Glycation compounds in peanuts

In the present study, the extent of the Maillard reaction in peanuts was investigated, using N-epsilon-fructosyllysine (epsilon-Fru-Lys, determined via furosine) as an indicator for the early stage, and pyrraline and N-epsilon-carboxymethyllysine (CML) as representatives for advanced glycation. In commercial samples, epsilon-Fru-Lys ranged between 1.5 and 13.3 mmol/mol lysine. Pyrraline was found in amounts between not detectable (below 0.3 mmol/mol lysine) and 9.0 mmol/mol lysine, and CML between 0.8 and 2.7 mmol/mol lysine. Lysine modification by glycation products was very low in cooked and fried peanuts (below 1%). In laboratory-scale roasting experiments, the amount of epsilon-Fru-Lys reached maximum values of 12.0 mmol/mol lysine after 20 min at 160 degrees C, whereas pyrraline increased up to 38.5 mmol/mol lysine after 25 min at 170 degrees C. Amount of CML was up to 1.8 mmol/mol lysine in peanuts roasted for 25 min at 170 degrees C. Such high amounts of pyrraline have not yet been described for any other food item. Only about one tenth of the totally observed lysine modification of up to 50% can be explained by the three glycation compounds, indicating that currently unknown reactions occur during peanut roasting. Reactions between proteins and carbonyl compounds, most likely originating from oxidative degradation of lipids, may play an important role for lysine derivatization in peanuts and should be analyzed more in detail.