Effect of high pressure pretreatment on myrosinase-glucosinolate system, physicochemical and bacterial properties during fermentation of brine-pickled radishes

Abstract

The myrosinase-glucosinolate system, physicochemical properties, and bacterial community were profiled during fermentation of high hydrostatic pressure (HHP) pretreated brine-pickled radishes; traditionally brine-pickled radishes were utilised as the control. Scanning electron microscopy (SEM) analysis revealed that 300 MPa pretreatment promoted brine infiltration in radish cells and damaged cellular microstructures, which activated the myrosinase-glucosinolate system. The conversion of glucosinolate (GLs) to isothiocyanates (ITC) increased and significantly enhanced the raphasatin and sulforaphene contents of pickled radish. However, 600 MPa pretreatment suppressed myrosinase activity. HHP pretreatment altered the natural radish bacterial communities by reducing the total bacterial and lactic acid bacteria counts. Lactobacillus spp. became the dominant bacterial genus within 15 d of fermentation. However, the destruction of cellular structures by HHP pretreatment also significantly decreased hardness and caused the dissolution of amino acids and TTA into brine. This caused reduced amino acid and TTA contents compared to the control group, as well as decreases in pH. HHP pretreatment suppressed the growth of spoilage bacteria (e.g. Pseudomonas, Staphylococcus, and Shewanella genera). This study provides new insight into the potential applications of HHP treatment in pickling, as it demonstrates that HHP can increase the ITC conversion rate of pickled radish, modify its physiochemical characteristics, and decrease microbial risk. Therefore, HHP is a promising preprocessing technique to be used for pickle manufacturing industry.

Keywords: Bacterial community; High hydrostatic pressure; Isothiocyanates; Pickle; Radish.