The influence of pH in key case-studies bacterial and fungal spores’ behaviour inoculated in food model solutions and food products stored under pressure hyperbaric storage

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The use of different fermentative approaches on paracoccus denitrificans: effect of high pressure and air availability on growth and metabolism

Publication . Mota, Maria J.; Lopes, Rita P.; Pinto, Carlos A.; Sousa, Sérgio; Gomes, Ana M.; Delgadillo, Ivonne; Saraiva, Jorge A.

The performance of fermentation under sub-lethal high pressure (HP) is a strategy for stimulation of microbial growth and/or improvement of fermentation titers, rates and yields. The present work intended to study the possibility of applying HP to Paracoccus denitrificans glycerol fermentation, considering that HP-fermentation usually involves some process constrains, such as limited air volumes. Consequently, the work was divided in two main goals: i) study the effects of air availability on P. denitrificans; ii) assess if the strain is able to grow and maintain metabolic activity under HP (10–35 MPa). Paracoccus denitrificans growth and metabolism were highly affected by air availability. Samples under higher air availability showed considerable cell growth, but no production of ethanol or organic acids. On the other hand, samples without air had lower cell growth, but active metabolic activity (with the production of ethanol and organic acids). Regarding the HP experiments, P. denitrificans was able to grow at 10, 25 and 35 MPa, but to a lower extent compared to atmospheric pressure. Application of HP promoted modifications in the production of ethanol, acetate and succinate, and the fermentative profile varied according to the pressure level. Overall, the present work demonstrated new metabolic features of P. denitrificans at atmospheric pressure and HP conditions. It also opened the way for further studies regarding P. denitrificans fermentation under HP, as well as utilization of this technology for other glycerol fermentations, in particular in the case of high requirements of air availability.

2020Journal article

Restricted access

Effect of high pressure pre-treatment on raw ewes’ milk and on subsequently produced cheese throughout ripening

Publication . Inácio, Rita S.; Pinto, Carlos A.; Saraiva, Jorge A.; Gomes, Ana M. P.

BACKGROUND: Raw ewe’s milk, used to manufacture Serra da Estrela Protected Designation of Origin (PDO) cheese, was pre-treated by high pressure processing (HPP), using previously optimized conditions (121 MPa/30 min), in order to evaluate its effect on milk technological properties for subsequent cheese production, namely the impact on resulting curd, whey, and cheese throughout ripening. RESULTS: The cheese yield increase 10.4% as a result of milk pre-treated by HPP, which also yielded inactivation of beneficial microbial groups. After 60 days of ripening, both treated and control cheeses showed neither significant differences (P ≥ 0.05) in quantified microbial load nor in basic physicochemical quality parameters. CONCLUSION: HPP seems to be a promising non-thermal treatment for ewes’ milk to inactivate contaminant bacteria yet with no negative effect on lactic acid bacteria, which are very important for the unique characteristics of Serra da Estrela cheese.

2021-06-01Journal article

Open access