Contents lists available at ScienceDirect Trends in Food Science & Technology journal homepage: www.elsevier.com/locate/tifs Novel thermal and non-thermal processing of watermelon juice Chiranjit Bhattacharjee * , V.K. Saxena, Suman Dutta Department of Chemical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, 826004, India ARTICLE INFO Keywords: Watermelon juice Non-thermal processing Microorganisms PEF Lycopene ABSTRACT Background: Watermelon juice has gained a lot of consumer interest in recent years due to its richness in phytochemical lycopene and its high antioxidant activity. The water activity of this juice is very high and it has a low acid content. Therefore the microbial activity in watermelon juice is comparatively high than most juices. Due to high percentage of spoilage microorganisms, it is quite difficult to store it for longer times without processing. Heat treatment has been used a pasteurization technique but it has a negative effect on its nutritional and sensory properties as bioactives are sensitive to high temperature processing. So the need arises for non- thermal processes to treat watermelon juice. Scope and approach: In recent years non-thermal or novel thermal processes have been successfully tested in research laboratories for processing of watermelon juice. These processes include pulsed electric field (PEF), ultraviolet irradiation (UV), sonication, ohmic heating (OH), high pressure processing (HHP), high pressure carbon dioxide (HPCD), nano fluid thermal processing (NFT) and membrane technology. The effects of these processes on micorobial activity and physicochemical properties of watermelon juice have been reported in this study. Key findings and conclusions: Non-thermal processes have been quite successfully analyzed for processing wa- termelon juice. They showed positive results in reducing the microbial spoilage of the juice and at the same time have retained a high portion of nutritional compounds. Among the non-thermal processes, PEF is the most widely used for watermelon juice processing and also showed most acceptable results. 1. Introduction The degradation of fruit juices is mainly caused by chemical, mi- crobial and enzymatic reactions. Polyphenol oxidase (PPO) and pectin methylesterase (PME) are the primary enzymes responsible for juice deterioration. They react with dissolved oxygen and thereby causing browning of the juice and off color. Maillard reaction is another factor which generates non-enzymatic browning in juices. In this reaction, intermediate is formed by the coming together of carbonyl group of reducing sugars and amino group of amino acid. Further the inter- mediate reacts to form brown colored pigments producing unpleasant changes in juice color (Bharate & Bharate, 2014). This microbial growth also leads to unwanted flavor and odor, high turbidity and gas pro- duction. Therefore it becomes inevitable to control the growth of these spoilage microorganisms so as to minimize the juice spoilage (Odumeru, 2012). In earlier days foodborne disease outbreaks were never associated with fruit juices primarily beacause of their low pH values (pH ≤ 4). Due to limited progress in scientific research at that time, the growth and survival of pathogens under such acidic pH was thought to be almost impossible. But since 1980s, with the increase of research in food science, acidic fruit juices were found to be responsible for many foodborne disease outbreaks. In recent times, with the progress in food science and increasing health consciousness of the consumers, search for exotic and seasonal fruits such as watermelon and berries have brought a challenging role for food technologists. Although these exotic fruits provide a high amount of nutritional bioactive compounds to the consumers, but they also are most susceptible to the growth and sur- vival of food borne pathogens. Since these fruits have a very high amount of antioxidants which are vulnerable to high temperature, re- searchers have to maintain a fine balance between stability of these bioactives and inactivation of unwanted pathogens. Watermelon is a highly nutritious and perishable juice. It has be- come popular recently among the consumer due to its unique refreshing flavor and various health benefits (Edwards et al., 2003; Giovannucci, 2002). As it has a pH close to neutral value and a high amount of water activity makes it an ideal medium for the growth of microorganisms. These microorganisms make it hard to store the juice for a longer period. Therefore it is very hard to find commercial watermelon juice products in the market. It is often mixed with other high acidic juices to https://doi.org/10.1016/j.tifs.2019.09.015 Received 3 April 2019; Received in revised form 14 August 2019; Accepted 14 September 2019 * Corresponding author. E-mail address: chiranjit@ce.ism.ac.in (C. Bhattacharjee). Trends in Food Science & Technology 93 (2019) 234–243 Available online 16 September 2019 0924-2244/ © 2019 Elsevier Ltd. All rights reserved. T