Rita Pinheiro

Growth and beta-galactosidase activity in cultures of Kluyveromyces marxianus under increased air pressure

Aims:  To investigate the effect of total air pressure raise on cell growth and intracellular β‐galactosidase activity in batch cultures of Kluyveromyces marxianus CBS 7894.

Fed‐Batch Cultivation of Saccharomyces cerevisiae in a Hyperbaric Bioreactor

Fed‐batch is the dominating mode of operation in high‐cell‐density cultures of Saccharomyces cerevisaein processes such as the production of bakerapos;s yeast and recombinant proteins, where the high oxygen demand of these cultures makes its supply an important and difficult task. The aim of this work was to study the use of hyperbaric air for oxygen mass transfer improvement on S. cerevisiaefed‐batch cultivation. The effects of increased air pressure up to 1.5 MPa on cell behavior were investigated. The effects of oxygen and carbon dioxide were dissociated from the effects of total pressure by the use of pure oxygen and gas mixtures enriched with CO2. Fed‐batch experiments were performed in a stirred tank reactor with a 600 mL stainless steel vessel. An exponential feeding profile at dilution rates up to 0.1 h−1 was used in order to ensure a subcritical flux of substrate and, consequently, to prevent ethanol formation due to glucose excess. The ethanol production observed at atmospheric pressure was reduced by the bioreactor pressurization up to 1.0 MPa. The maximum biomass yield, 0.5 g g−1 (cell mass produced per mass of glucose consumed) was attained whenever pressure was increased gradually through time. This demonstrates the adaptive behavior of the cells to the hyperbaric conditions. This work proved that hyperbaric air up to 1.0 MPa (0.2 MPa of oxygen partial pressure) could be applied to S. cerevisiaecultivation under low glucose flux. Above that critical oxygen partial pressure value, i.e., for oxygen pressures of 0.32 and 0.5 MPa, a drastic cell growth inhibition and viability loss were observed. The increase of carbon dioxide partial pressure in the gas mixture up to 48 kPa slightly decreased the overall cell mass yield but had negligible effects on cell viability.

Activation timing of soleus and tibialis anterior muscles during sit-to-stand and stand-to-sit in post-stroke vs. healthy subjects

Introduction. Sit-to-stand (SitTS) and stand-to-sit (StandTS) are very important functional tasks that become compromised in stroke patients. As in other voluntary movements, they require an adequate postural control (PC) involving the generation of anticipatory postural adjustments (APAs). In order to give clues for more efficient and directed rehabilitation programs, a deeper knowledge about APAs during challenging and daily life movements is essential. Purpose. To analyze the activation timing of tibialis anterior (TA) and soleus (SOL) muscles during SitTS and StandTS in healthy subjects and in post-stroke patients. Methods. Two groups participated in this study: one composed of ten healthy subjects and the other by ten subjects with a history of stroke and increased H-reflex. Electromyographic activity (EMGa) of SOL and TA was analyzed during SitTS and StandTS in the ipsilateral (IPSI) and the contralateral (CONTRA) limb to the side lesion in stroke subjects, and in one limb in healthy subjects. A force plate was used to identify the movement onset. Results. In both sequences, in the stroke group SOL activation timing occurred prior to movement onset, contrary to the pattern observed in the healthy subjects. Statistically significant differences were found in SOL activation timings between each lower limb of the stroke and healthy groups, but no significant differences were found between the IPSI and the CONTRA limb. The TA activation timing seems to be delayed in the CONTRA limb when compared to the healthy subjects and showed a better organization of TA timing activation in StandTS when compared to SitTS. Conclusion. Compared to healthy subjects, APAs seem to be altered in both limbs of the post-stroke subjects, with the SOL activation timing being anticipated in both SitTS and StandTS.

Physiological behaviour of Saccharomyces cerevisiae under increased air and oxygen pressures

Saccharomyces cerevisiae, in a pressure batch reactor, coped with higher air (1.2-3 bar) pressures better than with pure oxygen pressures (1.2-3 bar) for an equivalent dissolved oxygen concentration. However, pure oxygen pressure enhanced ethanol production. Both pressures did not influence the type of metabolism followed by the organism which was always oxidoreductive. Growth was inhibited with the increase of air and pure oxygen pressure and almost completely inhibited with 8 bar of pure oxygen. Above 3 bar activities of mitochondrial superoxide dismutase and glutathione reductase increased with air pressure, but cytosolic superoxide dismutase and catalase increased activity only in pure oxygen pressure.

