Vazquez-Landaverde P A, Qian M C, Torres J A
Dept. of Food Science and Technology, Oregon State Univ., Corvallis, OR 97331, USA.
J Food Sci. 2007 Sep;72(7):E389-98. doi: 10.1111/j.1750-3841.2007.00469.x.
Volatile formation in milk subjected to pressure-assisted thermal processing (PATP) was investigated from a reaction kinetic analysis point of view to illustrate the advantages of this technology. The concentration of 27 volatiles of different chemical class in milk subjected to pressure, temperature, and time treatments was fitted to zero-, 1st-, and 2nd-order chemical reaction models. Temperature and pressure effects on rate constants were analyzed to obtain activation energy (E(a)) and activation volume (deltaV*) values. Hexanal, heptanal, octanal, nonanal, and decanal followed 1st-order kinetics with rate constants characterized by E(a) values decreasing with pressure reflecting negative deltaV* values. Formation of 2-methylpropanal, 2,3-butanedione, and hydrogen sulfide followed zero-order kinetics with rate constants increasing with temperature but with unclear pressure effects. E(a) values for 2-methylpropanal and 2,3-butanedione increased with pressure, that is, deltaV* > 0, whereas values for hydrogen sulfide remained constant, that is, deltaV* = 0. The concentration of all other volatiles, including methanethiol, remained unchanged in pressure-treated samples, suggesting large negative deltaV* values. The concentration of methyl ketones, including 2-pentanone, 2-hexanone, 2-heptanone, 2-octanone, 2-nonanone, 2-decanone, and 2-undecanone, was independent of pressure and pressure-holding time. PATP promoted the formation of few compounds, had no effect on some, and inhibited the formation of volatiles reported to be factors of the consumer rejection of "cooked" milk flavor. The kinetic behavior observed suggested that new reaction formation mechanisms were not likely involved in volatile formation in PATP milk. The application of the Le Chatelier principle frequently used to explain the high quality of pressure-treated foods, often with no supporting experimental evidence, was not necessary.
从反应动力学分析的角度研究了压力辅助热处理（PATP）牛奶中挥发性物质的形成，以阐明该技术的优势。将经过压力、温度和时间处理的牛奶中27种不同化学类别的挥发性物质的浓度拟合到零级、一级和二级化学反应模型。分析温度和压力对速率常数的影响，以获得活化能（E(a)）和活化体积（deltaV*）值。己醛、庚醛、辛醛、壬醛和癸醛遵循一级动力学，其速率常数的特征是E(a)值随压力降低，反映出负的deltaV值。2-甲基丙醛、2,3-丁二酮和硫化氢的形成遵循零级动力学，其速率常数随温度升高，但压力影响不明确。2-甲基丙醛和2,3-丁二酮的E(a)值随压力增加，即deltaV > 0，而硫化氢的值保持不变，即deltaV* = 0。包括甲硫醇在内的所有其他挥发性物质在压力处理样品中的浓度保持不变，表明有很大的负deltaV*值。包括2-戊酮、2-己酮、2-庚酮、2-辛酮、2-壬酮、2-癸酮和2-十一烷酮在内的甲基酮浓度与压力和保压时间无关。PATP促进了少量化合物的形成，对一些化合物没有影响，并抑制了据报道是消费者拒绝“煮熟”牛奶风味因素的挥发性物质的形成。观察到的动力学行为表明，PATP牛奶中挥发性物质的形成不太可能涉及新的反应形成机制。经常用于解释压力处理食品高质量的勒夏特列原理的应用，通常没有支持性的实验证据，是不必要的。
