title: Enzymatic changes in pectic polysaccharides related to the beneficial effect of soaking on bean cooking time.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Departamento de Bioquímica, Facultad de Química, UNAM, México DF, Mexico.
authors: Enrique
authors: E
authors: Martínez-Manrique
authors: Carmen
authors: C
authors: Jacinto-Hernández
authors: Ramón
authors: R
authors: Garza-García
authors: Albino
authors: A
authors: Campos
authors: Ernesto
authors: E
authors: Moreno
authors: Irma
authors: I
authors: Bernal-Lugo