Application of Films Based on Chitosan and Xanthan Gum in Refrigerated Fish Conservation

Abstract This research aims to determine the efficiency of chitosan and xanthan gum films in conservation of croaker fillets kept in refrigeration for 9 days. Proximal composition, loss of mass, color, pH, TVB-N (Total Volatile Bases) and microbiological profile were assessed. The films were prepared with chitosan and xanthan gum in varying mass proportions 100:0, m:m (C100XG0); 60:40, m:m (C60XG40); 50:50, m:m (C50XG50). They presented the respective values for moisture content, water solubility, thickness and water vapor permeability: 24.59%, 19.50%, 0.086 mm and 11.45gm-1.s-1.Pa-1for C100XG0; 24.58%; 20.27%, 0.091 mm and 10.41 gm-1.s-1.Pa-1for C60XG40; 22.11%, 22.06%, 0.089 mm and 10.68 gm-1.s-1.Pa-1 forC50XG50.The films were made in small bags format capable to hold about 20 g of fish fillets. A control sample was prepared in parallel, using polyethylene bags under the same storage conditions. The results showed that the chitosan films combined with xanthan gum had excellent antimicrobial properties, capable of preserving the quality of chilled fish fillets during the studied period, since it inhibited the growth of Staphylococcus coagulase-positive, Salmonella spp and coliforms at 45 ° C. Mass loss of the croaker fillets was not significantly affected by xanthan gum addition to the films. On the other hand, xanthan gum addition affected pH and color parameters of the corvina fillets. It was also verified that the combination of these two polymers promoted the reduction of N-BVT, being the C50XG50 film that presented the best response.

A protein expression system for tandem affinity purification in Xanthomonas citri subsp. citri

Abstract Citrus canker, caused by the Gram-negative bacterium Xanthomonas citri subsp. citri (Xac), is one of the most devastating diseases to affect citrus crops. There is no treatment for citrus canker; effective control against the spread of Xac is usually achieved by the elimination of affected plants along with that of asymptomatic neighbors. An in depth understanding of the pathogen is the keystone for understanding of the disease; to this effect we are committed to the development of strategies to ease the study of Xac. Genome sequencing and annotation of Xac revealed that ∼37% of the genome is composed of hypothetical ORFs. To start a systematic characterization of novel factors encoded by Xac, we constructed integrative-vectors for protein expression specific to this bacterium. The vectors allow for the production of TAP-tagged proteins in Xac under the regulation of the xylose promoter. In this study, we show that a TAP-expression vector, integrated into the amy locus of Xac, does not compromise its virulence. Furthermore, our results also demonstrate that the polypeptide TAP can be overproduced in Xac and purified from the soluble phase of cell extracts. Our results substantiate the use of our vectors for protein expression in Xac thus contributing a novel tool for the characterization of proteins and protein complexes generated by this bacterium in vivo.