Impact of a Pilot-Scale Plasma-Assisted Washing Process on the Culturable Microbial Community Dynamics Related to Fresh-Cut Endive Lettuce

Antje Fröhling,Oliver Schlüter,Jörg Ehlbeck

doi:10.3390/app8112225

Abstract

Cold plasma is described as a promising technique for the treatment of fresh food. In particular, the application of plasma-treated water gained interest in fresh-cut produce processing. This study aimed to evaluate the effectiveness of plasma-treated water (PTW) to decontaminate lettuce during washing on a pilot-scale level with special interest in the dynamics of the culturable microbial community in a first approach. PTW was used in pilot-scale washing at different processing steps, and the total viable count (TVC) of endive lettuce was determined after treatment and after storage (seven days, 2 °C). Microflora representatives were identified using MALDI-ToF MS. The highest reduction of TVC (1.8 log units) was achieved using PTW for washing whole lettuce before cutting. The microbial community structure showed high variations in the composition along the processing chain and during storage with a decrease in diversity after washing with PTW. PTW reduced the microbial load of endive lettuce; however, this was not clearly detectable at the end of storage, similar to other sanitizers used in comparable studies. To assure the safety of fresh products, detailed knowledge about the microbial load and the composition of the microbial community close to the end of shelf life is of high interest for optimized process design.

Highlights

Processing of ready-to-eat salads includes a washing step to remove dirt, debris, and cellular juice from the product
plasma-treated water (PTW) reduced the microbial load of endive lettuce; this was not clearly detectable at the end of storage, similar to other sanitizers used in comparable studies
To assure the safety of fresh products, detailed knowledge about the microbial load and the composition of the microbial community close to the end of shelf life is of high interest for optimized process design

Summary

Introduction

Processing of ready-to-eat salads includes a washing step to remove dirt, debris, and cellular juice from the product. The microbial load can be reduced using a washing step to some extent. In addition to the positive impact of washing, attention must be paid to the fact that the wash water can transfer microorganisms [1], and this can lead to a cross-contamination of the products. The addition of disinfectants may improve the reduction of the microbial load; during storage of the products, the positive effect seems to disappear, and faster growth of the microorganisms can be observed [2,3]. Hydrogen peroxide and acid solutions [4], as well as ozone, organic acids, chlorine dioxide, and electrolyzed oxidizing water came into focus in recent years [5].

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