High pressure processing (HPP), conducted at 400, 500 or 600 MPa for 15 min at 30 °C, of raw skim milk was studied in comparison to high-temperature short-time (HTST) pasteurization (72 °C for 15 s), considering protein denaturation and immunogenicity. HTST pasteurization least impacted denaturation of native proteins leading to mostly unchanged milk immunogenicity. HPP resulted in denaturation of whey proteins, mostly β-lactoglobulin (BLG) and immunoglobulin G (IgG), and disturbed structure of the casein micelle. HPP at 600 MPa caused protein aggregation, involving mainly BLG and κ-casein, through thiol disulphide interactions. α-Lactalbumin (ALA) was least denatured. The balance between expression of T helper (Th)1 and Th2 type cytokines, which is believed to regulate adverse immune response, was initially shifted toward Th1 with increasing high pressure, then the immunogenic capacity of milk proteins diminished at 600 MPa. This could be related to exposure of T cell-specific linear epitopes followed by unfolding of protein structure firstly and masking of them by protein aggregation subsequently with increasing high pressure.

Industrial relevance

HPP of raw milk has been well studied as an alternative process for conventional thermal pasteurization, based on inactivation of microorganisms and extension of shelf life. However, HPP can denature native milk proteins leading to altered immunogenicity. Three recommended HPP conditions and a commercial HPP method were assessed in comparison to HTST pasteurization considering impact on denaturation of milk proteins and milk immunogenicity. Scientific findings of the current study would guide the industry to identify HPP conditions that not only achieve the required level of microbial inactivation and shelf life, but also to establish desired levels of native properties of milk and milk immunogenicity.

中文翻译：

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牛脱脂乳的热巴氏灭菌和高压处理与天然乳蛋白的变性和免疫原性的比较

与高温短时（HTST）巴氏灭菌法（72°C持续15 s）相比，研究了脱脂牛奶在30°C下于400、500或600 MPa下进行15分钟的高压处理（HPP）。考虑蛋白质变性和免疫原性。HTST巴氏灭菌法对天然蛋白质变性的影响最小，从而导致牛奶免疫原性基本保持不变。HPP导致乳清蛋白（主要是β-乳球蛋白（BLG）和免疫球蛋白G（IgG））变性，并干扰酪蛋白胶束的结构。600 MPa的HPP通过巯基二硫键相互作用引起蛋白质聚集，主要涉及BLG和κ-酪蛋白。α-乳清蛋白（ALA）变性最少。T辅助（Th）1和Th2型细胞因子的表达之间的平衡被认为可以调节不良的免疫反应，最初，随着高压的增加，其向Th1转移，然后在600 MPa时乳蛋白的免疫原能力减弱。这可能与T细胞特异性线性表位的暴露有关，随后是蛋白质结构的首次折叠，随后随着高压的增加而被蛋白质聚集所掩盖。

行业相关性

基于微生物的灭活和延长保质期，对原奶的HPP作为常规热巴氏灭菌法的替代方法进行了深入研究。但是，HPP可使天然乳蛋白变性，从而导致免疫原性改变。考虑到对牛奶蛋白质变性和牛奶免疫原性的影响，与HTST巴氏灭菌法相比，评估了三种推荐的HPP条件和一种商业HPP方法。当前研究的科学发现将指导业界确定HPP条件，这些条件不仅可以达到所需的微生物灭活和保质期水平，而且可以确定牛奶的天然特性和牛奶免疫原性的所需水平。