Abstract: The effects of heat sterilization and microwave sterilization on the stability and casein structure of fresh camel milk were compared. The microwave sterilization conditions were optimized using single factor experiments and response surface methodology based on Box-Behnken design. Changes in the structure and properties of camel milk casein after sterilization were investigated using a differential scanning calorimeter, a Fourier transform infrared spectrometer, and a scanning electron microscope. The centrifugal sedimentation rate of protein and the total number of colonies were taken as response variables, the optimum conditions were determined as follows: pH 7.0, microwave power 560 W and microwave irradiation time 120 s. After microwave treatment under these conditions, the centrifugal sedimentation rate of protein was 6.96%, and no bacterial colonies were detected. Differential scanning calorimetry (DSC) plot showed that microwave treatment resulted in higher enthalpy of camel milk casein compared with heat sterilization, indicating a lower degree of denaturation and higher stability. The results of scanning electron microscopy showed that both sterilization methods destroyed the micellar structure of casein to varying degrees, resulting in cross-linking and aggregation. However, after microwave sterilization, the casein showed ordered aggregation, forming small aggregates that assembled into an ordered network structure. Appropriately increasing the pH of camel milk before sterilization was conducive to its stability. Different sterilization methods had a significant effect on the secondary structure of camel milk casein. Both microwave and heat sterilization reduced the relative contents of α-helix and β-turn in the casein. The relative content of β-sheet in heat-sterilized camel milk casein was the highest, indicating the most significant change in the secondary structure of the protein.In summary, this study revealed the stability of camel milk and the structural change of camel milk casein under different sterilization conditions, which can help address the poor stability of thermally sterilized camel milk at this stage.

Key words: camel milk; microwave sterilization; casein structure; stability

摘要： 以新鲜驼乳为原料，比较加热杀菌与微波杀菌对驼乳稳定性及酪蛋白结构的影响。设计单因素试验和Box-Behnken响应面试验，通过双响应值联合优化驼乳微波杀菌工艺条件。采用差示扫描量热仪、傅里叶变换红外光谱仪、扫描电子显微镜分析驼乳酪蛋白结构与特性变化。以蛋白离心沉淀率和菌落总数为评价指标，确定驼乳微波杀菌最佳工艺条件为pH 7.0、微波功率560 W、微波时间120 s，此时蛋白离心沉淀率为6.96%，菌落总数未检出。差示扫描量热图谱显示，与加热杀菌驼乳酪蛋白相比，经微波杀菌的驼乳酪蛋白热焓较高，说明此处理条件下酪蛋白变性程度较小，稳定性更高。扫描电子显微镜观察结果显示，微波杀菌和加热杀菌均会不同程度破坏酪蛋白胶束结构，诱发交联和聚集，但微波杀菌后的驼乳酪蛋白呈现有序聚集，颗粒聚集体较小，且形成有序的网状结构。适当提高原料乳pH值后进行杀菌有利于产品体系稳定。不同杀菌方式处理对驼乳酪蛋白二级结构有显著影响，微波杀菌和加热杀菌均使酪蛋白的α-螺旋和β-转角相对含量减少，经加热杀菌的驼乳酪蛋白β-折叠相对含量最高，说明此时蛋白二级结构变化最显著。综上，本研究揭示了不同杀菌条件下驼乳稳定性及酪蛋白结构变化规律，能够较好地解决现阶段热杀菌驼乳稳定性差的问题。

关键词: 驼乳；微波杀菌；酪蛋白结构；稳定性