| Summary: | 碩士 === 國立高雄海洋科技大學 === 水產食品科學研究所 === 106 === High pressure processing (HPP) is an emerging non-thermal technology that can achieve food safety. The principle advantages of the HPP process is an expanded shelf life due to the inactivation of pathogen. The effects of blanching, HPP (600 MPa for 3 min), and blanching combined with HPP (blanching+HPP) treated on carrot juice during storage at 4°C were evaluated. After HPP and blanching+HPP treatments, the total plate count (TPC), coliform and Salmonella spp. in carrot juice were completely inactive, and the populations of TPC and coliform remained below the detection level during storage. Moreover, the pH and total soluble solid (TSS) values of control and blanching samples were decreased with increased storage time, whereas the total titratable acidity (TTA) in control and blanching sampleswas increased. However, the values of pH, TSS and TTA in HPP and blanching+HPP samples remained mostly unchanged during storage. The blanching and blanching+HPP samples had the higher DPPH radicals scavenging ability, whereas the lowest DPPH radicals scavenging ability was observed in HPP samples. However, the changes of DPPH radicals scavenging ability, total phenol content, vitamine C, and β-carotene in HPP and blanching+HPP samples were not obvious during storage.
In addition, carrot juice was inoculated with Salmonella Typhimurium, Escherichia coli or Listeria monocytogenes and the effect of pressure treatment on their survival was monitored during storage 4°C. The result showed that three food pathogens subjected to HPP in carrot juice, and their bacterial counts decreased with increasing pressure level and holding time. E. coli had a higher D-value than S. Typhimurium and L. monocytogenes at higher pressure (≧400 MPa), indicating it to be more resistant at HPP treatment. The bacterial counts of three pathogens inoculated carrot juice samples were below the detection level after 500 and 600 MPa treatments. In S. Typhimurium and E. coli inoculated samples, the numbers of control and 200 MPa treatments remained constant in the juice stored at 4 °C, whereas those of 300 and 400 MPa treatments decreased with increased storage time and no bacterial count was detected in 500 and 600 MPa treatments during storage of 27 days. In L. monocytogenes inoculated samples, the bacterial counts of control and HPP treatments continued to increased during storage, regardless of pressure. In conclusion, these results show that HPP offers a useful alternative for significantly extending the shelf-life and improving the microbiological safety of carrot juice.
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