CROSSPY

Hofmann et al.361 have obtained evidence that glycolaldehyde can interact with e-amino groups to crosslink proteins with generation of colour due to pyrazinium radical cations (cf. CROSSPY 84) under physiological conditions. This has direct bearing on, for example, cataract formation. 

CROSSPY A Radical Intermediate of Melanoidin Formation in Roasted Coffee... 

Figure 7. EPR spectrum of CROSSPY measured in a mixture of glucose heated in the presence of NcrFMOC-L-alanyl-L-lysyl-L-leucyl-L-glycine.

As shown in Table III no radicals could be detected clearly demonstrating that the CROSSPY formation was still in the induction period. In order to check the influence of reductones on radical formation, this ftiermally pre-treated mixture was incubated in the presence of ascorbic acid at room temperature. Analysis of the mixture by EPR spectroscopy revealed that instanftmeously after reductone addition the radical cation was generated (Table III). To investigate the effectivity of carbohydrate-derived reductones in CROSSPY formation, in comparative experiments, acetylformoin as well as methylene reductinic acid, both well-known to be formed during thermal treatment of hexoses (19), were added to the thermally pre-treated mixture. Both the Maillard reaction products were found to rapidly induce radical formation, however, in somewhat lower effectivity when compared to ascorbic acid (Table III). 

Figure 11. Disproportionation of CROSSPY leading to diquaternary l,4-bis-(S-amino-5-carboxy-l-pentyl)pyrazinium ions (diquats, I) and l,4-bis-(5-amino-5-carboxy-1-pentyl)-1,4-dihydropyrazirtes (II).

Figure 14. Reaction pathways leading to non-enzymatic browning via CROSSPY (I) and hydroxylated dihydropyrazines (IV, VI) as the key...

Hie radical cation CROSSPY was identified as a previously unknown type of cross-linking amino acid involved in melanoidin formation during roasting of coffee beans. Also for other browned foods such as wheat bread crust or roasted meat a tight relationship between the formation of CROSSPY and browning development could be observed (Hofinann, unpublished results), thus. 

In a similar way, EPR spectroscopy of orange-brown melanoidins, which were isolated from heated aqueous solutions of bovine serum albumin and glycolaldehyde, revealed the protein-bound l,4-bis(5-amino-5-carboxy-l-pentyOpyrazinium radical cation (CROSSPY) as a previously unknown type of cross-linking of proteins in vivo and during food processing (i). CROSSPY could be found in wheat bread crust, roasted cocoa, as well as coffee beans. 

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