J Food Process Preserv. 2018;42:e13747. wileyonlinelibrary.com/journal/jfpp | 1 of 11 https://doi.org/10.1111/jfpp.13747 © 2018 Wiley Periodicals, Inc. 1 | INTRODUCTION Corroborations from epidemiological reports have strongly recom‐ mended that consumption of diets rich in green leafy vegetables can lessen the risk of a variety of chronic diseases in humans due to the presence of different biologically active compounds that have antioxidant activities including polyphenols, anthocyanin, carotenoids and ascorbic acid (Kongkachuichai, Charoensiri, Yakoh, & Kringkasemsee, 2015). Vegetable derived antioxidants are best known to impede the activities of free radicals produced through oxidation that are capable of causing disorders in the human body (Vaidya & Brearley, 2014). However, when contaminated, vegetables become themselves vehicles of food‐borne illnesses and a health risk to consumers (Berger et al., 2010). Several pathogenic microbes Received: 27 March 2018 | Revised: 5 June 2018 | Accepted: 3 July 2018 DOI: 10.1111/jfpp.13747 ORIGINAL ARTICLE Effect of multi‐frequency ultrasound surface washing treatments on Escherichia coli inactivation and some quality characteristics of non‐heading Chinese cabbage Evans Adingba Alenyorege 1,2 | Haile Ma 1,3 | Ishmael Ayim 1,4 | Cunshan Zhou 1 | Ping Wu 1 | Chen Hong 1 | Richard Osae 1 1 School of Food and Biological Engineering, Jiangsu University, Zhenjiang, China 2 Faculty of Agriculture, University for Development Studies, Tamale, Ghana 3 Technology Integration Base for Vegetable Dehydration Processing, Ministry of Agriculture PR China, Jiangsu University, Zhenjiang, China 4 Faculty of Applied Science, Kumasi Technical University, Kumasi, Ghana Correspondence Haile Ma, School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, Jiangsu, China. Email: mhl@ujs.edu.cn Funding information Special Fund for the Transformation of Scientific and Technological Achievements in Jiangsu Province, Grant/Award Number: BA2016169; National Key R & D plan, Grant/Award Number: 2018YFD0700100; 2017YFD0400901 Abstract The effect of ultrasound washing with different frequencies including sweeping, fixed and combined fixed frequencies on Escherichia coli inactivation and selected physical and chemical qualities of Chinese cabbage were investigated. Colour, micro‐ structure, total chlorophyll, total carotenes, total phenolic content, DPPH radical scavenging, hydroxyl radical scavenging and reducing power activities were meas‐ ured using standard in vitro assays. In contrast with water washed samples, ultra‐ sound washing with a fixed frequency of 40 kHz resulted in >3 log CFU/g reduction in E. coli counts, approximately 20% improvement in total phenolic content and over 32% increase in reducing power activity. There was, however, a marginal improve‐ ment in DPPH radical scavenging activity and a decrease in hydroxyl radical scaveng‐ ing activity. Scanning electron micrographs revealed the presence of micro‐fractures and minute holes and dislodging of surface particles Ultrasound washing improved the perceptible visual colour (∆E) and the greenish appearance of the leaves. Practical applications Multi‐frequency power ultrasound washing of fresh produce is a recent application of varying frequencies in decontamination of fresh produce. The remarkable influ‐ ence of ultrasonic frequency aside other operating parameters in the removal of con‐ taminants on fruits and vegetable surfaces influenced this study. The results reported in this experimental study may be considered for application in the inactivation of microorganisms including E. coli and other Gram‐negative bacteria. This washing technique may also be used in combination with other studied physical or chemical preservation methods as a synergy to enhance microbial removal and quality charac‐ teristics of fresh produce in the food industry.