基于核磁共振技术分析奶酪在真空干燥中的水分迁移及货架期品质变化规律

Using Nuclear Magnetic Resonance to Detect the Cheese Moisture Transfer During Vacuum Drying and to Assess the Quality Changes During the Shelf Life

利用低场核磁共振及其成像技术分析奶酪真空干燥过程中的横向弛豫时间T2,分析峰面积A2x的变化,以揭示其内部水分迁移变化规律,建立奶酪水分变化动力学模型。以鲜牛乳为原料制作的直径4.8 cm、高1 cm、重20 g的奶酪块,置于50、60、70℃的温度下真空干燥,并于干燥2、3、4、5 h后取样,分析低场核磁共振横向弛豫时间(T2)和低场核磁成像;同时,对干燥样品置于37℃下进行7d的货架期加速实验,定期检测奶酪的蛋白质水解度、菌落总数、色差、质构、感官品质等指标变化。结果表明,真空干燥过程中,提高温度可显著提高干燥速率,加快结合水、不易流动水以及自由水的迁移。干燥过程中自由水和结合水先于不易流动水发生变化,水平衡的时间由330 min降到210 min。产品加速保藏过程中,细菌总数变化不显著;色差值L、a、b分别由92.75下降为91.78,a值由0.63上升到1.09,b值由13.25上升到15.08,ΔE则由93.69降低到93.13;随干燥的进行,奶酪的硬度明显增加(P<0.05),随着保藏时间延长,奶酪的感官品质基本保持不变,基本达到常温奶酪保藏流通的要求。

In order to study the regularity of internal moisture migration during the vacuum drying of cheese,low field nuclear magnetic resonance technology and imaging technology were used to analyze the lateral relaxation time T2 and the peak area A2x,and a kinetic model of cheese moisture change was established.Cheese made from fresh cow’s milk,cheese pieces with a diameter of 4.8 cm and a height of 1 cm and a weight of 20 g were placed at vacuum drying temperatures of 50,60,and 70℃,and samples are taken at 2,3 h,4 h,and 5 h respectively.Detection and analysis of low-field nuclear magnetic resonance transverse relaxation time(T2)and low-field nuclear magnetic resonance imaging;meanwhile,the dried samples were subjected to a 7 d shelf-life accelerated test at 37℃to study the protein hydrolysis degree,total number of colonies,color difference,and texture of cheese changes in sensory quality.The results showed that in the vacuum drying process,increasing the temperature can significantly increase the drying rate and accelerate the migration of bound water,immobilized water and free water.During the drying process,the free water and bound water changed before the immobilized water,and the water equilibrium time was reduced from 330 min to 210 min.After the free water was removed,the immobilized water and the bound water reached the maximum value in turn.As the drying progressed,the immobilized water was gradually removed,and then the bound water began to be removed to the end of drying.During the preservation process,the total number of bacteria did not change significantly;the color difference values L decreased from 92.75 to 91.78,a value increased from 0.63 to 1.09,the b value increased from 13.25 to 15.08,and theΔE decreased from 93.69 to 93.13.In cheese texture,the hardness of cheese was significantly increased(P<0.05).It can be seen in the sensory evaluation that as the preservation period is extended,the quality of the cheese remains basically unchanged.