Varoujan A. Yaylayan

Classification of the Maillard reaction: A conceptual approach

To facilitate the study of the complex pathways of the Maillard reaction, a conceptual representation of the processes occurring during the reaction has been developed in which the Maillard reaction is described as proceeding by the formation and interaction of ‘chemical pools’. A collection of products arising from the decomposition of well-defined precursor(s) is termed a fragmentation pool, and a group of related chemical reactions and their products is termed an interaction pool. The pools that are formed from the decomposition of the sugar, amino acid and Amadori or Heyns products are termed primary fragmentation pools. Further reactions among the populations of these pools lead to ‘interaction pools’. Three types of pool interactions are identified: ‘self-interaction’, ‘secondary interaction’ and ‘multiple-interaction’. In addition, the fundamental reactions that underlie the pool interactions are classified according to the type of chemical transformation effected. The importance of such classification lies in its ability to predict the formation of Maillard reaction products in model systems.

Isotope labeling studies on the formation of 5-(hydroxymethyl)-2-furaldehyde (HMF) from sucrose by pyrolysis-GC/MS

Although it is generally assumed that the reactivity of sucrose, a nonreducing sugar, in the Maillard reaction is due to its hydrolysis into free glucose and fructose, however, no direct evidence has been provided for this pathway, especially in dry and high temperature systems. Using specifically (13)C-labeled sucrose at C-1 of the fructose moiety, HMF formation was studied at different temperatures. Under dry pyrolytic conditions and at temperatures above 250 degrees C, 90% of HMF originated from fructose moiety and only 10% originated from glucose. Alternatively, when sucrose was refluxed in acidic methanol at 65 degrees C, 100% of HMF was generated from the glucose moiety. Moreover, the relative efficiency of the known HMF precursor 3-deoxyglucosone to generate HMF was compared to that of glucose, fructose and sucrose. Glucose exhibited a much lower conversion rate than 3-deoxyglucosone, however, both fructose and sucrose showed much higher conversion rates than 3-deoxyglucosone thus precluding it as a major precursor of HMF in fructose and sucrose solutions. Based on the data generated, a mechanism of HMF formation from sucrose is proposed. According to this proposal sucrose degrades into glucose and a very reactive fructofuranosyl cation. In dry systems this cation can be effectively converted directly into HMF.

Isolation and structural analysis of Maillard polymers : caramel and melanoidin formation in glycine/glucose model system

A water-methanol solution of glycine and d-glucose was refluxed at 65 °C for seven h. The solvent was evaporated under vacuum at room temperature and the residue was dialyzed against distilled water. After dialysis, the solvent was evaporated under vacuum at room temperature. The non-dialyzable fraction was further fractionated by gel filteration. The process yielded three polymeric materials (10 000 < MW < 20 000) termed A, B1 and B2. The isolated polymers were further analyzed by UV-VIS and FTIR spectroscopy and by pyrolysis/GC/MS. Elemental analysis indicated that polymer A has the following empirical formula C7H11N1O4 and polymers B1 and B2 have the same empirical formula as d-glucose (C1H2O1). The origin of nitrogen containing polymer A was assigned to Amadori intermediate or to its derivatives and the origin of polymers B1 and B2 was assigned to glucosone and/or to 3- or 1-deoxyglucosones; common non-nitrogen containing reactive intermediates formed during the Maillard reaction. Plausible mechanisms were proposed for the formation of polymers based on spectroscopic data.

Thermal processing, storage conditions, and the composition and physical properties of orange juice

Abstract Mexican orange juice bottled without pasteurization and frozen, or orange juice that was pasteurized, bottled, and frozen or orange juice pasteurized and stored at 1°C in plastic bins was sampled monthly for eight months. Juice density, cloud, and fructose levels were all significantly (P

Microwave-assisted Extraction of Phenolic Compounds from Grape Seed

Abstract A microwave-assisted extraction technique was developed to optimize the extraction of phenolic compounds from grape seeds. The microwave power (300-150W) and time of extraction (20-200s) were varied during the optimization process. The polyphenol content of the resulting extracts were measured as mg of tannic acid equivalent per gram of crude extract (mg TAE/g of crude extract), using a Folin-Ciocalteau reagent. In general, neither the time nor the power had a significant effect on the overall % yield (average of 13.5%) and on the polyphenol content (392 mg TAE/g of crude extract) of the extracts. However, when the solvent polarity was changed by the addition of 10% water, the yield increased to 15.2% and the polyphenol content increased to 429 mg TAE/g of crude extract.

Profiling of α-Dicarbonyl Content of Commercial Honeys from Different Botanical Origins: Identification of 3,4-Dideoxyglucoson-3-ene (3,4-DGE) and Related Compounds

The alpha-dicarbonyl contents of commercial honey samples from different botanical origins were analyzed as their quinoxaline derivatives using HPLC-DAD, HPLC-MS, HPLC-MS/MS, and HPLC-TOF-MS. A total of nine such compounds were detected, of which five were previously reported in honey (glucosone, 3-deoxyglucosone, glyoxal, methylglyoxal, and 2,3-butanedione) and three were reported only from sources other than honey [3-deoxypentulose, 1,4-dideoxyhexulose, and 3,4-dideoxyglucoson-3-ene (3,4-DGE)]. An unknown alpha-dicarbonyl compound was also tentatively identified as an oxidation product of 3,4-DGE and was termed 3,4-dideoxyglucosone-3,5-diene (3,4-DGD). Only glyoxal (0.3-1.3 mg/kg), methylglyoxal (0.8-33 mg/kg), and 2,3-butanedione (0-4.3 mg/kg) were quantified in all honey samples. Furthermore, analysis of the alpha-dicarbonyl profile of various honey samples indicated that certain alpha-dicarbonyl compounds are found in specific honey samples in much higher proportions relative to the average amounts. The free radical scavenging activity as measured by DPPH method has also indicated that the darker honey samples such as buckwheat, manuka, blueberry, and eucalyptus had higher antioxidant properties compared to lighter-colored samples.

