Potassium sorbate, sodium benzoate and citric acid together with vacuum packing have extended puree shelf life by 3-6 months in our trials at ambient conditions (T<25C). However, the gap lies on the efficacy of the preservative combination in retarding or stopping the growth of harmful pathogens in the puree, and also their effects on β-carotene retention is unknown.

1. Joyce Ndunge Musyoka
MSc. Student (Food Safety and Quality)
(University of Nairobi)

2. Ø Orange Fleshed Sweetpotato (OFSP) puree is an
ingredient in food processing e.g. bakery application
Ø Currently processors use freshly made puree or frozen
puree because puree is perishable, seasonal and
expensive to freeze, store and transport.
Ø Proposed solution is development of a shelf-storable
OFSP puree which does not require significant
refrigeration ( 3-6 months).

3. Ø Potassium sorbate, sodium benzoate and citric acid
together with vacuum packing have extended puree shelf
life by 3-6 months in our trials at ambient conditions
(T<25C).
Ø However, the gap lies on the efficacy of the preservative
combination in retarding or stopping the growth of
harmful pathogens in the puree, and also their effects
on β-carotene retention is unknown.

4. Ø Determine the effect of combination of potassium
sorbate, sodium benzoate and citric acid i.e. mild
acidification with vacuum package on the keeping
quality of OFSP puree.
Ø Determine the effect of combination of potassium
sorbate, sodium benzoate and citric acid on the growth of
the pathogens Staphylococcus aureus and Escherichia
coli during storage of OFSP puree.
Ø Determine the effect of combination of potassium
sorbate, sodium benzoate and citric acid on β-carotene
retention in stored OFSP puree.

5. Total Viable Counts and Yeast and Molds were analyzed at Time zero, 1
week, 2 weeks, 3 weeks, 5 weeks, 7 weeks and 10 weeks of storage.
Room Temperature(T<25oC) Temperature 4oC

6. Puree was inoculated with 5.2x109 cfu/ml E.coli and 1.53x109cfu/ml
S.aureus and analyzed for these pathogens at 1 week, 2 weeks, 3
weeks, 5 weeks, 7 weeks and 10 weeks of storage.
Room Temperature(T<25oC) Temperature 4oC

7. Plating puree sample on Coliform
agar for E.coli analysis
Cfu of E.coli after incubation

8. Sample (OFSP) puree
FANEL Extraction with methanol,THF
- Evaporationunder nitrogenusing N-Evap machine
-Reconstitution
-Transfer into HPLC vials
HPLC analysis (reverse phase gradient HPLC Method
-Injectioninto HPLC
-PDA detector
- C30 carotenoidcolumn (3µm, 150X4.6 mm)
-Mobile phase A: methanol/tert-butyl methyl ether/water
(85:12:3, v/v/v,with 1.5% ammonium acetate in the water)
-Mobile phase B : methanol/tert-butyl methyl ether/water
(8:90:2, v/v/v,with 1% ammonium acetate in the water).
- Quantification
-External standard curve

9. Growth of Total Viable Counts in
OFSP puree with preservatives at
Room Temperature.
Growth of Total Viable Counts
in OFSP puree with preservative
at Refrigeration Temperature.
0
2
4
6
8
10
0 1 2 3 5 7 10
LogCFU/ml
Storage period (Weeks)
A B C D E
0
2
4
6
8
10
0 1 2 3 5 7 10
LogCFU/ml Storage period (Weeks)
A B C D E
The treatments have an effect on destroying bacteria growth in OFSP
puree with more effect observed at 4oC compared to room temperature

10. Growth of Yeast and Molds in
OFSP puree with preservatives at
Room Temperature.
Growth of Yeast and Molds in
OFSP puree with preservative at
Refrigeration Temperature.
0
1
2
3
4
5
6
7
8
9
0 1 2 3 5 7 10
LogCFU/ml
Storage period (Weeks)
A B C D E
0
1
2
3
4
5
6
7
8
9
0 1 2 3 5 7 10
LogCFU/ml
Storage period (Weeks)
A B C D E
The treatments have an effect on destroying Yeast and Molds in stored
OFSP puree with more effect observed at 4oC compared to room
temperature .

