Campbell R E, Gerard P D, Drake M A
Department of Food, Bioprocessing and Nutrition Sciences, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh 27695.
Department of Mathematical Sciences, Clemson University, Clemson, SC 29634.
J Dairy Sci. 2014 Mar;97(3):1225-32. doi: 10.3168/jds.2013-7236. Epub 2014 Jan 17.
The lactoperoxidase (LP) system may be used to achieve the desired bleaching of fluid whey with the addition of low concentrations (<50mg/kg) of hydrogen peroxide. The addition of an exogenous peroxidase (EP) to whey may also be used to aid in whey bleaching when the LP system is not fully active. The objectives of this study were to monitor LP activity in previously refrigerated or frozen milk, fluid whey, and whey retentate (10% solids) and to evaluate peroxidase activity in fluid whey and whey retentate (10% solids), with and without additional EP (2, 1, or 0.5 dairy bleaching units), over a range of pH (5.5-6.5) and temperatures (4-60°C). Subsequent experiments were conducted to determine the relationship between enzyme activity and bleaching efficacy. Raw and pasteurized milk, fat-separated pasteurized whey, and whey retentate (10% solids) were evaluated for LP activity following storage at 4 or -20°C, using an established colorimetric method. A response surface model was applied to evaluate both endogenous and EP activity at various temperatures and pH in freshly manufactured whey and retentate. Refrigerated or frozen storage at the parameters evaluated did not affect LP activity in milk, whey, or retentate. In fluid whey, with and without added EP, as pH decreased (to 5.5) and temperature increased (to 60°C), peroxidase activity increased. Retentate with EP exhibited behavior similar to that of fluid whey: as pH decreased and temperature increased, activity increased. However, in retentate without EP, as pH increased and temperature increased, activity increased. Enzyme activity was negatively correlated to bleaching time (time for >80% norbixin destruction) in fluid whey but a linear relationship was not evident in retentate. When fluid whey is bleached enzymatically, if pH is decreased and temperature is increased, the rate of reaction increases (e.g., bleaching occurs in less time). When bleaching in retentate, a higher pH (pH 6.5 vs. pH 5.5) is desired for optimal bleaching by the LP system. Due to processing restraints, this may not be possible for all dairy producers to achieve and, thus, addition of EP could be beneficial to improve bleaching efficacy.
乳过氧化物酶（LP）系统可通过添加低浓度（<50mg/kg）的过氧化氢来实现对液态乳清的理想漂白。当LP系统未完全激活时，向乳清中添加外源过氧化物酶（EP）也可用于辅助乳清漂白。本研究的目的是监测先前冷藏或冷冻的牛奶、液态乳清和乳清截留物（10%固形物）中的LP活性，并评估在一系列pH值（5.5 - 6.5）和温度（4 - 60°C）下，添加和不添加额外EP（2、1或0.5个乳制品漂白单位）的液态乳清和乳清截留物（10%固形物）中的过氧化物酶活性。随后进行实验以确定酶活性与漂白效果之间的关系。使用既定的比色法评估了生乳和巴氏杀菌乳、脱脂巴氏杀菌乳清以及乳清截留物（10%固形物）在4°C或 - 20°C储存后的LP活性。应用响应面模型评估新鲜制备的乳清和截留物在不同温度和pH值下的内源和EP活性。在所评估参数下的冷藏或冷冻储存并未影响牛奶、乳清或截留物中的LP活性。在添加和未添加EP的液态乳清中，随着pH值降低（至5.5）和温度升高（至60°C），过氧化物酶活性增加。添加EP的截留物表现出与液态乳清相似的行为：随着pH值降低和温度升高，活性增加。然而，在未添加EP的截留物中，随着pH值升高和温度升高，活性增加。酶活性与液态乳清中的漂白时间（>80%胭脂树素破坏所需时间）呈负相关，但在截留物中线性关系不明显。当对液态乳清进行酶法漂白时，如果pH值降低且温度升高，反应速率会增加（例如，漂白所需时间减少）。当在截留物中进行漂白时，LP系统进行最佳漂白需要较高的pH值（pH 6.5对pH 5.5）。由于加工限制，并非所有乳制品生产商都能实现这一点，因此，添加EP可能有助于提高漂白效果。
