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theses

Lipid co-oxidation of proteins was studied in peanut butter packaged in laminated MRE pouches; incubated at 25, 40, and 60 C for twelve weeks; and analyzed weekly for physical properties (moisture content, texture, color), lipid degradation (conjugated dienes, hydroperoxides, aldehydes, free fatty acids), and protein characteristics (solubility, intrinsic fluorescence, Schiff base fluorescence, SDS and native polyacrylamide gel electrophoresis, and protein carbonyl products). Changes in nearly all properties increased with incubation time and were more marked at 60 C than at the two lower temperatures. Among physical properties, peanut butter darkened and became redder with incubation and texture hardened and became less cohesive and more sticky and gummy. Less than 1% moisture was lost so texture changes were due to chemical modifications rather than dehydration. Values of conjugated dienes and hydroperoxides cycled (+/) with a three week periodicity; levels remained low and showed a net decrease during incubation. Low levels of aldehydes formed during the first few days of incubation at 60 C, then decreased thereafter; aldehydes did not accumulate at lower temperatures. In contrast, fatty acids increased to 3% at 60 C and 1% at lower temperatures, due at least in part to oxidation of aldehydes. Peanut proteins showed unique modification of surface residues that resulted in differential loss of Coomassie blue and silver dye binding, structural reorganization of arachins, and shifting of albumins and globulins to SDS-soluble fractions. Surface modifications resulted primarily from extensive protein oxidation revealed in antibody reactions, especially in the SDS-soluble fraction, although low levels of carbonyl-amine reactions (Schiff base or Michael addition) and some decarboxylation of acidic residues were also detected. Only limited disulfide and non-disulfide crosslinking was observed, but there was notable fragmentation or disassociation of arachins. Protein modifications followed the same cycling pattern as lipid oxidation, suggesting that lipid oxidation products did not accumulate because lipid radicals, hydroperoxides, and to a lesser extent aldehydes reacted preferentially with proteins, broadcasting oxidation to these non-lipid molecules. Hardening of the peanut butter appears to be directly related to surface modifications and structural reorganization of the proteins mediated by oxidized lipids.

ETD_4870

Ph.D.

Includes bibliographical references

by Wanzunairah Wanibadullah

doi:10.7282/T38S4MZ1

ETD doctoral

The author owns the copyright to this work.