|YUK, HYUN-GYUN - National University Of Singapore
Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2010
Publication Date: 10/1/2010
Citation: Yuk, H., Geveke, D.J. 2010. Nonthermal inactivation and sublethal injury of Lactobacillus plantarum in apple cider by a pilot plant scale continuous supercritical carbon dioxide system. Food Microbiology. 28:377-383.
Interpretive Summary: Spoilage bacteria in apple cider, such as Lactobacillus plantarum, may cause undesirable flavors and damage to the container by fermentation during storage, resulting in shortened shelf-life of the product. Thermal processing at 72 to 88C is the most effective way to kill spoilage bacteria in apple cider; however, this method may cause side effects such as destruction of nutrients and off-flavors. To kill bacteria without deterioration of apple cider quality, several technologies that kill bacteria at low temperature have been developed. Among them, supercritical carbon dioxide (CO2) is a relatively new process that has many advantages including safety and consumer acceptance. This study evaluated the bactericidal effect of supercritical CO2 on L. plantarum in apple cider. Results showed that the antimicrobial effects were enhanced as CO2 concentrations and temperatures increased. Almost complete kill of L. plantarum was obtained at 42C. Supercritical CO2 also caused injury of L. plantarum and microscopic imaging showed that the bacteria were damaged. Refrigeration (4C) after processing prevented re-growth of L. plantarum during storage for 28 days. This study indicates that supercritical CO2 can kill spoilage bacteria in apple cider at low temperatures.
Technical Abstract: The objective of this study was to evaluate the efficacy of supercritical carbon dioxide (SCCO2) for inactivating Lactobacillus plantarum in apple cider using a continuous system with a gas-liquid metal contactor. Pasteurized apple cider without preservatives was inoculated with L. plantarum and processed using a SCCO2 system at a CO2 concentration range of 0 – 12% (g CO2/100 g product), outlet temperatures of 34, 38, and 42 C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Processing with SCCO2 significantly (P < 0.05) enhanced inactivation of L. plantarum in apple cider, resulting in a 5-log reduction with 8% CO2 at 42 C. The response surface model indicated that both CO2 concentration and temperature contributed to the microbial inactivation. The extent of sublethal injury in surviving cells in processed apple cider increased as CO2 concentration and processing temperature increased, however the percent injury dramatically decreased during SCCO2 processing at 42 C. Structural damage in cell membranes after SCCO2 processing was observed by SEM. Refrigeration (4 C) after SCCO2 processing effectively inhibited the re-growth of surviving L. plantarum during storage for 28 days. Thus this study suggests that SCCO2 processing is effective in eliminating L. plantarum and could be applicable for nonthermal pasteurization of apple cider.