Food Engineering and Physical Properties Pineapple Candying at Mild Temperature by Applying Vacuum Impregnation J. M. BARAT, P. TALENS, C. BARRERA, A. CHIRALT, AND P. FITO ABSTRACT: The candying process usually takes a long time and is accomplished at high temperatures, implying damage in the product sensory properties. Sample vacuum impregnation, followed by successive osmotic steps (2 or more) in sucrose solutions of increasing concentrations, at 15 and 30 °C, has been used in order to improve pineapple candying process. Sample weight (and volume in some cases) has been controlled throughout the process till no notable changes occurred. Then, sample composition and water activity were analyzed. A 3-step process (VI with 25 °Brix followed by successive immersions in 55 and 65 °Brix solutions) provided good process yield, with better sensory properties when working at 15 °C. Keywords: osmotic dehydration, candied pineapple, vacuum pulse, hydrodynamic mechanism Introduction C ANDIED FRUITS OR VEGETABLES ARE defined as solid products made by processing fruits or vegetables with sugars either by impregnating or cooking until the final soluble solid content is at least 65%. In this situation, such a high osmotic pressure within the tissues is developed that micro- bial and biochemical deterioration is pre- vented (DeGregorio and Cante 1992). A general procedure of candying implies the following steps: selecting fruits, washing, trimming, blanching, sulphiting, cooking or impregnation, finishing, and packaging (Chen 1994). Cooking or impregnation is one of the important operations in candy- ing, in which prepared fruits or vegetables, whole or in pieces, are immersed in a syrup. Then they are usually heated at high tem- peratures, although in some cases the ther- mal treatment is avoided (Chen 1994). One of the most important characteristics of the candied products is their translucent appearance. It is obtained by replacing the product gas with an external osmotic solu- tion. This objective is achieved when work- ing at high temperatures (or cycles of high and low temperatures), due to the expan- sion-compression of the gas, or by working under vacuum conditions which induce the degasifying of the sample (Twarogowska 1971). Another typical characteristic of candied products is their high sugar content, which is achieved by using highly concentrated sugar solutions in the last step of the pro- cess. The penetration of solutes in osmotic processes is favored by the use of low pres- sures (Fito 1994; Fito and Pastor 1994) and high temperatures (Lazarides and others 1995). Traditionally, these products are manufactured by submitting them to high temperatures both in the blanching step and during the “cooking” or “impregnation” step. One of the important characteristics of candied products is that their shape, size, and appearance resemble those of the fresh product. This aspect is correlated with the product sensory properties and the process yield, and is heavily dependent on the food volume changes during the process. To re- duce product volume losses during candy- ing, the fruits are initially treated with low concentrated osmotic solutions (OS) (Chen and others 1986), which favor the solute uptake (Lazarides and others 1995; Laz- arides 2001), and the solution concentration is increased until it reaches the level re- quired to obtain the final product. If prod- ucts are treated at the very beginning with a highly concentrated osmotic solution, sam- ple dehydration, with the subsequent shrinkage, is promoted (Barat and others 2001a, 2001b). A large sample shrinkage implies a lesser volume recovery after the concentration equilibrium is achieved (Bar- at and others 1998a). One of the disadvantages with the usual candying methods is that the high temper- atures alter the products’ natural flavor, and so they become very different from the fresh fruit. Nevertheless, when working at low temperatures, the candying process becomes an extremely long one, with low yields, and it is difficult to achieve the de- sired product translucency (Chen 1994; Bar- at and others 1998d, 2000). According to the current preferences for the consumption of fresh-like products, the use of mild temper- atures in fruit-vegetable candying would be desirable. The fruit canning industry has been us- ing vacuum to remove gas from fruit for many years (Macgregor and Kitson 1981). Strachan and others (1954) described a method for obtaining canned fruit by using vacuum to eliminate the gas from the fruit pores. Hawkes and Lazart (1977) observed that the use of vacuum during osmotic de- hydration increased the solute uptake in apples in comparison with those osmodehy- drated at atmospheric pressure. The use of a vacuum pulse to promote product impregnation before the concen- tration steps allowed us to obtain candied products using mild temperatures (Chen 1994, Barat and others 2000), and its appli- cation was patented (Barat and others 1998c). Nevertheless, a systematic analysis in order to improve the candying process for particular products by applying a vacuum pulse at the beginning of the process has not been carried out. In this work, the improvement of the pineapple candying process at mild temper- atures was carried out by analyzing the ef- fect of the osmotic solution concentration during both the vacuum impregnation (VI) step and the successive osmotic steps at at- mospheric pressure. Materials and Methods Sample preparation Fresh pineapple (var. cayenna lisa) ob- tained in a local market was used in the ex- periments. Pineapple rings 1-cm thick and 7 and 3-cm external and internal diameters, respectively, were divided into 8 (for the 1st