New Insights Into the Response of Metabolome of Escherichia coli O157:H7 to Ohmic Heating.

Xiaojing Tian,Qianqian Yu,Fei Jia,Donghao Yao,Xingmin Li,Zhihong Liang,Ruitong Dai,Teng Hui,Lele Shao

doi:10.3389/fmicb.2018.02936

Abstract

The objective of this study was to investigate the effects of ohmic heating and water bath heating (WB) on the metabolome of Escherichia coli O157:H7 cells at the same inactivation levels. Compared to low voltage long time ohmic heating (5 V/cm, 8.50 min, LVLT) and WB (5.50 min), the high voltage short time ohmic heating (10 V/cm, 1.75 min, HVST) had much shorter heating time. Compared to the samples of control (CT), there were a total of 213 differential metabolites identified, among them, 73, 78, and 62 were presented in HVST, LVLT, and WB samples, revealing a stronger metabolomic response of E. coli cells to HVST and LVLT than WB. KEGG enrichment analysis indicated that the significantly enriched pathways were biosynthesis and metabolism of amino acids (alanine, arginine, aspartate, and glutamate, etc.), followed by aminoacyl-tRNA biosynthesis among the three treatments. This is the first metabolomic study of E. coli cells in response to ohmic heating and presents an important step toward understanding the mechanism of ohmic heating on microbial inactivation, and can serve as a theoretical basis for better application of ohmic heating in food products.

Highlights

Thermal treatments, as conventional technology in food processing, are used for the pasteurization, sterilization, dehydration, evaporation, and blanching of foods
There was no significant difference of logarithmic reduction on the same plate among HVST, LVLT, and water bath heating (WB)-treated samples with similar final
The major functional group of metabolites that displayed upregulation after the three treatments were metabolites involved in lipid metabolism, while a down-regulation was metabolites involved in amino acid metabolism

Summary

Introduction

Thermal treatments, as conventional technology in food processing, are used for the pasteurization, sterilization, dehydration, evaporation, and blanching of foods. Heat energy is generated externally and transferred into the internal of food by conduction or convection in conventional thermal treatment methods. These methods are time consuming due to slow heat transfer through the product, for larger diameter products, and may lead to overcooked surface and quality deterioration (Jaeger et al, 2016; Kanjanapongkul, 2017). Compared to conventional thermal treatment methods, the heat of ohmic heating is generated from the internal of the food, it can prevent the surface of the solid food or particles from becoming overheated and preserve sensory attributes of food with a shorter heating time (Kanjanapongkul, 2017)

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Conclusion