Gamma-rays influence on microbiological and abiotic factors of sheep butter
M.I. Santos
(1,2),
J. Pinto
(1),
A.I. Pimenta
(1),
P. Matos
(2),
S. Cabo Verde
(1),
F.M.A. Margaça (1), E. Alves
(2)
1Centro
de Ciências e Tecnologias Nucleares (C2TN), Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, km 139.7, 2695-066 Bobadela, Loures, Portugal
2Laboratório de Aceleradores e Tecnologias de Radiação (LATR), Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, km 139.7, 2695-066 Bobadela, Loures, Portugal
Corresponding author: [email protected]
Food irradiation is one of the few technologies that address both food quality and safety by virtue of its ability to control spoilage and foodborne pathogenic microorganisms without
significantly affecting sensory attributes of the food [1, 2]. Butter is a product manufactured by processing raw milk. Besides fats, butter contains small percentages of proteins, lactose and water
which make it a suitable substrate for microorganisms and consequently butter spoilage [3].
OBJECTIVE
The aim of this study was to evaluate the effects of gamma radiation on microbial inactivation, water content and sensory quality of sheep butter, assessing the potential shelf-life extension.
METHODOLOGY
ASSESSMENT OF SHELF-LIVE EXTENSION
Fermented cream was irradiated in a Co-60 Equipment
Dose rate: 0.31 kGy/h
Absorbed dose: 0.93 KGy
Irradiated cream and non-irradiated cream were used
to produce two different samples of butter
• 5 g of fermented cream irradiated + 50 mL of peptone water
were put in a sterile bag and homogenized for 10 minutes.
Analysis timeline:
• Day collection- t0
•After 15 days - t15
•After 30 days - t30
• After 60 days - t60
•After 90 days - t90
SENSORIAL ANALYSIS
WATER CONTENT
MICROBIOLOGY ANALYSIS
• Inoculation of different aliquots in Tryptone Soya Agar (TSA)
and Malt Extract Agar (MEA) dishes followed by incubation at
30ºC and 27ºC, respectively.
• Drying oven method at 102°C during 3 h.
• Mass variation was asessed in time intervals of 1h
until not exceeding 1mg [4].
• Untrained panel
(18<age<65).
of
15
healthy
individuals
• The acceptability of each sample was evaluated by
a questionnaire based on regulation 273/2008.
• Each inoculation was performed in triplicate for each sample
and for each culture medium.
• The counts of the colonies in TSA and MEA were made after
24h, 48h, 72h and 7 days.
RESULTS
WATER CONTENT
M3
M3N2
Samples
B
t0
t15
t30
t60
t90
M3- Non-irradiated butter
M3 N2- Irradiated butter
M3
M3N2
Samples
Table 1- Filamentous fungi presente in butter samples.
Samples
t0
M3N2
t15
t30
t60
t90
M3
M3N2
M3
M3N2
M3
M3N2
M3N2
Relative
Filamentous fungi frequency
(%)
0.69
Phoma sp.
96.98
Geotrichium sp.
2.32
Alternaria sp.
100.00
Geotrichium sp.
100.00
Geotrichium sp.
100.00
Geotrichium sp.
100.00
Geotrichium sp.
Aureobasidium pullans
100.00
Phoma sp.
20.00
Penicillium sp.
60.00
20.00
Aerobasidium sp.
Phoma sp.
32.00
Chaetomium sp.
68.00
t0
t15
t30
t60
t90
M3
Figure 1- Average logaritmical counts of mesophilic bacterial population (A) and fungal population (B) before (t0) and after storage at 4°C during 15
days (t15), 30 days (t30), 60 days (t60) and 90 days (t90). Error bars correspond to 95% confidence intervals about mean values (n=18; α=0.05).
Analysis
timeline
5
• Regarding the bacterial and fungal load
of butter samples, there were no
significant differences between the
butter types and the storage times.
Average score value
t0
t15
t30
t60
t90
9
8
7
6
5
4
3
2
1
0
100
90
80
70
60
50
40
30
20
10
0
SENSORIAL ANALYSIS
B
A
4
3
2
1
0
M3N2
Organoleptic characteristics
Samples
M3- Non-irradiated butter
M3 N2- Irradiated butter
Figure 2 – Water content of the butter produced before (t0) and after
storage at 4°C during 15 days (t15), 30 days (t30), 60 days (t60) and 90 days
(t90). Error bars correspond to 95% confidence intervals about mean
values (n=2; α=0.05).
5
Average score value
A
Water content (%)
9
8
7
6
5
4
3
2
1
0
Log CFU/g
Log CFU/g
MICROBIOLOGY ANALYSIS
C
4
 M3- Non-irradiated butter
 M3 N2- Irradiated butter
3
2
Figure 3 - Sensory analysis performed by an untrained panel
of butter samples before (t0-A) and after storage at 4°C during
15 days- t15 (B) and 30 days - t30 (C). A hedonic scale was
used, ranging from 1 (dislike extremely) to 5 (like extremely).
Error bars correspond to 95% confidence intervals about mean
values (16< n<22; α=0.05).
1
0
• The water content on the irradiated butter was higher than
the non-irradiated sample.
Organoleptic characteristics
• The most frequent fungi isolated from
both butter samples was Geotrichium sp.
• The diversity of fungal population
of butter samples changed during
refrigerated storage.
• Comparing the different storage times, there were no
significant changes with the increase of shelf-life time up to 60
days (t0, t15, t30 and t60).
• Non-irradiated and irradiated butters had similar sensorial evaluation based on
the scored organoleptic characteristics.
• For 90 days of storage (t90) there was a significant decrease
of water content for both samples.
• Comparing the different storage times, there was a decrease in the
score of both butter types.
• The
sensorial analysis was not performed after t30
due to the visible fungal growth on both butters.
REFERENCES
CONCLUSIONS
• The irradiation treatment of fermented cream seems to have no effect on the extension of shelf-life of this butter product.
• The analysis of water content of irradiated and non-irradiated samples indicated an increase of ≃ 10% of water on butter produced
with irradiated cream, observed to remain in all storage time periods.
[1] FAO/IAEA/ WHO. 1999. Report of a Joint FAO IAEA WHO Study Group.
[2] J.F. Diehl, Radiat. Phys. Chem, 63, 2002, 211–215.
[3] A.H. Rady, H.M. Badr, Grasas y Aceites, 54(4), 2003, 410:418.
[4] Regulamento (CE) N.º 880/98
ACKNOWLEDGMENTS
This work was supported by:
• Tété II- Produtos Lácteos., Lda
• Programa Operacional Regional de Lisboa (POR)
• FCT (Portugal), RECI/AAG-TEC/0400/2012.
• C2TN/IST authors gratefully acknowledge the FCT support through the
UID/Multi/04349/2013 project.
• Gamma radiation treatment had no impact on the sensory quality attributes of butter. The irradiated samples were highly acceptable for
the panelists.
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