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Purpose: To investigate the effects of the consumption of Maillard reaction products (MRPs) from bread crust (BC) on iron, copper and zinc body retention and tissue distribution, determining whether these effects are related to the molecular weight of browning products., Methods: During an 88-day study period, rats were fed a Control diet or diets containing BC as source of MRPs, its soluble high or low molecular weight fractions (BC, LMW or HMW diets). A mineral balance was conducted throughout the experiment to determine iron, copper and zinc retention. At day 88, animals were killed, blood was drawn for haemoglobin determination and some organs removed to analyse minerals., Results: Copper and zinc balances were unchanged, and scant modification detected in their body delivery. However, the Fe retention rate from the diet increased (13, 22 and 32 % for BC, LMW and HMW diets), and a parallel higher Fe body concentration was observed (13-18 % higher than the Control group). Incoming iron accumulated particularly in the liver, femur and small intestine, but functional iron tended to decrease, as reflected by haemoglobin levels., Conclusions: The long-term intake of BC or derivatives did not produce a notable effect on copper or zinc balances, although slightly increased iron retention rate and the body concentration of this mineral were observed. Iron accumulated in some organs, but the production of haemoglobin was not improved. In view of the differences observed between the effects of BC and its derivatives, our results underline the importance of working with real food matrices, where the joint presence of different components modulates the in vivo final effects.

The behaviour of dietary Maillard reaction compounds (MRP) as metal chelating polymers can alter mineral absorption and/or retention. Our aim in this study was to analyse the long-term effects of the consumption of model MRP from glucose-lysine heated for 90 min at 150 °C (GL) on iron, copper and zinc whole-body retention and tissue delivery. For 88 days, weaning rats were fed a Control diet or one containing 3% GL, until reaching the adult stage. During the experimental period a mineral balance was conducted to investigate the mineral retention. At day 88, the animals were sacrificed, blood was drawn for haemoglobin determination and some organs were removed. Copper and zinc balances were unaffected (Cu: 450 vs. 375 μg; Zn: 6.7 vs. 6.2 mg for Control and GL groups, respectively) and no change was observed in whole-body delivery. Iron retention, too, was unaltered (11.2 mg for Control and GL groups) but due to the tendency toward decreased body weight in the GL group (248 vs. 233 g for the Control and GL groups), whole-body iron concentration was 13% higher in the GL group than in the Control group. Absorbed iron accumulated particularly in the liver (144 vs. 190 μg g(-1) for the Control and GL groups), thus reducing haemoglobin levels. The long-term intake of MRP induced iron accumulation in the body but this did not result in enhanced iron functionality, since the haemoglobin concentration declined. Taking into account the findings of our research group's studies of young and adult rats, we now corroborate the hypothesis that the negative effect of GL MRP consumption on iron functionality takes place regardless of the animals' stage of life.

Scope: Scarce data are available concerning effects of certain bioactive substances such as Maillard reaction products (MRP) on the gut microbiota composition, and the question of how a diet rich in MRP affects gut microbiota in humans is still open., Methods and Results: Two experiments were conducted. In expt. 1, adolescents consumed diets either high or low in MRP in a two-period crossover trial; in expt. 2, rats were fed diets supplemented or not with MRP model-systems. Intestinal microbiota composition in fecal (adolescents) or cecal (rat) samples was assessed by qPCR analysis. Negative correlations were found in the human assay between lactobacilli numbers and dietary advanced MRP (r = -0.418 and -0.387, for hydroxymethylfurfural and carboxymethyl-lysine respectively, p < 0.05), whereas bifidobacteria counts were negatively correlated with Amadori compounds intake. In the rat assay, total bacteria and lactobacilli were negatively correlated with MRP intake (r = -0.674,-0.675 and -0.676, for Amadori compounds, hydroxymethylfurfural and carboxymethyl-lysine respectively, p < 0.05), but no correlations were found with bifidobacteria., Conclusions: Dietary MRP are able to modulate in vivo the intestinal microbiota composition both in humans and in rats, and the specific effects are likely to be linked to the chemical structure and dietary amounts of the different browning compounds., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Background: Physical and biomechanical properties of bone can be affected by non-enzymatic crosslinks, which are implicated in bone pathologies such as osteoporosis. The purpose of this study was to analyse the effects of the consumption of model Maillard reaction product (MRP) from glucose-lysine heated for 90 min at 150 °C (GL90) on bone composition and features. Rats were fed either a control diet or a diet containing 30 g kg(-1) GL90 for 88 days. Food consumption and the animals' body weights were monitored. After sacrifice, the femur, pelvic bone and tibia were removed for analysis of their composition and physical and biomechanical properties., Results: The organic matrix of the femur and the density of the pelvic bone decreased after MRP intake, whereas pentosidine content increased greatly with respect to the control group (41.7 ± 9.9 vs 171.4 ± 3.3 mmol mol(-1) collagen). The rising level of C-telopeptide degradation products from type I collagen (β-CTX) suggested a possible situation of increased bone resorption and/or higher turnover., Conclusion: In conjunction, the detrimental effect on the organic matrix, the situation of higher resorption and/or bone turnover indicated by the β-CTX values and the high pentosidine content in bone provoked negative consequences on certain mechanical properties such as the ability to withstand force and absorb energy without failure., (© 2013 Society of Chemical Industry.)

