Ch

COOH

carboxymethyllysine hn^JO

HO2<t^NH2

pentosidine

Fig. 11.10 Some possible markers of the Maillard reaction.

directly related to the MR, called bound HMF, and total HMF that also derives from the degradation of other precursors (Morales et al, 1997). This method is considered more reliable than the previous spectrophotometric one of Keeney and Bassette (1959).

Many authors have observed that the values of furosine, carboxymethyllysine, and HMF are very well correlated (Corzo et al, 1994; O'Brien, 1995). Hewedy et al (1991), however, comparing several damage indicators for the classification of UHT milk have shown that carboxymethyllysine is suitable only for monitoring very severe damage, because it is formed only in very small amounts, whereas furosine and HMF have a more general applicability. e-Pyrrolelysine (known also as pyrraline, Fig. 11.10) is another substance that has been proposed to measure the MR in foods. It was observed for the first time in the reaction between glucose and lysine (Nakayama et al, 1980) and is particularly useful in dry foods because it is very stable: for example Resmini and Pellegrino (1994) have proposed a methodology for measuring protein-bound pyrraline in dried pasta. The formation of this MRP parallels very well the formation of furosine. Another useful substance for assessing protein damage is lysinoalanine (see section 11.7).

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