Inactivation of Escherichia coli in apple juice of different pH using

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					  Inactivation of Escherichia coli in apple
     juice of different pH using ozone



Sonal Patil, Vasilis P. Valdramidis, Jesus M.
  Frias, Patrick J. Cullen & Paula Bourke
                    Rationale

•   E. coli O157:H7 – acid resistance
•   Food borne outbreaks
•   Risk
•   USFDA -       5 log reduction of pathogens
•   USFDA -       Ozone direct additive
                  Ozone
 Ozone- strong oxidizing agent, GRAS
     & effective sanitizer
  Advantage- rapid decomposition
  Mechanism of inactivation-
molecular ozone or free radicals
                                Ozone bubble column
                                    Ozone destructor



                                                                  E. coli strains: ATCC
                                                               25922 & NCTC 12900
                                                                  Apple juice: pH levels
                                                               (3.0, 3.5, 4.0, 4.5 & 5.0)
                                             Juice sample         Ozone treatment-
                                                               flow rate 0.12L/min &
Oxygen tank
              Ozone generator
              Gas analyser                Ozone bubbles        concentration 33-40
                                                                 g/mL for up to 18 min
                                              Ozone diffuser
                    Inactivation kinetics
     The shoulder-log linear model (Geeraerd et al., 2000; Valdramidis et al., 2005)


                              kmax × ( t )    log10 e( max )
                                                        k × Sl
                                                                       ( − kmax ×t )
log10 ( N ) = log10 ( N 0 ) −              +                        ×e
                               ln (10 )           (
                                             1 + e(
                                                    k max × Sl )
                                                                 −1      )
                    ln (10 )
t xd = Sl + ( x ) ×
                     kmax
Ozone inactivation of E. coli NCTC 12900
                7                                                                       7
Log10(CFU/mL)   6                                   pH 5.0                              6                                       pH 4.5
                5                                                                       5
                4                                                                       4
                3                                                                       3
                2                                                                       2
                1                                                                       1
                0                                                                       0
                    0   2   4   6   8                   10 12 14 16 18                      0       1   2   3       4   5   6     7   8       9 10
                7                                                                       7
                                                    pH 4.0                                                                  pH 3.5
                6                                                                       6
Log10(CFU/mL)




                5                                                                       5
                4                                                                       4
                3                                                                       3
                2                                                                       2
                1                                                                       1
                0                                                                       0
                    0   1   2   3   4                   5       6   7       8   9           0           1       2       3        4        5      6
                                                        7
                                                        6                                               pH 3.0
                                                        5
                                        Log10(CFU/mL)




                                                        4
                                                        3
                                                        2
                                                        1
                                                        0
                                                            0           1           2           3           4           5
                                                                                    Time (min)
  Strain     pH    Weibull model     RMSE   Shoulder log linear   RMSE



ATCC 25922   5.0    17.37 ± 1.92a*   0.20      18.15 ± 0.71 a*    0.23

             4.5    10.07 ± 2.17b    0.46      10.34 ± 0.57 b     0.37

             4.0     8.10 ± 1.11c    0.53       8.28 ± 0.55 c     0.46

             3.5    5.27 ± 0.70d     0.49       5.36 ± 0.74 d     0.44

             3.0    4.30 ± 0.99d     0.74       4.01 ± 2.93 d     0.43

NCTC 12900   5.0    17.41 ± 3.03 a   0.31      18.16 ± 0.96a      0.31

             4.5    10.37 ± 1.84b    0.47      10.21 ± 0.65b      0.37

             4.0     8.31 ± 1.18c    0.62       8.48 ± 0.69c      0.50

             3.5     5.99 ± 0.67d    0.46       6.03 ± 0.69d      0.35

             3.0     4.88 ± 0.66e    0.68       4.88 ± 1.62e      0.55
A correlation was established between the t5d
and the different adjusted pH levels of apple
juice.

Exponential equation:


                         k× pH
   t5 d = a × e
                                               Correlation
                            ATCC 25922                                                     NCTC 12900

            25                                                              30

            20                                                              25

                                                                            20
t5d (min)




                                                                t5d (min)
            15
                                                                            15
            10
                                                                            10
             5                                                               5
             0                                                               0
                 2   2.5   3    3.5        4    4.5   5   5.5                    2   2.5   3   3.5        4   4.5   5   5.5
                                      pH                                                             pH



            . (-): fit, (.-.): 95 % prediction bounds, (--): 95% confidence bounds. (□) Validation point, (♦)
            Observed data values
Untreated   Ozone treated
              Conclusions
   Direct ozone treatment- inactivate E. coli in apple
juice.
   Efficacy of ozone treatment – a function of pH of
the apple juice.
   Inactivation by 5 log cycles- 4.0 to 18.16 min.
   Good degree of correlation between t5d and pH in
apple juice can be applied to design treatment time
period.
  Further studies - effect of ozone on sensory and
nutritional quality.
          Acknowledgement
Funding for this research was provided under
the National Development Plan 2000-2006,
through the Food Institutional Research
Measure, administered by the Department of
Agriculture, Fisheries & Food, Ireland.
Thank you

				
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posted:8/30/2011
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