OPTIMIZATION OF THERMAL AND THERMOSONICATION TREATMENTS ON PECTIN METHYL ESTERASE INACTIVATION OF SOUR ORANGE JUICE (CITRUS AURANTIUM) ROYA KOSHANI, ESMAEIL ZIAEE, MEHRDAD NIAKOUSARI 1 and MOHAMMAD-TAGHI GOLMAKANI Department of Food Science and Technology, College of Agriculture, Shiraz University, Shiraz, Iran 1 Corresponding author. TEL: 0098-917-300-1030; FAX: 0098-7112286110; EMAIL: Niakosar@shirazu.ac.ir Received for Publication June 2, 2013 Accepted for Publication March 19, 2014 doi:10.1111/jfpp.12262 ABSTRACT The objective of this study was to analyze and optimize the critical process param- eters in inactivation of pectin methyl esterase (PME) in sour orange juice by thermal and thermosonication processes using response surface methodology. A central composite design was employed for experimental design and process opti- mization. The thermal inactivation of PME was carried out at temperatures between 40 and 80C for 5–25 min. At thermosonication process, temperature and time were kept as before while the process was optimized with an ultrasound intensity of 60–100 W. Simultaneous application of ultrasound and thermal process enhanced the enzyme inactivation. The optimal process condition for PME inactivation in thermal process and thermosonication (at 80 W) were 21.80 min at 75C and 9.8 min at 63C, respectively. The results indicate that thermosonication of sour orange juice could entirely inactivate the PME. PRACTICAL APPLICATIONS Today, preservation by elevation of temperature for short periods of time (up to 90C) is still the most common processing method for microbial or enzyme inacti- vation that leads to longer shelf life. Because of the exposure to high temperature, this thermal method has disadvantages for many food products particularly fruit juice. The production of new substances from heat-catalyzed reactions and the modification of macromolecules as well as the deformation of plant and animal structures may reduce in a loss of quality. Therefore, thermal treatment can cause undesirable alterations of sensory attributes, i.e., texture, flavor, color, smell and nutritional qualities, i.e., vitamins and proteins. Ultrasound is an efficient nonthermal (minimal) processing alternative. INTRODUCTION Among citrus family, the sour orange (Citrus aurantium L.) is popular for its characteristics, such as being a source of vitamin C, organic acids, mineral, soluble and insoluble fibers and also its antioxidant capacity (Amiri and Niakousari 2008). In some parts of Iran, between mid- October and March, when fresh sour orange is abundant, consumers store a large amount of unpasteurized sour orange juice (SOJ) at room or low temperatures for their future consumptions. The SOJ is used as food additive, ingredient in salad dressing and also as a popular drink because of its rich flavor and aroma (Zenker et al. 2003). Pectin methyl esterase (PME) (EC 3.1.1.11), a thermostable enzyme, is abundant and produced by many plants, bacteria and fungi (Rouse and Atkins 1952). PME has the ability to remove methoxyl groups from pectin chains to form car- boxylate groups (polygalacturonic acid) and then release of methanol and H3O + (Jayani et al. 2005). During juice extraction, PME is entered into SOJ and breaks ester bonds in pectin, leading to cloud stability reduction (Zenker et al. 2003). Cloud stability is a critical factor in SOJ quality which affects its flavor, color and mouth-feel characteristics (Tiwari et al. 2009). In juice industry, PME is considered as an important enzyme mainly because of its cloud-reduction capability (Espachs-Barroso et al. 2006). In order to acceler- ate the PME inactivation during SOJ production, the appro- priate strategies can be planned to reach highest PME Journal of Food Processing and Preservation ISSN 1745-4549 Journal of Food Processing and Preservation •• (2014) ••–•• © 2014 Wiley Periodicals, Inc. 1