Evaluation of chlorine dioxide gas for sterilizing food processing lines.

摘要

Food processing lines are normally steam sterilized at 121°C for at least 30 minutes to eliminate presence of microorganisms. However with the energy cost rising recently, food companies' operational costs have tremendously increased. Therefore the needs to find alternative sterilization method, which are less expensive, have arisen.;Chlorine dioxide (ClO2) has a long history as sanitizer and/or disinfectant (Bernarde et al., 1965) and has been evaluated for its antimicrobial efficacy, in aqueous form, on fruits and vegetables (Sy et a.l, 1977; Pao et al., 2007), meat processing (Cutter et al., 1995), fruit juices (Lee et al., 2003), and poultry processing (Tsai et al., 1995). Additionally, recent studies have been done using gaseous ClO2 which indicated its potential to kill various pathogens (Han et al., 2000, 2001, 2004) and bacterial spores (Han et al., 2003). The goal of this research was to test the ability of gaseous ClO2 to sterilize a food processing line. In order to meet that goal, several preliminary experiments, such as residual ClO2 removal and effect of drying time and surface roughness on Bacillus atrophaeus spores killing efficacy were evaluated. Residual ClO2 could be easily removed from a 400 liter tank by aeration and water rinsing. Fifteen to eighteen air exchanges inside the system could bring the residual concentration down to ∼0 mg/l. However additional rinsing with water would be beneficial to ensure that any remaining ClO2 is dissolved and removed by the water. The effect of drying and different surface roughness on gaseous ClO2 effectiveness showed that drying reduced the spores' population by ∼2.5 log and that rougher surfaces reduced gaseous ClO2 killing efficacy. Additional experiments were done to obtain inactivation kinetics of Bacillus atrophaeus spores purchased from ATCC, NAMSA (as spore suspensions), and SGMBiotech (as spore strips). Spores obtained from ATCC were inoculated on the surface of stainless steel and Teflon strips and the effect of heat shock prior to treatment was studied. Statistical analysis at 95% confidence interval indicated no significant difference on the calculated D values between heat shocking and non-heat shocking Bacillus atrophaeus spores on both stainless steel and Teflon strips at concentrations between 1.0 mg/l and 4.0 mg/l. Therefore, average D values +/- standard deviation for B. atrophaeus spores (heat shocked and non-heat shocked) inoculated on stainless steel strips were 12.30 +/- 1.64 min, 9.00 +/- 1.58 min, 6.23 +/- 1.18 min, 4.84 +/- 2.16 min at 1.0 mg/l, 2.0 mg/l, 3.0 mg/l, and 4.0 mg/l, respectively. On the other hand, inoculation on Teflon strips significantly increased the spores' average D values +/- standard deviation (heat shocked and non-heat shocked), at alpha = 0.05, to 33.41 +/- 1.86 min, 12.56 +/- 1.91 min, 11.45 +/- 1.10 min, 7.36 +/- 1.38 min for 1.0 mg/l, 2.0 mg/l, 3.0 mg/l, and 4.0 mg/l, respectively.;With the SGMBiotech spore strips, the D value using intact strips at 4 mg/l was 1.15 min. The strips were also destroyed into pulp to dissolve the spores into a suspension for further inoculation on the stainless steel strips and the D values at 0.5 mg/l, 1.0 mg/l, and 2.0 mg/l concentrations were 23.60 min, 8.48 min, and 4.74 min, respectively. In addition, the D values using NAMSA's spore suspensions were 7.12 min, 4.12 min, and 2.39 min at 0.5 mg/l, 1.0 mg/l, and 2.0 mg/l, respectively.;In general the ATCC-grown Bacillus atrophaeus spores had higher resistance to the ClO2 gas, hence further analysis on the stock spores needs to be done.;Another research was done using Lactobacillus buchneri, grown in either MRS broth or TropicanaRTM orange juice, in a food processing line. Lactobacillus buchneri grown in Tropicana RTM orange juice had a higher D value (8 minutes at 1 mg/l), thus required longer treatment time compared to those grown in Lactobacillus MRS Broth (D value of 5 minutes at 1 mg/l). Pilot plant testing of chlorine dioxide gas for sterilizing an aseptic processing line was successful at showing that chlorine dioxide could be used to completely eliminate Lactobacillus buchneri in a high acid food environment.