5-HMF

The mechanism of HMF formation from D-fructose and sucrose was reviewed by Antal et a/.48 Several arguments were advanced for favoring a mechanism involving furanose rings and a fructose oxocarbonium ion over an open-chain [3-elimination mechanism that proceeds via an enediol intermediate to a... 

The chemical composition of caramel color is not yet fully understood but some compounds identified in the low weight fraction are considered caramel markers. All caramel classes contain 5-hydroxymethyl)-2-furaldehyde (5-HMF). In caramel classes in and TV, 4-methyUmidazole (4-MeI) has been detected, while 2-acetyl-4(5)-tetrahydroxybutylimidazole (THI) was found only in class HI caramel colors. The analysis of five caramel III samples by SPE/HPLC-MS revealed concentrations between 28.3 and 46.8 iglg THI and 73.3 to 187.8 for 4-MeP (see Figure 5.2.3). 

In the US, more than 80% of caramel is used to color drinks such as colas and beers. Another important application is the coloring of blended whiskeys produced by mixing straight whiskeys with neutral spirits. The addition of neutral spirits to the straight whiskey produces a loss of color that can be compensated by the addition of caramel. Straight whiskeys are colored during aging for 2 yr in freshly charred oak barrels and contain furfural and 5-HMF in a ratio of 2 to 2.6 1, while the ratio... 

Caramel color interacts with other food components. As an example, a concentration higher than 700 ppm caramel in cola increased the rate of hydrolysis of the aspartame, forming alpha-L-aspartyl-L-phenylalanine. Caramelization products inhibited enzymic browning by 85.8 and 72.2% when heated at pH 4 and 6, respectively, for 90 min. The highest inhibitory activity was found for the fraction with molecular weight of 1000 to 3000. Caramel is often used for adulteration of juices and other foods like honey or coffee. It can be determined by quantification of marker molecules such as 5-HMF, 4-Mel, and DFAs. ... 

Higher profits are the major incentive for unlawful adulteration. The traditional adulterants are inverted sugar syrup, conventional com syrup, and high-fructose com syrup. Dehydration of fructose can produce hydroxymethylfurfural (HMF). HMF is usually indicative of adulteration with inverted sugar syrup. However, it is somewhat ambiguous because HMF can legally be present in honey that has been subjected to heat or abusive storage. 

Enzyme activity can indicate the exposure of honey to heating and long storage. This criterion is not more accurate than the HMF content value because enzyme activities vary with honey samples. The diastase activity is usually associated with heat treatment. However, its activity gives only an indication about the processing (heat treatment) of the honey but is not suitable for the detection of the origin. 

HMF is an important versatile sugar derivative and is a key intermediate between bio-based carbohydrate chemistry and petroleum based industrial organic chemistry (1, 2). The most coimnon feedstock for HMF is fructose and reactions are carried out in water-based solvent systems using acid catalysis (3,4). HMF is unstable in water at low pH and breaks down to form levulinic acid and formic acid, resulting in an expensive HMF recovery process. In strongly polar organic co-solvents, such as dimethylsulfoxide (DMSO), levuhnic acid formation is reduced and HMF yields are improved (5). 

Recently several pubhcations have examined replacing aqueous solvents with ionic liquids. Since simple and complex sugars are soluble in many imidazolium hahdes, water is not required as a co-solvent and degradation of HMF is minimal. Lansalot-Matras et al. reported on the dehydration of fmctose in imidazolium ionic liquids using acid catalyst (6). Moreau et al. reported that l-H-3-methylimidazolium chloride has sufficient acidity to operate without added acid (7). And we reported that a 0.5 wt% loading (6 mole% compared to substrate) of many metal halides in 1-ethyl-3-methylimidazohum chloride ([EMIM]C1) result in catalytically active materials particularly useful for dehydration reactions (8). 

When starting with fmctose, we obtained high HMF yields using a number of metal halides (batch reaction, 3 h, 80°C). Metals halides successfully tested... 

Catalyst Model Compound Model Compound to Glucose Ratio (mole ratio) Glucose Conversion (mol%) HMF Yield (mol%) Other ( mol%)... 

The addition of glyceraldehyde dimer had a significant impact on the catalysis of glucose. CrCf is the preferred catalyst and resulted in a 94% conversion of glucose with a 70% yield of HMF. In the presence of glyceraldehyde the conversion decreased to about 60% and the yield of HMF fell to 20%. This means that HMF selectivity also decreased (selectivity = yield/conversion). The loss of selectivity was primarily due to formation of heavies via intermolecular condensation reactions. The heavies were not characterized. 

Fig. 10.1. Localization of Acanthocheilonema viteae chitinase in intrauterine and newborn mf by IFAT with mAb 24-4 (left panels) and corresponding light microscope photographs (right panels). (A), (B) Uterine contents of female A. viteae with nearly mature mf inside the eggshell, younger embryonic stages and a mature, hatched mf. (C), (D) Newborn mf. Note that fluorescent mf are swollen and stumpy. Bars represent 50 pm es, embryonic stages nmf, nearly mature mf hmf, hatched mf.

AW, Acid-washed Choi, Cholesterol DMAP, 4-(Dimethylamino)pyridine DMF, N,/V-Dimethylformamide DMTr, Di(p-niethoxyphenyl)phenyl methyl GalNAc, N-Acetylgalactosamine, 2-acetamido-2-deoxy-D-galactose HMF, 5-Hydroxymethylfur-fural, 5-(hydroxymethyl)-2-furaldehyde INOC, Intramolecular nitrile oxide-alkene cycloaddition Lea, Lewisa Lex, Lewisx MOM, Methoxymethyl MP, p-Methoxyphe-nyl MS, Molecular sieves NIS, N-Iodosuccinimide PCC, Pyridinium chlorochromate PDC, Pyridinium dichromate PMA, Phosphomolybdic acid PMB, p-Methoxybenzyl ... 

Heterogeneous catalysts, particularly zeolites, have been found suitable for performing transformations of biomass carbohydrates for the production of fine and specialty chemicals.123 From these catalytic routes, the hydrolysis of abundant biomass saccharides, such as cellulose or sucrose, is of particular interest. The latter disaccharide constitutes one of the main renewable raw materials employed for the production of biobased products, notably food additives and pharmaceuticals.124 Hydrolysis of sucrose leads to a 1 1 mixture of glucose and fructose, termed invert sugar and, depending on the reaction conditions, the subsequent formation of 5-hydroxymethylfurfural (HMF) as a by-product resulting from dehydration of fructose. HMF is a versatile intermediate used in industry, and can be derivatized to yield a number of polymerizable furanoid monomers. In particular, HMF has been used in the manufacture of special phenolic resins.125... 

SCHEME 29. Dehydration of fructose and xylose to HMF and furfural, respectively. 

Gonzales and Laird145 have shown that smectites abiotically catalyze dehydration of glucose to form furfural under conditions similar to those found in soils. Four smectite clay minerals were used (saturated with Na, Ca, Fe, or Al), and the formation of HMF and furfural was detected by high-pressure liquid chromatography. The polymerization of furfural may thus be a pathway to the formation of new humic materials in soils. 

The switch from feed to displacer changes M roots, generating M boundaries. All of these boundaries are self-sharpening, except the boundary associated with the transition from hMF to cti m+i that can be self-sharpening or diffuse depending on the relative value of these roots. Note that only one root changes value across a particular boundary. 

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