Browsing by Author "Huang, Yaoxin"
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Item Inactivation of bacterial and viral pathogens in berry products by high pressure and pulsed light(University of Delaware, 2015) Huang, YaoxinFoodborne pathogens such as Salmonella, Escherichia coli O157:H7 and human norovirus are major causative agents of foodborne illnesses and have been frequently associated with foodborne outbreaks of berry products in recent years. The objectives of the present study were to evaluate the application of high pressure processing (HPP) alone or in combination with frozen storage to inactivate bacterial pathogens in strawberry puree and to develop a feasible pulsed light (PL) treatment strategy to decontaminate berries from bacterial and viral pathogens. In the first project, strawberry puree with different levels of E. coli O157:H7 or Salmonella was stored at -18 °C. Both pathogens survived in frozen puree for at least 4 and 12 weeks depending on inoculation levels. A complete elimination of both pathogens could be achieved by pressure treatment at 450 MPa for 2 min at 21 °C or pressure treatment at 250-300 MPa for 2 min followed by 4-8 days of frozen storage. HPP did not adversely impact the physical properties of strawberry puree such as color, soluble solids content, pH and viscosity. The second project demonstrated a prototype water-assisted PL (WPL) treatment. This new strategy solved two main challenges in the application of PL, including sample heating and shadowing effects. After a 60-s WPL treatment, the populations of E. coli O157:H7 and Salmonella inoculated on calyx and skin of blueberries were reduced by ≥3.0 and >5.8 log CFU/g, respectively. In the third project, the combinations of WPL treatment with 1% H2 O2 or 100 ppm SDS were evaluated for the inactivation of E. coli O157:H7, Salmonella and murine norovirus (MNV), on strawberries and raspberries. The combination of WPL with 1% H2 O2 (WPL-H2 O2 ) was the most effective treatment in reducing bacterial pathogens. However, no significant difference (P>0.05) was observed between the effectiveness of WPL and WPL-H2 O2 for MNV inactivation. In the final study, a small scaled-up WPL system was developed. WPL-H2 O 2 was the most effective treatment which reduced Salmonella on raspberries and blueberries by 4.0 and > 5.6 log CFU/g, respectively, in clear water. The efficacy of the WPL-H2 O2 treatment was not significantly impacted (P>0.05) by the organic load, water turbidity, and PL intensity. No viable bacterial cells were recovered from the wash water, which showed that WPL-H2 O2 could effectively prevent the risk of cross-contamination during treatment.Item Inactivation of Escherichia coli O157:H7 on baby spinach by aqueous and aerosolized antimicrobials(University of Delaware, 2011) Huang, YaoxinAn increasing number of outbreaks associated with fresh produce such as baby spinach have been reported in the last two decades with Escherichia coli O157:H7 being one of the most frequent causative agents. Chlorinated water has been widely used by food industry to wash these fresh commodities, but this washing procedure has limited efficacy and can lead to the formation of carcinogenic substances. Thus, more effective and safer treatment methods are needed to control pathogens in fresh produce. In our first study, several generally recognized as safe organic acids and hydrogen peroxide in combination with mild heat (40 and 50 ̊C) was tested for their efficacies against E. coli O157:H7 on baby spinach. Chlorinated water (200 ppm free chlorine) only reduced the population of E. coli O157:H7 on baby spinach by 1.2-1.6 log CFU/g, which was not significantly different from DI water washing. Washing with 1% lactic acid (LA) alone or in combination with citric acid or hydrogen peroxide (H2O2) at 40 ̊C for 5 min was the most effective treatment achieving a 2.7 log reduction of E. coli O157:H7. In the second study, aerosolization was investigated as a potential way to apply allyl isothiocyanate (AIT), H2O2, acetic acid (AA) and LA on fresh baby spinach to control E. coli O157:H7 during 10 days of storage at 4 ̊C. Treatment of aerosolized 5% AIT resulted in > 5 log reduction of E. coli O157:H7 on spinach regardless if the samples are pre-washed or not; however, this treatment impaired the sensory quality of leaves. Addition of LA to AIT improved the efficacy of AIT against E. coli O157:H7 during the storage. Treatment of 3% H2O2 washing followed by a 2-min treatment of aerosolized 1% AIT + 2.5% LA reduced E. coli O157:H7 on spinach leaves by 4.8 log CFU/g after 10 days storage at 4 ̊C without causing noticeable adverse effects on the appearance of samples. Therefore, low dose application of AIT in combination with LA has the potential to control E. coli O157:H7 on fresh produce.