Soleus activity in post-stroke subjects: Movement sequence from standing to sitting

Introduction. The beginning of the movement sequence from standing to sitting requires the modulation of plantar flexors activity, including the soleus muscle (SOL), to allow the forward translation of the tibia in relation to the foot, preserving its antigravity function. Purpose. To analyze the SOL activity during the initial phase of standing to sitting in stroke subjects. Methods. Two groups of ten subjects each participated in this study, one composed of healthy subjects and the other with subjects with a history of stroke. Electromyographic activity (EMGa) of SOL was analyzed in the ipsilateral (IPSI) and contralateral (CONTRA) limb to side lesion in stroke subjects, and in one limb in healthy subjects during the initial phase of standing to sitting. A force plate was used to identify the movement sequence phase. Results. The mean values of SOL EMGa were higher in healthy subjects than the ones obtained in the IPSI and CONTRA limb in stroke subjects. Significant differences were only observed between the IPSI and healthy limb (p = 0.035). Conclusion. When compared to the healthy subjects, stroke subjects showed a decreased SOL EMGa in the IPSI limb, which suggests that therapeutic decisions must consider the need to promote a better postural control also in the IPSI limb.

Response of the thermophile Thermus sp. RQ-1 to hyperbaric air in batch and fed-batch cultivation

Abstract The effects of increased air pressure in a culture of the thermophilic microorganism Thermus sp. RQ-1 were investigated. Cell growth dependence on oxygen supply was investigated in a fermenter at atmospheric pressure. Total oxygen depletion from the medium for low values of kLa was observed during the exponential growth phase. It was possible with this strain to enhance the oxygen transfer rate by increasing the air pressure. Cell productivity was improved by pressurisation up to 0.56 MPa for batch cultivation; and an induction of the antioxidant enzymes, superoxide dismutase and catalase, was observed with the rise in pressure. Cell pre-cultivation under pressurised conditions conferred to the cells more resistance to an exposure to hydrogen peroxide and more sensitivity to paraquat (methyl viologen). The usefulness of bioreactor pressurisation on the cultivation of Thermus sp. RQ-1 was demonstrated for fed-batch operation, with the attainment of higher cell densities. A two-fold increase in cell mass productivity was obtained by the use of hyperbaric air (0.5 MPa). With the pressurisation of the head-space in the reactor, it was also possible to eliminate the loss of liquid by evaporation, which amounted to more than 10% at 70 °C and atmospheric pressure.

Monitoring the quality of sliced pork ham packed in different modified atmospheres during 45 days of storage

This study, financed by EXTRASLICED45 project, promoted by Primor Charcutaria-Prima S.A. and focused on extra-sliced pork ham, aims to use different modified atmosphere packaging (MAP) as a preservation technique for extending the lifetime of the product. In this study, physical, chemical, microbiological and organoleptic properties of sliced pork ham, packaged in MA, were monitored during 45 days of storage at 5 oC. Pork ham samples were packed in four different gas mixtures of 10, 30, 40 and 60% of CO2 (N2 for balancing), in thermoformed trays of APET/EVOH/PE film sealed with PE/PVDC. During the storage time the monitoring of the evolution of the gas mixture composition, pH, water activity (aw), moisture content, colour parameters and firmness of samples was performed. Searching for pathogenic (Salmonella spp., Enterobacteriaceae, Escherichia coli, Listeria monocytogenes and coagulase-positive staphylococci), total viable counts at 30 oC and lactic acid bacteria (LAB) was performed. For sensory evaluation, a trained panel of 6 elements, conducted a quantitative descriptive analysis (QDA®). The previously defined attributes were: brightness, colour, aroma, overall appearance, flavour, texture (hardness and cohesiveness) and salty taste, using a 6-point scale. The panel was also asked about their perception related to the overall appearance and offflavours defects. The results of instrumental analysis of texture and colour, and the chemical parameters showed no significant differences over the time of storage and between MAP. The results of analysed microbiological parameters were satisfactory (according to HPA) and no pathogenic were detected. The principal components analysis highlighted the existence of correlations between the studied parameters. The panel detected some differences between the short and long-term stored ham samples but those differences were no considered defects.