Contents lists available at ScienceDirect Innovative Food Science and Emerging Technologies journal homepage: www.elsevier.com/locate/ifset Multi-stage continuous and intermittent microwave drying of quince fruit coupled with osmotic dehydration and low temperature hot air drying Jalal Dehghannya ⁎ , Seyed-Hamed Hosseinlar, Maryam Khakbaz Heshmati Department of Food Science and Technology, University of Tabriz, Tabriz 51666-16471, Iran ARTICLE INFO Keywords: Continuous and intermittent microwave Drying time Energy consumption Quince fruit Rehydration Shrinkage ABSTRACT In recent years, using intermittent microwave (IM) to dry foodstuffs has been taken into consideration as one of the new drying methods in food industry. The aim of this research was to dry cubic pieces of pre-treated “quince” fruit by sucrose osmotic solution using IM – hot air (HA) drying at a low temperature (40 °C) in order to in- vestigate the effects of this process on improving the dried product quality. The variables of the process included sucrose osmotic solution in 5 concentration levels of 0 (control), 10, 30, 50, and 70% (w/w) and microwave at 4 powers of 0 (control), 360, 600, and 900 W, with 4 pulse ratios of 1, 2, 3, and 4. Findings indicated that compared to control samples, the samples pre-treated by osmotic solution had lower effective moisture diffusion coefficient (D eff ). However, D eff increased through increase in power and pulse ratio of the microwave. Increasing the concentration of the osmotic solution, power, and pulse ratio led to significant decreases in shrinkage. Due to high shrinkage, the quince samples dried by continuous microwave – HA method showed higher bulk density in comparison to the samples dried by IM – HA. In addition, samples dried by IM with low power showed the highest rehydration followed by those dried by IM with high power; however, the control samples dried merely by HA had the lowest rehydration. Moreover, a significant decrease in specific energy consumption was noticed through increasing the microwave power. Drying by IM – HA at the power of 900 W and the pulse ratio of 4 had the lowest specific energy consumption, while drying with only HA had the highest specific energy consumption. 1. Introduction “Quince” fruit, with the scientific name of “Cydonia oblonga,” is from “Rosaceae” family— known for its pleasant fragrance and dis- tinctive taste (Doymaz, Demir, & Yildirim, 2015). Like other fruits, quince is a perishable fruit with microbiological, chemical, and physical spoilage agents that decrease its shelf life (Akbarian, Ghanbarzadeh, Sowti, & Dehghannya, 2014). Quince is an ancient, delicious fruit with a dry and fluffy flesh and an almost sour taste. It is generally grown in Argentina, China, Iran, Morocco, Republic of Azerbaijan, Turkey, and Uzbekistan (Doymaz et al., 2015). This fruit is a rich source of vitamins A and B, calcareous salts, and tannin. In addition, quince contains glycoside, lipid, and fiber (about 12% on dry basis) and produces 112 kcal per 100 g (Koc, Eren, & Ertekin, 2008). Dried “quince” fruit is used in producing jam, marmalade, jelly, and pudding (Noshad, Mohebbi, Shahidi, & Mortazavi, 2012). In addition, dried quince is used as an ingredient of traditional dishes in Iran such as quince stew, soup and the like (Akbarian et al., 2014; Noshad et al., 2012). Convective HA drying is the most common method used in drying food (Zhao et al., 2014). > 85% of industrial dryers are convective HA dryers (Aghilinategh et al., 2015), but they have big disadvantages such as high energy consumption and longer drying time due to low thermal conductivity of foodstuffs(Zhao et al., 2014). Another reason for such disadvantages is the rapid decrease of surface moisture and, as a result, shrinkage of the product, which often results in decrease in moisture and, sometimes, heat transfer (Maskan, 2001). Increase in the process time with high temperature results in change in both fragrance and taste of the product. Furthermore, convective HA drying leads to re- duction of nutritional value and changes the color of foodstuffs(Zhao et al., 2014). Moisture removal during drying is greatly affected by HA conditions and foodstuff characteristics. HA temperature and moisture content of the foodstuff has a significant effect on qualitative characteristics of the foodstuff such as vitamins, smell, taste, color, tissue or nutritional composition during storage (Mota, Luciano, Dias, Barroca, & Guiné, 2010). Drying with HA results in destruction of the compounds which are sensitive to temperature (such as vitamins) and also leads to loss of important sensory features of the dried product. Although high drying http://dx.doi.org/10.1016/j.ifset.2017.10.007 Received 15 June 2017; Received in revised form 4 September 2017; Accepted 6 October 2017 ⁎ Corresponding author. E-mail address: J_dehghannya@tabrizu.ac.ir (J. Dehghannya). Innovative Food Science and Emerging Technologies 45 (2018) 132–151 Available online 07 October 2017 1466-8564/ © 2017 Elsevier Ltd. All rights reserved. MARK