Nonthermal Processing of Orange Juice Using a Pilot-Plant Scale Supercritical Carbon Dioxide System with a Gas-Liquid Metal Contactor

Abstract

This study compared the quality of fresh orange juice to that of supercritical carbon dioxide (SCCO2)-processed juice and equivalently thermally processed juice in terms of microbial lethality. A pilot-plant scale SCCO2 unit with a gas–liquid metal contactor processed juice with a CO2 concentration of ca. 8.5 wt % at 42C for 20 min. Thermal processing was conducted at 70C for 7.2 s. The number of naturally occurring microorganisms decreased from ca. 2.0–3.0 × 103 to 18–28 cfu/mL after both SCCO2 and thermal processing. No noticeable changes in pH, °Brix, titratable acidity and ascorbic acid content were observed between processed and unprocessed juice. SCCO2 and thermal processing inactivated 46.5 and 86.4% of pectin methylesterase, respectively. The cloud stability of the SCCO2-processed juice was greatly enhanced compared with fresh and thermally processed juices. This study demonstrated that SCCO2 processing can improve the microbial quality of orange juice without deterioration, suggesting the potential for commercialization. Practical Applications This study evaluated the effect of supercritical carbon dioxide (SCCO2) processing on safety and quality of orange juice (OJ). A pilot-plant scale SCCO2 system with a gas–liquid metal contactor nonthermally processed OJ, which was compared to fresh OJ and heat processed OJ. Results showed that the killing effect of SCCO2 was similar to heat processing. SCCO2 and heat processing did not affect pH, °Brix, titratable acidity and ascorbic acid contents in OJ, indicating no difference between fresh and processed OJ. SCCO2 processing reduced about 46.5% of pectin methylesterase activity, whereas heat processing inactivated 86.4% of total activity. Nonetheless, the cloud value was greatly improved by SCCO2 processing compared with fresh OJ and heat processed OJ. This pilot-plant study indicates that nonthermal SCCO2 processing is commercially feasible and is attractive from a quality standpoint.