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.

超声波，单独或与天然抗菌剂结合使用，是一种新颖的食品加工技术，可替代传统的食品去污方法，因为它比传统的灭菌（热处理）更温和，并保持理想的感官特性。然而，超声波的功效会受到食物结构/成分以及联合治疗的顺序的影响。更具体地说，如果以适当的顺序应用，针对不同细胞成分的治疗可能会导致增强的失活。微生物特性，即革兰氏阳性/革兰氏阴性也可以影响治疗效果。

这项工作对超声和乳酸链球菌肽在一系列空化条件（44、500、1000 kHz）下对无害李斯特菌（革兰氏阳性）和大肠杆菌（革兰氏阴性）灭活的综合影响进行了系统研究。处理应用的顺序不同，并且还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) 来研究系统结构的影响。监测微生物灭活动力学，并利用先进的显微镜和流式细胞术技术来量化治疗对细胞水平的影响。

超声波仅在 500 kHz 时对大肠杆菌有效，而无害乳杆菌对所研究的所有频率都有抵抗力。在 500 kHz 下，乳酸链球菌素和超声波的组合观察到了大肠杆菌的增强灭活，但仅在超声波处理前应用乳酸链球菌素时。系统结构对灭活效果产生负面影响。超声波和乳链菌肽对大肠杆菌的联合作用归因于超声处理导致外膜的短期不稳定，使乳链菌肽能够穿透细胞质膜并促进细胞失活。