Marcelo Cristianini

Effect of dynamic high pressure on functional and structural properties of bovine serum albumin

Dynamic high pressure (DHP) has been investigated as an innovative suitable method to induce protein modifications. This work evaluated the effect of DHP (up to three passes at 100, 150 and 200MPa, with an inlet temperature of 20°C) on functional and structural properties of bovine serum albumin (BSA). Results indicated that DHP process applied up to an energy limit of 100MPa increased the protein foaming capacity (FC) (p<0.05 - increase up to 63% after 1 pass at 100MPa) and the utilization of multiple passes at high pressure promoted a reduction in this property (p<0.05 - reduction up to 31.6% after 3 passes at 200MPa). Similar results were observed for sulfhydryl group, indicating an influence of free thiol groups on FC. Complementarily, DHP process promoted an increase of proteins particles size, suggesting a new rearrangement of their conformational structure. DHP did not affect tryptophan microenvironment in BSA; however, this process induced the rearrangement of secondary structure elements. In the first cycle, the pressure increase resulted in a loss of secondary structure, while in the second and third cycles the DHP process resulted in the gain of secondary structure elements. These results indicated that the second and third passes triggered a molecular rearrangement of the protein structure, giving rise to a novel and more stable conformational state. This conclusion was also supported by thermal unfolding studies (melting temperature reduction from 67.5 to 54.6°C after 1 pass at 200MPa), in which the additional cycles of DHP caused the occurrence of an initial denaturation at high temperatures, compared to the first cycle.

Effect of High-Pressure Technologies on Enzymes Applied in Food Processing

High isostatic pressure (HIP) and high-pressure homogenization (HPH) are considered important physical technologies that able to induce changes on enzymes. HIP and HPH are emerging food processing technologies that involve the use of ultra high pressures (up to 1200 MPa for HIP and up to 400 MPa for HPH), where the first process is based on the principle that the maintenance of a product inside vessels at high pressures induces changes in the molecules conformation and, consequently, in the functionality of polysaccharides, proteins and enzymes. To the contrary, for HPH process, the high shear and sudden pressure drop are the responsible phenomena for the changes on the processed product. This chapter aims to evaluate comparatively the effects of HIP and HPH on the activity of enzymes currently applied in food industry and to identify the main structural changes induced by each process. The overall evaluation of the results shows that mild conditions of both processes were recently highlighted as able to improve the activity and the stability of several enzymes, whereas extreme process conditions (pressure, time and temperature) induce enzyme denaturation with consequent reduction of biological activity. Considering the complexity and diversity involved in the enzyme structure and its ability to react, it is not possible to determine specific conditions that each process is able to promote increase or reduction of enzyme activity, being necessary to evaluate HIP and HPH for each enzyme. Finally, in terms of molecular structure, the effect of HIP and HPH on enzymes can be explained by the alterations in the quaternary, tertiary and secondary structures of enzymes, which directly affects its active site configuration.

Uso da água ozonizada na sanitização dos tetos de bovinos e sua influência na qualidade do leite

This study evaluated the efficiency of ozonated water compared with chlorhexidine to disinfect teats of cattle and their influence on milk quality. 48 cows were separated in 2 groups of sanitation: (I) using ozonated water at 2 mg.L -1 for 30s and (II) using 2%(v/v) chlorhexidine for 30s (standard methodology of disinfection). Before and after sanitation, swabs of teat were collected for carry out microbiological analysis. Additionally, after teats sanitation, the milking was performed and the obtained milk were evaluated by microbiological and physico-chemical parameters. The number of decimal reductions (NDR) reached after ozone sanitation was 2.52, 2.09 and 1.50 for aerobic mesophilic, Staphylococcus sp. and Enterobacteriaceae, respectively. The use of chlorhexidine promoted NRD of 2.38 (aerobic mesophilic), 2.04 ( Staphylococcus sp.) and 1.16 (Enterobacteriaceae). Therefore, no significant differences were found between NRD caused by chlorhexidine and ozonated water. Moreover, no significant differences were observed in the psychrotrophic and aerobic mesophilic counts of the milk obtained after teats sanitation with ozonated water and chlorhexidine. Furthermore, it was observed that only samples obtained from cows treated with chlorhexidine showed the presence of Enterobacteriaceae. There were no changes in the physico-chemical parameters of milk obtained after both treatments. Thus, the ozonated water is a potential substitute of chlorhexidine for cows teats sanitation, resulting in similar microbiological reductions without risks of bacterial resistance development and waste generation.