Date post: | 16-Dec-2015 |
Category: |
Documents |
Upload: | charles-murphy |
View: | 215 times |
Download: | 0 times |
Research Findings on the Application of Warming and
FreezingImme W. Kersten, Dr. Sita R. Tatini,
Kaushik Subramanian
Increased research devoted to finding alternatives to pasteurization
isostatic high pressure
pulsed electric field
filtration
ozone
UV light
Freeze/thawing
Freeze/thawing as a viable method
little start-up capital compared to pasteurization
minimal to no nutritional loss
possibly no change in sensory characteristics i.e taste, smell, appearance
Contradictory
generally thought of as a method of preservation
presence of sugar as a cryoprotective agent
Supportive
high acid, presence of preservative
Methods
Preparation of inoculated cider
Four strains of verotoxigenic Escherichia coli
OD (O157:H7)933(O157:H7)406(O22:H6)O104:H21
5 Minnesota Orchards
2 produce cider without sodium benzoate
pH range from 3.1 to 3.6 (early on in the season)
coliforms range from <10/ml to 50/ml
no E.coli detected
Fresh, unpasteurizd, non-autoclaved cider
Test tube experiments (10ml)
test tubes inoculated with each strain (106 CFU/ml target level)
• frozen @ -16.8°C, removed on a weekly basis, thawed in a room temperature water bath, enumerated and held @ 4°C until gone
test tubes subjected to 2 and 3 freeze/thaw cycles, then held @ 4°C until gone
test tubes frozen for 4 and 7 days, thawed, heated to 50°C
Large container experiments
similar experiment as with test tubes but with gallons and 1/2 gallons this time
also gallons and 1/2 gallons were inoculated with cells grown at a lower pH of 5.2
Influence of pH of apple cider on survival of freeze-thawed VTEC OD during storage at 4°C
Kaushik Subramanian M.S. Thesis
Influence of frozen storage (-16.8ºC) at varying lengths of time on strain 933 in test tubes
933(O157:H7)
0
2
4
6
week
0
week
1
week
2
week
3
week
4
week
6
week
8
Weeks Frozen at -16.8C
Lo
g C
FU
/ml
TSAYE
Influence of frozen storage (16.8C), defrosting and holding at 4C on verotoxigenic Escherichia coli in
unpasteurized apple cider containing no preservative – test tubes
01234567
Log
CFU/
ml Sample A
Sample B
933 OD 406 O104
Influence of frozen storage (16.8C), defrosting and holding at 4C on survival of verotoxigenic
Escherichia coli in unpasteurized apple cider containing sodium benzoate – test tubes
01234567
Log
CFU/
ml Sample C
Sample D
933 OD 406 O104
Applying heat (50°C) to cider which had been frozen
freeze 7 days and then heat• almost 5 log with sodium benzoate• 4 log without preservative
hold for 1 or 2 days
raise temperature to 55°C
Use of 3 freeze/thaw cycles
with benzoate, 2 days holding = 6 days total
without benzoate, 8 days holding = 12 days total
Time is shortened but….
energy expense
cycle time changes with larger sizes
Influence of frozen storage (-16.8°C) followed by thawing and holding @ 4°C on destruction of verotoxigenic Escherichia coli in unpasteurized apple cider without preservative
Source Size Strain Length of time for 5 log destruction
E1 1 gallon 933/406 2 wks, 13 days1 gallon OD/O104 2 wks, 13 days
A 1 gallon 933/406 4 wks, 5 days1 gallon OD/O104 4 wks, 5 days1/2 gallon all strains 4 wks, 7 days1/2 gallon all strains 4 wks, 5 days
Influence of 1 week frozen storage (-16.8°C) followed by thawing and holding @ 4°C on destruction of verotoxigenic Escherichia coli in unpasteurized apple cider with sodium benzoate
Source Size Strain Length of time @ 4°C for 5 log destruction
E2 1 gallon 933/406 9 days1 gallon OD/O104 9 days1/2 gallon all strains 9 days1/2 gallon all strains 14 days1/2 gallon all strains 14 days
C 1 gallon 933/406 3 days1 gallon 933/406 7 days1 gallon OD/O104 3 days1 gallon OD/O104 7 days
Influence of 1 week frozen storage (-16.8°C) followed by thawing and holding @ 4°C on destruction of verotoxigenic Escherichia coli in unpasteurized apple cider with sodium
benzoate (cells grown at pH 5.2)
Source Size Strain Length of time @ 4°C for
5 log death
D 1 gallon 933/406 1 day1 gallon 933/406 1 day1 gallon OD/O104 1 day1 gallon OD/O104 1 day
C 1/2 gallon all strains 1 day1/2 gallon all strains 4 days
E2 1/2 gallon all strains 3 days
Conclusion
sodium benzoate contributes to death of injured cells
behavior of E.coli in test tubes versus larger containers is not alike
cause of variability is unknown
Possible Explanations
variation in test tube versus gallon/ 1/2 gallon
• slow freezing/slow defrosting thought of as most damaging
• gallons/ 1/2 gallons are slow/slow
• test tubes are fast/fast
Distribution of liquid water to ice?
Size and number of crystals formed?• high cooling rates = small internal ice
crystals• slower cooling rates = external ice
crystals leading to dehydration
Freezing point of different apple cider?
Distribution of pectin and pulp in the test tubes?
• variation among orchards• may be protective