Author
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Wolf, Walter |
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SATHE, SHRIDHAR - FLORIDA STATE UNIVERSITY |
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Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/31/1998 Publication Date: N/A Citation: N/A Interpretive Summary: The United States is the world's number one producer of almonds but nuts have generally been avoided by dieters because of their high fat content. Recent studies, however, indicate that consumption of nuts may be beneficial to health. Almonds, for example, contain phytochemicals that are being investigated for their health benefits. These studies included feeding almond proteins to humans to determine their potential role in promoting better health. Little is known, however, about the composition and other properties of the proteins that are important in conducting such studies. This cooperative study with Florida State University showed that almonds are unusual in they contain a protein that makes up almost 70% of the total protein. This protein can be prepared in high purity by simple procedures. Such preparations and information about their properties will be useful to other research workers assessing the health benefits of almonds, to food scientists studying almond and other plant proteins, as well as to food companies that use almonds and derived products. Technical Abstract: Solubility and stability properties of almond proteins were determined using ultracentrifugation and gel electrophoresis to gain a better insight into the complexity of these proteins. Ultracentrifugal analyses of the water-extractable proteins of defatted almond meal revealed four fractions of 2S, 9S, 14S and 19S. The 14S fraction corresponds to amandin, the classical globulin 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 legume proteins. Gel electrophoresis of the water extractable proteins separated two pairs of major polypeptides of 44 and 42 kDa and 27 and 25 kDa that appeared to be the respective acidic and basic polypeptides of amandin corresponding to the classical legumin model. Sodium chloride had no effect on protein extractability but variation 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 protein solubility was narrower and shifted upward to pH 5 largely as a result of the precipitation of amandin. Interaction of amandin with phytate may explain the lower pH of minimum solubility when the meal was extracted directly as opposed to lowering the pH of an alkaline extract. Amandin is a cryoprotein 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 about 12 days revealed proteolytic nicking of the acidic polypeptides of amandin apparently as a result of attach by endogenous proteinase(s). |
