Download Decontaminating fresh produce: Considerations and future issues

Produce decontamination :
Considerations and future
issues
Linda Everis
Campden BRI, Chipping Campden, Glos,
UK.
[email protected]
Outline of presentation
• Where are the microorganisms?
• How do they get there?
• How do we get remove them:
decontamination
• Chlorine washing
• Alternatives to chlorine: acid, alkali,
ozone, chlorine dioxide
Microorganisms associated with
fresh produce
• Diverse microflora associated with fresh fruits and
vegetables
• Gram-negative spoilage bacteria
(Pseudomonas, Enterobacteriaceae)
• Yeasts and moulds
• Pathogenic bacteria
– Salmonella., E. coli 0157:H7, Shigella, Listeria,
Bacillus, Clostridium., Vibrio, Yersinia,
Aeromonas
• Viruses
– Hepatitis A, Norovirus
• Parasites
– Giardia, Cyclospora, Cryptosporidium,
Where are these
microorganisms?
• on natural surfaces
• on cut surfaces
• inside the plant tissues
How do the organisms get
there?
• Seed - contaminated with Salmonella,E.coli
• Major issue with sprouted seeds – need to ensure seeds
are decontaminated prior to use and much research being
done in this area
• Primary production- Fertilisers, irrigation water, animals
contaminated with pathogens
• Harvesting- contamination by pickers
• Processing-inadequate washing procedures fail to remove
or even add contamination
• Storage-inadequate hygiene, times and temperatures of
storage
Typical levels of microorganisms
on fresh produce before
processing
Vegetable TVC
Log10count/g
Broccoli
4.0
Cabbage
3.6-6.3
Lettuce
4.3
Carrotts
5.6
Corn
5.0-7.0
Spinach
6.3-7.4
Key bacterial pathogens
• Salmonella
• Listeria
• E.coli O157
Viruses
• Viruses that can cause foodborne illness
– Human Norovirus
– Hepatitis A
– Hepatitis E
Outbreaks
Year
Country
Food
Cases
Virus
2009
Australia
Semi dried
tomatoes
144
HAV
2010
Denmark
Lettuce
264
HuNV
2010
Finland
Frozen
raspberries
46
HuNV
2010
France &
Netherlands
Semi dried
tomatoes
72
HAV
2012
Germany
Frozen
strawberries
11000
HuNV
2013
10 European
countries
Frozen
1444
blackberries and
redcurrants
HAV
2013
USA
Pomegranate
seed
HAV
165
Key surrogates used to date
Virus
Source/comments
Murine norovirus (MNV)
Controlled by patent laws – owner
Washington University patent No
7,041,444 B2
Feline calicivirus (FCV)
ATCC
MS2
ATCC
How can microorganisms be removed:
Produce Washing
• Removal of debris and spoilage and pathogenic microorganisms
• Potable water containing biocides, disinfectants and
processing aids
– chlorine, chlorine dioxide, organic acids,
• Washing in potable water can give up to a 1 log reduction
but wash water becomes contaminated
• Washing in water containing sanitiser can give a 1-2 log
reduction (Beuchat 1998)
• Attached microorganisms can be difficult to remove as
there can be crevices, stomata, cut surfaces for
attachment
• Internalised organisms can’t be removed
Choice of Disinfectant
• Efficient against microorganisms on the produce
surface
• Removal of organisms from wash water
• On line monitoring of its efficiency
• No alteration of fresh produce quality
• No residues and harmful by-products
Chlorine
•
•
•
•
Widely used in the UK
Relatively cheap and easy to use
Na and Ca hypochlorites most commonly used
Must ensure system is optimised
Chlorine chemistry
1. Sodium hypochlorite + water
sodium hydroxide
NaOCl +H20
NaOH +HOCl
2. Chlorine + water
Cl2 + H20
hypochlorous acid +
hypochlorous acid
HOCl + HCl
3. Hypocholorous acid dissociates to hypochlorite ion
HOCl
H+ + OCl-
Chlorine
• The hypochlorite ion (OCl-) is less biocidal
and has 1/80th germicidal activity of HOCl
• Mode of action is not clearly elucidatedreactions with cell membrane proteins, cell
metabolism, inhibition of enzymes
• Important to maximize presence of HOCl
• pH control is important
pH control
pH
5
6
7
8
9
10
% HOCl
100
97
78
23
4
0
% OCL0
3
22
77
96
100
Chlorine washing
• <pH 4 chlorine in solution is chlorine gas
• Sodium hypochlorite + water produces NaOH
and therefore an alkaline pH
• pH adjustment is therefore necessary to lower
pH
• pH usually adjusted to 7.0 - 7.5 (commonly by
citric acid)
• Lower pH’s will give more HOCl but may effect
product quality and can be corrosive to
equipment
Chlorine washing
• In wash water there will be free chlorine and combined
chlorine
• Free chlorine compounds are: hypochlorous acid (HOCl),
hypochorite ion (OCl-),chlorine (gas) (Cl2)
• Combined chlorine is formed when free chlorine reacts
with organic nitrogen containing compounds (NHCl2,
NH2Cl)
• Combined chlorine is less effective as a disinfectant
• Free and Combined Chlorine = Total Chlorine
• Chlorine demand = chlorine lost to reaction with organic
matter
Log reduction (cfu/g)
Log reduction with 100ppm chlorine
Wash : 5 minutes, pH 7.0
1.3
Salmonella
1.2
Listeria
1.1
E.coli
1
Salmonella
Listeria
E.coli
Other considerations
• Agitation can enhance log reduction by
increasing removal of bacteria
• Temperature can be important if the produce is
warm and the water cold uptake of the water can
occur and therefore internalisation
• If water is warmer than produce influx is reduced
• Produce type can influence efficacy
– melon can neutralise chlorine
– some produce types are smoother (cabbage,
tomatoes)
Why we need alternatives to
chlorine
• Need a system which has less potential harmful
bi-products but achieves a similar effect
• New approaches which will increase the total
level of decontamination
• Novel techniques for specific targets e.g.
