Dept. of Food Science and Human Nutrition, Iowa State Univ., Ames, IA 50011-1061, USA.
J Food Sci. 2009 Oct;74(8):C581-7. doi: 10.1111/j.1750-3841.2009.01306.x.
Yolk contamination of egg white is a common problem in the egg breaking industry. Foaming properties of egg white protein are affected by such contamination, but proteins of basic nature may restore the foaming properties of the yolk-contaminated egg white protein. The purpose of this study was to chemically modify a soy protein, that is, to esterify the acidic groups on the protein and to study the potential of such modified protein in improving foaming. We showed that the modification changed the isoelectric point of soy protein isolate (SPI) from 4.5 to about 10. Sonication was proven to be a very effective means to redisperse the methanol-denatured soy protein during reaction, as shown by the improved solubility profile. Such modified basic protein, that is, the sonicated-modified SPI (SMSPI), when added to the yolk-contaminated (at 0.4% level, as-is basis) egg white, gave significantly improved foaming properties. We have shown that the slight change in pH due to the addition of SMSPI was not the reason for improved foaming performance; instead, the modified protein itself was the main reason for such improvement. Addition of SMSPI increased the foaming performance of both pure egg white and yolk-contaminated egg white. SMSPI consistently performed better than the unmodified SPI for improving foaming. Addition of SMSPI (16%, based on dry egg white, and 1.6% based on liquid egg white) fully restored foam expansion and foam liquid stability of 0.4% yolk-contaminated egg white, and it even out-performed the foaming of pure white protein. Therefore, a feasible solution to restore the foaming properties of yolk-contaminated egg white has been identified. It is expected that such modified SPI can be used as an additive or ingredient in foaming formulation, especially when the egg white protein is suspected of lipid contamination.
蛋清中的蛋黄污染是打蛋行业中的一个常见问题。这种污染会影响蛋清蛋白的起泡性能，但碱性蛋白可能会恢复受蛋黄污染的蛋清蛋白的起泡性能。本研究的目的是对大豆蛋白进行化学修饰，即将蛋白质上的酸性基团酯化，并研究这种修饰蛋白在改善起泡方面的潜力。我们发现，修饰改变了大豆分离蛋白（SPI）的等电点，从 4.5 左右变为约 10。超声被证明是一种非常有效的方法，可以在反应过程中重新分散甲醇变性的大豆蛋白，如溶解度谱所示。这种修饰的碱性蛋白，即超声改性的 SPI（SMSPI），当添加到受蛋黄污染的（在 0.4%水平，原样基础）蛋清中时，显著改善了起泡性能。我们已经表明，由于添加 SMSPI 导致的 pH 值的轻微变化不是起泡性能提高的原因；相反，修饰蛋白本身是改善起泡性能的主要原因。添加 SMSPI 增加了纯蛋清和受蛋黄污染的蛋清的起泡性能。SMSPI 在改善起泡方面始终比未修饰的 SPI 表现更好。添加 SMSPI（基于干蛋清的 16%，基于液体蛋清的 1.6%）完全恢复了 0.4%受蛋黄污染的蛋清的泡沫膨胀和泡沫液稳定性，甚至超过了纯蛋白的起泡性能。因此，已经确定了一种可行的解决方案来恢复受蛋黄污染的蛋清的起泡性能。预计这种改性 SPI 可以用作起泡配方中的添加剂或成分，特别是当蛋清蛋白怀疑受到脂质污染时。