Traditionally the effects of dietary Maillard reaction products (MRPs) on food intake and body weight have been described in different studies, but few investigations have been conducted to analyse the main contributors responsible. We studied the effects of long-term consumption of MRPs from bread crust (BC) on rat growth, investigating the efficiency of diet and protein utilization. Different soluble and insoluble fractions of BC were studied to analyse the possible contributors. Additionally, the colour of the faecal material and the amount of fluorescent MRPs in the urine were measured in order to demonstrate MRP excretion. Six groups of rats were fed the following diets for 88 days: control (AIN-93G diet); bread dough (BD) and BC (containing 10% of BD or BC, respectively); low and high molecular weight (LMW-HMW) (containing soluble compounds from BC with <5 kDa and >5 kDa, respectively); insoluble (containing insoluble compounds from BC). Dietary MRPs tended to reduce the food intake and body weight significantly after consumption of more complex compounds (HMW and insoluble). The L*-value in the faeces decreased in animals fed BC and its derivatives, providing evidence of the presence of MRPs. The fluorescence associated with MRP excretion in urine was higher when the LMW diet was consumed, suggesting the easier absorption and clearance of the smaller compounds of BC.

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.

Background: Consumption of Maillard reaction products (MRPs) present in food has been related to deterioration of protein digestibility and changes in mineral bioavailability. We aimed to investigate the effects of MRP intake from bread crust on magnesium balance and tissue distribution, seeking causative factors among its different components., Results: During the final stage of the trial, magnesium digestibility improved by around 15% in rats fed diets containing bread crust or its derivatives compared with the control diet. Despite certain enhancements in magnesium bioavailability in this stage, for the experimental period as a whole, this parameter remained unchanged. However, specific changes in the content and/or concentration in some organs were observed, particularly in the femur, where magnesium levels were higher due to the smaller size of the bones., Conclusions: Consumption of MRPs from bread crust or its different components did not modify the magnesium balance. Nevertheless, the bread crust fractions led to some changes in magnesium tissue distribution which did not match the effects induced by complete bread crust intake, suggesting the importance of designing studies with real-food systems, in order to reinforce the validity of the findings obtained., (© 2012 Society of Chemical Industry.)

Background: Maillard reaction products (MRP) improve food palatability and are linked to some positive biological actions. However, diverse negative consequences, some related to protein damage and mineral availability, have been established., Aim of Study: We investigated the effects of MRP, from a bread crust diet, on phosphorus bioavailability and tissue distribution in rats to determine whether these effects are related to the molecular weight of browning products., Methods: During a study period of 88 days, rats were fed either a control diet or one of the following: with bread crust as a source of MRP, or one with its soluble high molecular weight, soluble low molecular weight or insoluble fraction (bread crust, HMW, LMW and insoluble diets, respectively). In the final week, a phosphorus balance was performed, after which the animals were sacrificed and some organs removed to analyse phosphorus content. A second balance was carried out throughout the experimental period to calculate phosphorus retention., Results: Phosphorus balance in the last week was unchanged. However, considering the whole experimental period, a trend towards improved bioavailability, significant in the HMW group, was observed. Higher phosphorus concentrations were measured in the small intestine and bone., Conclusions: The consumption of MRP derived from bread did not alter phosphorus retention, due to increased bioavailability, especially concerning HMW compounds. The overall phosphorus body content remained unchanged and there were no changes in the bone, its principal metabolic destination. However, MRP consumption markedly raised phosphorus levels at the digestive level, especially when consumed as isolate fractions. The slower rate of stomach emptying is assumed to be related to this effect.

