Kocherginsky Nikolai M, Kostetski Yuri Yu, Smirnov Alex I
Division of Bioengineering and Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 119260.
J Agric Food Chem. 2005 Feb 23;53(4):1052-7. doi: 10.1021/jf034787z.
Intensity of EPR spectra of stable organic free radicals, nitroxides, is decreasing with time if the radicals are dissolved in beer. The process is determined by a chemical reaction of nitroxide reduction by components naturally present in beer. Kinetics can be described as a simple irreversible first order with respect to both nitroxide and one reducing agent. Effective concentration of the reducing agent and the corresponding reaction rate constant has been determined. It is demonstrated that the nitroxide reduction is sensitive to the presence of solvent-accessible SH groups of proteins present in beer. It is proposed that quantitative analysis of reduction kinetics of small water-soluble nitroxide radicals such as TEMPO and TEMPOL can be used to assess the reducing power of beer. The effect of accelerated aging of beer achieved at elevated temperatures on nitroxide reduction kinetics is demonstrated.
如果稳定的有机自由基、氮氧化物溶解在啤酒中，其电子顺磁共振（EPR）光谱强度会随时间降低。该过程由啤酒中天然存在的成分对氮氧化物的还原化学反应所决定。动力学可以描述为相对于氮氧化物和一种还原剂均为简单的不可逆一级反应。已确定了还原剂的有效浓度和相应的反应速率常数。结果表明，氮氧化物的还原对啤酒中蛋白质的溶剂可及巯基的存在很敏感。有人提出，对诸如TEMPO和TEMPOL等小水溶性氮氧化物自由基还原动力学的定量分析可用于评估啤酒的还原能力。还展示了在高温下实现的啤酒加速老化对氮氧化物还原动力学的影响。
