Monitorization of hexanal as lipid oxidation indicator in a processed meat product packaged with poly(lactic acid)/clay nanocomposite films

One of the most detrimental processes in fatty foodstuffs is lipid oxidation, which occurs during production and storage, and influences food composition and safety. Through the analysis of volatile lipid oxidation products we can have an insight into the oxidation, and some volatiles, such as hexanal, which can be markers of undergoing oxidation processes. Hexanal is formed when fatty acids are oxidized and is one of many well-documented aromatic components that contributes to flavour and aroma in common food products containing fatty acids. During the last decade, the interest in polymer layered silicate (PLS) nanocomposites has rapidly increased due to their potential for enhancing physical, chemical, and mechanical properties of conventional materials. Polymer nanocomposites are represented by a polymeric matrix reinforced with nanoscale fillers, among them the most common silicate clays are represented by montmorillonite (MMT), which is naturally occurring and readily available in large quantities. The presence of MMT can lead to materials which generally exhibit great property enhancements, mainly due to its intercalation or exfoliation into the polymer chains. In this work natural MMT Cloisite Na+ was incorporated in PLA. The PLA/Cloisite® Na+ films were prepared through a two-step process. In the first step, PLA pellets were fed into a corotating laboratory twin-screw extruder at 170 °C and 50 rpm for 2 min. Subsequently, Cloisite® Na+ powder (5%, w/w) were added and mixed. After extrusion, the melted matter was then pressed with a P300P hot press at 170 °C and 100 bar to obtain the PLA/Cloisite® Na+ films. Salami slices were packaged with PLA-OMMT film and with a control film (PLA). After different storage times (0, 15, 30, 60 and 90 days), salami slices were analysed regarding their hexanal content. The hexanal derivatization was performed in a solution of 2,4-dinitrophenylhydrazine in sulfuric acid during 4 h in the dark, and the hexanal extraction was performed with n-hexane and evaporation till dryness. The residue was dissolved in methanol, filtered and analysed. The quantification of hexanal was performed by Ultra High Performance Liquid Chromatography coupled with Diode Array Detector at 365 nm, with a Pre-column AcquityTM UPLC® BEH C18 (2.1 x 5 mm, 1.7 μm particle size) and a column AcquityTM UPLC® BEH C18 (2.1 × 50 mm, 1.7 μm particle size), the mobile-phase was acetonitrile-water (75:25, v/v). The amount of hexanal in packaged salami decreased in the first 60 days of storage. In this period of time the hexanal content of the salami packaged with the PLA/Cloisite® Na+ films was lower than the salami packaged with control film, except after 15 days of storage, where there was no difference between two films. After 90 days of storage, the amount of hexanal in the samples increased, although it was higher in the samples packaged with control film (94.7 ± 6.02 μg/100g salami) than salami packaged with PLA/Cloisite® Na+ films (65.1 ± 6.12 μg/100g salami). The presence of MMT in the polymer film can reduce the lipid oxidation of processed meat products, extending their shelf life. Further studies to evaluate differences between PLA and the nanocomposite (PLA-5%Cloisite®Na+) in what regards to the mechanical and barrier properties are in progress.This work was supported by the research project “Labelling and tracking of nanoclay from food packaging nanocomposites: a food safety issue – NanoPack4Food” (2014DAN1019) under the Cooperative Programme of the Agreement on Scientific Cooperation between National Research Council of Italy (CNR) and Foundation for Science and Technology of Portugal (FCT)N/

ATR is a multifunctional regulator of male mouse meiosis

Meiotic cells undergo genetic exchange between homologs through programmed DNA double-strand break (DSB) formation, recombination and synapsis. In mice, the DNA damage-regulated phosphatidylinositol-3-kinase-like kinase (PIKK) ATM regulates all of these processes. However, the meiotic functions of the PIKK ATR have remained elusive, because germline-specific depletion of this kinase is challenging. Here we uncover roles for ATR in male mouse prophase I progression. ATR deletion causes chromosome axis fragmentation and germ cell elimination at mid pachynema. This elimination cannot be rescued by deletion of ATM and the third DNA damage-regulated PIKK, PRKDC, consistent with the existence of a PIKK-independent surveillance mechanism in the mammalian germline. ATR is required for synapsis, in a manner genetically dissociable from DSB formation. ATR also regulates loading of recombinases RAD51 and DMC1 to DSBs and recombination focus dynamics on synapsed and asynapsed chromosomes. Our studies reveal ATR as a critical regulator of mouse meiosis