Bacterial inactivation mechanism of SC-CD and TEO combinations in watermelon and melon juices

Abstract Inactivation mechanism of supercritical carbon dioxide (SC-CD) combination with Thymbra spicata essential oil (TEO) treatments on bacteria in tryptone soy broth (TSB) and juices was investigated. Salmonella Typhimurium was significantly inactivated by 3.45 and 5.55 logs after SC-CD+TEO treatment of TBS for 35 min at 7.6 and 10.13 MPa respectively. Klebsiella pneumoniae showed higher resistance to treatments than other two bacteria and Escherichia coli showed higher resistance to treatments than S. Typhimurium. Approximately 5.27, 4.68 and 3.82 logs inactivation of S. Typhimurium, E. coli and K. pneumoniae were obtained in the treatment of watermelon juice with SC-CD+TEO at 10.13 MPa after 35 min, while 6.89, 4.82 and 4.55 logs inactivated, respectively, were observed in melon juice. Research indicated that the inactivation mechanism involves inducing cell damage, increasing membrane permeability, increasing cell rupture, precipitation of cytoplasmic contents, extracting cellular substances and lysing cells. Different sensitivities of Gram-negative bacteria to the treatments may be attributed to the differences in the cell structure, compositions of membrane and presence of capsule, pressure level and exposure time. pH, total soluble solid and browning degree of juice did not significantly change after treatments and during 7 days of storage.摘要 本研究探究了超临界二氧化碳（supercritical carbon dioxide, SC-CD）联合尖叶百里香精油（Thymbra spicata essential oil, TEO）对胰蛋白胨大豆肉汤（tryptone soy broth, TSB）及果汁中细菌的灭活机制。分别在7.6 MPa与10.13 MPa条件下，经SC-CD+TEO处理TSB 35 min后，鼠伤寒沙门氏菌（Salmonella Typhimurium）的灭活对数分别达到3.45 log与5.55 log，灭活效果显著。肺炎克雷伯菌（Klebsiella pneumoniae）对该处理的抗性高于其余两种受试菌，大肠杆菌（Escherichia coli）的抗性则高于鼠伤寒沙门氏菌。在10.13 MPa条件下经SC-CD+TEO处理西瓜汁35 min后，鼠伤寒沙门氏菌、大肠杆菌及肺炎克雷伯菌的灭活对数分别约为5.27 log、4.68 log及3.82 log；而在甜瓜汁中，三者的灭活对数分别为6.89 log、4.82 log及4.55 log。研究表明，该灭活机制涵盖诱导细胞损伤、提升细胞膜通透性、加剧细胞破裂、胞质内容物析出、胞内物质提取及细胞裂解。革兰氏阴性菌对该处理的敏感性差异，可归因于细胞结构、膜成分、荚膜存在情况、压力水平及暴露时间的不同。经处理后的果汁在7天贮藏周期内，其pH值、总可溶性固形物含量及褐变度均无显著变化。