Structural changes in casein aggregates under frozen conditions affect the entrapment of hydrophobic materials and the digestibility of aggregates
Structural changes in casein aggregates under frozen conditions affect the entrapment of hydrophobic materials and the digestibility of aggregates
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DOI：
10.1016/j.ces.2016.01.001
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发表时间：
2016-04
影响因子：
4.7
通讯作者：
K. Nakagawa;T. Jarunglumlert;S. Adachi
中科院分区：
文献类型：
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作者：
K. Nakagawa;T. Jarunglumlert;S. Adachi
在冷冻条件下老化后产生了可以捕获β-胡萝卜素的冻干酪蛋白纳米颗粒。研究了老化和模拟消化过程中发生的结构变化。由含有分散的β-胡萝卜素的酪蛋白酸钠溶液制备的酪蛋白颗粒的冻干样品成功地将这种分散体捕获在所得的冻干粉末中。包埋的β-胡萝卜素分布在这些干燥粉末的表面（表面负载）和内部（内部负载）之间。由于时效，内部载荷减少，而表面载荷同时增加。再水合酪蛋白颗粒的疏水性表明，由于老化过程，颗粒结构发生了变化。这些结构修饰增加了干燥样品的疏水性。当再水化时，这些疏水表面彼此重新结合以抵消疏水性的净增益。对冻融酪蛋白纳米颗粒的 SAXS 测量也表明形成了修饰的纳米和微米结构。这些改变的结构是通过冷冻和解冻以及簇之间或簇与冰之间的相互作用形成的。测量了模拟胃液中冻融样本的蛋白水解反应动力学。聚集程度和加工条件没有显着影响酪蛋白簇的消化动力学。然而，SAXS 分析表明这些条件影响消化过程中纳米和微观结构的形成。当聚集的酪蛋白簇暴露于胃条件下时，蛋白水解反应产生的断裂簇产生了 2-3 倍大的聚集体，具有由交联酪蛋白簇产生的中空网络和粗糙表面。加工条件，例如 pH 值和老化时间，可能会影响胃条件下这些纳米和微米结构的形成。如果结构修饰能够影响包埋材料的生物利用度，这些结果可能会提供令人兴奋的未来研究机会。
Freeze-dried casein nanoparticles that could entrap β-carotene were produced after aging under frozen conditions. Structural changes that occurred during aging and simulated digestion were investigated. Freeze-dried specimens of casein particles prepared from sodium caseinate solutions containing dispersed β-carotene successfully entrapped this dispersion in the resulting freeze-dried powders. The entrapped β-carotenes were distributed between the surface (surface load) and interior (inner load) of these dried powders. Because of aging, the amount of the inner load decreased while the surface load simultaneously increased. The hydrophobicity of rehydrated casein particles indicated that a change, caused by the aging process, occurred in particle structure. These structural modifications increased the hydrophobicity in the dried specimens. When rehydrated, these hydrophobic surfaces reassociated with each other to cancel the net gain in hydrophobicity. SAXS measurements on freeze-thawed casein nanoparticles also suggested the formation of modified nano- and microstructures. These modified structures were formed by freezing and thawing, along with interactions between clusters or between clusters and ice. The kinetics of the proteolytic reactions of the freeze-thawed specimens in a simulated gastric fluid were measured. The degree of aggregation and processing conditions did not significantly affect the digestion kinetics of the casein clusters. The SAXS analyses, however, suggested that these conditions affected nano- and microstructure formation during digestion. When the aggregated casein clusters were exposed to the gastric conditions, the fractured clusters produced by the proteolytic reactions produced 2–3 times larger aggregates with hollow networks and rough surfaces created by the crosslinked casein clusters. Processing conditions, such as pH and aging time, likely affected these nano- and microstructure formations under gastric conditions. These results may provide exciting future research opportunities if the structural modifications can impact the bioavailability of entrapped materials.