Novel thermal and non-thermal processing of watermelon juice

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 (NFf) 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 watermelon 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.