离心除菌UHT乳贮藏期内乳蛋白组成的变化

Milk Protein Composition of Bactofugation UHT Milk During Storage

通过凯氏定氮法、高效液相色谱法和氨基酸分析仪研究了离心预除菌的UHT乳(C-UHT)和常规UHT乳(N-UHT)在常温6个月贮藏过程中乳蛋白和氨基酸成分的变化。热处理和贮藏过程中乳清蛋白质量浓度逐渐降低,非蛋白氮(NPN)质量分数逐渐增加,N-UHT和C-UHT的NPN质量分数从4.2%分别增加到8.7%和7.9%。热处理导致部分酪蛋白胶束解聚和酪蛋白组分进入了乳清相,乳清蛋白聚合进入胶束相,贮藏过程中这种作用持续进行。N-UHT和C-UHT中酪蛋白的解聚量分别为28.6%和22.6%,乳清蛋白的聚合量分别为8.5%和11.3%。热处理导致所有的乳蛋白组分发生了降解,贮藏过程中乳蛋白继续降解。N-UHT和C-UHT中总蛋白由39.81 g/L分别降解到29.57 g/L和31.42 g/L;游离氨基酸总量由原乳的31.4 mg/L增加到35.1~35.7 mg/L。C-UHT乳的乳蛋白降解和乳蛋白相转移程度显著低于N-UHT乳。

This study focuses on the effect on milk protein and amino acid compositions of bactofugation UHT milk(C-UHT)and normal UHT milk(N-UHT)during 6 months of storage at room temperature by Kjeldahl method,high performance liquid chromatography and amino acid analyzer.It was revealed that during heat treatment and storage,whey protein mass concentration decreased and non-protein nitrogen(NPN)mass fraction increased.NPN of N-UHT and C-UHT mass fraction increased from 4.2%to 8.7%and 7.9%respectively.During heat treatment,some depolymerized casein micelles migrated into the whey phase and the polymerised whey protein migrated into the micelle phase.The amount of depolymerized casein in N-UHT and C-UHT was 28.6%and 22.6%respectively,and the amount of polymerized whey protein was 8.5%and 11.3%respectively.Heat treatment degraded all milk protein components and this degradation continued during storage.The total protein in N-UHT and C-UHT was degraded from 39.81 g/L to 29.57 g/L and 31.42 g/L respectively,and the total free amino acids increased from 31.4 mg/L to 35.1~35.7 mg/L.The degree of milk protein degradation and phase transfer of CUHT milk was significantly lower than that of N-UHT milk.