Furfural detection

Furfural is very thermally stable in the absence of oxygen. At temperatures as high as 230°C, exposure for many hours is required to produce detectable changes in the physical properties of furfural, with the exception of color (17). However, accelerating rate calorimetric data shows that a temperature above 250°C, in a closed system, furfural will spontaneously and exothermically decompose to furan and carbon monoxide with a substantial increase in pressure. The pressure may increase to 5000 psi or more, sufficient to shatter the container (18). 

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. 

Furfural gives two characteristic colour reactions which serve for qualitative detection. With phloroglucinol and hydrochloric acid (1 part concentrated acid, 1 part water) a cherry-red colour is produced on boiling with a solution of aniline acetate a red colour is produced even in the cold. 

When heated with a strong acid, pentoses and hexoses are dehydrated to form furfural and hydroxymethylfurfural derivatives respectively (Figure 9.20), the aldehyde groups of which will then condense with a phenolic compound to form a coloured product. This reaction forms the basis of some of the oldest qualitative tests for the detection of carbohydrates, e.g. the Molisch test using concentrated sulphuric acid and a-naphthol. 

Beer Analysis. Nine aldehydes were detected in analyzed beer (Figure 5). The resolution of two peaks, representing two geometrical isomers of each aldehyde, was good, except for furfural, where the first peak was clustered with a peak of an uncharacterized compound. 

A new, fast, sensitive, and solventless extraction technique was developed in order to analyze beer carbonyl compounds. The method was based on solid-phase microextraction with on-fiber derivatization. A derivatization agent, 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBOA), was absorbed onto a divinyl benzene/poly(dimethylsiloxane) 65- xm fiber and exposed to the headspace of a vial with a beer sample. Carbonyl compounds selectively reacted with PFBOA, and the oximes formed were desorbed into a gas chromatograph injection port and quantified by mass spectrometry. This method provided very high reproducibility and linearity When it was used for the analysis of aged beers, nine aldehydes were detected 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, furfural, methional, phenylacetaldehyde, and (E)-2-nonenal. (107 words)... 

Analytical procedures are found in Refs 6, 7, 12 14. Furfural may be detected by adding a few drops of aniline in acetic acid an intense red color develops at once if. present. Such other forfurals as the 5-methyl, and 5-hydtoxymethyl will also give a positive test. Furfural has low toxicity providing adequate ventilation and skin protection against contact is used Refs 1) Beil 17, 272, (145) [305]... 

Results of mass balance and recovery calculations for the components of the experimental system (sample drum, resin columns, and column effluent) are shown in Table III. Resin breakthrough was detected (and at high levels) for only three compounds furfural,... 

In order to detect furfural degradation products of possible carbohydrates in the rock specimens (4), a 25-gram sample of crushed rock was treated with excess 6N hydrochloric acid, and 25 ml. of the resulting solution was collected by boiling into the empty cup of a Soxhlet extractor. Scanning the distillates... 

A comprehensive study of the volatiles from strawberries was conducted by McFadden et al. (236). Over 150 components were detected, and the major volatiles were identified from strawberries. The major components included alcohols, esters, acetals, aldehydes, furfural, methyl furfural, aromatic aldehydes, and ketones. 

Detection and Determination of Furfural.—(A) Qualitative Test 10 c c of the spirits are shaken with 10 drops of aniline and 1 c.c. of concentrated acetic acid and then allowed to stand in presence of furfural, a red coloration forms either immediately or after some time. 

The same conditions also resulted in the maximum glucose yield, 17.2 g/ 100 g of SFF. At the pretreatment conditions used, the formation of fermentation-inhibiting compounds was very low (results not shown) (16). The concentration of furfural in the slurry pretreated at 190°C for 10 min was about 0.3 g/L. No HMF was detected. 

Pereira et al. (2010c,d) found that the levels of 5-hydroxymethyl-2-furfural and 2-furfural in sweet wines (Malvasia, Boal) increased slight for sweet (Malvasia) when estufagem was conducted at 30 °C. In dry wines (Sercial), their content was found below to its detection threshold. At higher temperatures (45 and 55 °C) a continuous increase was observed. Thus, the presence of 5-hydroxymethyl-2-furfural can be easily controlled during baking process by adjusting the temperature. 

Paperboard. Vaccaro identified several volatiles released from PET coated paperboard during heating (37.)- When the paperboard and PET films were analyzed separately to establish the origin of the released volatiles, no volatiles were detected from the PET film used for the coating during analysis. All of the volatiles detected were released from the paperboard. Seven compounds were identified acetone, 2,3-butanedione, chloroform, furan, furfural,... 

Likewise, furfural (peak 16, 8.1 minutes) was observed in both microwave and conventionally baked cake, but at a significantly higher level in the latter. Methyl pyrazine (peak 15, 7.8 minutes), furan methanol (peak 17, 9.0 minutes), and acetyl furan (peak 22, 10.9 minutes), were present in the conventional cake samples as were two unidentified compounds (peaks 3 and 9, 3.3 and 5.0 minutes) observed to have buttery, caramel-like aromas. Several other minor peaks were also observed only in the conventional cake. It should be noted that a few nutty, brown, and potato type smells were detected in areas of the conventional cake chromatogram where no peaks were integrated. These aromas suggest the presence of other Maillard compounds in the extract at levels too low for instrumental detection. 

The reaction of hemicellulose to heated, concentrated (12%) HC1 is a test of the former s presence. Detection is by the violet or red color developed by one or more of the reaction products (chiefly furfural) with orcinol or phloroglucinol. The coloration is either blue, greenish, or nonexistent with KI-I2 (Whistler and Smart, 1953). The quantity of furfural produced relates directly to the quantity of pentosan present (Smith and Montgomery, 1959). Under the same reaction conditions, hexoses produce hydroxyme-thylfurfural. Furfural is steam-distillable hydroxymethylfurfural is not. 

Adedeji et al. (1993) used a direct thermal desorption technique (220°C) to analyse the volatiles from beans that might cause the thermal degradation and transformation of sugar into common volatile compounds such as 3,5-dimethyl-2,4(3H,5H)-furandione and 3,5-dihydroxy-6-methyl-2,3-dihydro-4H-pyran-4-one. This last compound was detected at a high concentration (3880 ppm) in Mexican vanilla, being the third most abundant compound after vanillin and 2-furfural, and far more abundant than vanillic acid, p-hydroxy-benzaldehyde or p-hydroxybenzoic acid. 

---