PROCESSING CARROT JUICE BY SELECTED NONTHERMAL TECHNOLOGIES AS HURDLES
Pokhrel, Prashant Raj
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Nonthermal food processing technologies such as High Pressure Processing (HPP), Pulsed Electric Fields (PEF), and Ultrasound (US) are novel juice pasteurization methods. The objective of this study was to use these technologies in combination with other microbial stress factors (Mild heat, Nisin, and pH) in the mild-pasteurization of carrot juice. Microbiological inactivation and quality attributes retention were studied for selected combinations. Various processes were identified that rendered equivalent microbial load reduction and those processes were compared for energy consumption and quality retention. The ultrasound (37.87 W/cm2) processing of carrot juice at 58°C, was found to be effective in E. coli inactivation without impacting quality attributes. Mathematical modeling of the inactivation’s curve shows that Weibull and a biphasic model to be good fits to predict survivors. Further studies on ultrasound in combination with nisin (25 and 50 ppm) and mild temperatures (35 and 50°C) show synergism between these three factors. High pressure was combined with moderate heat and nisin to explore the inactivation of gram-positive and negative bacteria. The addition of nisin at 25 and 50 ppm at 20°C did not impact the lethal effect at mild-pressures (≤300 MPa). However, for the same level of pressures, a synergistic effect between nisin and pressure was found at 35°C. The microbial inactivation by combining HPP and nisin was further enhanced by increasing the temperature to 50°C. High pressure treatment was also carried out for carrot juice mixed with orange juice in different proportion. The developed interacting relations between pressure, pH, and processing time on microbial inactivation could be useful in predicting the inactivation at different pHs. The PEF processing of carrot-orange juice blend shows the application of High Electric Field-Low Frequency was found to be more efficient than Low Electric Field-High Frequency in microbial inactivation. The application of mild temperatures (35 and 50°C) and nisin (25 and 50 ppm) enhanced the inactivation by both processes without significantly impacting quality attributes. Findings from the present study will be useful in designing mild pasteurization processes for fruit and vegetable juices using nonthermal technologies such as HPP, PEF, and Ultrasound together with other selected hurdles.