INTERACTION OF PYRIDOXAL AND PYRIDOXAL PHOSPHATE WITH PEPTIDES IN A MODEL FOOD SYSTEM DURING THERMAL PROCESSING

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Abstract
A soluble model system was utilized to study the interactions of pyridoxal (PL) and pyridoxal phosphate (PLP) with proteins during the thermal processing of foods. Heat stable peptides, rather than intact proteins, were used in the model system to maintain solubility and permit subsequent evaluation of the peptide binding of the B6 vitamers. Ultraviolet and visible difference spectra and fluorescence emission spectra confirmed the binding of PL and PLP to the peptides during processing. Total peptide‐bound PLP (as the sum of Schiff base, pyridoxylamino, and substituted aldamine derivatives) comprised about 21% of the model system PLP. Approximately 60% of the peptide‐bound PLP was bound via nonreducible linkages, suggesting the possible formation of biologically unavailable pyridoxylamino complexes. The acid stability of the PLP complexes, tested to simulate gastric conditions, indicated that most of the nonreducible bound PLP was in the form of pyridoxylamino complexes. Therefore, approximately 10% of the model system PLP was rendered biologically unavailable during these process conditions. The presence of ascorbic acid and/or glucose in the model systems had no significant effect on the extent or manner of peptide‐binding of the B6 vitamers; however, glucose‐induced browning appeared to slightly inhibit pyridoxylamino complex formation. The results of this study indicate that losses of vitamin B6 bio‐availability during thermal processing may be lower than previously reported.

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