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

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 pre-treatment 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.

Automated summary

This study investigated the effects of high hydrostatic pressure (HHP) treatment on the myrosinase-glucosinolate system, physicochemical properties, and bacterial community of pickled radishes. The results showed that 300 MPa HHP pretreatment promoted the activation of the myrosinase-glucosinolate system and increased the content of raphasatin and sulforaphene in pickled radish. However, 600 MPa HHP pretreatment suppressed myrosinase activity. Additionally, HHP treatment altered the bacterial community of radish and reduced the counts of total bacteria and lactic acid bacteria.