Strand displacement of double-stranded DNA by triplex-forming antiparallel purine-hairpins

We characterize the binding affinity and the thermodynamics of hybridization of triplex-forming antiparallel purine-hairpins composed of two antiparallel purine domains linked by a loop directed toward single-stranded and double-stranded DNA (ssDNA, dsDNA). Gel retardation assays and melting experiments reveal that a 13-mer purine-hairpin binds specifically and with a Kd of 8 × 10-8 M to polypyrimidine ssDNA to form a triple helical structure. Remarkably, we show that purine-hairpins also bind polypurine/polypyrimidine stretches included in a dsDNA of several hundred bp in length. Binding of purine-hairpins to dsDNA occurs by triplex formation with the polypyrimidine strand, causing displacement of the polypurine strand. Because triplex formation is restricted to polypurine/polypyrimidine stretches of dsDNA, we studied the triplex formation between purine-hairpins and polypyrimidine targets containing purine interruptions. We found that an 11-mer purine-hairpin with an adenine opposite to a guanine interruption in the polypyrimidine track binds to ssDNA and dsDNA, allowing expansion of the possible target sites and increase in the length of purine-hairpins. Thus, when using a 20-mer purine-hairpin targeting an interruption-containing polypyrimidine target, the binding affinity is increased compared to its 13-mer antiparallel purine-hairpin counterpart. Surprisingly, this increase is much more pronounced than that observed for a tail-clamp purine-hairpin extended up to 20 nt in the Watson-Crick domain only. Thus, triplex-forming antiparallel purine-hairpins can be a potentially useful strategy for both single-strand and double-strand nucleic acid recognition.This research was supported by grants SAF02-0363 and SAF05-0247 from the “Comisión Interministerial de Ciencia y Tecnología” and 2001SGR141 from the “Comissionat d’Universitats i Recerca (CUR)”. S.C. is the recipient of a postgraduate fellowship from the Spanish Ministry of Education. We thank Jordi Robles from University of Barcelona for his help with the use of MeltWin software.Peer reviewe

In-situ physical analysis of cellulose fibre suspensions during enzymatic hydrolysis

In-situ physical analysis of cellulose fibre suspensions during enzymatic hydrolysi

Sustainable food packaging: An updated definition following a holistic approach

Food packaging solutions need to be redesigned to be more sustainable, but determining which solution is ‘more optimal’ is a very difficult task when considering the entire food product value chain. Previous papers paved the way toward a sustainable food packaging definition, but it is far from being commonly accepted or well usable in the broad food systems domain, which further results in uninformed choices for sustainable food packaging made by all stakeholders in the value chain: producers, distributors, practitioners and consumers. Therefore, this work aims first at giving a state-of-the-art overview of sustainable food packaging terms (38 similar terms were identified and grouped into four clusters: Sustainable, Circular, Bio and Other sustainable packaging) and definitions using systematic (narrative) review analysis and ‘controlled expert opinion feedback’ methodology. Second, it aims to offer an updated definition for sustainable food packaging, which is also specific to food packaging and be simple, coherent, easily understandable, and communicable to everybody. The applied holistic approach intends to include all aspects of the food-packaging unit, to consider food safety and packaging functionality, while taking into account different disciplines and challenges related to food packaging along the supply chain. Being a balancing act, a sustainable food packaging may not be a perfect solution, but contextual, suboptimal and in need of constant validation.info:eu-repo/semantics/publishedVersio

Sustainable food packaging: An updated definition following a holistic approach

publishedVersio

Antimicrobial and physicochemical properties of chitosan-HPMC-based films.

To prepare composite films from biopolymers with anti-listerial activity and moisture barrier properties, the antimicrobial efficiency of chitosan-hydroxy propyl methyl cellulose (HPMC) films, chitosan-HPMC films associated with lipid, and chitosan-HPMC films chemically modified by cross-linking were evaluated. In addition, the physicochemical properties of composite films were evaluated to determine their potential for food applications. The incorporation of stearic acid into the composite chitosan-HPMC film formulation decreased water sensitivity such as initial solubility in water and water drop angle. Thus, cross-linking of composite chitosan-HPMC, using citric acid as the cross-linking agent, led to a 40% reduction in solubility in water. The water vapor transfer rate of HPMC film, approximately 270 g x m(-2) x day(-1) x atm(-1), was improved by incorporating chitosan and was further reduced 40% by the addition of stearic acid and/or cross-linking. Anti-listerial activity of films was determined on solid medium by a numeration technique. Chitosan-HPMC-based films, with and without stearic acid, inhibited the growth of Listeria monocytogenes completely. On the other hand, a loss of antimicrobial activity after chemical cross-linking modification was observed. FTIR and 13C NMR analyses were then conducted in order to study a potential chemical modification of biopolymers such as a chemical reaction with the amino group of chitosan. To complete the study, the mechanical properties of composite films were determined from tensile strength assays

The use of lysozyme to prepare biologically active chitooligomers

Two types of crustacean commercial chitosans (CS1, CS2) were dissolved in lactic acid solutions, hydrolysed by lysozyme and finally fractioned by methanol solutions into two parts containing chito-oligomers (CS-O1, CS-O2). The antioxidant power and antimicrobial properties of both fractions were studied and compared with non-hydrolysed CS1 and CS2. The antioxidant properties were determined by the ferric ion reducing antioxidant power (FRAP) method while the bioactive properties were evaluated against a strain of Listeria monocytogenes. CS-O obtained from the solid fraction of the chito-oligomers solid fractions treated with 90% methanol showed the highest reducing power. Microbiological tests showed that CS-O exhibit higher antilisterial activity than CS