Effect Of High Hydrostatic Pressure Treatment On Microbial Inactivation In Sichuan Pickled

Sichuan pickled is one of the most popular traditional fermented vegetable products, which is widely consumed in China. High hydrostatic pressure (HHP) could improve the microbial safety and quality of food, which has been recognized as a promising alternative method to thermal processing among emerging food preservation technologies. In this study,3typical Sichuan pickles as raw materials, including pickled cowpea, pickled radish and Sichuan sauerkraut. The effect of HHP on microbial inactivation in pickled cowpea, the different effect of HHP and thermal processing on the quality of pickled radish during storage, and the microbial inactivation kinetics of HHP processed Sichuan sauerkraut was studied. These results were designed to provide a theoretical basis for using HHP in the actual production of Sichuan pickles. The details were as follows:(1) The pressure and treatment time had significant impact on bactericidal effect of pickled cowpea. With increased pressure and treatment time, the mortality of total aerobic bacteria, molds and yeasts were higher in pickled cowpea treated by HHP. The results also indicated that the treatment time on bactericidal effect was less efficient than pressure. However, extent treated time had no significant impact on mortality of microorganisms.(2) The coliform was much sensitive to pressure. After the pickled cowpea were treated by300MPa for10min, coliform is less than30MPN/100g. Besides, the coliform was not able to be detected in pickled cowpea after treated by400MPa. They could meet the standard level of Sichuan pickles.(3) The preserved performance of pickled cowpea treated by HHP was investigated. The results as follows:The samples appeared no phenomenon of bag inflation at37℃, and the preserved performance was fine after treated by400MPa for20min.(4) With better bactericidal effect, lower storage temperature, the counts of microorganisms was increased more slowly in pickled radish. The counts of microorganisms from the samples remained unchanged after treated by400MPa and heat under4℃storage, whereas the counts of microorganisms in200MPa treated samples showed a slow increase trend, and the microbial proliferated faster during storaged at20℃.(5) With higher pressure, the pH and titratable acidity (TA) of pickled radish treated by HHP maintained were more stable during storage. Treatment carried out at400MPa with heating could slow down the decline of pH and reduced the possibility of over acidification in samples efficiently. Furthermore, the result could be much better during storage at4℃. This result suggested that processing condition and storage temperature were important factors that could maintain the stability of the pH, TA of pickled radish.(6) Compared with thermal processing (85℃,20min), HHP had little influence on the original color of pickled radish. However, HHP accelerated the decline of color of samples during the storage. The color of samples fell more serious at400MPa than200MPa. Nevertheless, temperature at4℃could slow down the decline of color of samples and the color of HHP-treated samples were better than heat-treated samples.(7) At some pressures, microbial mortality increased rapidly in the early stage of HHP treatment, but the microbial mortality maintained a slow upward trend after awhile, thus the death curve of microorganisms had a "tail". For example, after treated5min, the mortality (log10S) of total aerobic bacteria increased2.71log10CFU/g at300MPa, whereas log10S only increased0.13log10CFU/g when the treatment time extended from20min to40min. Besides, after the samples were treated at300MPa for20min or at400MPa for15min, the molds and yeasts in Sichuan sauerkraut could not be detected (below1log10CFU/g of the detection limit).(8) The curves were fitted by linear, Log-logistic and Weibull models, the fitting parameters, evaluation parameters and residuals were also investigated. The results showed that the Logistic and Weibull model could have goodness-of-fit of HHP sterilization kinetic curves, and were also able to describe the death curve with tail better. Log-logistic model was more functional than Weibull model to describe the data.