/m 时，射频加热105 s，PPO 的灭活率为91.88%。PPO 的灭活动力学曲线不符合一级反应动力学模型，Log-Logistic 模型能最好地拟合射频加热条件下多酚氧化酶的失活曲线。（3）研究了射频加热对于PPO相对酶活、重量、质构、颜色和微观结构的影响。结果表明：当射频加热到80°C时，纯的马铃薯PPO几乎全部失活。当物料温度达到85°C时，马铃薯块中的PPO活性降到10%。圆二色谱分析表明射频加热导致马铃薯块中的PPO二级结构发生改变，α螺旋含量降低。极板间距和加热温度对马铃薯块的重量、质构和颜色有显著性的影响。显微分析表明马铃薯细胞和淀粉粒都发生了变化。（4）对苹果片进行射频加热，采用扫描电子显微镜( SEM) 观察苹果片微观结构，揭示苹果片射频加热过程中理化特性变化的机理。结果表明：苹果片细胞破坏程度随着烫漂温度的升高而增大，升温速度越快苹果片细胞破坏越小。（5）比较热水、射频和热水辅助射频处理过程中苹果块的升温速率。研究PPO相对酶活、苹果块颜色、硬度、可溶性固形物（SSC）和多酚含量的变化。结果表明：苹果的介电常数和损耗因子均随频率的增加而下降，介电常数随温度的升高而下降，损耗因子随温度的升高而上升；边缘苹果块加热升温速率快，中间苹果块加热升温速率慢；苹果块中心温度至85℃时，PPO相对酶活降至20％以下；苹果块硬度、可溶性固形物和多酚含量均随温度的升高而降低。