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Using Sanitizers in Postharvest Water

Amanda Deering, Ph.D.Department of Food ScienceIlliana Vegetable Growers Symposium

March 4th, 2014

Outline

• What is the purpose of sanitizers?• What does “log reduction” mean?• Common sanitizers used• Factors that can influence effectiveness• How do you measure the concentration?• Sampling your water source and where to send samples

Sanitization

• What is the purpose of sanitizing?– Hygienic measures used to ensure the safest possible food

– Goal of a reduction of microorganisms to a safe level

– Good sanitizers will achieve a 3‐5 log reduction

What Does Log Reduction Mean?

• A log reduction is when the population of bacteria is reduced by 90%

Number Total Log Reduction

Percent Reduction

1,000,000 -- --

100,000 1 90%

10,000 2 99%

1,000 3 99.9%

100 4 99.99%

10 5 99.999%

Postharvest Water – Why is it Important?

• Large amounts of produce, possibly from different growing areas, come in contact with postharvest water

• If the water is not properly sanitized, bacteria (pathogenic and/or spoilage) can be transferred to other products = cross contamination

Chemicals Used to Sanitize Water and Produce

• Chlorine – Sodium hypochlorite, calcium hypochlorite, potassium hypochlorite

• Chlorine dioxide– Selectrocide, Sanova, etc.

• Peroxyacetic acid (paracetic acid)– Tsunami, Sanidate

• Hydrogen peroxide• Others

Chemicals Used to Sanitize Water and Produce

• The most important things to consider:– Make sure the sanitizer has been approved for use with fresh fruits and vegetables

– Always use a sanitizer at the level it has been approved

– Never use a chemical that has not been approved

Chlorine

• Inexpensive compared to other sanitizers• Has been shown to effectively kill bacteria present in water

• Can kill some existing pathogenic/spoilage bacteria present on plant surface

• Can reduce the transfer of spoilage organisms

Chlorine

• Typically sold as:– Sodium hypochlorite (NaOCl), 6‐15% solutions– Calcium hypochlorite (Ca(OCl)2, tablets or powder in formulations of 65%

• Does not readily dissolve, especially in cold water. Undissolved particles can damage fruits and vegetables

• First dissolve powder in warm water before adding to tank

• Continuous, slow release tablets should be place where water circulates well

– Chlorine gas

Chlorine

• Do not use household bleach. These contain surfactants and/or fragrances

• Product must be registered for use with fruits and vegetables

Examples:Zep FS FORMULA 4665 Dry Tec FG

www.zep.com 800‐478‐5727

The Chemistry

• When sodium hypochlorite is added to water it forms sodium hydroxide (NaOH) and hypochlorous acid (HOCl).

• Hypochlorous acid is what kills bacteria!– Also called available or active chlorine

NaOClCa(OCl)2 HOCl

The Chemistry

• When chlorine combines with contaminates, such as ammonia, soap, and other nitrogen‐containing organic compound, it becomes combined chlorine, or chloroamines– Monochloramine predominant – This form has little to no sanitizing ability – Total chlorine = Free chlorine + Combined chlorine

Chlorine and pH

• At high pH, hypochlorous acid coverts to hypochlorite (OCl‐)– Hypochlorite ion is not as effective at killing bacteria compared to hypochlorous acid

HOCl H+ + OCl-

Chlorine and pH

• At low pH, hypochlorous acid converts to chlorine gas and water.– Chlorine gas is highly toxic– Low pH solutions can be corrosive to equipment

HOCl Cl2 + H2O

Chlorine Efficacy

0

10

20

30

40

50

60

70

80

90

100

5 6 7 8 9 10

SOLUTION pH

% C

hlor

ine

in A

vaila

ble

Form

OC (32F)20C (68F)30C (86F)

EFFECTIVE RANGE6.5‐7.5

Maintain the pH

• Use food grade chemicals to adjust the pH of the water

• Examples– If pH is too high it can be brought down using sulfuric acid

– If pH is too low it can be buffered using lime (CaOH)

Example of How More is Not Always Better

• Normally use 150 ppm at pH 6.5• But you REALLY want to make sure you kill those bacteria!– Increase concentration to 1,500 ppm– However, this will increase the pH (let’s say to around 8.5)

How Much Available Chlorine Do You Have?

