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Maillard reaction products (MRP) consumption has been related with the development of bone degenerative disorders, probably linked to changes in calcium metabolism. We aimed to investigate the effects of MRP intake from bread crust on calcium balance and its distribution, and bone metabolism. During 88 days, rats were fed control diet or diets containing bread crust as source of MRP, or its soluble high molecular weight, soluble low molecular weight or insoluble fractions (bread crust, HMW, LMW and insoluble diets, respectively). In the final week, a calcium balance was performed, then animals were sacrified and some organs removed to analyse calcium levels. A second balance was carried out throughout the experimental period to calculate global calcium retention. Biochemical parameters and bone metabolism markers were measured in serum or urine. Global calcium bioavailability was unmodified by consumption of bread crust or its isolate fractions, corroborating the previously described low affinity of MRP to bind calcium. Despite this, a higher calcium concentration was found in femur due to smaller bones having a lower relative density. The isolate consumption of the fractions altered some bone markers, reflecting a situation of increased bone resorption or higher turnover; this did not take place in the animals fed the bread crust diet. Thus, the bread crust intake does not affect negatively calcium bioavailability and bone metabolism.

The influence of glucose-lysine and glucose-methionine Maillard reaction products (MRPs) on calcium availability was studied in rats and in Caco-2 cells. Equimolar glucose/lysine and glucose/methionine mixtures (40% moisture) were heated (150 degrees C, 30 or 90 min) to prepare samples (GL30, GL90, GM30, and GM90, respectively). For 21 days, the rats were fed the AIN-93G diet (control group) or diets containing separately 3% of the heated mixtures (GL30, GL90, GM30, and GM90 groups, respectively). In the last week of the trial, a calcium balance was performed. On day 21, the animals were sacrificed and their livers and femurs removed for analysis of calcium levels. The GL30 and GM30 samples and the corresponding raw mixtures were used for Caco-2 cells experiments. Fecal excretion of calcium decreased and urinary elimination increased in the GM30 and GM90 groups. In accordance, increased calcium transport in Caco-2 cells was found in the presence of the GM30 sample, compared with the raw sample. Bone calcium concentration was lower among the animals consuming MRP diets, compared with the control group. The possible long-term effects of MRP intake on calcium deposition in the bone should be further studied to ascertain the implications on related diseases.

During food thermal treatment Maillard's reaction may occur, which implicates mainly the carbonyl groups of reductory sugars and amino protein groups. Maillard's reaction products (MRP) may interfere with mineral bioavailability because of modifications of their physical-chemical moiety in the food or the lumen, disrupting the absorption process or its normal metabolism. In this study, we sought to investigate MRP influence on issues related to Ca bioavailability in vitro and in vivo. Equimolar mixtures of glucose-lysine (GL) and glucose-methionine (GM) (40% moisture) were heated at 150 degrees C for 90 minutes (samples GL90 and GM90, respectively). In vitro solubility was measured by additioning each samples to a 3.75 mM Ca solution at intestinal pH and ionic strength; after shaking and centrifugation, soluble and insoluble calcium was determined. Three percent of GL90 and GM90 were individually added to the AIN93-G diet to obtain D-GL90 and D-GM90 diets. Three Wistar rats groups were fed for 21 days with both diets and with AIN93-G as control, carrying out calcium balance during last week and extirpating various organs after sacrifice. GM90 did not affect calcium solubility; GL90 reduced it slightly, remaining in both cases more than 94% soluble. D-GL90 and D-GM90 did not modify calcium bioavailability, with as effective usage as with the control diet (57.6 +/- 1.3%, 57.8 +/- 2.3% and 63.9 +/- 2.6% in control diet, D-GL90 and D-GM90, respectively). MRP intake produced, however, metabolic changes that decreased bone calcium, accumulating compensatorily in other organs.

Two groups of female rats, non-pregnant (NP) and pregnant (P1), were fed ad libitum. A second group of pregnant rats (restricted diet, P2) were restricted for 14 d to the same intake as NP, and their ration was then increased by 5% from d 14 to d 21. For the first 3 d P1 and P2 absorbed a higher percentage of calcium than NP. During the final wk of pregnancy serum calcium decreased and 1,25-dihydroxycholecalciferol increased regardless of the dietary regimen. In both P1 and P2, femur calcium was higher than in NP on d 7 and apparent bone density increased during the 2nd wk of pregnancy and decreased from then on, this decrease being more pronounced in P2. On d 21, P2 fetuses were smaller and contained a smaller amount of calcium than those in P1, although the calcium concentration in the body remained similar in both groups of fetuses.

Five experiments were conducted in which various levels of calcium (Ca) and phosphorus (P) were fed to adult male quail (diets D-1: Ca = 1.54%, p = 0.80%; D-2: Ca = 3.20%, P = 0.81%; D-3: Ca = 1.57%, P = 1.66%; D-4: Ca = 3.40%, P = 1.71%; D-5: Ca - 2.20%, P = 0.81%). The interaction between Ca and P, and the effect on some nutritive hematic and osseous parameters were investigated for each diet. Feeding high P caused a body weight decrease in D-4 adult quail (P less than 0.05) and diminished food intake in the birds of trial D-3 (P less than 0.05). The results indicated that the excretion of Ca or P is a lineal function of its own intake. Neither the pattern of relationship between the intake and excretion of Ca was altered by the levels of phosphorus in the diets, nor the levels of calcium altered the pattern of P. With these levels of Ca and P interaction between both nutrients were not demonstrated. Plasma Ca levels and dry weight of femur as well as the ash content in them, were not significantly decreased, although the levels of the latter components were inferior in the groups fed non-adjusted diets in the Ca:P ratio (diets D-1, D-2, D-3 and D-4).

The influence of alimentary calcium deprivation on the nutritional utilization of phosphorus and its corporal retention, after ingestion of diethylstilbesterol has been studied in quail. When female quail are given a highly calcium-deficient diet, egg-laying stops and there follows a substantial decrease in phosphorus utilization and retention, as well as a clear drop in bone mineralization, with calcium and phosphorus content losses in the femur. In males, deprivation of alimentary calcium shows tangible effects on phosphorus retention only when this situation concurs with prior ingestion of diethylstilbestrol.

A study was made of the Ca and P balance, Ca and P content in the femur, physical characteristics of the egg, mineral structure of the shell, and the number of eggs in quails treated with dieldrin (20 mg/kg of diet) for 48 days. The diet contained 3.24% Ca and 0.72% P. The Ca and P balance, the bone contents of Ca and P and the calcemia in the males were not changed by the pesticide. In the females, the pesticide decreased the amount of excreted Ca and Ca in the egg, for which reason the coefficient of nutritive utilization (CNU), the coefficient of corporal retention (CCR), and the Ca level in the femur were greater in treated laying quails. The calcemia remained stable, and the balance of P was not significantly modified by the dieldrin. The study of weight, size, and strength of the egg did not reveal any influence of the dieldrin, and egg production fluctuated throughout the test period.