Antimicrobial lubricant formulations containing poly(hydroxybenzene)-trimethoprim conjugates synthesized by tyrosinase

Poly(hydroxybenzene)-trimethoprim conjugates were prepared using methylparaben as substrate of the oxida- tive enzyme tyrosinase. MALDI-TOF MS analysis showed that the enzymatic oxidation of methylparaben alone leads to the poly(hydroxybenzene) formation. In the presence of tri- methoprim, the methylparaben tyrosinase oxidation leads poly(hydroxybenzene)-trimethoprim conjugates. All of these compounds were incorporated into lubricant hydroxyethyl cellulose/glycerol mixtures. Poly(hydroxybenzene)-trimetho- prim conjugates were the most effective phenolic structures against the bacterial growth reducing by 96 and 97 % of Escherichia coli and Staphylococcus epidermidis suspen- sions, respectively (after 24 h). A novel enzymatic strategy to produce antimicrobial poly(hydroxybenzene)-antibiotic conjugates is proposed here for a wide range of applications on the biomedical field.The authors Idalina Gonçalves and Cláudia Botelho would like to acknowledge the NOVO project (FP7-HEALTH- 2011.2.3.1- 5) for funding. Loïc Hilliou acknowledges the financial support by FCT – Foundation for Science and Technology, Portugal (501100001871), through Grant PEst-C/CTM/LA0025/2013 - Strategic Project - LA 25 - 2013–2014, and by Programa Operacional Regional do Norte (ON.2) through the project BMatepro – Optimizing Materials and Processes^, with reference NORTE-07-0124-FEDER-000037 FEDER COMPETE

Preservation of cell viability in fruit and vegetable tissue after freezing and thawing

Cryoprotection of horticultural products has been a matter of concern for the food industry in its search for efficient ways of improving the quality of frozen-thawed products. Research on the cryoprotection of plant tissues should make progress through a better understanding of the natural protective mechanisms of plant tissues during winter survival. The present study reports results on the use of vacuum impregnation (VI) alone or in combination with pulsed electric field (PEF) to obtain cryoprotectant solutions in the tissues. Spinach samples were treated with a combination of PEF and VI prior to freezing in liquid nitrogen and thawing at room temperature. VI was used to impregnate trehalose (40% w/w solution) as cryoprotectant and PEF was used to distribute the cryoprotectant in the extra and intracellular spaces of the tissue. Strawberries were treated with VI prior to freezing in liquid nitrogen ant thawing at room temperature. VI was used to impregnate a combination of trehalose (12% w/w) and cold acclimated winter wheat extract (AWWE, 0.02% w/w) containing antifreeze protein. Results were evaluated by assessing the maintenance of the texture of the tissue as well as by cell viability analysis using fluorescence microscopy. Results provide evidence that impregnating fruit and vegetables tissues using VI alone or in combination with PEF with the tested cryoprotectants improves drastically the cryoprotection of the treated tissues. Cryoprotection is proved through the maintenance of cell viability and texture after one freezing/thawing cycle. In the case of strawberries, cryoprotection was influenced by the heterogeneity of the tissues in the fruit and the viability of cells close to the surface (epidermal and probably also hypodermal) could not be preserved

Effect of vacuum infused cryoprotectants on the freezing tolerance of strawberry tissues

Whole strawberries were vacuum infused with cryoprotectants to improve their freezing tolerance. The strawberries were infused with 12 g/100 g trehalose solution; 0.2 g/100 g cold-acclimated wheatgrass solution (AWWE) containing antifreeze protein (AFP) or combination of 12 g/100 g trehalose with 0.2 g/100 g AWWE under vacuum for 14 min. The fruits were frozen in liquid nitrogen and thawed at room temperature before being evaluated for cell viability, drip loss and preservation of texture. The results showed that the combined effects of both cryoprotectants significantly improved the freezing tolerance of the treated strawberries. The cryoprotection effect was influenced by the heterogeneity of the tissues in the fruits

Cryoprotective treatment of strawberries

Whole strawberries were impregnated using vacuum infusion with different cryoprotective solutions to improve their freezing tolerance. The cryoprotective solutions used were: 12% (w/w) trehalose solution; 0.2 % (w/w) cold acclimated wheatgrass solution (AWWE) containing antifreeze protein (AFP) and combination of 12% (w/w) trehalose with 0.2 % (w/w) AWWE. The strawberries (70±5 g) were immersed in the coresponding solution under vacuum for 14 min. After the infusion the fruits were removed from the solution, blotted, dipped in liquid nitrogen for 25 s to freeze and then thawed for 2 h at room temperature. The quality of the strawberries after one freezing/thawing cycle was evaluated trough determination of the cell viability, drip loss, colour loss and preservation of texture firmness. The cryoprotective effect of the solutions depended on the heterogeneity of the tissues in the fruit. The results proved that there was evident reduction in the drip loss of the strawberries by using the combined effects of both cryoprotectants. Furthermore this combination significantly improved the overall freezing tolerance of the treated fruits, by obtaining cell viability in most of the tissues; reducing the colour loss to non-significant level when compared to the fresh strawberries and preserving the flesh firmness

Pulsed electric fields in combination with vacuum impregnation for improving freezing tolerance of vegetables

Freezing is a widely used method of preserving food products. Efforts are currently being directed towards improving the quality of sensitive tissues of plant foods such as leaves, after freezing and thawing. One of the methods under investigation is the combination of vacuum impregnation (VI) with cryoprotectants and the application of a pulsed electric field (PEF) to the plant tissue prior to freezing. In this chapter were identify mechanisms for the efficient introduction of a cryoprotectant molecule into the heterogeneous structure of leaf tissue and improve our understanding of the consequences of the introduction of this foreign molecule into the tissue regarding cell metabolism, freezing point, and ice propagation rate. To obtain precise information on the electroporation of internally located cells, a three-dimensional numerical model of the cross section of a leaf was developed. Validation of the models showed the importance of the wax layer and stomata for the successful electroporation of all cells in the tissue. VI, and the subsequent application of PEF, increased the metabolic activity of the tissue. The increase in metabolic activity after VI was accompanied by the accumulation of trehalose-6-phosphate in the cells. Leaves impregnated with trehalose, sucrose, glucose, and mannitol exhibited significantly lower ice propagation rates and higher freezing temperatures than untreated controls. Leaves subjected to PEF also showed higher freezing temperatures than untreated leaves; however, the ice propagation rate was not influenced by PEF