Maillard reaction products derived from thiol compounds as inhibitors of enzymatic browning of fruits and vegetables: the structure-activity relationship.

Some thiol-derived Maillard reaction products (MRPs) may exert antioxidant activity, depending on the reaction conditions as well as on the sugar and the sulphydryl compound. Recently, we reported that MRPs derived from glucose or fructose with cysteine (CSH) or glutathione (GSH) mixtures greatly inhibited polyphenoloxidases (PPOs), oxidoreductases responsible for discoloration of fresh or minimally processed fruits and vegetables. Glucose and GSH were shown to be the most active in producing inhibitory MRPs. Therefore, we examined the way in which the nature of the reactants affected their synthesis, in order to establish a structure-activity relationship for the inhibitory products. Various aqueous (0.083 M, 0.125 M, or 0.25 M) mixtures of a sugar (hexose, pentose, or diholoside) with either a CSH-related compound (CSH, GSH, N-acetyl-cysteine, cysteamine, cysteic acid, methyl-cysteine, cysteine methyl ester), an amino acid (gamma-glutamic acid, glycine, methionine), or other sulfur compound (thiourea, 1,4-dithiothreitol, 2-mercaptoethanol) were heated at 103 degrees C for 14 h. Soluble MRPs were compared for their ability to inhibit apple PPO activity. In the presence of CSH, the rated sugars (same molar concentration) ranked as to inhibitory effect were pentoses > sucrose > hexoses > or = maltose. In the presence of glucose, the simultaneous presence of an amino group, a carboxyl group, and a free thiol group on the same molecule seemed essential for the production of highly inhibitory compounds.

Studies on the mechanism of intestinal passage of the food comutagen harman, in the rabbit.

The passage of harman (Ha) across rabbit jejunum and its effects on electrical parameters of the intestinal epithelium were studied in vitro using Ussing chambers. A linear relationship between mucosal to serosal flux (Jm-s) and the concentration of Ha (0.25-2 mM) was found. Ha elicited a dose-related decrease in short-circuit current, but did not affect transmural potential difference. At 2 mM, Ha decreased tissue conductance. Despite changes of electrical parameters, Jm-s of Ha was not modified by metabolic effectors such as glucose, colchicine, 2,4-dinitrophenol and ouabain, indicating that passage was dependent neither on membrane movements nor on cell energy. The transport of Ha was not dependent on Na+, but Ha inhibited in a dose-related manner the cotransport of Na+ and glucose. Luminal sodium taurocholate or beta-lactoglobulin had no appreciable effect on transport of Ha, but ethanol elicited a 45% increase in Ha permeability. These results indicate (1) that substantial amounts of Ha can cross the intestinal epithelium by the transcellular pathway and (2) that the passage of Ha, which appears to be diffusional, is not affected by luminal solutes such as glucose, sodium taurocholate and beta-lactoglobulin, but is markedly enhanced by ethanol.

Resolution of several racemic 3-hydroxy-1,4-benzodiazepin-2-ones by high-performance liquid chromatography on a chiral silica-bonded stationary phase.

The resolution of four racemic 3-hydroxy-1,4-benzodiazepin-2-ones, widely used in therapeutics, by means of a chiral stationary phase is described. The chiral selector used is (S)-N-(3,5-dinitrobenzoyl)phenylalanine. This chiral stationary phase showed both good enantioselectivity and efficiency for the compounds. Elution times were in all cases shorter than those previously reported for such compounds on different stationary phases. Racemic oxazepam was used to evaluate the loading capacity of the chiral stationary phase.

Effects of harmane on growth and in vivo metabolism of aflatoxin B1 in male and female rats.

The role of harmane, a beta-carboline formed during pyrolysis of tryptophan, on the metabolism of AFB1, growth and some parameters of the nutritional status was investigated in the rat. Male and female Wistar rats were fed a semi-synthetic diet containing AFB1 (2 ppm), harmane (250 ppm) or both compounds, for 33 days after weaning. Qualitative and quantitative differences in the urinary and faecal excretion of parental compound and metabolites were assessed by HPLC analysis. Harmane did not modify appreciably the growth and the other nutritional parameters studied. Similar excretion patterns of AFB1 metabolites were observed in males and females. Harmane caused a limited increase in the excretion of AFM1 in faeces but not in urine, without altering the growth process in rats of either sex.

[Fate of benzo(a)pyrene in the digestive tract. 1. Its disappearance]. / Evolution du benzo(a)pyrène dans le tube digestif. 1. Sa disparition.

In an early stage, diets with 0,1% or 0,05% of B(a)P decreased the intake and the growth of young rats (78 g) and adult rats (415 g). The stomach tissue adsorbed the B(a)P (30 micrograms/whole tissue) by a physical mechanism. Both in intestinal contents and wall, the amount of B(a)P was much higher in growing rats than in old animals; also, the faeces respectively contained 1.99 mg and 0.03 mg of B(a)P/g dry. The "digestibility" of B(a)P was of 88.7% (after 6-13 days of experiment) to 99.6% after 15-22 days. The blood serum of young rats contained 1.36 microgram de B(a)P/100 ml.

[Fate of benzo(a)pyrene in the digestive tract. 2. Appearance of metabolites]. / Evolution du benzo(a)pyrène dans le tube digestif. 2. Apparition des métabolites.

The degradation of the B(a)P - mainly by oxidative way - began in the stomach and greatly developed in the intestine. The quinones and other hydrosoluble derivatives were the main metabolites of the B(a)P digestive tractus. The quinones predominated in stomach tissue, but the most hydrosoluble metabolites also were present in this wall. In the intestinal content, these hydrosoluble metabolites were very abundant; they seemed easily absorbable by the intestinal wall. Conversely, the quinones were excreted in faeces. A reduced metabolite was formed in intestinal and faecal contents.