12. Ø High initial TVC 1.95x109 cfu/ml is attributed to poor
handling of puree during preparation.
Ø TVC ,Yeast and Molds were completely inhibited during
the storage period.
Ø Expansion of packages with citric acid at room
temperature and alcoholic odors.
Ø Potassium sorbate activity against bacteria but more on
yeast and molds. (Saranraj and Geetha, 2012) great effect
on molds in baked products.

13. Growth of Escherichia coli in
OFSP puree with preservatives at
Room Temperature.
Growth of Escherichia coli in
OFSP puree with preservative at
Refrigeration Temperature.
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0 1 2 3 5 7 10
LogCFU/ml
Storage period (Weeks)
A B C D E
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0 1 2 3 5 7 10
LogCFU/ml Storage period (Weeks)
A B C D E
The treatments have an effect on reducing E.coli growth in stored
OFSP puree with more effect observed at 4oC compared to room
temperature .

14. Growth of Staphylococcus
aureus in OFSP puree with
preservatives at Room
Temperature.
Growth of Staphylococcus aureus in
OFSP puree with preservative at
RefrigerationTemperature.
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0 1 2 3 5 7 10
LogCFU/ml
Storage period (Weeks)
A B C D E
0.00
2.00
4.00
6.00
8.00
10.00
0 1 2 3 5 7 10
LogCFU/ml Storage period (Weeks)
A B C D E
Growth of Escherichia coli in
OFSP puree with preservative at
Refrigeration Temperature.
Growth of Staphylococcus aureus in
OFSP puree with preservative at
Refrigeration Temperature.
Growth of Staphylococcus aureus in
OFSP puree with preservatives at
Room Temperature.
The treatments have an effect on reducing S.aureus growth in stored
OFSP puree with more effect observed at 4oC compared to room
temperature .

15. Ø Use of preservatives and citric acid led to significant
reduction (p<0.05) in growth of both S.aureus and E.coli
by 6 log cycles.
Ø Citric acid alone led to significant reduction by 5log
cycles. (Seo et al, 2013) - 4 log reduction in chicken
meat, 2% citric acid –most effective in reduction of
S.aureus under refrigeration.
Ø The preservatives were more active against Gram
negative bacteria (E.coli).

16. Baseline β-
carotene
(g/100g)
End
line(mg
/100g)
% β-carotene
loss
9.88 5.55 43.83
9.88 5.58 43.52
9.88 5.21 47.24
9.88 6.66 32.59
9.88 6.09 38.36
Baseline β-
carotene
(mg/100g)
End line
(mg/100g)
% β-carotene
loss
9.88 6.24 36.84
9.88 5.37 45.65
9.88 6.58 33.4
9.88 6.11 38.16
9.88 6.7 32.19
OFSP puree with preservatives at
Room Temperature.
OFSP puree with preservatives
at Refrigeration Temperature.
Even with the highest β-carotene loss (47.24%),there is β-carotene
content of 5.21mg/100g of puree (RAE 434)-100% requirement for
children under 10 years of age and half for adults.

17. Ø Sodium benzoate, potassium sorbate and citric acid
combinations are able to destroy pathogens and ensure
extensive use of puree.
Ø Citric acid (pH) alone is not effective in inhibiting the
growth of these pathogens.
Ø Preservative combinations with 4oC puree storage
conditions is more effective in destroying pathogens
compared to ambient conditions of storage (T<25oC).

18. Ø The preservatives used had an effect in β-carotene
retention.
Ø High preservative concentrations (>0.2%) in puree
should be studied to determine the effect on β-carotene
loss.

19. Ø CIP for providing the funding for this work and a
learning platform through an internship.
Ø My supervisors Dr. Abong’ and Dr. Tawanda for the
guidance and mentorship, keeping me going when
times were tough, asking insightful questions, and
offering invaluable advice.
Ø Daniel and Derick with Laboratory assistance during the
internship.
Ø All CIP staff for the warmth and all kinds of support
during my stay. I am thankful for being part of this team.