PRODUCTION, PURIFICATION AND CHARACTERIZATION OF PECTIN METHYLESTERASE (PME) FROM ARTHROBOTRYS OLIGOSPORA

Arthrobotrys oligospora, when grown in synthetic medium with pectin as sole carbon source, produced pectin methylesterase (PME) on the fourth day under static conditions at 25C. Through ammonium sulfate fractionation and successive chromatography on hydroxyapatite and Sephadex G-100 a 26.4 fold purification was achieved. PME was stable between pH values of 5–8. Its optimum activity was at pH 7.5 and at 37C. The energy of activation (E_a) was determined to be 11.9 kcal/mole. It had K_m of 0.9 mg/ml for pectin. The molecular weight of PME was found to be 50 kilo daltons by both Sephadex G-100 column chromatography and by SDS-PAGE. During electrophoresis PME appeared as a lipoprotein when prestained with sudan black-B.     

Oil-in-Water Emulsions Stabilized by Sodium Caseinate or Whey Protein Isolate as influenced by Glycerol Monostearate

Competitive adsorption between glycerol monostearate (GMS) and whey protein isolate (WPI) or sodium caseinate was studied in oil-in-water emulsions (20 wt % soya oil, deionized water, pH 7). Addition of GMS resulted in partial displacement of WPI or sodium caseinate from the emulsion interface. SDS-PAGE showed that GMS altered the adsorbed layer composition in sodium caseinate stabilized emulsions containing < 1.0 wt % protein. Predominance of β-casein at the interface in the absence of surfactant was reduced in the presence of GMS. The distribution of α-lactalbumin and β-lactoglobulin between the aqueous bulk phase and the fat surface in emulsions stabilized with WPI was independent of the concentration of added protein or surfactant.