Liu KeShun, Hsieh Fu-Hung
Grain Chemistry and Utilization Laboratory, National Small Grains and Potato Germplasm Research Facility, Agricultural Research Service, US Department of Agriculture, 1691 South 2700 West, Aberdeen, Idaho 83210, USA.
J Agric Food Chem. 2008 Apr 23;56(8):2681-7. doi: 10.1021/jf073343q. Epub 2008 Mar 18.
Soy protein, mixed with gluten and starch, was extruded into fibrous meat analogues under high-moisture and high-temperature conditions. The protein solubility of samples collected at different extruder zones and extrudates made with different moistures was determined by 11 extraction solutions consisting of 6 selective reagents and their combinations: phosphate salts, urea, DTT, thiourea, Triton X-100, and CHAPS. Protein solubility by most extractants showed decreasing patterns as the material passed through the extruder, but the solution containing all 6 reagents, known as isoelectric focus (IEF) buffer, solubilized the highest levels and equal amounts of proteins in all samples, indicating that there are no other covalent bonds involved besides disulfide bonds. With regard to relative importance between disulfide bonds and non-covalent interactions, different conclusions could be made from protein solubility patterns, depending on the type of extracting systems and a baseline used for comparison. The observation points out pitfalls and limitation of current protein solubility methodology and explains why controversy exists in the literature. Using the IEF buffer system with omission of one or more selective reagents is considered to be the right methodology to conduct protein solubility study and thus recommended. Results obtained with this system indicate that disulfide bonding plays a more important role than non-covalent bonds in not only holding the rigid structure of extrudates but also forming fibrous texture. The sharpest decrease in protein solubility occurred when the mix passed through the intermediate section of the extruder barrel, indicating formation of new disulfide bonds during the stage of dramatic increase in both temperature and moisture. After this stage, although the physical form of the product might undergo change and fiber formation might occur as it passed through the cooling die, the chemical nature of the product did not change significantly.
大豆蛋白与面筋和淀粉混合，在高水分和高温条件下挤压成纤维状肉类替代品。用由6种选择性试剂及其组合（磷酸盐、尿素、二硫苏糖醇、硫脲、吐温X-100和3-[(3-胆酰胺丙基)二甲基铵]-1-丙磺酸）组成的11种提取溶液，测定在不同挤出机区域收集的样品以及用不同水分制成的挤出物的蛋白质溶解度。随着物料通过挤出机，大多数提取剂的蛋白质溶解度呈下降趋势，但含有所有6种试剂的溶液（即等电聚焦（IEF）缓冲液）能溶解所有样品中最高水平且等量的蛋白质，这表明除二硫键外不存在其他共价键。关于二硫键和非共价相互作用之间的相对重要性，根据提取系统的类型和用于比较的基线，从蛋白质溶解度模式可以得出不同结论。该观察结果指出了当前蛋白质溶解度方法的缺陷和局限性，并解释了文献中存在争议的原因。使用省略一种或多种选择性试剂的IEF缓冲系统被认为是进行蛋白质溶解度研究的正确方法，因此被推荐。用该系统获得的结果表明，二硫键不仅在维持挤出物的刚性结构方面，而且在形成纤维质地方面比非共价键起着更重要的作用。当混合物通过挤出机机筒的中间部分时，蛋白质溶解度下降最为明显，这表明在温度和水分急剧升高的阶段形成了新的二硫键。在此阶段之后，尽管产品的物理形态可能会发生变化，并且在通过冷却模头时可能会形成纤维，但产品的化学性质没有明显变化。
