Jiménez-Guzmán J, Cruz-Guerrero A E, Rodríguez-Serrano G, López-Munguía A, Gómez-Ruiz L, García-Garibay M
Departamento de Biotecnología, Universidad Autónoma Metropolitana, Mexico City DF, Mexico.
J Dairy Sci. 2002 Oct;85(10):2497-502. doi: 10.3168/jds.S0022-0302(02)74332-4.
The effects of heat treatments of milk and whey prior to lactose hydrolysis with Kluyveromyces lactis beta-galactosidase were studied. It was observed that heat treatment of milk significantly increases lactase activity, with a maximum activity increase found when milk was heated at 55 degrees C. In whey from 55 up to 75 degrees C, beta-galactosidase activity decreased slightly. Nevertheless, heating whey at 85 degrees C for 30 min raised the rate of hydrolysis significantly. Electrophoretic patterns and UV spectra proved that the activity change correlated with milk protein denaturation, particularly that of beta-lactoglobulin. Heating whey permeate did not increase the enzyme activity as heating whole whey; but heating whey prior to ultrafiltration also resulted in enzyme activation. Measurement of free sulfhydryl (SH) groups in both whey and heated whey permeate showed that the liberation of free SH is highly correlated to the change of the activity. Furthermore, this activation can be reversed by oxidizing the reactive sulfhydryl groups, proving that the observed effect may be related to the release of free SH to the medium, rather than to the denaturation of a thermolabile protein inhibitor.
研究了用乳酸克鲁维酵母β-半乳糖苷酶水解乳糖之前，对牛奶和乳清进行热处理的效果。观察到牛奶的热处理显著提高了乳糖酶活性，当牛奶在55℃加热时，活性增加最大。在55℃至75℃的乳清中，β-半乳糖苷酶活性略有下降。然而，将乳清在85℃加热30分钟显著提高了水解速率。电泳图谱和紫外光谱证明，活性变化与牛奶蛋白变性有关，尤其是β-乳球蛋白的变性。加热乳清渗透物并没有像加热全乳清那样提高酶活性；但在超滤之前加热乳清也会导致酶活化。对乳清和加热后的乳清渗透物中游离巯基（SH）的测量表明，游离SH的释放与活性变化高度相关。此外，通过氧化反应性巯基可以逆转这种活化，证明观察到的效果可能与向培养基中释放游离SH有关，而不是与热不稳定蛋白抑制剂的变性有关。