Investigation of vibrational theory of olfaction with variously labelled benzaldehydes

Abstract Vibrational theory of olfaction was investigated with the following three labelled analogues of benzaldehyde; 13 C 6 (ring)-benzaldehyde, 13 CHO-benzaldehyde and benzaldehyde-d 6 . Sensory analysis, by a trained panel of 30 subjects, using a duo-trio test, showed that the benzaldehyde-d 6 gave a statistically significant difference in odour perception ( P =0.002) relative to the unlabelled benzaldehyde. The odour changes in the other substituted analogues were found to be less significant ( P =0.058 for ring- 13 C 6 and P = 0.017 for 13 CHO). Analysis of the infrared spectra revealed that benzaldehyde-d 6 also experienced the most drastic shifts (Δλ ∼ 700 cm −1 ) in the absorption frequencies of the aromatic and aldehydic C–H stretching bands (3085, 2819 and 2738 cm −1 ), in addition to smaller shifts (Δλ ∼ 25–100 cm −1 ) in the C–H bending or deformation bands (828, 745, 688 and 650 cm −1 ). In addition, molecular modelling studies indicated that the shape of the molecule was retained after isotopic substitution but the molecular volume increased by less than 1%. The data suggested that one of the required vibrational bands for the perception of bitter almond aroma lies in the 3000 to 2500 cm −1 frequency range.

Investigation of dl-glyceraldehyde–dihydroxyacetone interconversion by FTIR spectroscopy

Abstract Interconversion of dihydroxyacetone and dl -glyceraldehyde was studied in different solvents and temperatures by FTIR spectroscopy. Dissolution in water or triethylamine, and increasing temperatures caused the dissociation of the dimeric forms of both compounds into monomers and subsequently inter-conversion of dihydroxyacetone and dl -glyceraldehyde. Dioxane, on the other hand, did not initiate such inter-conversions. FTIR analysis in different solvents has also indicated that monomeric dl -glyceraldehyde can exist in two distinct intramolecularly H-bonded forms. A five-membered ring form was predominant in aqueous solutions of the dissociated dl -glyceraldehyde dimer, whereas a six-membered ring form was preferred in triethylamine solution or in aqueous solution of dissociated dihydroxyacetone dimer. However, in aqueous solutions of dl -glyceraldehyde dimer, the five-membered ring conformation was slowly transformed into the six-membered ring form under slightly basic pH. In addition, dihydroxyacetone predominantly converted into the six-membered H-bonded conformation of glyceraldehyde when dissolved in water. This was attributed to the preferential formation of the trans - or E -enediol as an intermediate. Temperature-dependent spectra have also indicated that increasing the temperature favored the formation of glyceraldehyde in the aqueous equilibrium mixtures of dimeric dl -glyceraldehyde and dihydroxyacetone.

Determination of Acid Number and Base Number in Lubricants by Fourier Transform Infrared Spectroscopy

This paper describes the development of practical Fourier transform infrared (FT-IR) methods for the determination of acid number (AN) and base number (BN) in lubricants through the combined use of signal transduction via stoichiometric reactions and differential spectroscopy to circumvent matrix effects. Trifluoroacetic acid and potassium phthalimide were used as stoichiometric reactants to provide infrared (IR) signals proportional to the basic and acidic constituents present in oils. Samples were initially diluted with 1-propanol, then split, with one half treated with the stoichiometric reactant and the other half with a blank reagent, their spectra collected, and a differential spectrum obtained to ratio out the invariant spectral contributions from the sample. Quantitation for AN and BN was based on measurement of the peak height of the v(C=O) or v(COO−) absorptions, respectively, of the products of the corresponding stoichiometric reactions, yielding a standard error of calibration of <0.1 mg KOH/g oil. The AN/BN FT-IR methods were validated by the analysis of a wide range of new and used oils supplied by third parties, which had been analyzed by ASTM methods. Good correlations were obtained between the chemical and FT-IR methods, indicating that the measures are on the whole comparable. From a practical perspective, these new FT-IR methods have significant advantages over ASTM titrimetric methods in terms of environmental considerations, sample size, and speed of analysis, as well as the variety of oil types that can be handled. FT-IR analysis combining stoichiometric signal transduction with differential spectroscopy may be of wider utility as an alternative to titration in the determination of acid or basic constituents in complex nonaqueous systems.

A fluorescamine-based assay for the degree of glycation in bovine serum albumin

Abstract The fluorescence resulting from the reaction of a protein with fluorescamine is an indication of the number of free amino groups in that protein, consequently glycated proteins which have fewer free amino groups will show less fluorescence. With the appropriate standards, the difference in fluorescence of glycated and non-glycated proteins can be translated into the number of glycated sites in a protein. Glucose (0·22 m final concentration) was incubated with bovine serum albumin (BSA) (0·1 mg/ml) in a total volume of 50 ml of 0·1 m phosphate buffer pH 7·2 at 37°C for a period of 35 days. In order to assess the effect of metal catalyzed free radical damage to the protein, the incubation was also carried out in the presence of a metal chelating agent EGTA (0·38 mg/ml). As expected, the fluorescence of both mixtures decreased with time, as more lysyl groups became glycated. Calculations based on the standard curve of t -BOC-lysine showed that approximately 18 mol of glucose were incorporated per mol of BSA during the incubation in the presence of EGTA and 23 mol in the absence of EGTA. This difference is explained by the metal catalyzed free radical fragmentation of BSA which exposes more N -terminal amino groups for reaction with glucose.