Vol. 67, Nr. 2, 2001—JOURNAL OF FOOD SCIENCE 855 © 2002 Institute of Food Technologists Sensory and Nutritive Qualities of Food JFS: Sensory and Nutritive Qualities of Food Copper Metabolism in Rats Fed Diets Containing Maillard Reaction Products C. DELGADO-ANDRADE, I. SEIQUER AND M.P. NAVARRO ABSTRACT: Equimolar mixtures of glucose/lysine (GL) or glucose/methionine (GM) (both 40% moisture) were heated (150 °C, 30 and 90 min) to prepare the samples: GL30, GL90, GM30 and GM90. Copper balance and concentration in some organs was determined in rats fed 5 diets: control diet and diets containing 3% of the samples. Comparisons with respect to the control group were as follows: Fecal Cu excretion decreased in GM groups, and urinary excretion in all groups. Copper absorption, retention, and the efficiency of both processes increased in all groups except GM30. Copper concentrations were significantly higher in spleen, kidney, and skin in the GM90 group. Kidney Cu concentration was higher in the GM30 group. Adding GL and GM samples to a balanced diet increased copper absorption and retention, and copper accumulated in some organs. Keywords: Maillard reaction products, copper, absorption, balance, tissue concentration Introduction A S COPPER IS A COMPONENT OF MANY proteins and enzymes, Cu deficien- cy can lead to severe derangement of growth and metabolism. Cu acts as a catalytic cofactor in different metallo- proteins and several cuproenzymes, participating in various cellular and ex- tracellular activities (Failla 1999). Thus, Cu is essential for iron metabolism, bone and elastic tissue development, myelination and normal functioning of the central nervous system, melanin pigment formation, and other physio- logical functions (Turnlund 1994). When copper is severely limited in the diet, rats show specific signs of deficiency, including depressed body weight gain, mortality, anemia, enlarged hearts, hy- percholesterolemia, decreased copper- dependent enzyme activities, increased tissue iron concentrations, reproduc- tive failure, and impaired immune com- petence (Danks 1988; O’Dell 1993). It would therefore be useful to identify factors which can affect copper avail- ability in the diet, modifying its nutritive utilization and the Cu status. When foods containing reducing sugars and proteins are subjected to thermal processing, Maillard reaction products (MRP) may be formed. The rate of browning and the characteristics of MRP depend on many factors: the nature and molar ratio of reactants, moisture content, pH, and miscella- neous factors such as the presence of copper salts, which appear to acceler- ate the reaction (Kato and others 1981). Lysine destruction is the most signifi- cant consequence of the Maillard reac- tion (MR) (O´Brien and Morrissey 1989); methionine is also involved in MR and its participation is interesting due to its low content in foods and the possible toxicity of MRP formed (Bene- venga and Steel 1984). MRP, which can be formed even during food storage, can cause undesir- able decreases in mineral bioavailability, because they may behave as chelating agents for metals. This is especially true for copper, which is very strongly bound by insoluble products, melanoi- dins, produced in this reaction (Rendle- man and Inglett 1984; Friedman 1996). Rendleman (1987) demonstrated the importance of MRP in the binding of metal ions in foods, noting that toast made from bread containing milk had a stronger affinity for Ca and Cu than toast prepared from milk-free bread. The ability of brown pigments in coffee to bind copper ions was reported by Homma and others (1986). The com- plexes formed between MRP and metal ions were less soluble than the free metal ion or the ligand (O’Brien and Morrissey 1997). There is evidence that some low- molecular-weight water-soluble MRP are absorbed from the digestive tract (Erbersdobler and others 1977; Johnson and others 1983), but further com- pounds of the reaction, which are of higher molecular weight and water in- soluble, may affect fecal metal excre- tion and absorption (Furniss and others 1989). In rats, a diet containing 3% of heated mixture of glucose and glycine caused a significant decrease in copper retention in axenic but not in holoxenic animals (absence or presence of micro- flora, respectively) (Andrieux and oth- ers 1980). Another assay in rats fed diets containing 0.5% MRP from glucose/ glutamate showed increased urinary ex- cretion of copper in comparison with animals fed a control diet (O’Brien and others 1986). Previous reports suggest- ed that compounds from the fructose/ arginine formed in autoclaved solutions were not absorbed in the intestine in significant quantities. Increased urinary copper excretion was also found in sub- jects intravenously infused with a glu- cose/casein hydrolysate solution; how- ever, when these solutions were administered orally, urinary copper ex- cretion did not increase (Stegink and others 1981). The aim of this study was to com- pare the effects of diets containing heated mixtures of glucose/lysine and glucose/methionine during 30 or 90 min on the copper balance in rats and on copper concentrations in different organs. Materials and Methods Sample preparation Glucose (Merck, Darmstad, Germa- ny), lysine and methionine (Sigma Chemical Co., St. Louis, Mo., U.S.A.) were used to prepare samples. Equimo- lar mixtures of glucose-lysine-HCl or glucose-DL-methionine (both 40% moisture) were heated in an oven (Se- lecta 2000210, Barcelona, Spain) at 150 °C for 30 min (GL30 and GM30) or 90 min (GL90 and GM90), using open recipients. After heating, samples were placed initially in a cool water bucket and then in crushed ice in order to stop the reaction. The product obtained was