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

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 20min. Thermal processing was conducted at 70C for 7.2s. The number of naturally occurring microorganisms decreased from ca. 2.0-3.0×10³ to 18-28cfu/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.