School of Chemistry, Chemical Engineering and Biotechnology, Nanyang Technological University, Singapore 637459, Singapore.
Int J Mol Sci. 2024 Jun 8;25(12):6369. doi: 10.3390/ijms25126369.
A high alkaline pH was previously demonstrated to enhance the extraction yield of brewer's spent grains (BSG) proteins. The effects of extraction pH beyond the extraction yield, however, has not been investigated before. The present work examined the effects of extraction pH (pH 8-12) on BSG proteins' (1) amino acid compositions, (2) secondary structures, (3) thermal stability, and (4) functionalities (i.e., water/oil holding capacity, emulsifying, and foaming properties). The ideal extraction temperature (60 °C) and BSG-to-solvent ratio (1:20 /) for maximizing the extraction yield were first determined to set the conditions for the pH effect study. The results showed that a higher extraction pH led to more balanced compositions between hydrophilic and hydrophobic amino acids and higher proportions of random coils structures indicating increased protein unfolding. This led to superior emulsifying properties of the extracted proteins with more than twofold improvement between pH 8 and a pH larger than 10. The extraction pH, nevertheless, had minimal impact on the water/oil holding capacity, foaming properties, and thermal denaturation propensity of the proteins. The present work demonstrated that a high alkaline pH at pH 11-12 was indeed ideal for both maximizing the extraction yield (37-46 wt.%) and proteins' functionalities.
先前的研究表明，高碱性 pH 值可提高啤酒糟（BSG）蛋白的提取率。然而，之前并未研究过提取 pH 值超出提取率范围的影响。本研究考察了提取 pH 值（8-12）对 BSG 蛋白的（1）氨基酸组成、（2）二级结构、（3）热稳定性和（4）功能特性（即水/油保持能力、乳化和泡沫性能）的影响。首先确定了最佳提取温度（60°C）和 BSG 与溶剂比（1:20/），以最大限度地提高提取率，从而为 pH 值影响研究设定条件。结果表明，较高的提取 pH 值导致亲水和疏水氨基酸之间的组成更加平衡，无规卷曲结构的比例更高，表明蛋白质展开程度增加。这导致提取蛋白具有更好的乳化性能，在 pH 值 8 和大于 10 之间提高了两倍以上。然而，提取 pH 值对蛋白质的水/油保持能力、泡沫性能和热变性倾向的影响最小。本研究表明，高碱性 pH 值（pH 值 11-12）确实是同时最大化提取率（37-46wt.%）和蛋白质功能特性的理想选择。
