Pyridosine

The extent of heat-induced changes in protein-rich foods can be measured by determining some early Maillard reaction products (O Brien and Morrissey, 1989). Acid treatment of protein-bound or free A -fructoselysine liberates lysine, with a yield of 50%, and two other amino acids, furosine (20%) and pyridosine (10%) (Figure 13.1). The three products that result from hydrolysis of A -lactuloselysine are formed in the proportions of approximately 5 3 to 4 1 to 2, however the yield of different derivatives is variable. Therefore, in order to use these unique amino acids as indicators of changes in lysine content, the hydrolysis should be carried out in strictly-defined conditions. Furosine is present in various food products in a very wide range of concentrations (Table 13.2). 

Figure 13.1 Acid treatment of M-fructoselysine (a), liberates lysine (b) and two modified amino acids, furosine (c) and pyridosine (d).

R. Krause, K. Knoll, and T. Henle, Studies on the formation of furosine and pyridosine during acid hydrolysis of different Amadori products of lysine, Eur. Food Res. Technol, 216 (2003) 277-283. 

The pyridine (dihydropyridine) derived amino acid P-(3-hydroxy-4-pyridon-l-yl)-L-alanine, L-mimosine (2-62), is thyreotoxic (causes over-activity of the thyroid gland) to nonruminant animals. It occurs in the subfamily Mimosoideae of the legume family Fabaceae, in plants of the genera Mimosa and Leucaena. Leucaena leucocephala (syn. Mimosa glauca) is native to the tropical and subtropical Americas, known as White Leadtree, and is used as livestock fodder. The mimosine content in seeds can reach up to 5% of dry matter (see Section 10.3.2.7.1). The amino acid pyridosine arising from lysine in the Maillard reaction can also be considered a dihydropyridine derivative (see Section 4.7.5.12.3). 

Figure 4,102 Formation of furosine and pyridosine from lactose and milk proteins.

Several efforts have beenmade to estimate these quality features or determine heat treatment of food by analyzing Maillard products. Especially Amadori conq)ounds or their analogues fiirosine and pyridosine (2,3), as well as advanced products, such as pyrraline, have been suggested for this use (4). 

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