Hydroxymethyl furfural, honey

The steps in the formation of 5-hydroxymethyl furfural (HMF) from 1,2-enediol is shown in Formula 4.37. HMF is also used as an indicator for the heating of carbohydrate containing food, e. g., honey. The (retro-Michael addition) water elimination at C-3 and subsequently at C-4 leads to a 1,2-diulose (3,4-dideoxyosone), which after cyclization to a hemiacetal, a dihy-drofuran, releases another molecule of water, producing HMF. In the same way, e. g., furfural can be made from pentoses and 5-methylfurfural from the 6-methylpentose rhamnose. 2-Hydroxyacetylfuran, which is preferentially formed from fructose, can be obtained starting from the corresponding 2,3-enediol by water elimination at C-4, followed by C-5 (Formula 4.38). 

The most prominent enzymes in honey are a-glucosidase(invertase or saccharase), a- and P-amylases (diastase), glucose oxidase, catalase and acid phosphatase. Average enzyme activities are presented in Table 19.14. Invertase and diastase activities, together with the hydroxymethyl furfural content, are of significance for assessing whether or not the honey was heated. 

Honey color generally darkens on storage, the aroma intensity decreases and the content of hydroxymethyl furfural increases, depending on pH,... 

Fig. 19.16. Hydroxymethyl furfural formation in honey versus temperature and time (according to White, 1978)...

Artificial honey contains invert sugar (>50%), sucrose (<38.5%) water (<22%), ash (<0.5%) and, when necessary, saccharified starch products (<38.5%). The pH of the mixture should he >2.5. The aroma carrier is primarily phenylacetic acid ethyl ester and, occasionally, diacetyl, etc. Hydroxymethyl furfural content is 0.08—0.14%. The product is often colored with certified food colors. 

Artificial honey is mostly inverted sucrose from beet or cane sugar and is produced with or without starch sugar or starch syrup. It is adjusted in appearance, odor and flavor to imitate tme honey. Depending on the production method, such creams contain nonsugar constituents, minerals, sucrose and hydroxymethyl furfural. 

To illustrate the use of LDA for food authentication, an example involving the classification of honey samples according to their floral origin will be used [15]. In particular, the data set comprises the results of 15 determinations— pH free, lactone, and total acidity diastase water content specific conductivity dextrose, fiructose and DP2 colour specific rotation hydroxymethyl-furfural (HMF) content and (on the whole sample and on the... 

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