Mechanism of pressure-induced hardening and optimization for the hardness control of vegetables

据报道，蔬菜、水果和豆类通过低温热烫、干燥、加盐和储存而变硬，并且在这些预处理之后在99.5 ℃下烹饪时它们的软化被抑制。我们已经发现，诸如日本萝卜之类的根菜类蔬菜通过施加几百Mpa的高压而硬化，并且即使在压力已经释放之后，这种硬化过程仍在继续。细胞膜被破坏的压力处理，并在果胶的酯化度降低。这种压力诱导硬化的机制不能仅用果胶酯化程度的降低来解释。有人认为，一些其他因素促成了硬化。通过压力处理和在压力释放后静置长达11小时来增加硬度。pH值降低，水溶性蛋白减少，碱不溶性蛋白增加， ...更多信息 观察n个加压样品。果胶和纤维素的量不因加压或压力释放后静置而改变。半纤维素I和略有下降，而半纤维素II增加。由于半纤维素II具有比半纤维素I更强的氢键，因此已经提出半纤维素II的增加将导致细胞壁强度的增强。果胶中钙离子浓度增加，半纤维素I和II中钙离子浓度降低，而半纤维素II中钾离子浓度降低。镁离子主要存在于果胶中，其浓度不随加压或减压后静置而变化，提出了几百Mpa压力下的硬化机理是导致细胞膜完整性的丧失。这允许细胞内钾离子扩散到细胞壁中，并且随后是果胶的酶促脱甲基化和随后在钙离子和游离羧基之间形成桥键。蛋白质通过加压变性导致不溶性蛋白质的增加。由于压力处理导致的细胞膜塌陷的传质过程被认为是通过改变组织组分如果胶、半纤维素和蛋白质之间的相互作用而在静置期间引起硬化。少

It has been reported that vegetables, fruits and beans are hardened by low temperature blanching, drying, addition of salt and storage, and that their softening during cooking at 99.5℃ after these pretreatments are suppressed. We have found that such root vegetables as Japanese radish are hardened by the application of a high pressure of several-hundred Mpa, and that this hardening process continues even after the pressure has been released. The cell membranes were destroyed by the pressure treatment, and a decrease in the degree of esterification of pectins followed. The mechanism for this pressure-induced hardening could not be explained only in terms of the decreased degree of pectin esterification. It was suggested that some other factors contributed to the hardening. The hardness was increased by the pressure treatment and by standing for up to 11 hours after the pressure had been released. A decrease in pH, derease in water-soluble protein, and increase in alkali-insoluble protei … More n of the pressurized samples were observed. The quantities of pectin and cellulose were not changed by pressurization or by standing after the pressure had been released. Hemicellulose I and slightly decreased, whereas hemicellulose II was increased. Since hemicellulose II has stronger hydrogen bonds than hemicellulose I, it has been suggested that the increase in hemicellulose II would lead to reinforcement of the strength of the cell wall. The concentration of calcium ions increased in pectin and decreased in hemicellulose I and II, while the concentration of potassium ions decreased in hemicellulose II. Magnesium ions existed mainly in pectin, and their concentration was not changed by pressurization or by standing after the pressure had been released.The mechanism for hardening under a pressure of several-hundred Mpa is proposed to lead to a loss of integrity of the cell membrane. This allows the diffusion of intracellular potassium ions into the cell walls, and is followed by the enzymic demethylation of pectins and the subsequent formation of bridge bonds between the calcium ions and free carboxyl groups. Protein denaturation by pressurization causes an increase in insoluble protein. A mass transfer process followed by collapse of the cell membranes due to the pressure treatment are considered to cause hardening during standing by changing the interaction among tissue components such as pectin, hemicelluloses and proteins. Less