Modelling of 5-hydroxymethylfurfural photo-degradation by UV irradiation. Influence of temperature and pH Karla Aguilar a , Alfonso Garvin a, ⁎, Ebner Azuara b , Albert Ibarz a a Food Technology Department, University of Lleida (Catalonia), Av. Rovira Roure, 191, 25198 Lleida, Spain b Food Science and Technology Department, Institute of Basic Sciences, University of Veracruz Mexico, Dr. Luis Castelazo Ayala Av., Xalapa, Veracruz 91190, Mexico abstract article info Article history: Received 18 December 2014 Received in revised form 17 February 2015 Accepted 28 February 2015 Available online 8 March 2015 Keywords: UV Radiation Photo-reactor Photo-degradation Juice HMF Treatment The main aims of this study were (a) to prove that the UV irradiation of juices prevents the formation of 5- hydroxymethylfurfural (HMF), (b) to know the influence of temperature and pH on the UV photo-degradation of the HMF when it is unfortunately present in the juice (for example, after a previous thermal treatment or after a long storage period) and (c) to model this photo-degradation, proposing a reaction mechanism related to the power absorbed by the solution that depends on the HMF concentration. For these purposes a mid-pressure mercury lamp with emission wavelengths between 250 and 740 nm was used. Firstly, nectarine juice was irradiated to be sure that HMF was not synthesised. Then, aqueous solutions of 100 mg·L -1 HMF at pH 3, 4 and 5 were irradiated at 12, 25, 35 and 45 °C for 120 min. Aliquots were analysed to measure their HMF contents and absorption spectra. The photo-degradation data fitted well to both zero-order and pseudo-first-order kinetic models and the constant values were similar. The increases in both temperature and pH enhanced the photo-degradation, the optimal conditions inside the ranges studied being 45 °C and pH = 5, when a reduction of 60% of the initial content of HMF was reached. The spectral radiant power absorbed by the whole solution and the incident spectral radiant power reaching any depth of the reactor were evaluated taking into account the linear spherical emission model and using the Simpson integration method. Its dependence on the HMF concentration was also studied. A three stage degrada- tion mechanism was proposed, matching both the zero-order and pseudo-first-order kinetic models previously obtained. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction 5-Hydroxymethylfurfural (HMF) has been identified in many heat- processed foods including fruit juices (Anese, Manzocco, Calligaris, & Nicoli, 2013; Anese & Suman, 2013; Morales, 2009). It is formed in the Maillard reaction as well as during caramelization as the result of dehy- dration of ketopentoses, particularly in acidic or high-temperature envi- ronments (EFSA, 2011; Ibarz, Casero, Miguelsanz, & Pagan, 1989; Lee, Sakai, Manaf, Rodhi, & Saad, 2014). As HMF is not present in fresh fruit and is generated naturally in sugar-containing food during processing, it has become a parameter related to the freshness and quality of foods (Gaspar & Lucena, 2009). High values reveal excessive thermal treatment, inappropriate storage conditions and a likely loss of quality, i.e., loss of L-ascorbic acid, changes in such physical properties as colour, and sensorial characteristics (AIJN, 2001; Chen, Yang, Chen, & Liu, 2009). In addition, HMF may induce genotoxic and mutagenic effects in bacterial and human cells and promote colon and liver cancer in rats and mice (Glatt & Sommer, 2006; Monien, Engst, Barknowitz, Seidel, & Glatt, 2012; Zhang et al., 1993), although there is no evidence for carci- nogenic and genotoxic effects in humans (Abraham et al., 2011; Capuano & Fogliano, 2011; EFSA, 2011). Given its probable genotoxicity, subchronic toxicity and carcinoge- nicity, the EFSA considered that it would be prudent to reduce the HMF content as much as technologically feasible (EFSA, 2011). AIJN (2001) recommended a maximum content between 10 and 20 mg·kg -1 depending on the fruit juice. In order to reduce the HMF content in cooked foods, some recent re- views (Anese & Suman, 2013; Anese et al., 2013) summarize the possi- bilities studied to date. The first option is a temperature reduction in the thermal treatment in order to minimize the synthesis reaction of HMF. It can be achieved by heating at low temperatures and low pressures for long times. Dielectric (radiofrequency and microwave) heating can also be used because heat is generated by the movement of the water molecules in the solution. Thus, a lower temperature is necessary to achieve the desired hygienic and sensory properties. The second option Food Research International 71 (2015) 165–173 ⁎ Corresponding author. Tel.: +34 973 702907; fax: +34 973 702596. E-mail address: garvin@tecal.udl.cat (A. Garvin). http://dx.doi.org/10.1016/j.foodres.2015.02.019 0963-9969/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres