基于红外光谱分析巴氏杀菌乳贮藏期间蛋白质二级结构的变化

Analysis of the Secondary Structure of Pasteurized Milk Protein under Different Storage Conditions Based on Infrared Spectroscopy

巴氏杀菌乳因最大限度地保留了乳的营养物质和风味,深受国内外消费者的普遍青睐,然而,因其杀菌温度低、货架期很短,大大限制了大规模生产、远距离销售。其中,在贮运期间发生的蛋白质腐败性变质,是导致巴氏杀菌乳在贮运期间品质劣变的主要原因之一。在前期研究的基础上,结合蛋白质含量与氨基酸含量的分析,利用傅里叶变换红外光谱技术(FT-IR)分别对采集的不同贮藏温度和时间条件下的巴氏杀菌乳样品的蛋白质二级结构进行测定,并对不同巴氏杀菌乳样品的蛋白及其酰胺Ⅰ带及酰胺Ⅲ带进行了拟合,对不同贮藏温度和时间条件下的巴氏杀菌乳的蛋白质二级结构的变化规律进行进一步研究。结果表明:贮藏温度和时间对巴氏杀菌乳中蛋白质二级结构具有显著的影响,其中,在0℃和4℃贮藏条件下,巴氏杀菌乳乳清蛋白中的α-螺旋结构所占比例显著降低,无规卷曲结构所占比例显著上升,β-折叠、β-转角结构所占比例趋于稳定。而在15℃和25℃贮藏条件下α-螺旋结构的比例先下降后上升,总体来看,乳清蛋白二级结构随着贮藏时间的增加,由有序向无序转变。该结果表明了在不同贮藏条件下巴氏杀菌乳中蛋白质二级结构由有序向无序变化,二级结构的变化降低了巴氏杀菌乳在贮藏期间的营养价值。从蛋白质二级结构的角度来看,4℃的贮藏条件能更好保持巴氏杀菌乳的营养品质。

Pasteurized milk is widely favored by consumers at home and abroad because it retains the nutrients and flavor of milk to the utmost extent.However,due to its low sterilization temperature and short shelf life,it has greatly restricted large-scale production and long-distance sales.Among them,the deterioration of protein spoilage during storage and transportation is one of the main reasons leading to the deterioration of quality of pasteurized milk during storage and transportation.Based on the previous research,combined with the analysis of protein content and amino acid content,Fourier transform infrared spectroscopy(FT-IR)was used to separate the proteins of pasteurized milk samples under different storage temperatures and time conditions.Meanwhile the proteins of different pasteurized milk samples were fitted with their amide I and amide III bands.Under different storage temperatures and time conditions,the changes of protein secondary structure of pasteurized milk were studied.The results showed that storage temperature and time had a significant effect on the secondary structure of protein in pasteurized milk.Among them,under the storage conditions of 0℃ and 4℃,the proportion ofα-helical structure in pasteurized milk whey protein decreased significantly,and the proportion of random coil structure increased significantly.β-sheet andβ-turn structure The proportion tended to be stable.Under the storage conditions of 15℃and 25℃,the proportions ofα-helical structure decreased first and then increased.Overall,the secondary structure of whey protein changed from ordered to disorder with the increase of storage time.The results indicated that the secondary structure of protein in pasteurized milk changed from ordered to disorder under different storage conditions.Changes in secondary structure reduced the nutritional value of pasteurized milk during storage.From the perspective of protein secondary structure,storage conditions at 4°C can better maintain the nutritional quality of pasteurized milk.