Departamento de Bioquímica, Facultad de Química, UNAM, México DF, Mexico.
J Sci Food Agric. 2011 Oct;91(13):2394-8. doi: 10.1002/jsfa.4474. Epub 2011 May 20.
Cooking time decreases when beans are soaked first. However, the molecular basis of this decrease remains unclear. To determine the mechanisms involved, changes in both pectic polysaccharides and cell wall enzymes were monitored during soaking. Two cultivars and one breeding line were studied.
Soaking increased the activity of the cell wall enzymes rhamnogalacturonase, galactanase and polygalacturonase. Their activity in the cell wall was detected as changes in chemical composition of pectic polysaccharides. Rhamnose content decreased but galactose and uronic acid contents increased in the polysaccharides of soaked beans. A decrease in the average molecular weight of the pectin fraction was induced during soaking. The decrease in rhamnose and the polygalacturonase activity were associated (r = 0.933, P = 0.01, and r = 0.725, P = 0.01, respectively) with shorter cooking time after soaking.
Pectic cell wall enzymes are responsible for the changes in rhamnogalacturonan I and polygalacturonan induced during soaking and constitute the biochemical factors that give bean cell walls new polysaccharide arrangements. Rhamnogalacturonan I is dispersed throughout the entire cell wall and interacts with cellulose and hemicellulose fibres, resulting in a higher rate of pectic polysaccharide thermosolubility and, therefore, a shorter cooking time.
豆类经浸泡后可缩短烹饪时间。然而，这一现象背后的分子机制仍不清楚。为了确定相关机制，本研究监测了浸泡过程中果胶多糖和细胞壁酶的变化。对两个品种和一个品系进行了研究。
浸泡提高了细胞壁酶鼠李半乳糖醛酸聚糖酶、半乳糖醛酸酶和多聚半乳糖醛酸酶的活性。细胞壁中这些酶的活性可通过果胶多糖化学成分的变化来检测。浸泡后，多糖中鼠李糖含量降低，半乳糖和糖醛酸含量增加。果胶部分的平均分子量在浸泡过程中降低。浸泡后，鼠李糖含量降低和多聚半乳糖醛酸酶活性与烹饪时间缩短相关（r = 0.933，P = 0.01 和 r = 0.725，P = 0.01）。
果胶细胞壁酶是浸泡过程中诱导半乳糖醛酸聚糖 I 和多聚半乳糖醛酸变化的原因，是赋予豆细胞壁新多糖排列的生化因素。半乳糖醛酸聚糖 I 分布在整个细胞壁中，与纤维素和半纤维素纤维相互作用，导致果胶多糖的热溶性更高，因此烹饪时间更短。
