**4.2 Hydroxymethyfurfural**

Hydroxymethylfurfural (HMF) is an intermediate compound formed during the Maillard reaction and by the degradation of hexoses at high temperatures at acid conditions (Figure 4) (Arribas-Lorenzo & Morales, 2010).

#### Fig. 4. Chemical structure of HMF

Spectrophotometric (colorimetric) methods, which are the most usual methods for HMF determination in food, are of limited accuracy since other chromophores in foods may absorb radiation in the same wavelength region, interfering with the results. In addition, colorimetric methods have low sensitivity. Chromatographic methods (liquid or gas high resolution chromatography) are more accurate and sensitive for this purpose, and one of the major advantage of the use of chromatographic methods is the individual determination of HMF and furfural, what can not be achieved by spectrophotometric methods (Erbersdobler & Somoza, 2007; Morales *et al.*, 1997; Rufiàn-Henares *et al.*, 2001).

HMF formation is directly linked to the heat intensity applied to food, and because is not usually present in raw and fresh foods, it is considered a thermal damage marker for products containing high carbohydrate concentrations. Moreover, it can be used to monitor the thermal process applied to several different food products such as: breakfast cereals containing dried fruits; caramel and honey; pasta and bakery products (Rufiàn-Henares & Delgado-Andrade, 2009; Rufiàn-Henares *et al.,* 2006).
