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Pathogen Prevention in
Refrigerated Pickles
Fred Breidt
USDA/ARS Microbiologist
@ NC State University
Raleigh, NC
2011 Pickle Packers International
Spring Meeting
Wednesday, April 13th
9:30 AM (19 slides)
Taste the pickles!
• Two samples of refrigerated pickles
– Typical commercial formula (or slight modification)
– Specially prepared by a local pickle company
• Lisa Moeller and Jane Caldwell
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Do you taste a difference? Which is better?
Texture? Flavor? Appearance?
Comments? 2
Disease outbreaks 1990s-2010
• Escherichia coli O157:H7 outbreak in Osaka prefecture, Japan
– Radish sprouts
– Sakai City outbreak among school children responsible for more than 5,000 cases with 3 deaths.
• Outbreaks of disease from acid foods – Apple cider (E. coli O157:H7), Orange Juice (Salmonella)
• pH values similar to acidified vegetable products (pH 3 to 4)
• Salmonellosis from refrigerated pickles
– Salmonella Newport • Refrigerated (half sour) pickles, Chicago 2010
• Cross contamination ?
3
A model emerging pathogen:
E. coli O157:H7 and related serotypes
• Healthy cattle, deer, goats, and sheep harbor the organism in their intestines. • Bacteriophage borne Shiga‐like toxin genes (slt‐I and slt‐II)
– Toxins inhibit protein synthesis.
– Vascular endothelium (small blood vessels in the intestines) break down.
• Acid resistant compared to commensal strains, being better able to survive exposure to stomach acid.
– Most acid resistant pathogen in acidified foods…
• 3‐4 days post infection bloody diarrhea and abdominal cramps occur, typically self limiting.
• The organism may be isolated from stool samples on sorbitol‐
MacConkey agar.
• Roughly 8% may (children and seniors) develop HUS, which can result in kidney failure and death. 4
Refrigerated pickles and food safety
• Safely produced for many years but…
– No kill step for vegetative pathogens
– Cold temperature, anaerobic conditons, pH 3.5 to pH 4.0 – Similar to fresh‐cut vegetable products but with acid…
• Can we develop a process that will lead to a five log reduction?
– Acid formulations?
• Cost and acceptability
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Is there a cost effective solution?
Labeling?
Flavor and sensory characteristics?
Will we have to destroy the product to make it safe? 5
Applied and Basic Research
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An interesting trend: what about
refrigerated pickles and related products?
120
30oC
20oC
100
10oC
80
a = acetic acid
s = high fructose corn syrup (25%)
60
40
20
pH
3.
7s
pH
4.
1
pH
3.
1a
pH
3.
7a
pH
3.
7a
s
pH
4.
1a
3.
7
pH
3.
1
0
pH
Dp Value (h)
140
Breidt F Jr, Hayes JS, McFeeters RF. 2004. J Food Prot 67(1):12‐18.
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Cold fill and hold
A heat process is not needed for some acidified foods
10oC
E. coli O157:H7
• pH 3.3 or below
• Acetic acid as the primary acidulent
• Holding times and temperatures recorded
– 6 Days for 10oC
– 48 hr. for 25oC
Listeria monocytogenes, a cold‐and‐acid sensitive psychrotroph? Breidt et al., Appl. Environ. Microbiol. 70(11):2638‐2641. 2007. • 5 log reduction achieved
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Biochemistry of typical commercial
refrigerated pickle brines
Company
A1
A2
B1
B2
C1
C2
D
Mean:
Acetic Benzoic
(mM)
(mM)
72.8
5.3
62.68
4.6
90.19
6.7
83.01
6.0
68.34
6.6
65.51
6.3
72.93
6.5
73.64
6.0
(0.07%)
pH NaCl (%)
3.83
2.42
3.89
2.20
3.79
2.00
3.77
1.67
3.86
1.83
3.8
2.10
3.77
3.18
3.82
2.20
Low amounts of acetic acid, refrigeration temperatures, anaerobic conditions
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Survival of E. coli in commercial
refrigerated pickle brines at pH 3.8, 4oC
– Reformulate brines
– Different acids in combination with benzoic and acetic acid
10
Cell Count (Log 10 cfu/ml)
• E. coli O157:H7 and related serotypes can survive for 1 month or more
• Refrigeration is not always the best thing!
