LWT - Food Science and Technology 146 (2021) 111466 Available online 11 April 2021 0023-6438/© 2021 Elsevier Ltd. All rights reserved. Comprehensive investigation into quality of pasteurized Oncorhynchus keta Walbaum fllets and non-thermal effects of microwave Qianqian Xue a , Changhu Xue a , Donglei Luan b, ** , Yunqi Wen a , Shijie Bi a , Zihao Wei a, * , Haijin Mou a a College of Food Science and Engineering, Ocean University of China, Qingdao, 266003, China b College of Food Science and Technology, Shanghai Ocean University, Shanghai, 201306, China A R T I C L E INFO Keywords: Non-thermal effects Microwave pasteurization Retort pasteurization Oncorhynchus keta Walbaum fllet Quality analysis ABSTRACT Microwave processing is a novel technology in shortening food processing time and improving product quality. These advantages are achieved through the thermal and possible non-thermal effects of microwave. The main objective of the study was to explore the non-thermal effects of microwave electromagnetic (EM) felds on quality traits of pasteurized Oncorhynchus keta Walbaum fllets. A single-mode microwave processing system processed the fllets with a pasteurization thermal lethality value of F 90 = 10 min. Corresponding pasteurization process with synchronous heating was designed to match the time-temperature profle of microwave processing. Retort pasteurization was used as a conventional process to compare the fllet quality performance with microwave pasteurization. With the pasteurization thermal treatment level, the proportion of six free amino acids was signifcantly different (P < 0.05) between the microwave pasteurized fllets and synchronous heating pasteurized fllets. The result could be attributed to the non-thermal effects of microwave EM felds. Compared with the retort pasteurization, the microwave process performed better in overall quality. Results suggested that micro- wave pasteurization exerted non-thermal effects in individual quality traits and caused less damage to fllet quality than the retort process in overall quality. 1. Introduction Microwave treatment is a novel technology in food processing and preservation (Guo, Sun, Cheng, & Han, 2017; Lopes et al., 2015). Mi- crowave technology has been used to sterilize many different foods (Joyner, Jones, & Rasco, 2017; Orsat, Raghavan, & Krishnaswamy, 2017; Tang, Hong, Inanoglu, & Liu, 2018). Compared with conventional treatments such as water bath or retort, microwave volumetric heating can signifcantly reduce the processing time (Tang, 2015) and quality damage. These thermal effects related to temperature and time are used to calculate the thermal treatment level in microwave processing to ensure food safety (Arjmandi et al., 2017). In addition to the thermal effects, many researchers have found some particular phenomena, behaviors and results are associated with some special effects. These special effects are named non-thermal effects. Non- thermal effects are not related to a macroscopic temperature effect, so it could not be repeated in the conventional heating process (Shamis, Croft, Taube, Crawford, & Ivanova, 2012). Non-thermal effects are the interaction of alternating electromagnetic (EM) felds and specifc (polar) molecules or ions in the reaction medium (Guo, Wang, & Luan, 2020). According to previous studies, microwave non-thermal effects contributed to the bacteria inactivation and enzyme denaturation (Arj- mandi et al., 2017). However, some other studies stated that no evidence could prove the existence of microwave non-thermal effects (Stratakos, Delgado-Pando, Linton, Patterson, & Koidis, 2016; Xu et al., 2015). Thus, the issue of microwave non-thermal effects is still a controversial topic (Hamoud-Agha, Curet, Simonin, & Boillereaux, 2013). Exploring the non-thermal effects of microwave is very important to promote the application of microwave technology in the food industry. It is essential to exclude the thermal effects from the microwave treatment to explore the possible non-thermal effects. Nevertheless, microwave thermal and non-thermal effects occur in the meantime. The same time-temperature profle method has been developed in recent years (Guo et al., 2020; Siguemoto, Pereira, & Gut, 2018a). This * Corresponding author. College of Food Science and Engineering, Ocean University of China, 5 Yushan Road, Qingdao, Shandong Province, 266003, China. ** Corresponding author. College of Food Science and Technology, Shanghai Ocean University, 999 Hucheng Ring Road, Shanghai, 201306, China. E-mail addresses: dlluan@shou.edu.cn (D. Luan), weizihao@ouc.edu.cn (Z. Wei). Contents lists available at ScienceDirect LWT journal homepage: www.elsevier.com/locate/lwt https://doi.org/10.1016/j.lwt.2021.111466 Received 30 December 2020; Received in revised form 3 April 2021; Accepted 6 April 2021