乳样保存条件对乳尿素氮浓度测定的影响

Effect of Preservation Conditions on the Concentration of Milk Urea Nitrogen

研究了3种常用的防腐剂(重铬酸钾、苯甲酸钠和山梨酸钾)以及室温、冷藏和冷冻等3种不同温度的保存条件对牛奶中乳尿素氮浓度测定的影响。结果表明,添加常规剂量和加倍剂量重铬酸钾乳样的尿素氮浓度与原乳样差异不显著(P>0.05),而添加行业标准量及加倍剂量苯甲酸钠、山梨酸钾的乳样中乳尿素氮浓度显著高于原乳样(P<0.05);室温和冷藏温度条件下随保存时间的延长,原乳样乳尿素氮浓度迅速降低,而冷冻保存条件下原乳样乳尿素氮浓度基本不变;添加重铬酸钾的乳样在室温、冷藏和冷冻条件下,随着保存时间的延长乳尿素氮浓度均无明显变化。乳样收集后若不能及时测定乳尿素氮浓度,建议添加重铬酸钾防腐剂,未添加重铬酸钾时冷冻保存。

The impacts of three commonly used preservatives（potassium dichromate,sodium benzoate,potassium sorbate） at different temperatures（room temperature,chilled and frozen） on the determination of the concentration of milk urea nitrogen（MUN） were studied comparatively.The results showed that the concentration of MUN with potassium dichromate of conventional dose or doubling dose had no significant difference with the original milk sample（P〈0.05）,the concentration of MUN with sodium benzoate and potassium sorbate of conventional dose or doubling dose was significantly higher than the original milk sample（P〈0.05）,preservation at room temperature or chilled would make the concentration of MUN reduce rapidly with the time extended,preservation at frozen would made the concentration of MUN remain in the initial level,the milk sample with potassium at room temperature,chilled and frozen conditions,the concentration of MUN had no significant change.Once the sample could not be analyzed immediately after being collected,it was proposed that the potassium dichromate to be added or frozen method to be used when the potassium dichromate wasn＇t added.