Effect of sugar, citric acid and egg white type on the microstructural and mechanical properties of meringues Fabio Licciardello b , Pierangelo Frisullo a , Janine Laverse a , Giuseppe Muratore b , Matteo Alessandro Del Nobile a,c,⇑ a Department of Food Science, University of Foggia, Via Napoli, 25, 71100 Foggia, Italy b Department of Agricultural and Food Productions (DISPA), Section of Food Technology and Microbiology, University of Catania, Via Santa Sofia, 98, 95123 Catania, Italy c Istituto per la Ricerca e le Applicazioni Biotecnologiche per la Sicurezza e la Valorizzazione dei Prodotti Tipici e di Qualità, Università degli Studi di Foggia, BIOAGROMED, Via Napoli, 52, 71100 Foggia, Italy article info Article history: Received 7 March 2011 Received in revised form 2 August 2011 Accepted 19 August 2011 Available online xxxx Keywords: Food microstructure Egg white Mechanical properties Meringues X-ray microtomography abstract Meringues are characterized by a predominant air phase and their overall quality is intimately related with microstructure. The formation of meringues microstructure relies on the capacity of egg white (EW) proteins to form voluminous and stable foams and it is ultimately related with the chemical prop- erties of proteins and with the addition of ingredients such as sugars, salts, acids and surfactants. The study aimed at assessing the influence of sugar/EW ratio, citric acid and EW type on the micro- structural and mechanical properties of meringues. Meringues prepared with different sugar/EW, citric acid level and different EW type were subjected to microstructural analysis by X-ray microtomography and to mechanical assessment by compression tests. Results demonstrate the ability of X-ray microtomography to reconstruct the 3D microstructure of meringues allowing the measurement of porosity, size, shape and distribution of pores. Citric acid, sugar concentration and EW type play a fundamental role on meringues microstructural parameters and mechanical properties. Low sugar/EW ratios as well as increasing citric acid levels increase the air phase and result in a softer texture of meringues. Moreover, low sugar/EW ratios and increasing citric acid in the meringue result in a reduction of pore size and also influence the shape of pores. Meringues micro- structural and mechanical properties are affected by the EW quality: fresh and pasteurized EWs and EWs stored at refrigerated temperatures scored the highest structural and mechanical performances, while powdered and frozen EWs and albumens from old eggs showed the worst results. Not only the balance among ingredients but also the choice of raw materials can strongly affect the final quality of meringues. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Meringues are confectionery products simply made of EW sugar and small amounts of salts and acids added as foam stabilizers, characterized by a predominant (>80%) air phase. Such characteris- tic relies on the capacity of EW proteins to form voluminous and stable foams. Meringues, due to their simple composition, repre- sent a model system to study the behavior of EW froths, which are the basis for other, more complex, bakery products. The characteristics of meringues are related to their microstruc- ture that, in turn, depends on the composition and on the balance among ingredients. The formation of food microstructure is a com- plex phenomenon which, in the specific case of EW froths, relies on a structure-building phase, i.e. whipping, and on the opposite con- curring stage of structure disruption, i.e. foam drainage (Kato et al., 1983; Campbell and Mougeot, 1999; Foegeding et al., 2006). Such phases are regulated by foamability and foam stability, respec- tively, two properties related with the chemical properties of pro- teins and with the addition of other ingredients such as sugars, salts, acids and surfactants (Li-Chan and Nakai, 1989; Raikos et al., 2007). Meringues are subject to a heat treatment aimed at ‘‘freezing’’ the formed structure by converting the foam from a li- quid to a solid. The 3D microstructural information can provide a better under- standing of the physical structure of the product and from an engi- neering perspective; knowledge about the microstructure of foods can be used to identify the important processing parameters that affect the quality of a product. Structure–property relationships can strongly affect the physiochemical, sensorial, technological and even nutritional properties of foods. Processes are no longer designed from a macroscopic level; knowing the properties of foods on the micro scale determines the process specification. Given the enormous success of X-ray microtomography (lCT) in medical applications, material science, chemical engineering, 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.08.021 ⇑ Corresponding author at: Department of Food Science, University of Foggia, Via Napoli, 25, 71100 Foggia, Italy. Tel./fax: +39 881 589 242. E-mail addresses: delnobil@unina.it, ma.delnobile@unifg.it (M.A. Del Nobile). Journal of Food Engineering xxx (2011) xxx–xxx Contents lists available at SciVerse ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng Please cite this article in press as: Licciardello, F., et al. Effect of sugar, citric acid and egg white type on the microstructural and mechanical properties of meringues. Journal of Food Engineering (2011), doi:10.1016/j.jfoodeng.2011.08.021