Њ ЊC. Pure chitosan films reduced C. Pure chitosan films reduced C. Pure chitosan films reduced C. Pure chitosan films reduced C. Pure chitosan films reduced L. monocytogenes L. monocytogenes L. monocytogenes L. monocytogenes L. monocytogenes by 2 logs, by 2 logs, by 2 logs, by 2 logs, by 2 logs, whereas the films with 1% and 2% oregano EO decreased the numbers of whereas the films with 1% and 2% oregano EO decreased the numbers of whereas the films with 1% and 2% oregano EO decreased the numbers of whereas the films with 1% and 2% oregano EO decreased the numbers of whereas the films with 1% and 2% oregano EO decreased the numbers of L. monocytogenes L. monocytogenes L. monocytogenes L. monocytogenes L. monocytogenes by 3.6 to 4 logs and by 3.6 to 4 logs and by 3.6 to 4 logs and by 3.6 to 4 logs and by 3.6 to 4 logs and E. coli E. coli E. coli E. coli E. coli by 3 logs. Pure chitosan films were 89 by 3 logs. Pure chitosan films were 89 by 3 logs. Pure chitosan films were 89 by 3 logs. Pure chitosan films were 89 by 3 logs. Pure chitosan films were 89 m thick, whereas addition of 1% and 2% oregano EO increased m thick, whereas addition of 1% and 2% oregano EO increased m thick, whereas addition of 1% and 2% oregano EO increased m thick, whereas addition of 1% and 2% oregano EO increased ength, but incr ength,
Lycopene plays an important role as an antioxidative and anticancer agent, and is an increasingly valuable commodity in the global market. Rhodobacter sphaeroides, a carotenogenic and phototrophic bacterium, is an efficient and practical host for carotenoid production. Herein, we explored the potential of metabolically engineered Rb. sphaeroides as a novel platform to produce lycopene. The basal lycopene-producing strain was generated by introducing an exogenous crtI from Rhodospirillum rubrum to replace the native crtI and deleting crtC in Rb. sphaeroides. Furthermore, knocking out zwf blocked the competitive pentose phosphate pathway and improved the lycopene content by 88%. Finally, the methylerythritol phosphate pathway was reinforced by integration of dxs combined with zwf deletion, which further increased the lycopene content. The final engineered strain produced lycopene to 10.32 mg/g dry cell weight. This study describes a new lycopene producer and provides insight into a photosynthetic bacterium as a host for lycopene biosynthesis.
An astaxanthin-overproducing (∼1000 μg g(-1)) strain of Phaffia rhodozyma, termed MK19, was established through 1-methyl-3-nitro-1-nitrosoguanidine and Co60 mutagenesis from wild-type JCM9042 (merely 35-67 μg g(-1)). The total fatty acid content of MK19 was much lower than that of the wild type. Possible causes of the astaxanthin increase were studied at the gene expression level. The expression of the carotenogenic genes crtE, crtI, pbs, and ast, which are responsible for astaxanthin biosynthesis from geranylgeranyl pyrophosphate, was highly induced at the mRNA level, leading to excessive astaxanthin accumulation. In contrast, transcription levels of the genes (hmgs, hmgr, idi, mvk, mpd, fps), responsible for the initial steps in the terpenoid pathway, were essentially the same in wild type and MK19. Although fatty acid and total ergosterol content were reduced by 40-70 mg g(-1) and 760.3 μg g(-1) , respectively, in MK19 as compared with the wild type, but the transcription levels of rate-limiting genes in fatty acid and ergosterol pathways such as acc and sqs were similar. Because fatty acids and ergosterol are two branch pathways of astaxanthin biosynthesis in P. rhodozyma, our findings indicate that enhancement of astaxanthin in MK19 results from decreased fatty acid and ergosterol biosynthesis, leading to precursor accumulation, and transfer to the astaxanthin pathway. Strengthening of the mevalonate pathway is suggested as a promising metabolic engineering approach for further astaxanthin enhancement in MK19.
A moderate-temperature mutant strain of the yeast Phaffia rhodozyma, termed MK19, was selected by 1-methyl-3-nitro-1-nitrosoguanidine (NTG) and Co60 mutagenesis. MK19 displayed fast cell growth and elevated astaxanthin content at 25 degrees C, whereas optimal temperature for growth and astaxanthin synthesis of wild-type P. rhodozyma was 17-21 degrees C. Optimized astaxanthin yield for MK19 after 4 days culture in shaking flask at 25 degrees C, determined by response surface methodology, was 25.8 mg/l, which was 17-fold higher than that of the wild-type. MK19 was tolerant of high initial concentration of glucose (>100 g/l) in optimized medium. Total fatty acid content of MK19 was much lower than that of the wild-type. Acetyl-CoA is a common precursor of fatty acid and terpenoid biosynthesis, and it is possible that decreased fatty acid synthesis results in transfer of acetyl-CoA to the carotenoid biosynthetic pathway. Our results indicate that astaxanthin content is negatively correlated with fatty acid content in P. rhodozyma. Nutrient analysis showed that MK19 cells are enriched in lysine, vitamin E, and other rare nutrients, and have potential application as fish food without nutritional supplementation. This moderate-temperature mutant strain is a promising candidate for economical industrial-scale production.
Chitosan films prepared with oregano essential oil were applied on bologna slices. Release of the essential oil compounds during film preparation and application on the meat product and consumer acceptability of bologna enriched with oregano essential oil were tested. Oregano essential oil compounds were quantified by gas chromatography mass spectroscopy (GCMS) after extraction from the filmforming solution, films before and after application on bologna and from bologna slices before and after application of the films. The results indicated that the concentration of components of the essential oil sharply decreased during film preparation, e.g. from 757.7 ppm carvacrol in film-forming solution to 2.1 ppm in dried films. No carvacrol was detected in the films after application on bologna for 5 days at 4°C, mainly due to its diffusion into bologna. It seemed that the moisture and high lipid content of bologna helped the diffusion of the oregano essential oil from the chitosan film matrix into the product. Sensory evaluation suggested that addition of 45 ppm or less of oregano oil to bologna would be acceptable to consumers. Results support the potential use of chitosan–oregano essential oil films as an antimicrobial packaging material for processed meat.
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