Mucilage of yellow mustard (Sinupis alba L.) exhibits completely different rheological behaviour, depending on where it has been extracted from. Whereas mucilage isolated from intact mustard seeds or from separated brans acts like many hydrocolloids (e. g. increasing viscosity significantly at low concentrations) these and related properties (i. e. shear thinning behaviour) are lost, once mustard seeds are processed. Mucilage extracted from processed mustard only raises viscosity slightly. Although the supernatant of processed mustard consists of 3-5 % mucilage (dry matter), it exhibits Newtonian flow. Changes of rheological properties of mustard mucilage were attributed to a change of molecular shape from an extended to a globular state due to processing. Chemical analysis has shown a significant raise of nitrogen content of mucilage after processing and during storage, indicating some chemical reaction taking place, possibly involving proteins.
Materials and methods
2.1 Chemicals
Citric acid trisodium salt dihydrate, dichloroisocyanuric acid sodium salt, dioxane, salicylic acid sodium salt, sodium nitroprusside dihydrate, 5-sulfosalicylic acid were obtained of analytical grade from Fluka, Neu-Ulm, Germany. Also Dextran standards were obtained there. Ammonium stock solution (1 g/l, certified), selenium catalyst, sodium chloride, sodium hydroxide, sulfuric acid (free of nitrogen) were obtained of analytical grade from Merck, Darmstadt, Germany. Isopropanol was obtained of reagent grade from Roth, Karlsruhe, Germany. Double-distilled or demineralized water was used to prepare aqueous solutions.