Effects of pH and the gel state on the mechanical properties, moisture contents, and glass transition temperatures of whey protein films
Effects of pH and the gel state on the mechanical properties, moisture contents, and glass transition temperatures of whey protein films
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DOI：
10.1021/jf981115d
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发表时间：
1999-05-01
影响因子：
6.1
通讯作者：
Hermansson, AM
中科院分区：
文献类型：
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作者：
Anker, M;Stading, M;Hermansson, AM
以山梨醇（S）为增塑剂，研究了不同pH值下乳清分离蛋白（WPI）膜的力学性能、含水量（MC）和玻璃化转变温度（T-g）。膜由加热的水溶液流延，并在23 ℃和50%相对湿度（RH）的气候室中干燥16小时。发现冷却水溶液的临界凝胶浓度（c（g））对于pH 7、8和9分别为11.7、12.1和11.3%（w/w）WPI。冷却速率影响c（g），因为当施加较慢的冷却速率时，需要较低量的WPI来实现凝胶化。本研究中使用的两种冷却速率均显示在pH 8时c（g）最大。在c（g）以上和c（g）以下改变WPI的浓度，阐明了聚合物网络对膜性能的影响。对于所有pH值，断裂应变（ε（B））在c（g）处显示出最大值，因此意味着在该浓度下形成关于膜拉伸能力的最有利结构。对于pH 7和8，杨氏模量（E）和断裂应力（σ（B））在c（g）处显示最大值。pH从7升高到9时，MC和pH值（B）增加，T-g降低。因此，对于pH 7、8和9，T-g值分别为-17、-18和-21 ° C。随着环境相对湿度的增加，E和σ（B）降低，σ（B）和厚度增加。WPI薄膜的厚度也随着WPI浓度的增加而增加。
The mechanical properties, moisture contents (MC), and glass transition temperature (T-g) of whey protein isolate (WPI) films were studied at various pH values using sorbitol (S) as a plasticizer. The films were cast from heated aqueous solutions and dried in a climate chamber at 23 degrees C and 50% relative humidity (RH) for 16 h. The critical gel concentrations (c(g)) for the cooled aqueous solutions were found to be 11.7, 12.1, and 11.3% (w/w) WPI for pH 7, 8, and 9, respectively. The cooling rate influenced the c(g), in that a lower amount of WPI was needed far gelation when a slower cooling rate was applied. Both cooling rates used in this study showed a maximum in the c(g) at pH 8. The influence of the polymer network on the film propel-ties was elucidated by varying the concentration of WPI over and under the c(g). Strain at break (epsilon(b)) showed a maximum at the c(g) for all pH values, thus implying that the most favorable structure regarding the ability of the films to stretch is formed at this concentration. Young's modulus (E) and stress at break (sigma(b)) showed a maximum at c(g) for pH 7 and 8. The MC and epsilon(b) increased when pH increased from 7 to 9, whereas T-g decreased. Hence, T-g values were -17, -18, and -21 degrees C for pH 7, 8, and 9, respectively. E and sigma(b) decreased and epsilon(b) and thickness increased when the surrounding RH increased. The thickness of the WPI films also increased with the concentration of WPI.