Decontamination of berries with ozone and pulsed UV-light
Katherine Bialka and Ali Demirci
Thesis, Doctor of Philosophy (Agricultural and Biological Engineering),The Pennsylvania State University, 227 pages. 2007.
2007
บทคัดย่อ
This research investigated the use of gaseous ozone, aqueous ozone, and pulsed UV-light for the purpose of decontaminating Escherichia coli O157:H7 and Salmonella spp. on the surfaces of blueberries, raspberries, and strawberries.
Blueberries, strawberries, and raspberries were artificially contaminated with five strains of Escherichia coli O157:H7 and Salmonella spp. Combined continuous and pressurized treatment yielded high log10 reductions of 3.6 and 3.8 CFU/g of Salmonella and E. coli O157:H7, respectively, for raspberries, whereas 2.6 and 2.9 CFU/g of Salmonella and E. coli O157:H7, respectively, for strawberries. For blueberries, the highest log10 reductions resulted after treatment with continuous ozone for E. coli O157:H7 and was 2.2 CFU/g and for Salmonella the highest reductions resulted after the 64-min pressurized treatment and were 3.0 log10 CFU/g.
The efficacy of ozone as a water additive for washing blueberries, raspberries, and strawberries was investigated. Pathogen inoculated fruit were treated with aqueous ozone at 20°C for 2 to 64 min at ozone concentrations of 1.7 to 8.9 mg/L, at 4°C for 64 min at a concentration of 21 mg/L, and with water as a control. Washing with water (sparging with air as control) resulted in reductions of only 1 log 10 CFU/g.
Pulsed UV-light was applied to blueberries, strawberries, and raspberries at varying UV doses and times. On raspberries, maximum reductions of E. coli O157:H7 and Salmonella were 3.9 and 3.4 log10 CFU/g at 72 and 59.2 J/cm2, respectively. On the surfaces of strawberries maximum reductions were 2.1 and 2.8 log10 CFU/g at 25.7 and 34.2 J/cm2, respectively. Maximum reductions of 4.3 and 2.9 log10 CFU/g were achieved on blueberries after a UV dose of 22.6 J/cm2 for E. coli O157:H7 and Salmonella, respectively. There was no observable damage to the fruits at these UV doses.
The inactivation data from the studies conducted on blueberries, raspberries, and strawberries inoculated with Escherichia coli O157:H7 and Salmonella after treatment with gaseous ozone, aqueous ozone, and pulsed UV-light were used to construct models to estimate the inactivation. Two models were constructed, a log-linear (based on first-order kinetics) and a Weibull model. The results indicated that first-order kinetics are not suitable for the estimation of microbial inactivation on berries treated with ozone or pulsed UV-light, but that the Weibull model can be successfully used to estimate the reductions of E. coli O157:H7 and Salmonella on blueberries, raspberries, and strawberries treated with ozone or pulsed UV-light.
The ability of pulsed UV-light to effectively inactivation microorganism in clear liquids has been well documented; however, the effect of opaque food materials on the penetration of pulsed UV-light has not been adequately studied. Inactivation data and energy penetration obtained from the treatment of agar and whey protein gels after treatment with pulsed UV-light was used to construct several models to estimate the amount of energy penetrating the sample at a given depth and the inactivation of E. coli K12. The inactivation curves obtained indicated that the relationship between UV dose and inactivation was non-linear and the Weibull model was used to estimate these inactivations. The model further incorporated a modified exponential model to characterize the decay of UV energy through either agar or whey protein isolate. It was determined that energy measurements were not a good basis for the estimation of microbial inactivation and that each depth had to be treated as a unique scenario due to filtration of wavelengths by the material. The results indicated that pulsed UV-light can penetrate materials up to 10 mm in the depth, and that the Weibull model can be successfully used to model the inactivation of E. coli K12. (Abstract shortened by UMI.)