6/19/2013. Field Harvest Operations Cleaning knives Cleaning tools Field packed products. Rinsing/Washing product

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1 UC Postharvest Technology of Horticultural Crops June 20, 2013 Trevor Suslow UC Davis Dept. Plant Sciences Field Harvest Operations Cleaning knives Cleaning tools Field packed products Rinsing/Washing product Wash and dip tanks Flume wash systems Spray wash systems 1

2 Pre cooling operations after harvest (remove heat field) Top icing of broccoli Hydro cooling by water spray Hydro cooling by drench shower 2

3 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 crosscontamination The reduction of the microbial load on plant and fruit surfaces is a secondary consequence 3

4 Water utilized for post harvest operations will be in direct contact with raw product Incoming Lettuce leaves Contaminated with E. coli Batch 1 Incoming Lettuce leaves Batch 2 Clean process water Contaminated water With E. coli Lettuce leaves Contaminated with E. coli Batch 1 Lettuce leaves Contaminated with E. coli Batch 2 Unwashed E. coli on lettuce Washed E. coli Post washed E. coli 100 ppm Hypochlorite Lopez Galvez, F., et al., Cross contamination of fresh cut lettuce after a short term exposure during prewashing...,food Microbiology (2009) Apples Cantaloupe Peppers Spinach Mango Citrus Cucumber Squash Temp Pressure Depth Water deficit Vacuum credit: M.J. Mahovic, UF/IFAS Fruit pulp must be < 10F {6 o C} warmer than water temperature to prevent infiltration. Microbes in water Adequate water sanitation will prevent problems 4

5 Examples Jacuzzi bath Ultrasonic bath CO 2 cavitation Multiple chemical choices Multiple product types Diverse microbe types Different load throughput Varying wash/cooling conditions Different equipment designs Different retention times 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 Self purging filtration Flume Flocculant 5

6 Non Chemical Ultra Violet Ultra Filtration Chemical Oxidizer Oxidizer and Acid Non Oxidizer Chlorine Gas Sodium Hypochlorite Calcium Hypochlorite Chlorine Dioxide Acidified Sodium Chlorite Electrolyzed Oxidizing Water Chlorobromination Peroxyacetic Acid or Peroxyoctanoic Acid Hydrogen Peroxide Carbonic Acid Ozone Copper 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 6

7 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 mv) % Free Chlorine Form HOCl Highly active Solution ph OC (32F) 20C (68F) 30C (86F) OClless active Fast Spot Checking Simple Dip & Read 1 Step Colorimetric Analysis Visual Reading Low Cost 7

8 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 Treatment ph Free Cl ORP (mv) % Spore Kill 15 secs % Spore Kill 5 min 100 ppm Cl ppm Cl ppm Cl

9 ORP Are you achieving the microbial control objectives? Cl2 (ppm) The relationship between free chlorine and ORP is often very weak across the desired range of operation J. Brennan; New Leaf Foods Relationship between ORP and ppm in Low Turbidity Water Approx. $ ORP (mv) ph 6 ph 7 ph 8 ph Approx. $ Measured Free Chlorine (ppm) E. coli Salmonella Molds Tough Molds Listeria Common Free Cl needed for control ORP (mv) ph 6 ph 7 ph 8 ph Measured Free Chlorine (ppm) TIME OF CONTACT IS IMPORTANT 9

10 NO FEAR DUDE We re exempt * Most common as Retrospective Data for system improvements Soil + Organic matter reduces disinfection potential FAU (Units of turbidity) Water turbidity (NTU) Salmonella serovars Time of 5 ppm ClO 2 Newport (PTVS 077) Gaminara (PTVS 041) Poona (PTVS 026) Enteritidis (PTVS 044) Montevideo (PTVS 045) >120 >120 >120 >120 10

11 WHY COD vs BOD? 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 Start Finish Log CFU/ml Standard limit of detection Time (sec) mg/l O 2 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

12 2 min contact 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 WRAP UP POINTS 12

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 13