Caramel analysis

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). 

Other compounds identified in caramels are di-D-fructose and poly(glycosyl) dianhydrides (DFAs). DFAs were found in caramels prepared from D-fructose, D-glucose, and sucrose. The analysis was done after derivatization as TMS (per-0-trimethylsilyl) derivatives or as TMS-oxime (per-O-trimethylsilyl oxime) by... 

Coffey, J.S. and Castle, L., Analysis for caramel colour (Class III), Food Chem., 51, 413, 1994. 

A systematic study was carried out using in parallel 50 standard solutions for each concentration of three natural colorants (curcumin, carminic acid, and caramel as yellow, red, and brown, respectively). No false positive results for synthetics were obtained up to concentrations of 15 and 20 ng/ml for natural red and yellow colorants, respectively, or 110 ng/ml for natural brown colorant. The concentrations have to be high enough to prove that the screening method is able to accurately discriminate natural and synthetic colorants. To make a clear interpretation of the quantitative UV-Vis spectrum, linear regression analysis was used. Quantitative UV-Vis analysis of a dye ° can be calculated according to the following formula ... 

Food colourant analysis characterisation of caramel colours and discrimination of malts from malt extracts. 

To develop a validated method for the quantitative analysis of Class IV caramels in soft drinks. 

Numerous CE separations have been published for synthetic colours, sweeteners and preservatives (Frazier et al., 2000a Sadecka and Polonsky, 2000 Frazier et al., 2000b). A rapid CZE separation with diode array detection for six common synthetic food dyes in beverages, jellies and symps was described by Perez-Urquiza and Beltran (2000). Kuo et al. (1998) separated eight colours within 10 minutes using a pH 9.5 borax-NaOH buffer containing 5 mM /3-cyclodextrin. This latter method was suitable for separation of synthetic food colours in ice-cream bars and fmit soda drinks with very limited sample preparation. However the procedure was not validated for quantitative analysis. A review of natural colours and pigments analysis was made by Watanabe and Terabe (2000). Da Costa et al. (2000) reviewed the analysis of anthocyanin colours by CE and HPLC but concluded that the latter technique is more robust and applicable to complex sample types. Caramel type IV in soft drinks was identified and quantified by CE (Royle et al., 1998). 

There is a recent trend towards simultaneous CE separations of several classes of food additives. This has so far been applied to soft drinks and preserved fruits, but could also be used for other food products. An MEKC method was published (Lin et al., 2000) for simultaneous separation of intense sweeteners (dulcin, aspartame, saccharin and acesulfame K) and some preservatives (sorbic and benzoic acids, sodium dehydroacetate, methyl-, ethyl-, propyl- and isopropyl- p-hydroxybenzoates) in preserved fruits. Ion pair extraction and SPE cleanup were used prior to CE analysis. The average recovery of these various additives was 90% with good within-laboratory reproducibility of results. Another procedure was described by Frazier et al. (2000b) for separation of intense sweeteners, preservatives and colours as well as caffeine and caramel in soft drinks. Using the MEKC mode, separation was obtained in 15 min. The aqueous phase was 20 mM carbonate buffer at pH 9.5 and the micellar phase was 62 mM sodium dodecyl sulphate. A diode array detector was used for quantification in the range 190-600 nm, and limits of quantification of 0.01 mg/1 per analyte were reported. The authors observed that their procedure requires further validation for quantitative analysis. 

Twenty-nine odour-active compounds were detected by using aroma extract dilution analysis (AEDA) [60]. The results of AEDA together with GC-MS analysis showed ethyl 2-methylbutanoate (described as fruity flavour), followed by methyl 2-methylbutanoate and 3-methylbutanoate (fruity, apple-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (sweet, pineapple-like, caramel-like), d-decalactone (sweet, coconut-like), l-( ,Z)-3,5-undecatriene (fresh, pineapple-like), and a unknown compound (fruity, pineapple-like) as the most odour-active compounds. 

The caramel-like smelling HDF has been established as a main contributor to the flavors of several processed foods (Table 17). In addition, it should be noted that in all these foods, on the basis of a high FD-factor, HDF was also by far the most important caramel-like smelling odorant. In the following, the strategy in the HDF precursor analysis will be shown using wheat bread crust, popcorn [88] and malt as the examples. Quantitative measurements were performed by using a stable isotope dilution assay (cf. Section 3.2.). 