• MS student
8
6
4
2
0
0
10
20
30
40
Time (days)
10
Acid killing of E. coli O157:H7 under
anaerobic conditions
Lu, Breidt, Perez‐Diaz, and Osborne. 2011. J. Food Protect. In press.
pH 3.2, 2% NaCl
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Survival of E. coli in commercial
refrigerated pickle brines at pH 3.8, 10oC
with different amounts of fumaric acid
White bars
Light gray Dark gray
Black
0 mM fumaric
15 mM
25 mM
35 mM
12
From Wikipedia: Fumaric acid or trans‐
butenedioic acid is the chemical compound with the formula HO2CCH=CHCO2H. This white crystalline
compound is one of two isomeric
unsaturated dicarboxylic acids, the other being maleic acid. In fumaric acid the carboxylic acid groups are trans (E) and in maleic acid they are cis (Z). Fumaric acid has a fruit‐like taste. The salts and esters are known as fumarates. As a food additive, it is used as an acidity regulator and is denoted by the E number E297.
NOTE: pKa’s are 3.0 and 4.4
In 2% NaCl brine at pH 3.8 the protonated form is only 0.83 mM!
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Use of fumaric acid in refrigerated pickle
brine formulations
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•
25 mM fumaric acid, 70 mM acetic acid, 5 mM benzoic acid, 2% salt, and pH 3.8
Incorporate fumaric acid, reduce acetic acid
– Solubility (about 0.63% max)
• Sodium fumarate is much more soluble (add salt!)
– Needed: about 0.64% – 25 mM final (for 55:45 packout, need 0.64%)
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Flavor
– No specific flavor associated with fumaric acid – Sour taste associated with two protonated forms
• Singly and doubly protonated
• Neta et al., 2007, J Food Sci 72(6):S352‐S359.
– Use 20% less acetic for equivalent sour taste
•
Make brine at “elevated” temperature (37oC)
– Fumaric remains in solution on cooling
14
Cell Count (Log 10 cfu/ml)
Survival of E. coli in refrigerated pickle
brines at 10o , 20o, and 30oC
10
8
10o
6
20o
30o
4
2
0
2
4
6
8
10
12
Holding Time (day)
Figure 3. The die‐off of E. coli O157:H7 in cucumber jars filled with simulated brine solutions prepared with the effective formulation (25 mM fumaric acid, 70 mM acetic acid, 5 mM benzoic acid, 2% salt, and pH 3.8) at a holding temperature of 10°C (filled circle), 20°C (open circle) and 30°C (filled triangle).
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Results from refrigerated pickle taste panel
• Product prepared at a local manufacturing plant
– Typical commercial formula
• pH was 0.3 lower in the fumaric acid product
– 3.58 (control), 3.32 (fumaric)
• 104 participants with complete ballots
– No significant difference (p < 0.05) in preference
– Overall liking similar to control (based on preference
• 9 point hedonic scale
• Other sensory properties similar
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Conclusions
• A modified refrigerated pickle formula with fumaric acid can improve the safety of the product
• Common food additive (GRAS)
• 25 mM fumaric acid is maximum practical amount in refrigerated pickles
– Solubility issues
• Salt and warmer temperatures improve solubility
• Acceptable sensory characteristics…
17
Future research
• Why is fumaric acid better than other acids?
– Internal pH measurements
– GCxGC TOF Mass Spec
• Heat processing with fumaric acid?
– Lower temperatures?
• pH 3.3 or below
http://www.feebleminds‐gifs.com/wizard‐flames.jpg
– Reduce cold fill hold times and/or increase pH? 18
Food Science Research Unit
NC State University, Raleigh, NC
[email protected]
Acknowledgements
Ms. Jenny Lu (currently Ph.D. student at NCSU)
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Collaborators
Dr. Hosni Hassan
Dr. Roger McFeeters
Dr. Ilenys Perez‐Diaz
Former students
Dr. Kristin Bjornsdottir
Dr. Audrey Kreske
Dr. Althea Hosein Technical staff
Ms. Janet Hayes
Ms. Jane Caldwell
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