0

10

20

30

40

50

60

70

80

90

100

5 6 7 8 9 10

SOLUTION pH

% C

hlor

ine

in A

vaila

ble

Form

OC (32F)20C (68F)30C (86F)

150 ppm yields about 135 ppmHOCl @ pH 6.5

1,500 ppm yields about 150 ppm HOCl @ pH 8.5

Exposure Time and Organic Matter

• High available chlorine concentrations (100ppm) kill bacteria after exposure times less than 1 minute– Lower concentrations require a longer exposure time

• Organic matter in the water (fruit, leaves, soil) will inactivate hypochlorous acid and quickly reduce the amount of available chlorine

Maintaining Proper Concentrations

• Chlorine test kits/stips– Make sure they measure FREE chlorine (not total)– Know the range of measurement of the kit

• Most swimming pool‐type kits measure 1‐5 ppm• Use distilled water to dilute the sample to the range the kit can measure


• HACH® Meters– Colorimetric DPD

• DPD (N,N,‐diethyl‐p‐phenylenediamine) is oxidized by chlorine turning it a red color

• The intensity of the color is directly proportional to the chlorine concentration


• Oxidation‐Reduction Potential (ORP)– Measures the potential oxidizing properties of the sanitizer in water

– Hypochlorous acid (ClOH) is an oxidizer (more active) and has a higher ORP value

– A target ORP value of 700‐750 mV should be sufficient to kill most bacteria


• Advantages of ORP:– Easy to use– Indicates if enough chlorine is present regardless of pH and organic matter

– Can help avoid over chlorination• Disadvantages:

– Need to clean and calibrate the instrument often– High levels of metals or minerals can interfere with ORP reading

– Should double check measurement using chlorine test strips

Water Testing• You should test your water at least once per year for bacteria– Total coliforms – Naturally found in the soil and surface water

• Presences indicates that surface water may be entering the well• While most of these bacteria won’t cause disease, they can be a warning of more harmful bacteria present

– E. coli – Found in the intestinal tract of animals and humans

• Presences indicates fecal contamination• Examples: Failing septic system or runoff from livestock area close to the well

• However, it is good to know the water over the course of a growing season and if there are any changes from the “norm”

How to Collact a Water Sample

• Take sample as close to the application point as possible because that is the water that will be in contact with the product.

Purdue Extension bulletin WQ3, How to Take a Water Sample.

How to Collect a Water Sample

2. Flame sterilize the faucet using a lighter or wash with bleach



3. Run the water for at least 5 minutes.



4. Collection bottles are typically supplied by the lab doing the testing. They contain sodium thiosulfate that neutralizes any sanitizer, like chlorine, that could be present.


ISDH Water Analysis

• The amount of water collected in each bottle must NOT go about the 100 ml line marked on the bottle

• Fill out the label on the bottle completely and accurately

• Fill out the request form and send that along with the water sample. NOTE: If there is a question that can’t be answered, leave it blank

• Samples must be received within 30 hours of collection

• Samples should not be shipped on Friday• Results will be mailed, emailed, or faxed

Costs for Analysis with ISDH

• Bottle and test = $10.00 + $6.50 shipping• Can order up to 24 bottles at a time for a total of $6.50 shipping.

• Need to ship overnight via FedEx or UPS– No more than 30 hours from time of collection to analysis

– Costs approximately $5.00 ‐ $6.00 to ship samples– Look at www.theUPSstore.com to find your nearest location for shipping

Contact ISDH For Water Sample Containers

• Sterile sample bottles must be obtained from ISDH– Contact the Container Section:

• Phone: 317‐921‐5874• Email: [email protected]

Other Labs Can Test Your Water

• Silliker:– Collection bottles can be purchased for $1.00 + shipping– Shipping material (if wanted) and pay for shipping:

• Small cooler ‐ $15.00• Ice pack ‐ $1.00

– Coliform test: $24.75– E. coli test: $24.75

• List of Indiana certified microbiology drinking water laboratories available at:http://www.in.gov/isdh/22450.htm

Contact:Gwyn SerbentasTechnical Sales CoordinatorPhone: 224‐600‐2012Email: [email protected]

Questions

Amanda [email protected]

765‐494‐0512

Thanks to:• Jennifer Coleman ‐ ISDH Farm Food

Safety Consultant• Engra Castiglione – ISDH Water Testing

using sanitizers in postharvest water - purdue agriculture · using sanitizers in postharvest water...

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