With regard to a glucose-proline system, Roberts and Acree277 have examined the sensory aspects in much more detail by applying Charm analysis (see the Olfactory Threshold section above). Four compounds provided most of the aroma 2-acetyl-3,4,5,6-tetrahydro-l//-pyridine (burnt, caramel 63%), 2-acetyl-1-pyrroline (popcorn 19%), 2-acetyl-l,4,5,6-tetrahydro-l//-pyridine (burnt, caramel 12%), and UDMF (cotton candy 4%). All Maillard systems of interest need to be submitted to similarly detailed analyses. 

R. Hardt and W. Baltes, The analysis of caramel colours. Part 1. Differentiation of the classes of caramel colours by Curie-point pyrolysis-capillary gas chromatography-mass spectrometry, Z Lebensm. Unters. Forsch., 1987, 185, 275-280. 

Analysis of the volatile compounds of tamarind revealed the presence of more than 80 compounds. Aromatic and furan derivatives were dominant. The major constituents were 2-phenyl acetaldehyde (25.4% of total volatiles), which has a fruity and honey-like odour, 2-furfural (20.7%), having a caramel-like flavour, followed by hexadecanoic acid (18.1%) and limonene, which has a citrus flavour. A list of the volatile compounds detected in tamarind is given in Table 20.5. 

Hewala II, ZoweU AM, Onsi SM. Detection and determination of interfering 5-hydroxymethylfurfural in the analysis of caramel-colored pharmaceutical syrups. J CUn Pharm Therapeut 1993 18 49-53. 

Because the information on the caramel composition is of practical importance, several procedures have been proposed for their analysis. One such analytical procedure is Py-GC/MS, which has been used for a rapid classification of caramels. The differentiation can be done based on the nature of the compounds generated by pyrolysis. Using GC/MS analysis [1,3] of the pyrolysates, the nature of the caramel can be obtained from the peak intensities, which vary as shown in Table 11.1.2. 

Besides standard Py-GC/MS, a faster procedure to identify the type of caramel color using a pyrolytic step has been developed [4,4a] using comparisons of cumulative mass spectra (see also Section 5.3). These were generated by adding the spectra obtained from a Curie point Py-GC/MS analysis. 

When sucrose is heated above its point of fusion it becomes coloured and ends by becoming transformed into a brown mass, caramel. Glucose also yields a like product. Caramel is evidently a carbohydrate of high molecular weight and a condensation product of sucrose or glucose. From cryoscopic determinations and analysis of its barium compound its formula has been given as Ci26Hx8808o. 

Detection of Caramel, and Some Aspects of the Analysis of Caramel. 234... 

The standardization of ammonia caramek presents a special task. In the course of the manufacture of caramek in the presence of ammonia and ammonium compounds, 4(S)-methylimidazole is formed, and it is neurotoxic. Its content " in caramel is limited by the Food Laws of several countries (for instance, in Austria and the United Kingdom ) and by the WHO r jdations (see also articles by Thier and Wood ). (The specification and analysis of ammonia caramek manufactured in the United... 

Scheme 16 Oxunation-trimethylsilylation derivatization reactirais prior to GC analysis of caramel...

The use of phenyl p-o-glucopyranoside as internal standard and authentic samples of DFAs obtained by synthesis allowed determination of the corresponding response factors for quantitative analysis. The relative abundance of DFA diaster-eomers in a D-fructose caramel obtained by heating a concentrated solution of sucrose in the presence of 10% citric acid was found to correspond to a kinetic distribution, the ot-D-fructofuranose p-o-fructofuranose l,2 2,l -dianhydride 10 being the major component in the mixture (Fig. 4). 

YAYLAYAN, V. A. and KAMINSKY, E. (1998). Isolation and structural analysis of Maillard polymers caramel and melanoidin formation in glycine/glucose model system. Food Chemistry, 63, 25-31. 

Identified by GC/IR by Gianturco et al. (1963) also by Vitzthum and Werkhoff (1976b) after steam distillation at normal pressure and analysis of the neutral fraction by GC/MS. Nishimura and Mihara (1990) found a concentration of 9.8 ppm (MS data given). It is one of the non-volatile caramel... 

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