Furosine

Hartkopf, J. and Erbersdobler, H. F., Stability of furosine during ion-exchange chromatography in comparison with reversed-phase high-performance liquid chromatography, /. Chromatogr., 635, 151, 1993. 

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).

Guerra-Hernandez, E., Corzo, N. and Garcia-Villanova, B. (1999). Maillard reaction evaluation by furosine determination during infant cereal processing, J. Cereal ScL, 29, 171-176. 

Kuncewicz. A., Panfil-Kuncewicz, H. and Michalak, J. (2000). Lactulose and furosine as indices of the degree of heating of milk and other food products, Przemysl Spozywczy, 5, 20-22. 

Several markers for the Maillard reaction have been described in the literature. For example, the product initially formed between glucose and lysine is partly transformed into furosine (Heyns et ah, 1968) on acid hydrolysis. Conversely, the fluorescent amino acid pentosidine (Sell and Monnier, 1989) is an advanced glycation endproduct (AGE) and may form covalent bonds between proteins (cross-linking). Furthermore, the Maillard reaction leads to an increase in characteristic fluorescence (excitation 370 nm, emission 440 nm) (Monnier et ah, 1984 Pongor et ah, 1984). 

Materials. All reagents were analytical grade. Solutions were prepared in demineralized water. Central incisors were extracted from lower jaws of four-year old cows obtained from a local slaughterhouse. Pentosidine was a kind gift from Prof. V. Monnier, Case Western Reserve University, Cleveland OH, USA. Furosine was from Neosystem, Strasbourg, France, and hydroxylysylpyridinoline and lysylpyridinoline from Metra Biosystems, Palo Alto CA, USA. 

HPLC. Furosine and pentosidine, indicators of the initial and advanced stages of fhe Maillard reaction, respectively, increased in glucose-exposed slices (figs. 3,4 fable 3). Hydroxylysylpyridinoline apparenfly did nof form in fhe demineralized dentin at 37°C, as it did not increase in dentin exposed at 37°C (table 3). 

Furosine and fluorescent cross-links (mol amino acid/ mol collagen, except pentosidine mmol/mol) determined by HPLC in hydrolyzates of dentin slices exposed to glucose and buffer, pH 7.4, and non-exposed controls (n=2). 

HPLC analysis of furosine (-peak II) in hydrolyzates of non-exposed- (bottom), buffer-exposed (middle), and glucose-exposed (top) dentin samples. Dentin was not reduced prior to hydrolysis. Only the relevant parts of the chromatograms are shown. Amino acids are visualized after post-column labelling with a fluorescent dye. I lysine, II furosine. III homoarginine (internal standard). Column Merck Polyspher AA-NA 120 x 4.6 mm flow 0.2 ml/min gradient pH 5.0 -10.2 postcolumn reagent 0.2 ml/min fluorescence Xgx 330 nm, 440 nm 100-yl injections in buffer pH 2. 

Por fhe specimens of bafch III, bofh fhe collagenase and borohydride freafmenfs were omiffed fo enable analysis of furosine, which is formed by acid hydrolysis of fhe non-reduced glucose-lysine condensation producf. 

Eluent buffers A 0.067 M sodium citrate, 0.33 mM thymol, pH 3.0, except pH 5.0 for furosine analysis B 0.25 M sodium nifrafe, 0.024 M boric acid, pH 10.2 (pH adjusted with NaOH and HNO3). 

Furosine was only observed in two carious samples out of four, with 0.22 and 0.24 mol furosine/mol collagen, representing a very low level of lysine glycosylation (fig. 4). 

In the field of apiculture, legal limits were set for HMF content in honeys [49], as a tool to check both for applied technology (pasteurization) and for aging, while furosine is not an official parameter at present, but several researches were carried out on its application to royal jelly quality control [50,51]. 

Royal jelly SPE (Sep Pak) Alltech Furosine dedicated column DAD (280 nm) [51] ... 

Figure 9.8 Initial steps of the Maillard reaction with the formation of furosine (after hydrolysis with 7.8 M HCi) as well as of. Y-s-carboxymethyl lysine and erythronic acid (from Erbersdobler...

Figure 9.9 Effect of heating temperature and time on the concentration of furosine in directly heated UHT milks (from Erbersdobler and Dehn-Miiller, 1989).

We determined the content of furosine, which is an amino acid derivative formed by acid hydrolysis of fructose-lysine or lactulose-lysine ( (Fig. 1). 

N-a-acety1-L-lysine (0.5 mmole) and glucose (1.0 mmole) are dissolved in 1 ml 0.1 M K2HP0 buffer solution. The solution is heated in a closed vessel for 5 h at 100°C. Then the solution is made 6 N with HC1 and heated at 105° for 24 h. The hydrolysate is evaporated in vacuo. A solution of the residue in 20 ml water can be used for the TLC production of furosine spots. For quantitative evaluation the same absorbance was assumed for the ninhydrin reaction product both arginine and furosine. 

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