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Title:Effect of Ph Manipulation During Aqueous Extraction of Peanut Proteins
Author(s):Noor, Zuheid
Department / Program:Food Science
Discipline:Food Science
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Agriculture, Food Science and Technology
Abstract:The effect of extraction pH and heat treatment on soluble proteins, amino acid composition, gel electrophoretic properties, lipoxygenase, trypsin inhibitor and phytic acid were studied using Spanish Variety Commet type peanuts.
Absorbance at 280 nm and the difference between the absorbance at 215 and 225 nm were selected for rapid determination of soluble proteins. However, some factors brought about by pH adjustment may affect absorbance measurements. As expected, some differences were observed between the soluble protein values measured by these two methods.
Apparently, the protein-phytic acid complex begins to dissociate near pH 5. At higher than pH 6, extractability of phytic acid decreases, probably due to the formation of insoluble salts of phytic acid. No consistent effect of heating on the extractability of phytic acid was observed.
The solubility of proteins was low in the isoelectric region of pH 3, 4 and 5 but increased rapidly at lower and higher pH, reaching maximum of about 97% at pH 9 as measured by the difference between the absorbance at 215 and 225 nm.
In general, heating at 60(DEGREES)C for 30 minutes increases protein solubility. However, heating the pH 6 extract caused the pH to shift toward the isoelectric region, and lowered about 40% of its solubility as measured by absorbance at 280nm.
The nitrogen-to-protein conversion factors calculated from the anhydro amino acid data and assigning the free carboxylic acid residues equally to aspartate and glutamate, yielded values ranging from 5.52 to 5.72.
A total of 48 different components were observed in the polyacrylamide gel electrophoretic patterns. At least 16 components were found in each gel. All samples extracted on the alkaline side of pH 5, except the heated pH 6 sample, exhibited similar patterns, characterized by two major bands, 2nd-arachin dimer and 2nd-arachin monomer.
All samples extracted below pH 6 and the heated pH 6 sample exhibited different patterns from those above, characterized by less intensity of the slow moving components and greater intensity of the medium and fast moving components.
Maximum lipoxygenase activity measured at the optimum assay pH of 6 was found in the pH 7 extract with an activity of about 17.9 absorbance units/g. Below pH 6, the lipoxygenase activity diminished. Above pH 7, the lipoxygenase activity decreased and reached about 7.7 absorbance units/g at pH 9.
Heating at 60(DEGREES)C for 30 minutes destroyed most of the lipoxygenase activity. Heating the pH 7 extract at 80(DEGREES)C for 30 minutes completely inactivated the lipoxygenase. On the other hand, even after heating to 100(DEGREES)C for 30 minutes, residual lipoxygenase activity of about 2 absorbance units/g was still observed in the pH 2 and pH 9 extracts.
It was found that peanut trypsin inhibitor was quite stable to heat treatment, particularly at pH 6 and lower. However, about 50% of trypsin inhibitor was inactivated upon heating at 60(DEGREES)C for 3 minutes at pH 9. The highest trypsin inhibitor activity was observed in the heated pH 2 extract, but it was only about 1 TU1/mg.
Issue Date:1980
Description:197 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
Other Identifier(s):(UMI)AAI8026565
Date Available in IDEALS:2014-12-13
Date Deposited:1980

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