Wash Water and Food Safety
S.P. Singh
Research Horticulturist-Food Safety
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Overview
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Sources of wash water
Wash water quality
Selection of a sanitiser
Wash water monitoring
Compatibility of sanitisers and fungicides
Conclusions
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Sources of Wash Water
Surface water
1
Ground water
2
Town water
1/2
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Risk assessment of wash water
Surface water
Ground water
Town water
River/channel/
dam/creek/
rainwater
Bore well
Council supply
Quality
Highly variable
Usually consistent
Less variable
Chemical
Risks
Medium to high
Low to medium
Low
Microbial
Risks
High
Low to medium
Low
Overall
risk
High
Medium
Low
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Wash water quality
Drinking water quality for:
– washing fruit
– fungicide drench/spray
– diluting waxes (if required)
Microbiological test report
 Escherichia coli not detected in 100 mL water sample
 E.coli <1CFU/100mL
Presence of E. coli- a high probability of faecal
contamination
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Wash water- single use vs. recirculation?
• Single use wash water- the best option
• Recirculation-more monitoring and management
• Maintain effective concentration of a sanitiser so
that E. coli <1cfu/100mL
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Wash water quality
must use a sanitiser
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Wash water
• Safe sanitising wash water
• kills or inactivates microorganisms on
fruit surface
• Contaminated wash water
• introduces microorganisms on fruit
surface
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Selection of a sanitiser
Chlorine dioxide
Iodine
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Selection of a sanitiser
• Water quality
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pH of water
organic load
microbiological quality
Sanitiser application & monitoring (manual or automatic)
Packing-line (corrosiveness)
Suppliers/market requirements
Economics
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Chlorine chemistry- basics
NaOCl: Sodium hypochlorite
HOCl: Hypochlorous acid
OCl-: Hypochlorite ion
Hypochlorous acid is highly active form
pH 6.0 to 7.0
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Wash water- a snapshot of practice
Packing
house
A
B
C
D
Water source
Bore well
Channel
water
Channel
water
Town water
5.4
8.7
8.7
8.0
Sanitiser used
Calcium
hypochlorite
Sodium
hypochlorite
Peracetic
acid
None
Concentration
45 ppm
18 ppm
80 ppm
0.05 ppm
Wash water
pH
7.5
9.0
4.0
8.0
ORP (mV)
>650- good
750
600
675
450
Water pH
ORP-Oxidation reduction potential- an indirect measure of the sanitation potential
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Why do we need a high concentration of
a sanitiser in wash water?
Inactivation of bacteria
Pathogen
Escherichia coli
Salmonella typhi
Vibrio cholerae
Yersinia
enterocolitica
Variables affecting Ct
factor
Temp (C)
pH
Chlorine
(mg/L)
Time of
exposure
(min)
Ct
factor
%
Inactivation
0.5
<0.5
<0.25
99.99%
23.0
7.0
0.05
20
1
99.2%
20-25
7.0
2.0
20
40
99.99%
20.0
7.0
1.0
>30
>30
82-92%
20.0
7.0
Source: https://www.cdc.gov/safewater/effectiveness-on-pathogens.html
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Sanitiser efficacy monitoring
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Sanitiser concentration
Uniform application of sanitiser
pH, ORP values
Corrective actions
Record keeping
HACCP plan
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Sanitation monitoring tools
pH meter
ORP meter
Test strips
pH
Chlorine
Chlorine meter
Peracetic acid
Chlorine dioxide
Disclaimer: No endorsement of products and brands,
for information only
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Sanitisers and Fungicides
If incompatible or unknown compatibility
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Sanitisers and Fungicides
Incompatible tank mix: chlorine and imazalil
Chlorine
(100 ppm)
Chlorine (100 ppm) +
Imazalil (500 ppm)
pH
ORP
(mV)
Measured
chlorine
(ppm)
7.2
707
92
8.7
487
43
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Conclusions
• Wash water- drinking water quality
• Water treatment with a sanitiser
• Sanitiser efficacy: concentration, pH and
exposure/contact time
• Monitoring, recording and management
• Sanitisers and fungicides – don’t mix if
incompatible or compatibility unknown
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Acknowledgments
Citrus Packing Houses
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Selection of a sanitiser
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