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6/19/2013
1
Trevor SuslowUC Davis ‐ Dept. Plant [email protected]
UC Postharvest Technology of Horticultural Crops
June 20, 2013
Field Harvest Operations
Cleaning knives
Cleaning tools
Field packed products
Rinsing/Washing product
Wash and dip tanks
Flume wash systems
Spray wash systems
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Top‐icing of broccoli
Hydro‐cooling by water spray
Hydro‐cooling by drench‐shower
Pre‐cooling operations after harvest (remove heat field)
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Treatment of process water to inactivate ; Pathogenic bacteria Plant pathogens
Human pathogens Spoilage Microbes Fungi
Bacteria
Yeast Human Parasites Viruses Human pathogens
The role of process water disinfection is to prevent and to minimize the redistribution of plant and human pathogens from incoming produce into the water
Prevent cross‐contamination
The reduction of the microbial load on plant and fruit surfaces is
a secondary consequence
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Water utilized for post‐harvest operations will be in direct contact with raw product
Incoming Lettuce leaves
Contaminated with E. coliBatch 1
Incoming Lettuce leaves
Batch 2
Clean process water
Contaminated waterWith E. coli Lettuce leaves
Contaminated with E. coliBatch 2
Lettuce leavesContaminated with
E. coliBatch 1
Lopez‐Galvez, F., et al., Cross‐contamination of fresh‐cut lettuce after a short‐term exposure during prewashing...,Food Microbiology (2009)
Unwashed E. colion lettuce
Washed E. coli100 ppm Hypochlorite
Post‐washed E. coli
Fruit pulp must be < 10F {6oC} warmer than water temperature to prevent infiltration.
Microbes in water
credit: M.J. Mahovic, UF/IFAS
ApplesCantaloupePeppersSpinachMangoCitrusCucumberSquash
TempPressureDepthWater deficitVacuum
Adequate water sanitationwill prevent problems
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“Jacuzzi” bathUltrasonic bathCO2 cavitation
Examples
• Multiple chemical choices• Multiple product types• Diverse microbe types• Different load throughput•Varying wash/cooling conditions• Different equipment designs• Different retention times
Flume Flocculant
Self‐purging filtration
Common practice to minimize water consumption and wastewater discharge rates
Effectiveness of chemical sanitizer can be affected by water quality
Investment in filtration/sedimentation makes all recirculating systems perform better
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6
Non Chemical
Ultra Violet
Ultra‐FiltrationChemical
Oxidizer
Oxidizer and Acid
Non‐Oxidizer
Chlorine GasSodium HypochloriteCalcium HypochloriteChlorine Dioxide Acidified Sodium ChloriteElectrolyzed Oxidizing Water ChlorobrominationPeroxyacetic Acid or Peroxyoctanoic Acid Hydrogen PeroxideCarbonic AcidOzoneCopper ions + low HOCl (+ Silver ions)
pH (acidity) Critical when hypochlorite is used
Use of organic acids to maintain right pH values (citric acid)
Can use phosphoric, muriatic (food grade)
Water temperature
Water turbidity Soil, dirt, leaves, debris
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Determine the concentration of the disinfectant agent
▪ 75 to 200 ppm of sodium hypochlorite
▪ Up to 5 ppm for chlorine dioxide
Determine the oxidative state of the water (how much disinfection potential is there?)
▪ Oxidation reduction potential (ORP)
▪Measures disinfection potential not ppm
▪ >650 mV (most systems 750‐825 mV)
0
10
20
30
40
50
60
70
80
90
100
5 6 7 8 9 10
Solution pH
% F
ree
Ch
lori
ne
Fo
rm OC (32F)
20C (68F)
30C (86F)
4
HOClHighly active
OCl‐less active
• Fast Spot Checking
• Simple “Dip & Read” 1 Step
•Colorimetric Analysis
•Visual Reading
• Low Cost
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• Chemical Test Kit
o Titration – visually read
o Colorimetric
Visual
Hand‐held devices
• Portable ORP and pH Meters
• In‐line Sensors
o Measure
o Record
o Control
Free Chlorine or Chlorine Dioxide
Potentiostatic or Amperometric
Low Maintenance Membrane or Double
Platinum Disc design Fast Response
Sensor flow cell
99.9207422019.8200 ppm Cl
99.9909001007.1100 ppm Cl
550.96981008.2100 ppm Cl
% Spore Kill 5 min
% Spore Kill 15 secs
ORP (mV)Free ClpH Treatment
99.9207422019.8200 ppm Cl
99.9909001007.1100 ppm Cl
550.96981008.2100 ppm Cl
% Spore Kill 5 min
% Spore Kill 15 secs
ORP (mV)Free ClpH Treatment
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600
650
700
750
800
850
900
950
1000
0 10 20 30 40 50 60 70 80 90 100
ORP
Cl2 (ppm)
The relationship between free chlorine and ORP is often very weak across the desired range of operation
J. Brennan; New Leaf Foods
Are you achieving the microbial control objectives?
Relationship between ORP and ppm in Low Turbidity Water
Measured Free Chlorine (ppm)
Approx. $150.00
Approx. $750.00
350
450
550
650
750
850
950
0.5 2 10 20 40 80 100
pH 6
pH 7
pH 8
pH 9
ORP (mV)
Measured Free Chlorine (ppm)
350
450
550
650
750
850
950
0.5 2 10 20 40 80 100
pH 6
pH 7
pH 8
pH 9ORP (mV)
E. coli Salmonella Molds Tough MoldsListeria Common Free Cl
needed for control
TIME OF CONTACT IS IMPORTANT
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NO FEAR DUDEWe’re exempt
* Most common as Retrospective Data for system improvements
Soil + Organic matter reduces disinfection potential
0 15 150 300 3000
FAU (Units of turbidity)
Water
turbidity
(NTU)
Salmonella serovarsTime of inactivation(s) @ 5 ppm ClO2
Newport
(PTVS 077)
Gaminara
(PTVS 041)
Poona
(PTVS 026)
Enteritidis
(PTVS 044)
Montevideo
(PTVS 045)
43 5 30 60 90 120
160 90‐120 >120 >120 >120 >120
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1. all organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions
2. COD is few hour test vs BOD is a 5 day test
WHY COD vs BOD?
Start Finish
0
1
2
3
4
5
6
0 5 10 20 30 45 60 75 90
E. coli O157 ‐ COD 20
Salmonella ‐COD 20
Listeria‐ COD 20
E. coli O157 ‐ COD 140
Salmonella ‐COD 140
Listeria‐ COD 140
E. coli O157 ‐ COD 280
Salmonella ‐COD 280
Listeria‐ COD 280
mg/L O2
Time (sec)
Log CFU/m
l
Standard limit of detection
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12
2 min contact
WRAP‐UP POINTS
1. Preventing cross‐contamination in wash water requires coordination between field and process
2. COD strongly influences ability to maintain critical dose levels throughout system
3. Setting industry performance standards with single pathogen surrogates is risky
4. Advanced system management is attainable
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13
Water that will be in contact with raw food is likely to become a vehicle to distribute microbial pathogens if a disinfection strategy is not applied
There is not a perfect disinfectant! Define the objective of the water disinfection
program to achieve microbial reduction objectives FOR THE SYSTEM