Inactivation of listeria innocua and Escherichia coli in carrot juice by combining high pressure processing, nisin, and mild thermal treatments

Abstract

This study explored the effectiveness of high pressure (200-500 MPa) alone or in combination with mild thermal treatments (35 and 50 degrees C) and nisin (25 and 50-ppm) on the inactivation of L. innocua and E. coil in carrot juice. Processing at 500 MPa at 20 degrees C for 2 min without nisin resulted in 4- and 5-log CFU/mL reduction of L. innocua and E. coli, respectively while incorporating 25-ppm nisin at same pressure and temperature rendered 7-log CFU/mL reduction. There was synergism between high pressure, nisin, and heat in all treatments to inactivate both microorganisms. After a 28-d of refrigerated storage, total plate counts were < 2-log CFU/mL in carrot juice treated with combination of 300 MPa and 25-ppm nisin at 35 degrees C. All combinations resulted in less intense use of pressure, i.e. more energy efficient, cost effective processes while attaining high quality juices. The results of this study suggest that by using selected combinations of high pressure, nisin and mild temperatures, safe, clean label, high-quality juices can be produced. Industrial relevance: The results from this study show a synergistic effect on the inactivation of L. innocua and E. coil in carrot juice from the combined application of HPP, nisin, and mild temperatures. By replacing the use of HPP alone by these combinations will allow the use of reduced pressures over shorter period of times to process low-acid juices, lowering energy requirements and increasing throughput. This study will aid the beverage processing industry in the development of clean label juice products with fresh-like quality attributes and using considerable less energy to conventional processing.