Study of cooking quality of spaghetti dried through microwaves and comparison with hot air dried pasta Teresa De Pilli * , Roma Giuliani, Antonio Derossi, Carla Severini Department of Food Science, University of Foggia, Via Napoli 25, 71100 Foggia, Italy article info Article history: Received 11 November 2008 Received in revised form 28 May 2009 Accepted 2 June 2009 Available online 6 June 2009 Keywords: Cooking quality Drying Hot air Microwave Spaghetti abstract The aim of this work is to evaluate and compare the effects of microwave and conventional drying (hot air) on the quality characteristics of cooked pasta. Experiments were carried out on pasta type spaghetti. A huge difference was noticed between times necessary to dry samples by hot air and by microwaves, in fact in the first case, the drying time was on the average 204.5 min vs. 61.7 s of microwave treatment (average). The gelatinization degree of samples dried by hot air was faster than that of those dried by microwaves: the medium values of kinetic constant of gelatinization of samples dried by hot air and microwaves were 7.5 and 5.2, respectively. Similar total organic matter values suggest that the cooking quality of samples differently dried was comparable. Moreover, samples dried by microwaves were thicker than pasta dried by hot air (37.8 vs. 27.4). Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Heating of foods exposed to a microwave field is practically instantaneous, contrasting with the conventional methods of heat- ing whereby heat is transported from the surface to the center 10– 20 times more slowly. Even though the industrial applications of microwaves, mainly in the food industry, have not had the same development like the microwave domestic applications (Schiffmann, 1992), one of the most well succeeded industrial operations was the microwave assisted drying of pasta. Several advantages came out for the first time after the joint work of a pasta processor in Canada (Lipton) and an equipment manufacturer in USA (Cryodry) that was en- gaged with the task of adapting a microwave stage to an existing dryer operating with a conventional process. Such an experiment is described in a paper by Maurer et al. (1971), where they enumer- ated a few factors to be considered when evaluating the economy of the microwave process as compared with the conventional one: advantages for the product reflected by the pasta re-hydration or cooking time reduced to half; advantages for the process that is shorter production time, thus reducing the area occupied by 90%, in spite of doubling the final capacity; higher temperatures al- lowed by the process granting a sharper pasteurization effect on the final product; operational costs appreciably reduced (26% less) in relation to the conventional drying. An industrial drying system for short cut pasta, adapted to be assisted by microwaves (915 MHz), usually consists of three stages: a hot air pre-drying at 82 °C for 35 min, where the moisture content in pasta drops from 30% to 18% (w.b.); microwaves and hot air (82 °C) for 12 min, where the moisture content reduces from 18% to 13.5–12% (w.b.); and a final equalizing stage without any heat or air movement. The total microwave process takes 1.5 h compared to the 8–12 h conventional process (Schiffmann, 2001). Smith (1979) studied the influence of applying microwaves dur- ing drying process, concluding that the combined dielectric plus forced convection heating, introduced after the pasta critical mois- ture content had been reached, exhibited a synergistic effect over the drying process, that is a higher drying speed as compared to the forced convection drying and microwave drying considered separately. This was possible because the pressure gradient inside the food due to the dielectric heating favors the transport of mois- ture to the surface, from where it is removed by the hot air. In such a way, the microwaves actuate in the limiting mechanism of the conventional drying the moisture diffusion keeping the rate of dry- ing from being slowed down, thus reducing the overall drying time (Smith, 1979; Svenson, 1987; Datta, 1990; Funebo and Ohlsson, 1998). Berteli and Marsaioli (2005) evaluated the efficiency of air dry- ing of short pasta with the assistance of microwave energy, from 23% to 12% (w.b.) product moisture (without the hot air pre-dry- ing), using at first an adapted microwave domestic oven with a temperature controlled hot air provision system and then transfer- ring the experimental parameters from bench scale to the opera- tion of a continuous pilot scale microwave assisted hot air rotary dryer, at the frequency of 2.45 GHz. The results showed the high efficiency of this treatment, not only as regards the shorter drying time, but also because a final product without fissures was 0260-8774/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2009.06.005 * Corresponding author. Tel.: +39 (0) 881589245; fax: +39 (0) 881581308. E-mail address: t.depilli@unifg.it (T. De Pilli). Journal of Food Engineering 95 (2009) 453–459 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng