Effects of pulsed electric energy on sucrose nucleation in supersaturated solutions Oleksii Parniakov a, * , Pierre Adda a , Olivier Bals a , Nikolai Lebovka a, b , Eugene Vorobiev a a Sorbonne Universites, Universite de Technologie de Compiegne, Laboratoire de Transformations Integrees de la MatiereRenouvelable, EA 4297, Centre de Recherches de Royallieu, BP 20529, 60205, CompiegneCedex, France b Institute of Biocolloidal Chemistry Named After F. D. Ovcharenko, NAS of Ukraine, 42, blvr. Vernadskogo, Kyiv, 03142, Ukraine article info Article history: Received 15 September 2016 Received in revised form 27 November 2016 Accepted 7 December 2016 Available online 10 December 2016 Keywords: Pulsed electric energy Sucrose Crystallization Nucleation abstract The effects of pulsed electric energy (PEE) on sucrose nucleation in supersaturated aqueous solutions are studied. The supersaturation degree (S ¼ 1.32) and temperature (T ¼ 25  C) were fixed. Pulsed electric field (PEF) treatment without discharge was performed in the chamber with plane-to-plane electrodes geometry using exponential pulses and electric field strength of E ¼ 20e80 kV/cm. High voltage electrical discharge (HVED) treatment was applied in the chamber with rod-to-plane electrodes geometry at E ¼ 20e80 kV/cm. Different number of PEE pulses was applied, n ¼ 1e20. An insignificant reduction of the induction period of nucleation was observed for the PEF treated sample (n ¼ 10), t ind z 100 min. However, after the HVED treatment (n ¼ 10) the induction period was only t ind z 55 min. For the HVED assisted nucleation, the time of effective crystallization decreased and a maximum rate of crystallization increased with increasing of E and n. The obtained data evidence promising perspectives for enhancing sucrose crystallization by the HVED treatment. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Sugar is one of the most consumable products in the world (Asadi, 2007; Schiweck et al., 2007). It is used predominantly in the production of sweet food and beverages, such as petit suisse cheese (Pereira et al., 2016), yogurt (Batista et al., 2015), and dulce de leche (Gaze et al., 2015). However, there are need for sugar reduction or optimisation of its level in food products (Esmerino et al., 2015; Morais et al., 2014; Paix~ao et al., 2014). Crystallization is the vital step in manufacturing of sugar (Vaccari and Mantovani, 1995). Crystallization includes nucleation and crystal growth. The phe- nomenon of nucleation reflects transition from the metastable supersaturated phase to a thermodynamically stable phase and it occurs spontaneously when the Gibbs free energy becomes nega- tive (DG < 0). For spherical nucleus of a crystal with radius of r the value of DG is a sum of the surface (positive) and volume (negative) contributions: DG ¼ 4pr 2 g ð4p=3Þr 3 DG t (1) where g is the surface tension of the crystal fluid interface, DG t is the free energy change of the transformation per unit volume. The critical nucleus radius is of order 1e7.5 nm (Khaddour et al., 2010). To stimulate nucleation, seeding is most commonly used in the sugar industry. Introduction of numerous seeds into the supersat- urated solution provokes nucleation on seeds and minimizes spontaneous nucleation. The nucleation controlled by seeding gives a narrow size distribution and a uniform structure of crystals. Ef- fects of different physical factors (for example, stirring, air bubble injection, ultrasonication, action of electric and magnetic fields) on the rate of sucrose nucleation attract great attention (Asadi, 2007). For example, a good stirring is important in crystallization to equalize the concentration and the temperature, and to increase the rate of crystal growth (Asadi, 2007; Brunner and Geckert, 1996; Li et al., 2003; Stasiak and Dolatowski, 2008). The air bubble in- jection in sucrose solution (with supersaturated degree of 1.2) can result in shock nucleation (Brunner and Geckert, 1996). Power ultrasound has been proved to be a promising technique to stimulate or enhance the nucleation (Saclier et al., 2010; Zhang et al., 2015). The nucleation is provoked by pressure changes, cavitation phenomena and formation of cavitation bubbles that act as the nuclei themselves (Stasiak and Dolatowski, 2008). Ultra- sonication provokes air bubbles cavitations and influences on the mean size, size distribution and shape of sucrose crystals (Li et al., * Corresponding author. E-mail address: oleksii.parniakov@utc.fr (O. Parniakov). Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng http://dx.doi.org/10.1016/j.jfoodeng.2016.12.003 0260-8774/© 2016 Elsevier Ltd. All rights reserved. Journal of Food Engineering 199 (2017) 19e26