Department of Chemical and Process Engineering, University of Surrey, Guildford GU2 7XH, UK.
Department of Chemical and Process Engineering, University of Surrey, Guildford GU2 7XH, UK; Centre for 3D Models of Health and Disease, Division of Surgery and Interventional Science, University College London, London W1W 7TY, UK.
Ultrason Sonochem. 2021 Nov;79:105776. doi: 10.1016/j.ultsonch.2021.105776. Epub 2021 Oct 7.
Ultrasound, alone or in combination with natural antimicrobials, is a novel food processing technology of interest to replace traditional food decontamination methods, as it is milder than classical sterilisation (heat treatment) and maintains desirable sensory characteristics. However, ultrasound efficacy can be affected by food structure/composition, as well as the order in which combined treatments are applied. More specifically, treatments which target different cell components could result in enhanced inactivation if applied in the appropriate order. The microbial properties i.e. Gram positive/Gram negative can also impact the treatment efficacy. This work presents a systematic study of the combined effect of ultrasound and nisin on the inactivation of the bacteria Listeria innocua (Gram positive) and Escherichia coli (Gram negative), at a range of cavitation conditions (44, 500, 1000 kHz). The order of treatment application was varied, and the impact of system structure was also investigated by varying the concentration of Xanthan gum used to create the food model systems (0 - 0.5% w/v). Microbial inactivation kinetics were monitored, and advanced microscopy and flow cytometry techniques were utilised to quantify the impact of treatment on a cellular level. Ultrasound was shown to be effective against E. coli at 500 kHz only, with L. innocua demonstrating resistance to all frequencies studied. Enhanced inactivation of E. coli was observed for the combination of nisin and ultrasound at 500 kHz, but only when nisin was applied before ultrasound treatment. The system structure negatively impacted the inactivation efficacy. The combined effect of ultrasound and nisin on E. coli was attributed to short-lived destabilisation of the outer membrane as a result of sonication, allowing nisin to penetrate the cytoplasmic membrane and facilitate cell inactivation.
超声，单独或与天然抗菌剂联合使用，是一种有前途的食品加工技术，可以替代传统的食品消毒方法，因为它比经典的灭菌（热处理）温和，并且保持了理想的感官特性。然而，超声的效果可能会受到食品结构/组成以及联合处理应用顺序的影响。更具体地说，如果以适当的顺序应用针对不同细胞成分的处理，则可以增强失活效果。微生物特性，例如革兰氏阳性/革兰氏阴性，也会影响处理效果。本工作系统研究了超声和乳链菌肽对革兰氏阳性的无害李斯特菌（Listeria innocua）和革兰氏阴性的大肠杆菌（Escherichia coli）的联合灭活效应，在一系列空化条件（44、500、1000 kHz）下。处理应用的顺序有所变化，通过改变用于创建食品模型系统的黄原胶浓度（0-0.5% w/v），还研究了系统结构的影响。监测了微生物失活动力学，并利用先进的显微镜和流式细胞术技术在细胞水平上定量评估了处理对微生物的影响。结果表明，只有在 500 kHz 时超声对大肠杆菌有效，而所有研究的频率都对无害李斯特菌无效。在 500 kHz 时，观察到乳链菌肽和超声联合处理对大肠杆菌的增强灭活，但只有在乳链菌肽先于超声处理时才会出现这种情况。系统结构对灭活效果有负面影响。超声和乳链菌肽对大肠杆菌的联合效应归因于超声处理导致外膜的短暂不稳定，从而使乳链菌肽能够穿透细胞质膜并促进细胞失活。
