Micronutrient flow to the osmotic solution during grapefruit osmotic dehydration R. Peiro ´ a , V.M.C. Dias b , M.M. Camacho a , N. Martı ´nez-Navarrete a, * a Department of Food Technology, Universidad Polite ´cnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain b Escola Superior de Biotecnologia, Universidade Cato ´ lica Portuguesa, Rua Dr. Anto ´ nio Bernardino de Almeida, 4200-072 Porto, Portugal Received 27 July 2004; accepted 7 March 2005 Available online 26 April 2005 Abstract The purpose of this work was to quantify the flow of soluble micronutrients, such as acids, minerals and pectins, from the grape- fruit to the osmotic solution (OS) used to dehydrate the fruit when recycling it in successive osmotic dehydration (OD) operations, without reconcentrating. OD was carried out for 3 h at 30 °C with an OS:fruit rate 5:1, using a 55 °Brix sucrose solution. Soluble solids (°Brix), water activity (a w ), pH, ascorbic (AA), citric acid (CA), galacturonic acid and major minerals were measured in the fruit and in the OS as a function of the number of uses (up to 8). Electrical conductivity (EC) and viscosity (l) of the OS were also analysed. The characteristics of the obtained dehydrated grapefruit and the observed recovery of the quantified micronutrient loss by the fruit in the OS allows us to propose the reuse of the OS as a good way of contributing to the economic and ambient profi- tability of the OD operation. Moreover, its final use as ingredient in new food formulations may be proposed. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Osmotic solution; Ascorbic acid; Citric acid; Minerals; Pectin; Electrical conductivity; Viscosity 1. Introduction Fruits are an important part of the human diet as, be- sides contributing with some nutrients, they contain a series of non-nutritive substances, called phytochemical. These bioactive compounds, although having neither a classically defined nutritional function nor being considered essential for the human health, can have a significant impact on prevention of some diseases. Phy- tochemicals have multiple biological effects, including antioxidant activity (Liu et al., 2002; Prior & Guohua, 2000; Wolfe & Liu, 2003), antimutagenic (Wargovich, 2000) antibacterial and angioprotective properties (Venant, Borrel, Mallet, & Van Neste, 1989). This group of compounds mainly includes phenolic compounds, lignans, monoterpenes, etc. Their intake has been asso- ciated with a reduced risk of coronary heart disease and strokes (Hertog, Hollman, & Van de Putte, 1993). On the other hand, also micronutrients present in fruits, such as vitamins, acids, fiber, etc. also contribute to their well known beneficial properties. Nevertheless, in general, fruits are products with a relatively short post-harvest life-span and recent food habits (easy and quick to eat food) have promoted a decrease in the consumption of fresh fruit, which has been replaced by juices, dairy products with added fresh or processed fruits, preserves, confectioneries, etc. (Torreggiani & Bertolo, 2001). To this end, many technologies have been used to make the food system formulation more suitable. One of the possible tech- niques for fruit processing is osmotic dehydration (OD) with sugar solutions, working at middle tempera- tures to preserve product flavour and other sensory properties. 0260-8774/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.03.022 * Corresponding author. Tel.: +34 96 387 9362; fax: +34 96 387 7956. E-mail address: nmartin@tal.upv.es (N. Martı ´nez-Navarrete). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 74 (2006) 299–307