Determination of ε-N-Pyrrolylnorleucine in Fresh Food Products

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Abstract
ε-N-Pyrrolylnorleucine was determined in different fresh food products to study its presence as a normal component of food proteins. Twenty-two different products were screened: cod, cuttlefish, salmon, sardine, trout, beef, chicken, pork, broad bean, broccoli, chickpea, garlic, green pea, lentil, mushroom, soybean, spinach, sunflower, almond, hazelnut, peanut, and walnut. Foods were homogenized, their proteins were precipitated with trichloroacetic acid and hydrolyzed with 2 N NaOH for 20 h, and the ε-N-pyrrolylnorleucine content was determined by capillary electrophoresis. The ε-N-pyrrolylnorleucine, which was identified by HPLC/MS in sardine muscle hydrolysate, ranged in the 22 foods analyzed from 0.24 to 6.36 μmol/g. This concentration was correlated with the protein content of the food (r = 0.687, p = 0.00041). In addition, the ε-N-pyrrolylnorleucine/lysine ratio was found to be a function of the lipid, iron, and protein contents of the food (r = 0.881, p < 0.0001) and was directly correlated with lipid and iron contents and inversely correlated with the protein content. These results are in agreement with the oxidative stress origin proposed for ε-N-pyrrolylnorleucine and suggest that the ε-N-pyrrolylnorleucine/lysine ratio is a characteristic of each food. In addition, ε-N-pyrrolylnorleucine seemed to be a normal component of many fresh food products, in which it may be acting as a natural antioxidant. Keywords: ε-N-Pyrrolylnorleucine; fishes; meats; vegetables; nuts; capillary electrophoresis; natural antioxidants; amino−carbonyl reactions; oxidative stress