pathogens
• Chlorine not permitted for use with organic
produce
• Chlorine not permitted for use in some EU
countries (Germany, Denmark)
• Chlorate limits maybe introduced
Chlorine Alternatives
• Popular chlorine alternatives:
– chlorine dioxide
– Electrolysed water
– Peracetic acid
– Ozone
– Organic acid based washes
– Ultrasound
– Combination treatments/sequential treatments
review of decontamination methods Beuchat
(1999: Surface decontamination of fruits and
vegetables eaten raw: a review.
WHO/FSF/FOS/98.2).
Chlorine Dioxide
• Not affected by pH and organic matter to the same
extent as chlorine
– pH range: 3.0-9.0
– can be unstable and require on-site generation
however, stabilised (liquid) forms of chlorine
dioxide are now commercially available
• Oxidising power 2.5 times greater than chlorine
• Similar efficacy to chlorine
Mean Log reduction of bacteria from Iceberg and spinach
after
3 washing for 1 min in 2 - 3 ppm Chlorine dioxide and 1
min in 20ppm free chlorine
2.5
2
Salmonella 2
1.5
Salmonella 3
1
Pseudomonas 1
0.5
Pseudomonas 3
0
-0.5
Lettuce
Spinach
Ozone
• Lethal to micro-organisms at low concentrations
• Strong oxidising agent
– reactive, unstable, on-site generation
– no residues in water, decomposes to oxygen
– short half-life, less than 20 min. in water at
20oC
– aqueous or gaseous
– Need to consider employee exposure
• Can be used to decontaminate wash water
Mean Log reduction of bacteria from Spinach after washing
3.0
for 2 mins in 2ppm ozonated water
log reduction log cfu
2.5
2.0
Salmonella 2
1.5
Salmonella 3
1.0
Pseudomonas 1
0.5
Pseudomonas 3
0.0
-0.5
Control
Alginate lyase
Organic Acids
• Occur naturally in many fruits and vegetables
– Acetic acid, citric acid, lactic acid
• Do not generally kill micro-organisms
• 6-log reduction of Yersinia on parsley with 2%
acetic acid (Karapinar & Gonul, 1992)
• Organic acid based products Citrox, Drywite and
Anti-bac, Aqua-a- live permitted for use on
organic produce
Washing in organic acid for 2
mins
Wash
type
100ppm
chlorine
(50ppm
after
washing)
Acetic acid
Lactic acid
Log reduction of
S. Typhimurium
(log cfu)
0.95
0.53
Log reduction of
L. monocytogenes
(log cfu)
0.71
0.89
1.55
1.59
1.33
1.27
1.34
1.19
0.87
0.99
UV light
•
•
•
•
UV light has been studied
Useful for decontaminating water
Need to ensure the whole surface is exposed
Campden BRI has UV tunnel which can be used
in trials to decontaminate produce in particular
soft fruits
Electrolysed water
• Salt and water are passed through and
electrode and hypochlorous acid is
produced
• Literature suggests this could be a
viable alternative to chlorine
Other novel techniques
• Other techniques include:
– Cold plasma
– In pack ozone treatments
– Irradiation- studies in US have found this to be
effective
– Natural compounds (carrot extract, essential
oils)
– Hot water
– Biocontrol
– Combination treatments (e.g. hydrogen
peroxide and heat, acid/alkali)
Conclusions
• Fresh produce is not sterile
• Risks from pathogens need to be controlled
during primary production, harvesting and
processing
• Decontamination procedures are the final control
point in the chain as fresh produce is consumed
without cooking
• Current systems in general use have limitations
and at best achieve a 2-log reduction in total
microbial levels
• New systems are needed which will increase the
level of microbial reduction or specifically target
pathogens to give some assurance of produce
safety