Redirection of Pyruvate Pathway of Lactic Acid Bacteria to Improve Cheese Quality

Metabolic engineering in Lactic acid bacteria (LAB) has focused on changing of pyruvate metabolism to increase production of desired flavor compounds. A constructed mutant strain should contain no foreign DNA and antibiotic resistance genes. Therefore, food grade lactate dehydrogenase (ldh ^d) and diacetyl reductase (dar ^d) mutant strains were created using two plasmid system in this study. Metabolic end products (pyruvate, lactate, formate and acetoin) of these strains in glucose medium and in cheese were determined using HPLC. Created mutant and wild type strains were used as a starter culture in cheese. Compared to the wild type strain, different levels of metabolites were observed in cheese during three weeks of ripening. The ldh ^d strains produced less lactate but high acetoin as a result of gene deletion. Deletion of dar gene decreased the production of acetoin. The dar deficient strains have low diacetyl reductase activity and are able to reduce significant amounts of acetoin but not terminate it completely. Genetic modification made the shift from homolactic to mixed acid fermentation, but the desired compound production hardly improved. The basis of these results and techniques are promising for the further studies.     

Synthesis and characterization of hydrogels based on poly(2-hydroxyethyl methacrylate) for drug delivery under UV irradiation

The present study aims to create a controlled release system through the preparation and characterization of hydrogels based on 2-hydroxyl ethyl methacrylate (HEMA). In order to investigate the influence of photo-initiators on the drug release behavior of the resulting hydrogels, three different photo-initiators [2,2-dimethoxy-2-phenyl-acetophenone] (Irgacure 651), 1-hydroxycyclohexyl phenyl ketone (Irgacure 184) and 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) were used. In addition, hydroxyapatite (HAp) was employed to modify HEMA hydrogels. The synthesis of hydrogels was confirmed by characterization through Fourier transform infrared spectroscopy, nuclear magnetic resonance (¹³C NMR) spectroscopy and digital microscope. The responsive behaviors were investigated by recording swelling ratios under different conditions. In vitro drug release studies were performed for donepezil hydrochloride-loaded hydrogels at pH 1.2, 6.8 and 7.4. The results indicated that hydrogels synthesized using Irgacure 2959 released the maximum amount of donepezil hydrochloride. Moreover, the release rate decreased in the presence of HAp.