1. Shelf life study of newly developed Meal Complement Beverages
Jova L.S.ª, Oliveira J.C.ª1
and Carbonell S.a
ª Department of Process Engineering, University College Cork Ireland.
¹ Phone: +353 21 490 2006, E-mail: j.oliveira@ucc.ie
Tea is a popular beverage widely consumed around the world. Research has
shown health benefits from tea consumption, i.e. tea drinking could raise
human metabolism and increase fat oxidation rates, and may also have
antioxidant activity, cholesterol lowering and cardio protective effects due to
the antioxidant properties of the phenolic compounds (Deng et al., 1998).
Functional food has been gaining support from consumers because of the
increasing concern for healthy eating and the growing scientific evidence
which connects food with health care issues. Beverages that can be used as a
complement of the high fat, high cholesterol and high sodium lunches, which
can be called meal complements, appeared in the market as part of a more
accepted healthy life style. These products are often minimally processed, to
protect the functional ingredients, which enhance the importance of the
assessment of critical shelf life parameters as pH, changes on colour and
microbial growth.
The Weibull model, a very flexible life distribution model which includes 2
parameters (scale (Τ) and shape (Β)) was considered. Lopez et al. (2004)
reported the Weibull model as a suitable mathematical model for the analysis
of microbial growth curves.
The objective of this work was to study the shelf life of some Meal
complement beverages (based on green tea or oolong tea), to ascertain the
critical shelf life indicators.
Materials and MethodsMaterials and Methods
Two different meal complements were developed according to the recipes
obtained in a previous project: oolong tea based also included prunes and fruit
juices, while Green tea based was made mixing with herbs (ginger and
liquorice root) and Inulin. These prototypes were then thermally processed:
batch pasteurization at 72°C for 1 minute holding time. Pasteurised and
unpasteurized (control) samples, with or without protection from light
(duplicate), were stored for up to 3 weeks at 20°C in an incubator (Sanyo MIR-
253), and the changes on pH (pH meter, 3310 Jenway), Browning Index (B.I)
(measured as optical density by HACH spectrophotometer at 420nm) (Garza et
al., 1999) and microbial growth by general total count (IDF, 1986) were
followed.
Results and DiscussionResults and Discussion
Fig 1 and 2 show the effect of pasteurization on the drop of the pH value and the
increase in colour (B.I.), after 3 weeks of storage at 20°C. It can be seen that
both indicators were positively improved by the pasteurization treatment in both
samples. Oolong tea based samples had a better result regarding colour changes,
and light did not affect the results with statistical significance, while in the green
tea based samples, light protection reduced the browning index (statistically
significant differences in a Tukey HSD test). Fig 3 shows the total colony count
after 3 weeks storage at 20°C for all un-pasteurized samples.
Pasteurization was effective in preventing changes on pH and also reducing
colour changes and microbial growth in all samples. Unpasteurized Green tea
based samples showed a lower growth of micro-organisms which was attributed
to the presence of prunes in the Oolong tea recipe. Pasteurized green tea
samples had the lower rate of growth. Oolong tea based samples had a better
result in colour changes (light did not affect the results) while in the green tea
based samples, light protection reduced the browning index value. Results
showed that both pH changes and microbial growth in unpasteurized samples
could be fitted to a Weibull model, showing thus a steeper curvature than the
simple exponential first order kinetics.
It can be seen (fig. 3) that green tea samples showed a lower microbial growth,
which may be because of the presence of prunes in the Oolong tea recipe.
Samples protected from light gave slightly higher count. Pasteurised samples
(fig.4) gave the better result, of course: below the 103
(CFU/ml) thresholds
considered as acceptable microbial load for thermally pasteurised orange juice
(Leizerson & Shimoni, 2005). Light did not affect the results (no statistically
significant differences in a Tukey HSD test).
Fig 5 and 6 shows the behaviour of the B value (shape) and the scale parameter (T
) for the microbial growth kinetics curves fitted to a Weibull model. It can be seen
in fig.5 that in all cases B>1, however, un-pasteurized samples shown a wider
deviation from the typical (exponential) first order kinetics (B=1) (statistical
significant differences in a Tukey HSD test). Pasteurized green tea samples had
the best result on the scale parameter (fig. 6) hence the rate of growth of
microorganisms was slower in these samples.
IntroductionIntroduction
Fig. 1: pH drops after 3 weeks storage at
20°C. White fills indicate light exposed. G
is green tea, O oolong tea, NP un-
pasteurised and P pasteurised
Fig. 2: Colour changes after 3 weeks storage
at 20°C. White fills indicate light exposed,
Grey fills light protected. G is green tea, O
oolong tea, NP un-pasteurized and P
pasteurized
Fig. 3: Colony count after 3 weeks storage
of un-pasteurized samples at 20°C. See Fig.
2 for details
ConclusionsConclusions
ReferencesReferences
Deng ZY, Tao BY, Li X., He J. & Chen Y. (1998). Effect of green tea and black tea on blood
glucose, triglycerides, and antioxidants in aged rats. J Agricult Food Chem;46:3875-78
Lopez S., Prieto M., Dijkstra, Dhanoa M.S. & France J.(2004). Statistical evaluation of
mathematical models for microbial growth. Intern. J. of Food Microbiol; 96: 289-300
Garza S., Ibar A., Pagán J. & Giner J. (1999). Non-enzymatic browning in peach puree during
heating. Food Research International, 32: 335-343
International Dairy Federation (1986). Milk and milk products. Enumeration of micro-
organisms. Colony count at 30°C. International IDF Standard 100A: 1987
Leizerson S. & Shimoni E. (2005). Stability and Sensory Shelf Life of Orange Juice
Pasteurized by Continuous Ohmic Heating. J. Agric. Food Chem.: 53, 4012- 4018
Serafini M, Ghiselli A & Ferro-Luzzi A.(1996). In vivo antioxidant effect of green and black
tea in man. Eur J Clin Nutr; 50: 28-32
AcknowledgmentsAcknowledgments
This work was funded by Enterprise Ireland, with the support of the Irish Government under
the National development plan 2000-2005
Fig 5: Weibull parameter of shape (Β) for
the microbial kinetics curves fits. See Fig. 2
for details
0.000
0.050
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GNP GP ONP OP
B.I
Fig. 4: Colony count after 3 weeks
storage of pasteurized samples at 20°C.
See Fig. 2 for details
Fig. 6: Weibull parameter of scale (Τ)
for the microbial growth kinetics
curves fit. See Fig. 2 for details
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phunits
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OPD OPL GNPL ONPL ONPD GNPD GPL GPD
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