0139–3006 © 2018 Akadémiai Kiadó, Budapest Acta Alimentaria DOI: 10.1556/066.2018.0003 DEVELOPMENT OF A MICROWAVE-ASSISTED UV STERILIZATION SYSTEM FOR MILK S.S. SINGH, S. MISHRA*, R.C. PRADHAN and K. VIVEK Department of Food Process Engineering, National Institute of Technology, Rourkela, Odisha, India (Received: 4 December 2017; accepted: 15 February 2018) A microwave-assisted ultraviolet sterilization system was developed to study the synergistic effect in the sterilization of milk. Electrodeless lamps emitting ultraviolet radiation inside the microwave chamber gave a synergistic effect without challenging food safety standards. This study compared the results of both microwave and microwave assisted ultraviolet sterilizations of milk in terms of various microbial tests and physicochemical properties. The microwave-assisted ultraviolet system was found to be more effective compared to microwave alone. A significant difference (P<0.05) was observed for total plate count and methylene blue reduction test between microwave and microwave assisted ultraviolet treatment from 5 to 15 secs. Microwave-assisted ultraviolet treatment decreased the microbial count exponentially and showed <1 log (CFU ml –1 ) after ten seconds of treatment. During the treatment period, no significant difference was observed in physicochemical properties of the milk. Keywords: microwave, electrodeless lamp, ultraviolet, microbial tests, physicochemical properties Milk is almost a complete food with all the essential nutrients and is highly susceptible for microbial spoilage. Different thermal treatments as pasteurization, ultra-high temperature sterilization (UHT), thermization, and innovative steam injection treatment (ISI) have been used to protect milk from microbial spoilage with different temperature-time combinations (CLAEYS et al., 2013; ION-TITAPICCOLO et al., 2013). However, these thermal treatments result in nutrients degradation. Sterilization of milk makes the product safe with longer shelf life. Conventional thermal treatment of milk degrades amino acids resulting in off-flavour and changes in pH and colour (SIEBER et al., 1996). Therefore, it is required to develop alternative non-thermal sterilization techniques that would preserve nutrients. Application of microwave, ultraviolet (UV) light, and ultrasound has been explored for sterilization of various liquid foods with some positive results (KINDLE et al., 1996; ION-TITAPICCOLO et al., 2013; TANG, 2015). Microwave heating works superior to conventional heating, and reduces the treatment time significantly. Microwave pasteurisation and sterilisation preserve quality due to lower thermal exposure. It requires less time to inactivate enzymes and most heat-resistant microbes. Vitamin (B1, B2, and B6) retention in microwave-treated milk is higher (GÉCZI et al., 2013). UV radiation can be generated by an electrodeless lamp powered by the electromagnetic waves generated by microwaves at the frequency of 2450 MHz. UV treatment of food is a USFDA and USDA approved method. USFDA has defined a performance criterion for UV processing of vegetables and fruit juices to a 5-log reduction for different target microorganisms (IWAGUCH et al., 2002; KEYSER et al., 2007). UV treatment is effective and non-toxic in nature. UV radiation has lower penetration depth and hence, good for surface sterilisation only. * To whom correspondence should be addressed. Phone: 0661-2462905; email: mishrasa@nitrkl.ac.in