牛乳热力学性质与时间-温度关系的实验研究

利用差示扫描量热仪(differentialscanningcalorimeter,DSC)测量了牛乳分别在4、10、15、25℃存放1～5d后的冰点、比热变化。研究结果表明,在4、10、15、25℃存放1d后,杯装牛乳的冰点由-0.13℃分别降到-0.22、-0.76、-1.62、-2.55℃。新鲜牛乳在4、10、15、25℃存放5d后,牛乳的比热(约56℃)由3.870J/g·℃增加至3.939、3.945、3.961、3.962J/g·℃。以牛乳存放4℃下1～5d后,各营养成分随存放时间的变化为例,对牛乳的比热进行了估算。牛乳比热的估算结果比牛乳比热(约56℃)实测值小。与新鲜牛乳比热相比,存放不同时间的牛乳比热(约56℃)实测值变化量与比热估算值的变化量之间的偏差在0.008J/g·℃。

This experimental study focused on investigating the relationships between milk thermodynamic characteristics and storage conditions by Differential Scanning Calorimeter （DSC）. Freezing point and specific heat of cup-packaged milk were obtained when stored at 4,10,15and 25℃ for one to five days. After one day stored at 4, 10, 15, 25℃, the freezing point decreases from -0.13℃ to -0.22, -0.76, -1.62, -2.55℃ , respectively. The specific heat of the milk stored at 4, 10, 15, 25℃ for five days, the specific heat （56℃） increases from 3.870 J/g·℃ to 3.939, 3.945,3.961,3.962 J/g ·℃, respectively. The specific heat was estimated by taking example from cup-packaged milk stored at 4℃ for one day to five days. The difference of the variation in specific heat between measurement （56℃） and estimate is less than 0.008 J/g·℃.