Presence of furosine in honeys Mar Villamiel, M Dolores del Castillo, Nieves Corzo* and Agustı ´n Olano Instituto de Fermentaciones Industriales (CSIC), C/Juan de la Cierva 3, E-28006 Madrid, Spain Abstract: Nineteen commercial samples with a shelf-life of 2 years) and two artisanal samples freshly collected and stored for 1 year respectively) of Spanish honeys were analysed for pH, protein content and furosine content. Most of the samples had pH values and protein contents within the limits reported in the literature. The presence of furosine was con®rmed by comparison of its retention time with that of a furosine standard and by HPLC±MS. The level of furosine in the samples studied ranged from 4.32 to 13.62g kg 1 protein. The lowest furosine value was observed in the freshly collected artisanal sample. Heat treatment under severe conditions 90 °C for up to 135min) increased the furosine content from 4.43 to 14.38g kg 1 protein. The results show that furosine seems to be a promising indicator to detect overheating during honey manufacture. # 2001 Society of Chemical Industry Keywords: furosine; honeys; Maillard reaction INTRODUCTION Honey is a complex food mainly composed of carbo- hydrates 607±778gkg 1 ) and water 124±203g kg 1 ). 1 A large number of minor components includ- ing proteins 5gkg 1 ) 2 and free amino acids 1gkg 1 ) 3 are also present in this food. To destroy yeast and stabilise liquid honey, the processing of this product consists of heating com- bined with ®ltration under pressure. 4 Owingtothelow pH value of honey about 3.9) and its high fructose and glucose content, the heating has to be mild eg 65 °C for 30s). 3 However, some honey samples are subjected to higher temperatures for liquefaction and/or pasteurisation purposes. In addition, honey is usually stored at room temperature for very long periods years). These processes may lead to changes due to caramelisation of carbohydrates. In the acid medium of honey, dehydration of carbohydrates is favoured, leading to the formation of 5-hydroxymethyl)-2- furaldehyde HMF) and other furfural compounds. Since honey contains low amounts of protein, the Maillard reaction can also take place. The Amadori rearrangement, giving rise to Amadori compounds, is considered the key step of the Maillard reaction, and further reactions yield HMF and some products similar to those resulting from caramelisation. Although considerable work has been reported on theMaillardreactioninhoney,nodataareavailableon the presence of Amadori compounds. Furosine, which is generated during acid hydrolysis of the Amadori compound fructosyl-lysine, is considered a useful indicator of the extent of damage during the early stages of the Maillard reaction. Furosine is used to test processing and storage effects in foods such as dairy products, baby cereals and pasta 5±7 as well as tomato products, soybeans, barley and malt. 8±10 In the present paper we investigate the presence of furosine in the acid hydrolysates of several commercial honeys to evaluate the early stages of the Maillard reaction in this product. MATERIALS AND METHODS Honey samples Nineteen commercially available honeys from various sources were purchased at different local markets. Two of them were honeydew A, B), nine were uni¯oral orange blossom: C±F; eucalyptus: G, H; rosemary: I, J; heather: K) and eight were multi¯oral the honey contained nectar from various plants) L±R). All samples had a shelf-life of 2 years. In addition, two unheated artisanal multi¯oral samples, S and T freshly collected and stored for 1 year at room temperature respectively), were directly purchased from the same beekeeper. The pH of the honey samples was measured in a MicropH2001 pH meter Crison Instruments, Barcelona, Spain) according to AOAC method 962.19. 11 Heating experiments Sample I 13g) was heated in a screw-capped Pyrex vial with PTFE-faced septa, immersed in a thermo- statically controlled 0.5 °C) water bath, with stir- ring, to 90 °C for 45, 90 and 135min. After treatment, samples were immediately cooled for 10min in an ice- water bath. (Received 7 April 2000; revised version received 29 June 2000; accepted 19 February 2001) * Correspondence to: Nieves Corzo, Instituto de Fermentaciones Industriales (CSIC), C/Juan de la Cierva 3, E-28006 Madrid, Spain E-mail: ifics19@ifi.csic.es Contract/grant sponsor: European Union Contract/grant sponsor: Ministerio de Agricultura, Pesca y Alimentacio ´n; contract/grant number: API 99-016 # 2001 Society of Chemical Industry. J Sci Food Agric 0022±5142/2001/$30.00 790 Journal of the Science of Food and Agriculture J Sci Food Agric 81:790±793 online: 2001) DOI: 10.1002/jsfa.874