INVESTIGADORES
MAZZOBRE Maria Florencia
congresos y reuniones científicas
Título:
Freezing effects evaluated on complex biological systems by DSC: Bakers yeast and microalgal cells
Autor/es:
SANTAGAPITA, PATRICIO R.; MAZZOBRE, MARÍA FLORENCIA; BUERA, MARÍA DEL PILAR; GALVAGNO, MIGUEL
Lugar:
Rosario
Reunión:
Encuentro; 49th Annual meeting of the Society of Cryobiology (CRYO 2012).; 2012
Resumen:
When biomass is to be used in the food,
feed, or pharmaceutical industry, it should be preserved and stored in order to
permit transport from production to consumer. The most frequent preservation
methods are freezing and drying.
Differential scanning calorimetry (DSC)
can be considered a powerful technique for studying thermal transitions of
biological molecules related to their functionality and with biomass viability.
On the other hand, DSC has been shown to
provide a convenient way to determine the chemical stability of some biomass
components, such as lipids [Tan et al. Food Chem. 76 (2002) 385-389].
The objective of this work was to analyze
the feasibility to employ DSC as a tool to evaluate the cryo-resistance of Saccharomyces
cerevisiae yeasts towards freezing and thawing and the long term
conservation of intracellular lipids in Aurantiochytrium limacinum SR21 frozen microalgal cells.
Yeast in stationary growth phase were
exposed to two cycles of freezing (20 h and 4 h) at −20°C after being exposed
to various physical and chemical mild stresses. DSC runs were performed at 10°C/min
from 20°C
to 100°C.
Media with different C:N balances (55:1
and 6:1) were used to obtain microalgae with different PUFAs and carotenoid
contents. Cells were frozen for 1, 8.5 and 30 months at -20ºC. The changes in the
saturated/poly-unsaturated fatty acids (SFA/PUFAs) ratios in microalgal cells
were detected by DSC under oxidative conditions (at 5°C/min) through shifts in
the onset oxidation temperature (OOT) values.
Thermograms of the yeasts systems showed
two peaks that were attributed to low and high protein onset denaturation
temperatures: 4758°C and 6777°C, respectively. Some pre-stress treatments
(temperature, ethanol and NaCl) increased both enthalpy values and survival
after freezing and thawing.
DHA (C22:6,n-3) and palmitic acid were
the major PUFA and SFA respectively produced by the SR21 cells. Microalgal
growth carried out in media with 55:1 C:N ratio produced cells with higher
levels of DHA and of carotenoids, when compared with those grown in media with
a 6:1 C:N ratio. OOT of cells and of lipidic extracts were influenced by
cellular carotenoids.
Fatty acids stability in frozen microalgae
could be evaluated by analyzing the shift of OOT values: the OOT values were
lower for the frozen cells compared to the fresh ones and decreased as a
function of frozen storage time. This behaviour could be associated with DHA content
diminish, in addition to carotenoids degradation.
DSC determinations clearly correlated
with protein stability and the decrease in the enthalpy values obtained from
the thermograms can provide valuable information about the corresponding effect
on yeast viability. Besides, lipids stability in frozen media could be
evaluated in whole microalgae cells as well as in their lipidic extracts
analyzing the shift of OOT values. DSC has a high potential, as a non-chemical
method, to determine stability parameters in complex biological systems and could
be employed as an efficient, reliable and
fast method to study proteins and fatty acids stability in whole cells
and in their extracts.