Boatright William L, Lei Qingxin, Shah Jahan M
Department of Animal and Food Sciences, University of Kentucky, Lexington, Kentucky 40546-0215, USA.
J Agric Food Chem. 2009 Sep 9;57(17):7969-73. doi: 10.1021/jf900087v.
Using electron paramagnetic resonance (EPR) spectroscopy, the levels of carbon-centered radicals in retail samples of isolated soy protein (ISP), soy protein concentrate (SPC), and powdered soy milk were estimated to contain from 6.12 x 10(14) to 1.98 x 10(15) spins/g of soy product. Roasted soy nuts contained about 5.70 x 10(15) spins/g. The peak to peak line width of the carbon-centered radicals from soy nuts was about 10 gauss, whereas ISP samples with a similar peak height had a peak to peak line width of about 8 gauss. Retail snack bars containing ISP, SPC, and/or roasted soy nuts with a total protein content of either 13, 21, or 29% contained 5.32 x 10(14), 6.67 x 10(14), and 5.74 x 10(14) spins/g of snack bar, respectively. Levels of carbon-centered radicals in newly prepared samples of ISP were much lower than levels in the retail soy protein products and levels previously reported for commercial ISP and laboratory ISP samples. The levels of radicals in ISP samples increased over a 12-25 week period of storage in the dark at 22 degrees C and exposed to air from about 8.00 x 10(13) spins/g immediately after preparation to 9.95 x 10(14) spins/g of ISP. Storing the ISP samples under nitrogen at 22 degrees C greatly reduced the increase in radical content, whereas storing the ISP in 99.9% oxygen at 40 degrees C accelerated the formation of stable carbon-centered radicals. ISP samples hydrated at either 22 or 92 degrees C, rapidly frozen, and dried lost about 92% of the trapped radicals. The level of carbon-centered radicals in these same ISP samples immediately began to increase during subsequent storage exposed to the air and gradually returned to similar levels obtained before they were hydrated.
利用电子顺磁共振（EPR）光谱法，对分离大豆蛋白（ISP）、大豆浓缩蛋白（SPC）和豆奶粉零售样品中碳中心自由基的含量进行了估算，结果表明每克大豆制品中含有6.12×10¹⁴至1.98×10¹⁵个自旋。烤大豆坚果中约含有5.70×10¹⁵个自旋/克。大豆坚果中碳中心自由基的峰-峰线宽约为10高斯，而具有相似峰高的ISP样品的峰-峰线宽约为8高斯。总蛋白质含量分别为13%、21%或29%的含有ISP、SPC和/或烤大豆坚果的零售能量棒，每克能量棒中分别含有5.32×10¹⁴、6.67×10¹⁴和5.74×10¹⁴个自旋。新制备的ISP样品中碳中心自由基的含量远低于零售大豆蛋白产品中的含量以及先前报道的商业ISP和实验室ISP样品中的含量。在22℃黑暗中储存12 - 25周并暴露于空气中时，ISP样品中的自由基含量从制备后立即的约8.00×10¹³个自旋/克增加到9.95×10¹⁴个自旋/克。在22℃氮气环境下储存ISP样品大大减少了自由基含量的增加，而在40℃ 99.9%氧气环境下储存ISP则加速了稳定碳中心自由基的形成。在22℃或92℃水合、快速冷冻并干燥的ISP样品损失了约92%捕获的自由基。在随后暴露于空气中的储存过程中，这些相同ISP样品中碳中心自由基的含量立即开始增加，并逐渐恢复到水合前的相似水平。
