Maillard reaction products and lysinoalanine: urinary excretion and the effects on kidney function of preterm infants fed heat-processed milk formula.

Heat processing is essential for the preservation of milk-based infant formulas. Heating, however, induces a number of chemical changes during which lysine in the milk proteins reacts with reducing sugars to form Maillard reaction products (MRPs) and also reacts with the dehydroalanine resulting from cystine degradation to form lysinoalanine (LAL). Both products have been reported to induce histological changes in the straight portion of the proximal tubule in the rat kidney. This pilot study was made to investigate the urinary excretion by healthy preterm babies of MRPs and LAL contained in infant formula and to determine their influence on kidney function. Twelve healthy male preterm babies were first fed for 10 days with pooled human milk and then for 5 days with each of two experimental premature infant formulas in a cross-over design. The infant formulas were sterilized either by ultra-high temperature (UHT) treatment or by a conventional retort process to give products with low and high levels of MRPs and LAL, respectively. In total, some 15.6% of the initial lysine had been modified in the in-can-sterilized product, compared to 6.2% in the UHT product. Urinary excretion of MRP lactulosyllysine ranged from 1.3 to 3.9% of the ingested amount, whereas that of LAL ranged from 6.2 to 9.3%. The higher level of MRPs and LAL in the formulas compared to breast milk had no influence on creatinine clearance or electrolyte excretion. There was no evidence of tubular damage as determined by the urinary excretion of four kidney-derived enzymes. Feeding of formula, however, did result in a general increase in urinary microprotein levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of Maillard reaction products on zinc metabolism in the rat.

The effect of giving Maillard reaction products (MRP) on zinc metabolism was investigated in the rat. In Expt 1, MRP were prepared by incubating casein with either glucose or lactose under controlled reaction conditions, and were quantified as either 'early' or 'advanced' after estimation of lysine loss and lysine destruction respectively. In Expt 2, the effect of the purified early MRP fructose--lysine (FL) on Zn metabolism was studied. The experimental diets containing 20 mg Zn/kg were given to weanling rats for 21 d. Zn balance was assessed over 9-14 d (Expt 1), or 1-14 d (Expt 2). Femur, liver, kidney and serum Zn concentrations were determined at 21 d. The major effect of the MRP in the casein-sugar mixtures was on urinary Zn excretion. The casein-glucose MRP induced up to a 6-fold increase in the quantity of Zn excreted in the urine. The magnitude of the hyperzincuria increased with the extent of the Maillard reaction. Similar dietary levels of casein-lactose MRP increased urinary Zn loss 2-fold. Free FL had no effect on urinary Zn. Faecal Zn, Zn retention, liver, femur and serum Zn were generally not influenced by giving MRP from casein-sugar mixtures or by giving free FL, although kidney Zn was decreased in rats fed on FL. It was concluded that although urinary Zn excretion can be increased by the presence of MRP in the diet, this is only a minor excretory pathway and would have little influence on overall Zn nutrition in individuals fed on a diet adequate in Zn.

Iron fortification of infant cereals: a proposal for the use of ferrous fumarate or ferrous succinate.

Hemoglobin-repletion tests in rats, organoleptic studies, and iron-absorption studies in humans were used to search for Fe sources with high bioavailability that could be added to infant cereals as alternatives to the Fe compounds currently used for fortification. From rat and organoleptic studies on 11 alternative Fe sources, ferrous fumarate, ferrous succinate, and ferric saccharate were selected as the most suitable for infant-cereal fortification and, by use of radioactive labels, absorption of those compounds from fortified cereal was measured in adult human volunteers. There was no difference in absorption between ferrous fumarate and ferrous sulfate whereas the values for ferrous succinate, ferrous saccharate (10% Fe), and ferric pyrophosphate were 92%, 74%, and 39% of the ferrous sulfate values, respectively. We conclude that ferrous fumarate and ferrous succinate are highly available Fe sources in man that can be used to fortify infant cereals without causing fat oxidation or discoloration.

Metabolic transit and toxicity of Maillard reaction products.

The feeding of Maillard reaction products (MRP) has been reported to lead to a variety of effects on metabolism which may be classed as "anti-nutritional" or "anti-physiological", depending on whether they are due to the loss of essential nutrients or to the presence of the MRP per se. This paper describes the sensitivity of essential nutrients in the "early" and "advanced" stages of the Maillard reaction, the metabolic transit of Amadori compounds, premelanoidins, melanoidins, hydroxymethyl-furfural, carboxymethyl-lysine, as well as the effects of MRP on pancreatic amylase and on urinary zinc excretion.