Dept. Food Science and Technology, Univ. of California, Davis, CA, USA.
J Food Sci. 2010 Sep;75(7):E417-25. doi: 10.1111/j.1750-3841.2010.01766.x.
Proton nuclear magnetic resonance (¹H-NMR) relaxometry was used to study the effects of high pressure and thermal processing on membrane permeability and cell compartmentalization, important components of plant tissue texture. High pressure treated onions were subjected to pressure levels from 20 to 200 MPa at 5 min hold time at initial temperatures of 5 and 20 °C. Thermally treated onions were exposed for 30 min at temperatures from 40 to 90 °C. Loss of membrane integrity was clearly shown by changes in transverse relaxation time (T(2)) of water at temperatures of 60 °C and above. Destabilization effects on membranes exposed to high pressure were observed at 200 MPa as indicated by T(2) measurements and cryo-scanning electron microscopy (Cryo-SEM). T(2) relaxation successfully discriminated different degrees of membrane damage based on the T(2) shift of the vacuolar component. Analyses of the average water self-diffusion coefficient indicated less restricted diffusion after membrane rupture occurred in cases of severe thermal treatments. Milder processing treatments yielded lower average diffusion coefficients than the controls. ¹H-NMR proved to be an effective method for quantification of cell membrane damage in onions and allowed for the comparison of different food processes based on their impact on tissue integrity.
质子磁共振（¹H-NMR）弛豫测量法被用于研究高压和热加工对细胞膜通透性和细胞区室化的影响，这些是植物组织质地的重要组成部分。经过高压处理的洋葱在初始温度为 5 和 20°C 时，在 5 分钟的保持时间内，接受 20 至 200 MPa 的压力水平处理。经过热处理的洋葱在 40 至 90°C 的温度下暴露 30 分钟。在 60°C 及以上的温度下，水的横向弛豫时间（T（2））的变化明显表明了细胞膜完整性的丧失。在 200 MPa 下，对暴露于高压的膜的破坏作用通过 T（2）测量和冷冻扫描电子显微镜（Cryo-SEM）观察到。T（2）弛豫根据液泡成分的 T（2）位移成功区分了不同程度的膜损伤。基于膜破裂后水自扩散系数的平均分析，在严重热处理的情况下，扩散受到的限制较小。较温和的处理比对照产生更低的平均扩散系数。¹H-NMR 被证明是定量洋葱细胞膜损伤的有效方法，并允许根据其对组织完整性的影响比较不同的食品加工方法。