Objective: To examine the effects of consuming diets rich in Maillard reaction products (MRPs) on phosphorus bioavailability in male adolescents., Methods: A 2-wk randomized two-period crossover trial was performed among healthy male adolescents aged 11-14 y (n = 20), with a 40-d washout period. The diets consumed were rich (brown diet) or poor (white diet) in MRPs. Three-day balances were performed on the last of each dietary period, and fasting blood samples were obtained. Dietary phosphorus utilization was examined by phosphorus intake in diet and phosphorus output in feces and urine, as measured colorimetrically by the vanadomolibdate procedure. Serum phosphorus, parathyroid hormone, and total alkaline phosphatase were determined., Results: A tendency to increase daily phosphorus fecal excretion was observed subsequent to the brown diet consumption compared with the white diet (P = 0.10), which led to significant reductions in phosphorus apparent absorption (P = 0.03) and fractional absorption (P = 0.04). Values of apparent phosphorus retention and bioavailability tended to decrease after the high-MRP diet. Serum parameters analyzed remained unchanged between diets and were within normal values., Conclusion: The consumption of a rich-MRP diet in male adolescents had a negative influence on dietary phosphorus absorption, tending to decrease the phosphorus balance. Given the actual dietary habits of adolescents, possible long-term repercussions of this kind of diet should be studied., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The effects of the high intake of Maillard reaction products (MRP) on calcium availability in adolescents and across Caco-2 cell monolayers were examined. In a 2 week randomized two-period crossover trial, 18 male adolescents consumed two diets, named white diet (WD) and brown diet (BD), which were poor and rich in MRP, respectively. A 3 day balance was performed at the end of each period, and fasting blood samples were collected. Calcium solubility and absorption across Caco-2 cells were studied after the in vitro digestion of the diets. The in vitro assay showed similar solubility after the in vitro digestion and similar transport across Caco-2 cells. In accordance, calcium bioavailability in adolescents did not vary between the diets (%WD = 40.4 +/- 5.1, %BD = 38.2 +/- 3.6). Serum and urine biochemical parameters related to calcium status and bone metabolism remained unaltered. Only deoxypyridinoline values were significantly lower after consumption of the BD (13.0 +/- 1.1 compared to 18.3 +/- 2.1 nM/Mm Cr in the WD), possibly indicative of less efficient bone turnover during this period. As calcium acquired during adolescence is essential to maximize peak bone mass and to prevent osteoporosis, possible long-term effects of excessive MRP intake during this period warrant attention.

Contents of some indicators of the Maillard reaction (MR) in two diets adjusted to the adolescent requirements are compared: the A-diet, usually consumed by the adolescent population containing their preferred foods cooked by the culinary techniques more frequently chosen; and the B-diet, with the same foods, except those industrially processed and with high content of Maillard reaction products (MRP), cooked in softer processes to minimise the MR. Aliquots of a lunch-dinner (LD) and breakfast-afternoon (BA) snack pools separately from both diets were ground and lyophilised. Fluorescence associated to MRP, CIELAB colour parameters, furosine, hydroxymethylfurfural (HMF), carboxymethyllysine (CML) and sugar contents were investigated in the samples. Significant losses of lightness were manifested in A samples compared to the B ones. Fluorescence intensity was significantly higher in the LD and BA samples from the A-diet. Furosine measured in the A-diet was similar to that found in the B-diet. However, HMF content was significantly higher in the A-diet, as well as CML. Data showed significant higher levels of advanced MRP in the usual diet. Thus, MRP intake associated to alimentary pattern in the adolescence population might be studied in order to assess the health implications of the MRP consumption and its possible synergic effect with endogenous advanced glycation endproducts.

Background: Adolescents are nutritionally at risk because of their physiologic needs and dietary habits. Maillard reaction products (MRPs) are widely consumed by this population, mainly as a result of their high intake of fast food and snacks., Objective: We compared the effects of diets with different MRP contents on dietary protein utilization in adolescent males aged 11-14 y. The brown diet (BD) was rich and the white diet (WD) was poor in MRP content (hydroxymethylfurfural: 3.87 and 0.94 mg/kg; fluorescence intensity: 21.04% and 7.31%, respectively)., Design: In a 2-period crossover trial, 18 healthy adolescent males were randomly assigned to 2 groups. The first group consumed the WD for 2 wk, observed a 40-d washout period, and then consumed the BD for 2 wk. The second group received the diets in the opposite order. Subjects collected urine and feces on the last 3 d of each dietary period. Fasting blood samples were collected after both periods., Results: Compared with consumption of the WD, consumption of the BD resulted in 47% higher fecal nitrogen fecal excretion (P = 0.002), 12% lower apparent nitrogen absorption (P = 0.000), and a 6% lower nitrogen digestibility (P = 0.000). The apparent nitrogen retention and the utilization of ingested nitrogen did not differ significantly between the diets, although values after the BD tended to decrease. Serum biochemical variables related to nitrogen metabolism did not differ significantly., Conclusions: The consumption of a diet rich in MRPs negatively affects protein digestibility. The possible effects of an excessive intake of MRPs during adolescence warrant attention, and long-term effects should be considered.

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.

The effect of the heat treatment of casein in presence of reducing sugars on some aspects of Zn availability was investigated. Samples were prepared by mixing casein with glucose-fructose, and were used unprocessed (C) or heated (HC). Changes in Zn speciation after the in vitro digestion of the samples, both as part of a diet and in isolation, were studied. The uptake of soluble Zn from the digested samples was investigated in Caco-2 cells. After in vitro digestion, the percentage of precipitated Zn was significantly higher with the HC sample, both when digested alone and as a part of the diet. In assays with Caco-2 cells, a significant decrease in Zn uptake was observed when the uptake buffer contained the sample C digest, by comparison with the control buffer, without casein digest. When the digested heated mixture was added, Zn uptake by the cells was significantly lower than in either of the two other cases. It may be concluded that the heat treatment of casein in the presence of glucose-fructose has a negative effect on Zn availability because, after in vitro digestion, Zn insolubilization was enhanced and Zn uptake by the enterocyte was impaired, compared with the unheated mixture. In addition, the usefulness of Caco-2 cells in this kind of research has been shown.