Ultracentrifugal and polyacrylamide gel electrophoretic studies of extractability and stability of almond meal proteins

Solubility and stability properties of almond proteins were determined usin g ultracentrifugation and gel electrophoresis to gain a better insight into the complexity of these proteins. Ultracentrifugal analyses of the water-e xtractable proteins of defatted almond meal revealed four fractions of 2S, 9S, 14S and 19S. The 14S fraction corresponds to amandin, the classical glo bulin isolated earlier, and constitutes 65-70% of the extractable proteins. Variation of ionic strength from 0 to 1.0 at pH 6-8 showed no evidence of association-dissociation reactions that are typical of many oilseed and leg ume proteins. Polyacrylamide gel electrophoresis of the water-extractable p roteins under reducing conditions separated two pairs of major polypeptides of 44 and 42 kDa and 27 and 25 kDa that appeared to be the respective acid ic and basic polypeptides of amandin corresponding to the classical legumin model. Sodium chloride had no effect on total protein extractability but v ariation of extraction pH showed a broad minimum in extractability at pH 3- 5. In contrast, when a pH 9 extract was lowered in pH, the minimum in prote in solubility was narrower and shifted upward to pH 5 largely as a result o f the precipitation of amandin. Interaction of amandin with phytate may exp lain the lower pH of minimum solubility when the meal was extracted directl y as opposed to lowering the pH of an alkaline extract. Amandin is a cryopr otein and was obtained in 90% purity by cooling a water extract of defatted meal. Incubation of a water extract of meal in the presence of azide for a bout 12 days revealed proteolytic nicking of the acidic polypeptides of ama ndin apparently as a result of attack by endogenous proteinase(s). (C) 1998 Society of Chemical Industry.